IRSAPS Bulletin Volume 1, Issue 2 by J Sharma

IRSAPS Bulletin

Vol. 1, Issue 1 January-April 2011 http://irsaps.org

A periodical of Indian Research Scholars’ Association for Promoting Science

 Conductance enhancement of carbon nanotubes via surface metal decoration  Recent trends in cancer treatment  An overview of solar photovoltaic technologies  Neutron activation analysis  Protein folding: understanding nature’s intelligent ergonomics  Science behind ocular dietary supplements: lutein and zeaxanthin © Indian Research Scholars’ Association for Promoting Science, 2011. All rights reserved. Reproduction in whole or in part, for any purpose other than educational interest, is prohibited without prior written consent. Contact publication and distribution department for further details (E-mail:pubs.irsaps@gmail.com).

Scope and Aim of Indian Research Scholars’ Association for Promoting Science Indian Research Scholars’ Association for Promoting Science (IRSAPS) is created to spread brotherhood through scientific research to every part of our country! The aim of the association is to help all research scholars who are desperate to excel in scientific research and to provide necessary support, share knowledge with proper attention in terms of research articles, infrastructure, and guidance. The association will take appropriate steps to highlight and encourage the achievements of talented research scholars.

Since India’s future equally depends on the knowledge pool in basic sciences, the association will endeavor to encourage budding researchers by encouraging them at school and higher secondary levels through the network of volunteers. Though the association is a nonprofit organization, it will encourage entrepreneurship among the members through scientific innovations. The scope of the forum will change with time depending on the requirements of the forum members. No discrimination will be tolerated in terms of regional, ethnic, or any other means. The association will have a governing body constituted by at least one member from each state of India (depending on the availability of volunteers). Any organizational dispute arising in due course will be sorted out through a democratic voting process among the governing body members. For a general dispute, all members of the association will be invited to register their opinion through opinion polls. IRSAPS will carry out online voting only.

Date of establishment: 14 August 2010 Total number of members (January 2011): 302

IRSAPS Bulletin 2011, Vol. 1, Issue 1

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IRSAPS Bulletin Volume 1, Issue 1 Issue Editor: Dr. Jadab Sharma Release date: 3rd February 2011 This journal is published by Indian Research Scholars’ Association for Promoting Science. To join IRSAPS, please visit: http://irsaps.org 1st Issue: January-April 2nd Issue: May-August 3rd Issue: September-December Statement on journal policy: IRSAPS Bulletin does not have a peer review policy for articles (any changes in this regard will be notified). It is a free open source online journal. Cover page details: Self-assembled gold nanorods (left panel, SEM image) are able to confine and enhance the optical light fields in the near field (right panel, map of intensity of electromagnetic field superimposed with the SEM image). Courtesy: Jadab Sharma and Erik Dujardin*, CEMES CNRS, Toulouse, France. Contact person: Dr. Erik Dujardin E-mail: dujardin@cemes.fr. Description: By controlling the shape, size and inter-particle distance of crystalline gold nanorods, the spectral and spatial features of surface plasmons can be tailored at the nanometer scale offering unique opportunities to confine, enhance and guide light (as electromagnetic fields) below the diffraction limit while minimizing the dissipation losses.

©Indian Research Scholars’ Association for Promoting Science, 2011. All rights reserved. Reproduction in whole or in part of this journal for any other purpose except for the educational interest is prohibited without the prior written consent.

IRSAPS Bulletin 2011, Vol. 1, Issue 1

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Editorial Board Members 1. Dr. Jadab Sharma

5. Dr. M. Buchi Suresh

NanoSciences Group CEMES CNRS UPR 8011

Center for Ceramic Processing International Advanced

B. P. 94347, 29 rue Jeanne Marvig 31055 Toulouse, France E-mail: jadab.s@gmail.com

Research Institute for Powder Metallurgy and Material Processing (ARCI) Balapur, Hyderabad-500005 India E-mail:suresh@arci.res.in

2. Dr. Amit K. Chattopadhyay School of Engineering and Applied Sciences

ujjalgautam@gmail.com 8. Prof. Ramesh C. Deka Department of Chemical Sciences Tezpur University, Tezpur 784 028 Tel: +91-3712-267008

6. Dr. Sonika Saddar

Mathematics (NCRG) Aston University Birmingham B4 7ET, UK E-mail: akchaste@gmail.com

Pulmonary and Vascular Biology Department of Pediatrics UT Southwestern Medical Center 5323 Harry hines Blvd Dallas, TX 75235 USA E-mail: sonikasaddar@gmail.com

3. Dr. Santosh B. Chavan Jay Biotech, Pune, India E-mail: sbchavan23@gmail.com 4. Dr. Sanjeev Malik

(extension 5058) E–mail: ramesh@tezu.ernet.in 9. Prof. Chandravanu Dash Center for AIDS Health Disparities Research Department of Cancer Biology and Biochemistry Hubbard Hospital Bldg-

7. Dr. Ujjal Gautam

Department of Mathematics, Indian Institute of Technology, Roorkee, India E-mail: malikdma@gmail.com

Science, 1-1, Namiki, Sukuba, Japan-3050044 E-mail:

ICYS-MANA Research Fellow National Institute for Materials

CAHDR Meharry Medical College School of Medicine 1005 Dr. DB Todd Jr Blvd, Nashville, TN 37208, USA E–mail: cdash@mmc.edu

Publication and Distribution 1. Dr. Amit Sharma (North Zone) Unite de Catalyse et de Chimie du Solide (UCCS)

3. Dr. Rupam Jyoti Sarma (East Zone) Department of Chemistry

UMR CNRS 8181 Ecole Centrale de Lille, Cité Scientifique, BP 48 Villeneuve d'Ascq, Lille, Nord, FRANCE 59651 E-mail: amitfrance@gmail.com

Gauhati University Gopinath Bordoloi Nagar Guwahati, Assam, India E-mail: rup.sarma@gmail.com

2. Mr. Qureshi Ziyauddin (West Zone)

4. Dr. P. R. Naren (South Zone)

Institute of Chemical Technology

Unite de Catalyse et de Chimie du Solide

Nathalal Parekh Marg, Matunga, Mumbai 400019, Maharashtra, India E-mail: qureshi.ziya@gmail.com

(UCCS), UMR CNRS 8181 Ecole Centrale de Lille, Cité Scientifique, BP 48 Villeneuve d'Ascq, Lille, Nord, 59651, France E-mail: naren_pr@yahoo.com

IRSAPS Bulletin 2011, Vol. 1, Issue 1

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IRSAPS Bulletin 2011, Vol. 1, Issue 1

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Contents

Welcome message by Prof. C. N. R. Rao

A.iv

1. Editorial

2. Conductance enhancement in carbon nanotubes via surface metal decoration by

Caterina Soldano

3. Recent trends in cancer by Manish Chandra Pathak

4. An overview of solar photovoltaic technologies by Snjay R. Dhage

5. Neutron activation analysis by Rupesh H. Gaikwad

6. Protein folding: understanding natureâ&#x20AC;&#x2122;s intelligent ergonomics by Ranjeet Kumar

7. The science behind ocular dietary supplements: lutein and zeaxanthin by Prakash

Bhosale

8. IRSAPS as an organization

B.i

9. Science cartoons by Sumanta Baruah

IRSAPS Bulletin 2011, Vol. 1, Issue 1

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ÂŠ IRSAPS

A.v

Few lines from the editorial desk…

It gives us immense pleasure to release

inventions and discoveries. The need of the

the first issue of IRSAPS Bulletin, a periodical

hour is to unite them to motivate and create

published by the Indian Research Scholars’

growth engines with direct involvements from

Association for Promoting Science (IRSAPS).

people with various societal backgrounds so as

This has been a collective effort from a

to expect a thriving India that is free of

multitude of science workers focused on a wide

unworthy vices. India had a great scientific past

spectrum of fields spanning physical to

but modern Indian science needs a lot of

biological sciences including social sciences, all

infusion from younger scholars who have

dedicated towards honing an Indian knowledge

traveled the globe around and have established

society. This indeed is a proud moment for us

themselves as leading lights in their respective

that after all these years of tireless toil, we now

fields. It is from these delegates the next

have a platform of knowledge exchange

generation of Indian scientific pall bearers

dedicated (but not limited) to Indian research

should be exchanging their batons with and

scholars, their ideas and their problems, the

aiding this process is what IRSAPS hopes to

joys and sorrows of an Indian research life.

achieve. There is an urgent need to facilitate the

At this nascent stage, IRSAPS will have a streamlined ethos focused on international researches but from the birds' eye view of Indian scholars. The idea is to develop a spirit of healthy scientific discussions that could aid and advance ideas through scientific knowledge exchange as well as acting as a communion of mundane necessities. It is said that research scholars are the backbones of scientific IRSAPS Bulletin 2011, Vol. 1, Issue 1

research in basic sciences and augment infrastructure facilities with renewed effort to make career in basic sciences a viable and attractive option for the younger generation. As an introspective starter, we might ask ourselves: why does our country with all its population might is still not in the leading front of the global scientific community? Collating with this will be: why do not we have our own growth

model that could cater to Indian needs and

and employ science to everyday issues and life

reciprocate an Indian society? Why Indians are

overall. Only then we shall be able to make

forced to serve other countries instead of

proper planning for the benefit of society. Or

involving them in the growth process of India?â&#x20AC;&#x2122;

otherwise, individual academic achievements

At the same time we should not have any

will always be regarded merely as spikes in a

dilemma in mind that scientific society is

sea of dysfunctional zeros and India has many

universal and it has nothing to do with a mere

such examples to its credit. Our immediate aim

geographical boundary or ambit of a particular

should be a positive increment in present

community or group of people.

Indian living standards instead of being in a

We believe that India, as a country is blessed with a multi-cultural and multi-lingual fabric, that can be utilized as a resource of a broader scientific base and thriving people's economy. We lack will power to think differently to change our approach or attitude towards obstinately hierarchical establishments. We need to re-discover self-belief and respect and understand our strength, but without any complacency or exaggeration. We also hope to encourage leading Indian academic institutes to create their own academic curriculum based on

farcical race with the advanced world. Of a more technical concern is the following: can we possibly link and value our scientific activities against Indian societal needs over and above the current trend of promotion based scientific activity judged by the number of publications? There are several other basic issues which have not been addressed at an appropriate level. One of the most concerning issue is the laboratory safety norms and working atmosphere in various laboratories, especially in Indian universities and small scale college laboratories.

the requirements of the surrounding society, to

Above are the points we wish to raise as

inspire them in focusing on niggling societal

Indian Research Scholarsâ&#x20AC;&#x2122; Association for

issues and local challenges. We need to look

Promoting Science. We do not envisage a

beyond our immediate academic curriculum

panacea to all our problems, rather we will be

IRSAPS Bulletin 2011, Vol. 1, Issue 1

ÂŠ IRSAPS

happy to initiate a cascade of thoughtful

we will be able to spread brotherhood through

debates that may culminate into actions from

science research. Science has the power to

responsible authorities. In our limited scope, the

bring a change in our society and we believe in

singular aim will be dissemination and

decentralization of knowledge to all remote

technology will play a vital role in our

corners of the country that could help

endeavors. All such issues, new and ongoing,

materialize dreams of the deserving ones who

will prosper in this journal that IRSAPS hopes

are focusing on science based careers. We are

will encourage our present and future

sure that this will ignite new thinking and

generations to catapult Indian science to the

aspirations from all sections of people from the

next level of prominence. Nothing less â&#x20AC;Ś but

various parts of our country. At the same time,

could be a lot more!

science

minded

scholars.

Indeed,

(Jadab Sharma)

No amount of experimentation can ever prove me right; a single experiment can prove me wrong! -Albert Einstein

IRSAPS Bulletin 2011, Vol. 1, Issue 1

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Research Article

Conductance enhancement of carbon nanotubes via surface metal decoration Caterina Soldano

Department of Chemistry and Physics for Engineering and Materials & SENSOR Laboratory, University of Brescia, Brescia Via Valotti 9, 25133 BRESCIA, Italy Tel: (+39) 030 3715767; Fax: (+39) 030 2091271 E-mail: caterina.soldano@ing.unibs.it

A simple method to increase the conductance of individual template-grown carbon nanotubes contacted with platinum electrodes using a high-bias treatment process which decreases the disorder density due to intense local Joule heating, and decorates the nanotubes with Pt nanoclusters is here presented. The temperature dependence of conductance follows very closely a Lüttinger-liquid to Al’tshuler-Aronov anomaly, and reveals decreased disorder-density and enhanced number of channels compared to the pristine tubes. Density functional theory calculations indicate the enhancement of the density of states near the Fermi level due to platinum decoration.

1. Introduction In the field of micro and nanoelectronics, as elements of integrated circuits downsize towards a few-nanometers, existing interconnect technologies face a tremendous bottleneck due to electromigration failure of copper lines.1, 2 Due to their immense failure current densities (>109Å/cm2), carbon nanotubes have been envisioned as possible replacement for copper as electrical interconnects for gigascale integration.3,

At the nanoscale, high-conducting carbon

nanotubes (CNTs) or nanotube bundles are expected to outperform copper in terms of failure current density, power dissipation, and on-chip signal transfer delays.5,

6, 7

However, although

high-purity arc-grown or catalyst-assisted CVD (CCVD)-grown CNTs have been demonstrated to have several promising applications, there has been limited progress in their implementation as future interconnects, while catalyst-free carbon nanotubes grown inside templates have received little or no attention.8-11 Template-grown CNTs offer a viable alternative for both IRSAPS Bulletin 2011, Vol. 1, Issue 1

horizontal and vertical interconnect assemblies, since they form dense, perfectly straight and aligned arrays of CNTs with highly uniform and controllable lengths, diameters, and wall thicknesses. Further, these nanotubes are free of any catalyst particles, and in addition, both their ends are open-capped, giving access to all the inner walls for electrical contacts from both sides. Despite these advantages, the high two-terminal resistance of template-grown CNTs is a big drawback, caused by the relatively low growth temperature (~650C) and poor (short-range) graphitic order.12 Overcoming this technological challenge is crucial before template-grown carbon nanotubes could be implemented in interconnects and other low-resistance electronic applications. While long-term (~hours) annealing at extreme temperatures (2000C) can restore their graphitization and decrease their resistance, a rapid, single-step, simple, roomtemperature and in-situ method that can simultaneously decrease the disorder density and enhance the number of conductance channels of individual template-grown carbon nanotubes is highly desirable, and is of extreme interest both from fundamental and applied point of view. 13 Rapidly cycling a high voltage across the two terminals of individual platinum-nanotubeplatinum devices is shown to increase their conductance. This high-bias treatment (HBT) induces sufficient local Joule heating to decrease the disorder density possibly by improving the long-range graphitic order, as well as decorates the nanotube surface with platinum nanoclusters that appear to provide additional conduction channels in the nanotubes. This technique for in-situ platinum-nanocluster decoration of nanotubes using the HBT method circumvents tedious, ex-situ physical, chemical or electrochemical routes usually approached for such surface decoration. This allows investigation of the low-temperature transport in the same device, pre- and post-modification, in controlled steps, revealing significant increase of the number of conduction channels and decrease of disorder density of the modified nanotubes when compared to the pristine ones. Ab-initio density functional theory (DFT) calculations of the density of states (DoS) of platinum decorated carbon nanotubes confirm that charge transfer from platinum-clusters on carbon nanotubes can provide the observed additional channels close to the Fermi level. 2. Results and Discussions Multiwall nanotubes were grown inside nanoporous alumina templates by a chemical vapor deposition technique with acetylene precursor gas at a temperature of approximately 650°C.11 CNTs grown in template are uniform in size (250nm). Past works have shown that the mechanism of growth involves a pyrolytic deposition of graphitic carbon, resulting in nanotubes IRSAPS Bulletin 2011, Vol. 1, Issue 1 © IRSAPS 5

(a)

(b)

D G

Figure 1. (a) SEM image of AAO template-grown MWNTs, showing the exposed tips at one side of the template. (Inset) HRTEM image of a typical MWNT released from the AAO template, near the wall, showing imperfect graphitization. (b) Raman spectra of the MWNTs inside a fractured AAO template taken in two configurations, top and side, as represented by the schematic.

which are highly disordered with poor long-range graphitization.12, 13 When the template surface is slightly etched off using a dilute solution of NaOH, the cylindrical open capped nanotubes get exposed. Figure 1a shows an SEM image of the exposed tips of the MWNTs grown inside the templates. The incomplete graphitization of the nanotube walls becomes clearer in a highresolution TEM image (inset, Figure 1a), where the short graphitic flakes of the walls can be identified. Figure 1b shows the Raman spectra (excitation wavelength = 532 nm) of the nanotubes inside a fractured template, obtained from two different orientations: top and side. The overall intensity of the Raman spectrum is stronger when taken from the fracture surface, due to a larger exposure of the nanotube surface in this configuration. In well-graphitized carbon nanotubes, the in-plane graphitic G peak appears typically at about ~1580 cm-1. However, owing to the different growth mechanism and low growth temperature (~650Ë&#x161;C), for templateassisted catalyst-free CVD grown MWNTs, the position of the G band can blue shift to values above 1600 cm-1.12 In MWNTs used in this work, the G-peak occurred at ~1605 cm-1, and is accompanied by a wide D band (at ~1340 cm-1), which arises from defects, for both spectra. Although the relative intensity ID/IG is slightly larger for the spectrum obtained from the top IRSAPS Bulletin 2011, Vol. 1, Issue 1

ÂŠ IRSAPS

surface, they are both of the order of 1, comparable to past reports for template-grown MWNTs.13 The large D band mostly arises from the edges of the large number of graphitic flakes that make up the walls of the nanotubes, with some contribution from the open caps, indicating that the pristine tubes were indeed quite defective. Then, the template is dissolved leaving behind individual and well separated tubes. MWNTs are dispersed in isopropanol, sonicated for 20 minutes and spin-cast on a Si/SiO2 substrate lithographically pre-patterned with larger contact pads of Ti/Au. Two-terminal devices were fabricated using individual MWNTs of diameter d=200-250 nm with platinum leads (separation L4-5 µm) attached by focused ion beam lithography. Platinum has been shown to form Ohmic contacts with carbon nanotubes, and in the present case, linear current-voltage characteristics in all our devices for biases up to 1V are found.14 The conductance enhancement of carbon nanotubes has been achieved by a sweeping-rate-controlled, high-bias application process in vacuum (p<10-5Torr). Past experiments have demonstrated that sweeping an applied bias across nanotubes can generate substantial local heating to melt metal nanoparticles, and re-structure nanotubes at the atomic level.15, 16 We find that by a controlled sweep of the applied bias, we can significantly change the surface morphology of MWNT devices, as shown in Figure 2. The HBT process is essentially a rapid cyclic current-voltage (IV) measurement process with increasing biases. Figure 2 (main

Figure 2. (Central panel) Change in the IV curve across an individual carbon nanotube device due to high-bias treatment. SEM images of a MWCNT device near the contact region before (left panel) and after (right pael) the HBT process. Pltinum nanoclusters decorate the nanotube after the HBT process.

IRSAPS Bulletin 2011, Vol. 1, Issue 1

panel) shows the IV during an HBT-induced decoration. It has been observed that at about a threshold bias, V  10V, the current jumps suddenly and irreversibly; this threshold bias required to “initiate” this current enhancement is usually larger for slower sweeps, indicating that the process is a non-equilibrium one, where the changes happen before the power dissipates through the contact or substrate. Subsequent cycling at lower biases does not recover the high resistance state, i.e., the change is permanent. We selected large (d > 200nm) nanotubes for (left) pre- and (right) post-HBT SEM imaging, which shows surface decoration of the nanotube with Pt nanoclusters after the HBT process. Upon closer view at the same nanotube-electrode junction after the HBT, clear evidence that the particles start from the bulk of the electrode as a thin continuous layer, and rapidly break into discontinuous islands till they become isolated nanoclusters is found. Upon repeating the HBT process many times (i.e. 5-10 cycles), one reaches a saturation of the conductance enhancement, and the entire nanotube surface is found to be covered with metal nanoclusters (not shown). The HBT process generates substantial local heating due to the rapid high-bias cycling. This heating

does

damage

the

not contact

region, but appears to affect the bulk area, indicating

that

the

maximum bias drop is across the bulk of the nanotube, and not at the contact. Low-bias

(V=1mV)

conductance pristine

and

the HBT-

modified devices were measured

for

5K<T<300K.

The

pristine

were

devices

highly disordered, with room-temperature

Figure 3: (a) Temperature dependence of G in a pristine device, and after each step of 2 successive HBTs. The solid lines show Lüttinger liquid (LL) fits in the higher T region and the dashed lines show the Al’tshuler-Aronov (AA) fits in the lower T region. (b) Bias dependence of dI/dV in HBT-modified devices at T=7K, showing the LL power-law behavior at high biases (solid lines).

IRSAPS Bulletin 2011, Vol. 1, Issue 1

resistances R300K10‟s of M. The HBT-modification dropped the R300K down to a few 10‟s of k. In the past, the Lüttinger liquid (LL) model has been successfully used to explain the temperature and bias dependence of conductance G in “clean” carbon nanotubes (such as arcdischarge grown carbon nanotubes): G(T ) ∝T α for eV / k BT << 1 , and G(V ) ∝V α for eV / k BT >> 1 . We find marked deviation from this “clean” Lüttinger liquid behavior in our systems. The presence of disorder in Lüttinger liquids can cause weak localization at low temperatures.17,18 Other reports have observed variable-range hopping, two-wall conductance, or environmentquantum-fluctuations at low-temperatures in carbon nanotubes.19-21 Attempts to analyze our data in the framework of these mechanisms, or the finite-temperature effect of interaction-driven dephasing in single-channel disordered LLs were unsuccessful.22 Recent predictions by Mora et al. suggest that electron-electron (e-e) interactions in manychannel LLs suppress the conductance G at low temperatures following an Al‟tshuler-Aronov (AA) correction.23, 24 We find that the observed temperature dependence of conductance could be quantitatively analyzed using this model. Figure 3 shows the temperature dependence (5K<T<300K) of low-bias (1mV) G in a typical pristine device and after each step of two HBTmodification process. The overall behavior in all our devices is a slow, power-law dependence of conductance G(T ) ∝T α at higher T, with sharp suppression of G at lower T. In a disordered multi-channel LL, at higher temperatures T>>T‟ (defined later), e-e interactions renormalize the

2e 2 2π Drude conductivity to give a temperature dependence, σ (T ) = Nv F τ 0 ( 1.577 ) h e

k T [ B ] ωc

where vF is the Fermi velocity  8105 ms-1, 0 is the elastic scattering time, c is the ultraviolet cutoff frequency, and N represents the number of LL channels. At lower temperatures (T<<T’), the interplay of disorder and interactions gives rise to an Al‟tshuler-Aronov correction to the Tdependence,  (T )  Nv F  0

 2e 2  0.782 1 h  (1  g )  -α

scattering rate ( τ 0' = τ 0 (ωC τ 0 )

(1+α ) ),

 k B T 0'    

   

1 / 2 

 , where (0‟)-1 is the renormalized elastic  

g is the Lüttinger parameter, g = (1 +

NU -1 / 2 ) , and U πv F

represents the interaction potential.21 U>0 indicates increasing repulsive e-e interactions, which drives g0. Using the LL-AA model, independent fits for the high- and low-temperature regimes (shown with solid and dashed lines in Figure 3a) were used to analyze our data. Table 1 summarizes the transport properties obtained in two devices, both for their pristine state, as well IRSAPS Bulletin 2011, Vol. 1, Issue 1

as after two HBT cycles, obtained from the LL-AA analysis of their temperature dependence of conductance. At higher temperatures, the pristine devices had large values of α (2<α<4 for most devices), unexpectedly high for single LL channels, but possible for sequential end-end tunneling of electrons across multiple LLs. Pristine devices were also found to have very short mean-free paths le (0vF) < 5 nm, and small values of 0, 10-15s. However, no self-consistent solution could be obtained for N 1. Additionally, at the lowest measured T, G showed no power-law dependence on the bias, V. Template-grown nanotubes have poor long-range graphitic order, as shown in Figure 1, the charge-transport being via end-end tunneling between shorter graphene flakes. Hence, pristine devices cannot be considered as a continuous channel, but rather, a tunneling network of short length-scale LLs, with high disorder density (L/le103). Table 1. Transport properties obtained from the LL-AA fits for two devices which have each undergone two HBT cycles. Here, D = Drude conductivity, N = number of channels, le = elastic mean free path, τ0 = elastic mean free time, T’ = [2kBτ0’/h]-1 = LL–AA transition temperature.

D (S.m) N le (10-9m) Nle(10-9m) L/le τ0 (10-15 s) T’(K)

Device 1 (L=4.5μm) Pristine HBT-1 HBT-2 2.785 0.46 0.24 -13 -11 2.110 2.110 5.810-11 7 21 <2.7 39 36 273 756 >1642 114 126 <3.4 49 45 187 179

Device 2 (L=4.1μm) Pristine HBT-1 HBT-2 2.2 0.16 0.15 -13 -11 3.610 4.110 4.710-11 11 5 <4.7 48 121 528 605 >872 85 34 <5.9 60 152 122 50

In contrast, in most of the HBT-modified devices the low-T/high-V differential conductance dI/dV vs. V follows a power-law behavior with the same exponents as seen in the corresponding high-T/low-V G vs. T (Figure 3b, T7K). Using U / πvF = 6 , we found a large increase in the number of channels (N= 5–21) and le ( 35–120 nm) in our HBT-modified devices (Table 1), which collectively cause the orders of magnitude enhanced conductance.24 The large increase of le (or decrease of disorder density, L/le<102) is clearly a result of improved graphitization during the HBT. Previous reports have shown that thermal annealing of defective carbon nanotubes up to 2000˚C can restore graphitization of the nanotube walls, improving the

IRSAPS Bulletin 2011, Vol. 1, Issue 1

conductivity of nanotubes by up to an order of magnitude, and we believe that the intense local Joule heating during the HBT improves the graphitization in our MWNTs as well.13, 15, 16 While

annealing

improved give

induced

graphitization

rise

can

improved

conductance up to an order of magnitude in these disordered nanotubes,

clearly

insufficient to explain the more than two orders of magnitude improvement

in conductance

seen in our MWNTs.13 The analysis shows that in addition to

the

decrease

defect

density, the number of channels have also increased in post-

Figure 4. Density functional theory (DFT) calculations of density of states (DOS) as function of addition of platinum atoms showing a systematic increase of the DoS near the Fermi level. (Right) Schematic representations of the corresponding energy-optimized structures of the SWNT-Pt cluster.

HBT devices. To investigate if platinum surface decoration can give rise to the observed channel enhancement in our HBT-modified devices, ab-initio DFT calculations on a (5, 5) singlewall nanotube using periodic boundary conditions along the tube axis are performed.25 Figure 4 summarizes the effect of placing 2 and 3 Pt atoms (per supercell) on the nanotube wall, on the density of states (DoS). The pristine nanotube has a finite but small DoS around the Fermi level. Addition of 2 Pt atoms gives rise to enhanced DoS near the Fermi level and the addition of a third Pt atom causes further enhancement of available states near the Fermi level. Calculations based on Landauer formalism and Green‟s function method using Au contacts confirm enhancement of conductance G (not shown) as the Pt atoms are added on the nanotube surface, and these effects can be expected to grow with further Pt coverage of the nanotube surface. Although these calculations are performed for a single-wall nanotube, similar behavior is expected for multi-wall nanotubes since inter-shell van der Waal‟s couplings are weak compared to the Pt-coupling, which is chemical in nature. Hence, platinum decoration is at least partially responsible for the experimentally observed channel enhancement. 3. Conclusions In conclusion, a simple method that simultaneously decreases the disorder density and increases the number of quantum channels of individual template-grown carbon nanotubes has IRSAPS Bulletin 2011, Vol. 1, Issue 1

been demonstrated. This procedure generates sufficient Joule heating to decrease the disorder by restoring the graphitization of the poorly graphitized pristine nanotubes as reported previously using bulk annealing of similar systems. In addition, the decoration of the nanotubes by Pt atoms can give rise to enhanced DoS near the Fermi level that increases the number of conducting channels in the nanotubes. Both these factors contribute towards the large decrease in resistance and pave the way towards the integration of template-grown carbon nanotubes in high-conductance technologies such as nanoscale electrical interconnects. Low-temperature transport in these systems undergoes a transition from a Lüttinger liquid to an Al‟tshuler-Aronov regime, providing the first experimental evidence of the recent theory by Mora et al.. We note that it is the presence of finite disorder density (even in the post-HBT devices) and its interplay with e-e interactions in a strongly correlated multi-channel 1D system that drives the Lüttinger liquid into an Al‟tshuler-Aronov anomaly at low T. Electron microscopy reveals that the HBT process decorates the carbon nanotubes with platinum nanoclusters, and modifies their surface morphology. The enhancement of the number of conducting channels due to Pt decoration of the MWNTs is also independently investigated using DFT calculations, which show enhanced electronic bands and DoS near the Fermi level, revealing the role played by platinum in the system. These results open up new avenues for field-theoretical, computational and experimental research in 1D hybrid structures. Further, the in-situ surface decoration technique can be extended to fabricate other new generations of 1D and 2D hybrid nanomaterials.

Acknowledgement The author thanks Proff. P. M. Ajayan (Rice University), S. Kar (Northeastern University) and S.K. Nayak (Rensselaer Polytechnic Institute) for their support during this work while at Rensselaer Polytechnic Institute. Financial support for this work was provided by the Interconnect Focus Center New York at RPI, one of the five Focus Center Research Programs of the Semiconductor Research Corporation. References and notes 1. Michael, N. L.; Kim, C.-U.; Gillespie, P.; Augur, R. J. of Elec. Mat. 2003, 32, 988. 2. International Technology Roadmap for Semiconductors 2007 edition: Executive Summary, page 42, (http://www.itrs.net/Links/2007ITRS/ExecSum2007.pdf). 3. Wei, B. Q.; Vajtai, R.; Ajayan, P. M. Appl. Phys. Lett. 2001, 79, 1172. 4. Kreupl, F.; Graham, A. P.; Duesberg, G. S.; Steinhoëgl, W.; Liebau, M.; Unger, E.; Hoënlein, W. Microelec. Eng. 2002, 64, 399. 5. Koo, K. H.; Cho, H.; Kapur, P.; Saraswat, K. C. IEEE Trans. Elec. Dev. 2007, 54, 3206.

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6. Naeemi, A.; Meindl, J. D. IEEE Trans. Elec. Dev. 2007, 54, 26. 7. Naeemi, A.; Meindl, J. D. IEEE Trans. Elec. Dev. 2006, 27, 338. 8. Ando, Y.; Iijima, S. Jpn. J. Appl. Phys. 1993, 32, L107. 9. Vajtai, R.; Wei, B. Q.; George, T. F.; Ajayan, P. M. Topics in App. Phys. 2007, 109, 188. 10. Avouris, P.; Chen, Z. H.; Perebeinos, V. Nature Nanotech. 2007, 2, 605. 11. Che, G.; Lakshmi, B. B.; Martin, C. R.; Fisher, E. R.; Ruoff, R. Chem. of Mater. 1998, 10, 260. 12. Cho, Y. S.; Song, I. K.; Hong, S.-K.; Im, W. S.; Choi, G. S.; Kim, D. J. J. Ko. Phys. Soc. 2005, 47, 344. 13. Mattia, D.; Rossi, M. P.; Kim, B. M.; Korneva, G.; Bau, H. H.; Gogotsi, Y. J. Phys. Chem. B 2006, 110, 9850. 14. Manohara, H. M.; Wong, E. W.; Schlecht, E.; Hunt, B. D.; Siegel, P. H. Nano Lett. 2006, 5, 1469. 15. Chen, S.; Huang, J. Y.; Wang, Z.; Kempa, K.; Chen, G.; Ren, Z. F. Appl. Phys. Lett. 2005, 87, 263107. 16. Papadopoulos, C.; Rakitin, A.; Li, J.; Vedeneev, A. S.; Xu, J. M. Phys. Rev. Lett. 2000, 85, 3476. 17. Langer, L.; Bayot, V.; Grivei, E.; Issi, J.-P.; Heremans, J. P.; Olk, C. H.; Stockman, L.; van Haesendonck, C.; Bruynseraede, Y. Phys. Rev. Lett. 1996, 76, 479. 18. Schönenberger, C.; Bachtold, A.; Strunk, C.; Salvetat, J.-P.; Forró, L. Appl. Phys. A 1999, 69, 283. 19. Jang, W. Y.; Kulkarni, N. N.; Shih, C.; Yao, Z. Appl. Phys. Lett. 2004, 84, 1177. 20. Skákalová, V.; Kaiser, A. B.; Woo, Y.-S.; Roth, S. Phys. Rev. B 2006, 74, 085403. 21. Tarkiainen, R.; Ahlskog, M.; Penttila, J.; Roschier, L.; Hakonen, P.; Paalanen, M.; Sonin, E. Phys. Rev. B 2001, 64, 195412. 22. Gornyi, I. V.; Mirlin, A. D.; Polyakov, D. G. Phys. Rev. Lett. 2005, 95, 046404. 23. Mora, C.; Egger, R.; Altland, A. Phys. Rev. B 2007, 75, 035310. 24. Mora, C.; Egger, R.; Altland, A. Semicond. Sci. Technol. 2006, 21, S46. 25. Parr, R. G.; Yang, W. Density-Functional Theory of Atoms and Molecules, Oxford University Press, Oxford 1989.

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Health Capsule

Recent trends in cancer treatment Manish C. Pathak Department of Biochemistry Emory University School of Medicine 1510 Clifton Road NE, Atlanta, GA 30322 USA E-mail: pcmanish@gmail.com

Many population groups across the world suffer disproportionately from cancer and its after-effects. Overcoming cancer health disparities is one of the best opportunities we can have for lessening the burden of cancer and its ill effects on society. The knowledge of the diseases and precautions necessary to overcome them has contributed significantly in recent trends of various cancer forms. Smoking can cause cancer almost anywhere in our body. Nearly 9 out of 10 men who die from lung cancer smoked. Breathing tobacco smoke causes increase in harmful triglycerides level. The damage of smoking is so severe that even after ten years of quitting, the risk of death from lung cancer drop by only half. However, on positive side, the risk for heart attack drops sharply just 1 year after quitting. After 2 to 5 years chances of stroke reduce to same as that of a nonsmokerâ&#x20AC;&#x;s. In a recent revelation, the breast cancer mortality rate in Pakistan is the highest in the world. The prime reason behind it could be its late detection due to the social stigma. In a correlation between breast cancer and abortion, Dr Joel Brind, professor of endocrinology at Baruch College, City University of New York and director at the Breast Cancer Prevention Institute asserts that abortion has led to 300,000 additional breast cancer deaths in the United States since 1970, when the Supreme Court decision legalized the act. In a recent study, it is observed that women who had radiation therapy for breast cancer in the days before widespread use of chemotherapy were at increased risk for cardiovascular mortality because of exposure of the heart to radiation. Breast cancer mortality has decreased 20 to 25 percent over the last 20 years.

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Lung cancer, which is mostly caused by cigarette smoking, is the leading cause of cancer-related deaths in the United States. In a study from Taiwan, the rate of lung cancer mortality is more than six times higher, in patients with tuberculosis than in non-tuberculosis patients. The risk of lung cancer may increase further to almost 16 times greater if patients with tuberculosis also suffer from chronic obstructive pulmonary disease. In the latest study, smokers screened with CT scans had a significantly lower 10-year mortality rate compared to unscreened smokers. Hexavalent chromium, widespread in US tap-water, has been known to cause lung cancer when inhaled, and when ingested causes liver and kidney damage as well as leukemia, stomach cancer and other cancers. An European study asserts that smoking-related deaths account for around 40 to 60% of the gender gap, while alcohol-related mortality typically accounted for 20 to 30% of the gender gap in eastern Europe and 10 to 20% elsewhere in Europe. Men being the smoker live shorter life than women. Around half a million cases of cervical cancer is diagnosed worldwide annually. In the United States, 11,000 women are diagnosed with cervical cancer each year, and 11 women die daily from the disease. In a study of 1,000 cases of cervical cancer worldwide, HPV was present in 99.7 percent of those cases. That is why we now understand that persistent HPV infection is strongly associated with cervical cancer. All women over age 30 are at risk for cervical cancer, which is highly preventable because screening tests (such as the Pap test) and vaccines to prevent HPV infections are available. In 2006, an HPV vaccine was approved by the U.S. Food and Drug Administration. HPV vaccine protects against certain HPV types that are responsible for 70 percent of cervical cancers. Prostate cancer is the most frequently diagnosed form of cancer among men in the United States and affects one in six U.S. men during their lifetime. More than 2 million men in the US and 16 million men worldwide are prostate cancer survivors. A new study of men with prostate cancer finds that physical activity is associated with a lower risk of overall mortality and of death due to prostate cancer. Thyroid cancer research indicates that the disease is being increasingly diagnosed in the U.S., although its mortality rate has slightly decreased recently. Similarly, lymphoblastic leukemia is now about 80 to 90 per cent curable. Bladder cancer is the most expensive cancer to treat, and one in which survival has not improved in last 25 years. Higher colon cancer mortality rates in the northeastern US and less in the Sunbelt, which offers naturally occurring higher levels of vitamin D, suggest a correlation between sunlight and colon cancer. In last century, exposure to the Sun was found to help heal tuberculosis patients too. In USA, liver IRSAPS Bulletin 2011, Vol. 1, Issue 1

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cancer mortality rates for african-american patients were significantly higher than that for white patients by 24%. Esophageal carcinoma, highly related with tobacco use is the sixth leading cause of cancer death in the world and despite multiple studies evaluating different treatment modalities the mortality rate remains high. For neuroendocrine cancer, the survival rate today is roughly 55 to 57%, up from less than 20% in 2004. A promising drug co-developed by Roche and Plexxikon, has helped previously untreated patients with advanced skin cancer to live longer without their disease getting worse in a phase III trial. Melanoma patients who took the pill, known as RG7204, found the size of their tumors had shrunk by 80 percent, according to scientists at the Royal Marsden National Health Service Trust in London. The drug works by finding the patientsâ&#x20AC;&#x; mutated gene, called BRAF, and shrinking the tumors. There are an estimated 40,000 deaths worldwide from the disease, with the number of cases in developed countries predicted to double from 138,000 a year to alarming 227,000 by 2019. In a breakthrough, a simple blood test is able to detect minute quantities of cancer cells that might be circulating in the bloodstream. In many cases, it will enable early treatment and hence will save numerous lives. However, this test could easily start a cancer epidemic including those individuals whom cancer was never going to bother, eventually. Omega-3 fatty acids have been shown to reduce the risk of various types of cancer, including colorectal cancer, prostate cancer mortality and breast cancer in women. In addition to being rich in healthy omega-3 fatty acids, fish and seafood provide a number of important nutritional benefits. This includes reduction in coronary heart disease and lower risk of strokes too. Since cancer patients and survivors are at higher risk for complications from the flu, including hospitalization and death, they should take extra precautions to help avoid spreading the flu. Healthy life appears to bring happiness to us but most of the time we do not know where to begin. To keep health as our priority every new year most of us accommodate health in our resolutions. Make healthy food choices e.g., fruits, nuts, or low-fat diet. Specific activities add up to the positive effects, for example taking the stairs instead of the elevator. Be well informed about health issues and take appropriate action/precaution. Wash your hands with soap and water. Be smoke-free and above all get enough sleep because sleep is a necessity, not a luxury.

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Mini review

An overview of solar photovoltaic technologies Sanjay R. Dhage Center for Solar Energy Materials International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI) Balapur, Hyderabad 500005, Andhra Pradesh, India E-mail: sanjay.dhage@gmail.com

In this article, a brief review on various solar cells is presented. Apart from a brief history of photovoltaic technologies, various classes of solar cells and the working principle are also presented. The article also gives an overview on current technological developments in Indian perspectives.

1. Background For the first time in the history of mankind, we are the ones influencing the climate â&#x20AC;&#x201C; a result of the constant increase in global energy consumption. At the same time we all know that fossil fuel supplies are limited. It is time to reconsider and to put words into action. The depleting stock of fossil fuel sources and the realization of the detrimental long-term effects of emissions of CO2 and other greenhouse gases into the atmosphere have forced mankind to think for alternative energy sources, especially renewable energy resources. Additionally, todayâ&#x20AC;&#x;s world is increasing sensitive toward energy security and price stability. The most common renewable energy sources are wind, hydro-electric and tidal, solar, etc. Amongst the renewable energy sources, harvesting energy from sunlight is increasingly being recognized as an essential component of future global energy solution. The last decade has seen photovoltaic (PV) as emerging technology for power generation. Nowadays, PV systems are used in many consumer appliances. From rooftop solar panels for homes and recreational vehicles to cellular-phones and laptop computer recharges, photovoltaic devices are available commercially. The price of such systems has fallen over the years, yet the technology remains expensive compared with other energy sources. In addition for some types of PV cells, the efficiency, stability, durability and other performance

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characteristics are much lower than theoretically predicted values. A typical solar system to generate electrical energy using solar cells is shown in figure 1. Brief history of PV: In 1839, Becquerel observed that there was a light dependant voltage between two electrode immersed in an electrolyte. Later, in 1876 the same effect was demonstrated in selenium. In 1941, first silicon based solar cell was demonstrated. However, 1954 was the year for the beginning of modern solar cell research. Till date, various types of PV devices have emerged and been undergoing research at various levels across the world.

Figure 1: Schematic of the solar PV system to generate electrical energy.

2. Working principle PV systems produce electricity when exposed to sunlight. When sunlight (composed of photons) strikes a PV material, photons will either pass through, be reflected, or be absorbed. If the photon is absorbed, it generates excitons in the PV material. With the new found energy, the excitons will generate a pair of electron and positron. Under normal conditions, the pair of electron and positron recombines and no net gain of electrical energy is observed. However, if certain conditions are fulfilled, the electron can flow into a circuit generating photocurrent, which in turn augments the process of solar energy conversion to electrical energies. This “photovoltaic effect” is the basic physical process through which sunlight is converted into electricity (Figure 2). The primary building block of a PV system is the PV cell. Figure 3 shows a schematic of PV cell, module and array. A typical PV cell is about 3” X 3” and very thin. By itself, a single PV IRSAPS Bulletin 2011, Vol. 1, Issue 1

cell produces only a small amount of electricity. Fortunately, it is easy to increase the total power in a PV system by connecting several cells to form larger units called modules. Modules, in turn, can be connected to form even larger units know as arrays, which can be interconnected to produce more power, and so on. In this way, a PV system can be built to meet almost any power need, no matter how small or large is the requirement.

Figure 2: Schematic and working principle of solar photovoltaic cell.

3. Present status of solar technology The last decade has seen PV technology emerging as a potentially major technology for power generation in the World. The robust and continuous growth experienced in the last ten years is expected to continue in the coming years. By the end of 2008, the World cumulative PV power installed was approaching 16 GW. Today, almost 23 GW is installed globally which produces about 25 TWh of electricity on a yearly basis. Europe is leading the way with almost 16 GW capacity facility was installed in 2009, representing about 70% of the World cumulative PV power installed at the end of 2009, while Japan (2.6 GW) and USA (1.6 GW) are following behind. The annual market has developed from less than 1 GW in 2003 to more than 7.2 GW in 2009 in spite of the difficult financial and economic circumstances. After a 160% CAGR (Compound Annual Growth Rate) growth from 2007 to 2008, the PV market in 2009 continued to grow another 15% in 2009.1 While Germany reclaimed its leadership, many other markets have started to show significant development. In 2008, the Photovoltaic industry production reached a world-wide production volume of 7.3 GWp of photovoltaic modules. Yearly growth rates over the last decade were in average more than 40%, which makes photovoltaics one of the fastest growing industries at present. Business analysts predict the market volume to increase and expect lower prices for consumers. The trend that thin-film photovoltaic grew faster than the overall PV market continued in 2009. India's power sector has a total installed IRSAPS Bulletin 2011, Vol. 1, Issue 1

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Figure 3: A schematic structure of cell, module and array.

capacity of approximately 1,46,753 MW, of which 54% is coal-based, 25% hydro, 8% is renewable and the balance is the gas and nuclear-based. Power shortages are estimated at about 11% of total energy and 15% of peak capacity requirements and are likely to increase in the coming years. 2

Figure 4: Solar energy resource locations in India.3

Among the Sunbelt countries (located between 30 degrees North and 30 degrees south of the equatorial line), India has a specific role to play. Figure 4 shows the locations in India for solar energy installations. High solar irradiation levels of 1700 kWh/m 2 per year are available at IRSAPS Bulletin 2011, Vol. 1, Issue 1

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such locations. With an increasing energy demand and high irradiation levels, the country has a huge potential for PV. The recent targets defined by the government in the solar mission (20 GW of PV in 2022) tend to favor the idea that this market could boom in the coming years. Starting from a low 30 MW installed in 2009, it could grow to 1.5 GW in 2014 in the PolicyDriven scenario and probably well beyond afterwards. According to the European Photovoltaic Industry Association‟s (EPIA) estimations, the market size in 2010-2011 will clearly depend on the policies and choices and will possibly reach between 50 MW and 300 MW. Despite the announcement of national solar mission in 2009, the market expects much of the possible decisions on the current year to define a long term power purchase agreement that could definitively trigger widespread PV deployment in India. 4. Available PV technologies Based on the different technologies and materials, the PV technology has been grouped in four different generations First generation PV cells are of large area, single-crystal, single layer p-n junction diode, capable to generate usable electricity from light sources with the wavelengths of sunlight. These are typically made using diffusion process with silicon wafers. The silicon wafer-based solar cells are the dominant technology towards commercial production of solar cells accounting for more than 85% of the terrestrial solar cell market. Second generation PV cells are based on the use of thin epitaxial deposits of semiconductors on lattice-matched wafers. There are currently a number of technologies/semiconductor materials under investigation or in mass production mainly amorphous silicon, polycrystalline silicon, micro-crystalline silicon, cadmium telluride (CdTe), copper indium gallium selenide or sulphide (CIGS). An advantage of thin-film technology is the reduced mass which allows fitting panels on light or flexible materials. Thin film PV cells represent a small share of global solar PV production, but it has been accepted as a “mainstream” technology in recent years, due partly to manufacturing maturity and lower production costs, and partly to its advantage in terms of feedstock - it requires just one-hundredth as much material as conventional cells.

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Third-generation PV cells are proposed to be very different from the previous semiconductor devices as they do not rely on a traditional p-n junction to separate photo-generated charge carriers. The dye sensitized solar cells fall in this category. Fourth generation PV cells are the hypothetical generation of solar cells, may consist of composite photovoltaic technology, in which polymers with nano-particles can be mixed together to make a single multi-spectrum layer. The multi-spectrum layers can be stacked to make tandem solar cells more efficient and cheaper.

Figure 5: Reported timeline for solar energy conversion efficiency. 4

The last two generations of solar cells are still at research and development stage. It will take few more years to understand the underlying science and technology to bring them to commercial level. Apart from various Si based solar cells, researchers are examining a wide range of materials for use in photovoltaic devices. The list includes various crystalline forms of inorganic IRSAPS Bulletin 2011, Vol. 1, Issue 1

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semiconductors and several types of electrolytes and organic polymers. Figure 5 shows the best research cell efficiencies of various solar cells reported over time. Scientist and engineers also are focusing on novel solar cell designs and low cost processing and manufacturing techniques. Table 1: Comparison of various PV technologies. Solar Materials

Thickness

Mono- Si

0.3 mm

Efficiency of cell (%) 24.4

Disadvantages

Poly- Si

0.3 mm

20.3

Poly- Si ribbon

0.3 mm

16.6

a- Si

0.0001 mm on substrate

9.5

Lower efficiency Shorter life span

Cadmium Telluride (CdTe)

0.008 mm on substrate

16.5

Poisonous raw materials

Cu(In,Ga)Se2 (CIGS)

0.003 mm on substrate

20.1

Limited indium supply

Dye sensitized solar cells

0.05 mm on substrate

11.6

Organic- inorganic nanocomposites

0.002 mm on substrate

5.5

Lower efficiency Degradation of dye Still under research and development state Lower efficiency Still under research and development state

Lengthy production procedure Wafer sawing necessary. Lengthy production procedure Wafer sawing necessary. Further reduction in price and increase in efficiency is difficult Limited use of this production procedure

Advantages and perspective Best researched solar cell material Highest power/area ratio Most important production procedure at least for the next ten years.

No wafer sawing necessary. Significant decrease in production cost is possible in future No sawing necessary Possible production in flexible form. Significant decrease in production costs expected in the future. Clear pathway to improve efficiency Significant decrease in production costs possible in the future. Possible production in flexible form. Lower efficiency. Easy processing

Lower efficiency Shorter life spam Easy printing process. Possible production in flexible form.

5. Comparison of various PV technologies Table 1 summarizes the comparison of existing PV technologies. All commercially viable PV products are made using one of two groups of technologies, crystalline silicon or thin-film IRSAPS Bulletin 2011, Vol. 1, Issue 1

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materials. Traditional crystalline silicon is by far the most common solar cell material for commercial applications.5 This is because it has been in use for more than 50 years, and its manufacturing processes are well known.6 Those processes are now largely in the public domain. The raw material used, silicon, is very abundant. Although raw silicon is readily available, the silicon used in solar cells must be refined to an extremely high purity (99.99 %) â&#x20AC;&#x201C; far more refined than most of the prescribed medicines.7 Refining to this degree makes the silicon quite expensive. Thin-film material produced by deposition or by sputtering is a promising low cost alternative for photovoltaic appliances in future. The tested laboratory solar cells efficiency is up to 20.1%.8 CIGS thin-film material with efficiency of up to 20.1% is one of the most promising thin film technologies due to their high-attained efficiency and low material costs.9 Amongst thin film solar cells, the advantage of CIGS solar cell is its extended operational lifetime without significant degradation. The inherent properties of CIGS also provide an opportunity for maximizing the efficiency. The CdTe and CIGS technologies are promising and being explored extensively to replace Si based PV.10-13 The main disadvantage for CIGS and CdTe based technology is due to production specific procedures and poisonous material being used in production. Amorphous Silicon (a-Si) modules are the first thin film solar module to be commercially produced and at present has the maximum market share out of all thin film solar cell technologies despite lower efficiency. The dye sensitized and organic-inorganic composite solar cells are still at research and development stage.14,15 It will take few more years to understand the underlying science and technology to bring them to commercial level. Due to the scope and limitations of the present article, a detailed discussion on various solar technologies is not given. For more information, interested readers are referred to the works previously cited as well as to the following resources on specific aspects of solar technology and the references cited therein: Si and thinfilm inorganic photovoltaics, organic photovoltaics, third-generation photovoltaics.16-22 6. Summary It is clear from the preceding discussions that the solar power industry is on track to become a significant component of future global energy supplies. Although the industry is currently based on Si, ultimately, Si might not be able to meet long-term cost goals, opening the door to thin films and organic/composite materials. Significant materials challenges exist for IRSAPS Bulletin 2011, Vol. 1, Issue 1

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these technologies as well, but they are nearing manufacturability on a large scale, as evidenced in the recent growth of CdTe and CIGS production. New high-efficiency or low-cost technologies such as multi-junction and organic-based devices are advancing rapidly and might have second- and third-generation embodiments. Finally, new highly efficient approaches to solar energy conversion offer the potential in the extended time frame to produce devices that can convert much larger portions of the solar spectrum. Given the anticipated market growth, nearly all of these approaches will have to be investigated in parallel to meet the demand.

References and notes: 1. European Photovoltaic Industry Associations 2. www.solarpowerindia.com 3. www.refexenergy.com 4. National Renewable Energy Laboratory, USA 5. Bergmann, R. B. Appl. Phys.1999, A 69, 187. 6. Saga, T. NPG Asia Mater. 2010, 2, 96. 7. Bathey, B. R.; Cretella, M. C. Journal of Materials Science 1982, 17, 3077. 8. Green, M. A. Progress in Photovoltaics: Research and Application 2010, 18, 144. 9. Dhere, N. G. Solar Energy Materials & Solar Cells 2006, 90, 2181. 10. Shah, A. V.; Platz, R.; Keppner, H. Solar Energy Materials and Solar Cells 1995, 38, 501. 11. Meyers, P. V. Solar Cells 1988, 23, 59. 12. Mathew, X.; Enriquez, J. P.; Romeo, A.; Tiwar, A. N. Solar Energy 2004, 77, 831. 13. Romeo, A.; Terheggen, M.; Abou-Ras, D.; Ba¨tzner, D. L.; Haug, F. J.; Ka¨lin, M.; Rudmann, D.; Tiwari, A. N. Prog. Photovolt: Res. Appl. 2004, 12, 93. 14. Li, B.; Wang, L.; Kang, B.; Wang, P.; Qiu, Y. Solar Energy Materials & Solar Cells 2006, 90, 549. 15. Oregan, B.; Graztel, M. Nature 1991, 353, 737. 16. Miles, R. W.; Zoppi, G.; Forbes, I. Mater. Today 2007, 10, 20. 17. Messenger, R.; Goswami, D. Y.; Upadhyaya, H. M.; Razykov, T. M.; Tiwari, A. N.; Winston, R.; McConnell, R. in Energy Conversion (Editors: Goswami, D. Y.; Kreith, F.) CRC Press, Boca Raton, FL, 2007, p. 20. 18. Green, M. J. Mater. Sci. 2007, 18 (Suppl.1) S15. 19. Mozer, A. J.; Sariciftci, N. S. in Handbook of Conducting Polymers (Editors: Skotheim, T. A.; Reynolds, J.) CRC Press, Boca Raton, FL, ed. 3, 2007, 2, p 10. 20. MRS Bull. 2005, 30 (1). 21. Conibeer, G. Mater. Today 2007, 10, 42. 22. Luque, A.; Marti, A.; Nozik, A. J. MRS Bull. 2007, 32, 236.

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Feature article

Neutron activation analysis Rupesh H. Gaikwad Department of Chemistry, Institute of Chemical Technology, University of Mumbai, N. P. Marg, Matunga, Mumbai 400019, India E-mail: rupeshhgaikwad@gmail.com

Activation analysis ( Neutron ) is altogether become a very important tool in nuclear analytical chemistry due to its high accuracy, sensitivity and the quantitative analysis even at trace level. Activation analysis found extensive application in many fields of science and technology such as biomedical, metallurgy, agriculture, geology, chemical industry, forestry, environmental science

etc. In short

subject area which is remained untouched by activation analysis. In present paper a generic attempt is made to elaborate the activation analysis (NAA) growth from its inception and its application in various subject areas.

“The world is full of a number of things, I‟m sure we should all be as happy as kings”, said poet R. A. Steverson. He wanted to convey that the world indeed filled with number of things of which we know nothing about. Thus, most of our comparisons are in unknown class. The trace elements play a very significant and vital role in every sphere of technology, environment and human life is only re-enunciating the obvious.1 The indispensability of micronutrients for the well being of life, the role of toxic trace constituents, their profound effect on the mechanical, electrical properties of materials and their ecological and an environmental behavior have been well recognized by the scientific community.Efforts have been therefore focused on developing ultra trace elemental analytical techniques for their determination in a wide variety of matrices. It is in this context that the subject of nuclear and radiochemistry provided a very elegant and sensitive analytical tool in the form of neutron activation analysis (NAA). The copious number of neutrons required in NAA is obtained either from a nuclear reactor or a neutron source.2-8 Radioanalytical chemists throughout the world IRSAPS Bulletin 2011, Vol. 1, Issue 1

resort to exploit 26

this tiny tool for their analytical requirements. Near-universal appeal of this technique can be judged by its applications in such wide spectrum of fields as material science, forensic science, geology, analytical chemistry, archeology, cosmochemistry etc. Neutron is a part of nucleus which does not carry any charge but carries mass similar to that of proton. In 1932, James Chadwick in England discovered the neutron.2 In his words “The experimental results are very difficult to explain on the hypothesis that the beryllium radiation was a quantum (i.e. electromagnetic) radiation, but followed immediately if it were supposed that the radiation consisted of particles of mass nearly equal to that of proton and with no net charge”. In 1936, Prof, George de Havesy and Hilde Levi described the determination of dysprosium in the yttrium by irradiating the sample with neutrons from Ra-Be source and thus demonstrated the analytical utility and capability of neutron irradiations.9 In fact, they were investigating effects of neutron irradiation on rare-earth elements and stumbled upon „Neutron Activation Analysis (NAA)‟. The nuclear activation analysis is based on activation of the isotopes of chemical elements and subsequent measurement of induced radioactivity.10, 11 It provides information on both qualitative and quantitative chemical analysis of samples. If the activating source is neutron then it is called as neutron activation analysis. As being electrically neutral in nature, neutrons do not exhibit any columbic force of attraction or repulsion, and directly hit the nucleus of the element.

Principle Beta particle Target Nucleus

Prompt Gamma Ray

Radioactive nucleus

Product Nucleus

Incident Neutron

Compound nucleus

Delayed Gamma Ray

Figure 1. Interaction of neutron with target nucleus followed by emission of gamma rays.

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Due to its simplicity, selectivity and sensitivity NAA occupies an important place among the analytical techniques where macro, micro and trace elemental analysis is required.12 Table 1. Stepwise growth of NAA.

1936-1944

The induction period

1944-1950

The nuclear reactor

1950-1960

The NaI(Tl) detector

1960-1970

The Germanium detector

1970-2007

Extensive application

NAA is based on principle of irradiation of a sample with neutrons, preferably in a nuclear reactor and subsequently counting of the induced radioactivity (Figure1), employing γray spectrometers. NAA have precision of the order of 10-12 g. It gone through a stepwise growth in area as mention in Table 1.13, 14 Neutrons used for the activation purpose are classified on the basis of energy as, E > 1 MeV

Fast neutrons

E > 0.4 eV

Resonance neutrons

0.025 eV

Thermal neutrons

E = 0.1 – 1.0 eV

Epithermal neutrons.

There are different modes of approach of NAA depending upon sample matrix and element to be analyzed.15, 16 These are as mention in Table 2. NAA is divided into mainly three categories. If no chemical treatment is done, the process is called as INAA. After irradiation if radiochemical separation is carried out to remove interference or to concentrate the radionuclide of interest, the technique is called RNAA. If pre irradiation chemical separations are employed, the procedure is called as CNAA. A different form of NAA called PGNAA is also used, where it is the prompt γ- rays emitted by the excited IRSAPS Bulletin 2011, Vol. 1, Issue 1

intermediate nucleus that are monitored. DAA is a novel composite analytical approach that is used for elements that are poorly determined element is chemically exchanged for, or complexed with an element that is amenable to NAA. CAA is based on the concept of enhancing the sensitivity of the activation method for the determination of elements with short lived indicator radionuclides by use of repeated short irradiation are counting periods and summing of the Îł- ray spectra obtained. Table 2. Different approaches of NAA.

INAA

Instrumental NAA

CNAA

Chemical NAA

RNAA

Radiochemical NAA

PNAA

Prompt gamma NAA

DNAA

Derivative NAA

CAA

Cyclic activation analysis

INAA is more advantageous than RNAA in following aspects, RNAA

INAA

Destructive

Non-destructive

Chemical treatment required

No chemical treatment required

High chances of chemical contamination

Chemical contamination does not exist.

Activity formed in neutron activation: The absolute activity of the radionuclide, formed when an element is subjected to neutron activation, is given in equation (I),10, 11

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N. σ. Φ. S. D.

(NA .θ W/M ). σ. Φ. S. D.

Where, NA = Avogadro‟s number

(I)

θ = isotopic abundance

W = weight of the element

M = atomic mass

σ = capture cross –section

Φ = neutron flux

S = 1- e- λt = saturation factor

D = e- λt = decay factor

λ = decay constant

t = duration of irradiation and

T = cooling time Radioactivity of activation product is assayed by γ- ray spectrometry and in some cases by counting and is related to the concentration of the analyte by principle methods like absolute and relative method.10, 17, 18 Absolute method Radioactivity of activated products is measured by γ-ray spectrometry as given in equation (II), A = I W/M σ. Φ (6.023 x 1023 ) 1- e- λt . e- λt1 Where; I

(II)

= neutron flux which is used for bombardment

= weight of sample

= mass of the element to be determined

= neutron cross section in barns

= time of irradiation

= activity

6.023 x 1023 λ

= Avagadro‟s number = decay constant

Relative method (Comparator method) In this, a chemical standard with a known mass of the element is co-irradiated with the sample of a known mass and both are counted at detector. IRSAPS Bulletin 2011, Vol. 1, Issue 1

The ratio of activities of an isotope in sample and standard is related to the concentration of that isotope and hence the element Weight of element in standard x activity in sample Weight of the element in sample = Activity in standard Application of NAA NAA has found extensive applications in many science and technology fields for macro, micro and trace element analysis in the sample corresponding to the following fields; archaeology, biomedicine, biochemistry, animal and human tissues, environmental science and related fields, forensic, geology and geochemistry, industrial products, nutrition, quality assurance of analysis and certification reference materials some of them are described here.10, 19-24

Chromium content of a ruby: the 50Cr in natural chromium becomes by (n, Îł) reaction the 27.7 day

Cr. By irradiating ruby with a series of Al2O3 + Cr2O3 of known Cr content. It was

found that the rubies have 0.1 to 0.4 % of Cr. Due to non-destructive property the precious ruby remain undamaged. Determination of the manganese in tea leaves : The monoisotope Îł) reaction 2.58 hr.

Mn becomes by (n,

Mn. Neutron irradiation of a known weight of dry tea leaves, along with a

series of samples of known manganese content reveal that tea leaves contain around 0.13% of Mn about half of which passes into the brew and rest goes to waste. Certification of reference materials: The NAA methods have played an important role in the certification of inorganic constituents in many environmental certified/standard reference materials (CRMs/SRMs). Since the concentration

of an element is CRM / SRM certified by

agencies like NIST, IAEA, IRMM and USGS is usually determined by two or three independent analytical methods, the use of INAA as one method eliminates the possibility of common error sources resulting from sample dissolution. Other advantages includes; its property in its radiochemical mode of allowing trace element radiochemistry to be performed under controlled conditions by carrier additions, and the ease of obtaining the chemical yield by the carrier recovery or radiotracer method. Moreover, the method is theoretically very simple and the IRSAPS Bulletin 2011, Vol. 1, Issue 1

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source of uncertainty can be modeled and well estimated as per the international organization for standardization (ISO) guidelines. The estimation of combined uncertainty is an independent exercise and it is different than the calculation of standard deviation from the mean value of replicate measurements. The different uncertainty components were divided into three steps pre-irradiation step, irradiation step and γ-ray spectrometry measurement step. An additional step is considered if chemical separation step is done. The source of uncertainty components (μi) is converted into standard deviation. The combined uncertainty (μc) is calculated using error propagation formula. Finally the expanded uncertainty (Eu) is calculated using coverage factor of 2 at 95.5% confidence level (CL). Forensic application: INAA / RNAA methods are frequently used for analysis of forensic samples like gunshot residue, glass, hair ornamental gold and paper. Air pollution particulates determination(25) : Thirty three elements such as Ca, Ti, V, Cr, Al, S, Na, Mg, Mn, In, Cl, Br, I,K, La , Sm, Eu, Cu, Zn, W, Au, Ga, As, Sb, Sc, Ce, Th, Fe, Co, Ni, Ag, Hg, Se are determined by neutron activation analysis in air pollution particulates. The concentration of Cd, Co, Cr, Fe, Mo, Ni, Se, Ti, V and Zn in biological fluids, human blood serum and market milk (26) were determined by Neutron activation analysis. Geo and Cosmochemistry: The NAA results on rare earth elements in meteorites, rocks and sediments were a significant contribution to the development of morden geo and cosmochemistry (27). Trikatu, an Ayurvedic formulation of three dried powder spices, ginger, black pepper and pipali in equal proportion is widely used to promote digestion, assimilation and bioavailibility of food. Five different brands and its three constituents were analyzed for 31 elements by instrumental neutron activation analysis (INAA) using 5-minute and 6-hour thermal neutron irradiation followed by high-resolution γ-ray spectrometry.28 As coin have two sides NAA have advantages and limitations. Advantages  Sensitivity and applicability for minor and trace elements in a wide range of matrices. IRSAPS Bulletin 2011, Vol. 1, Issue 1

 Non-destructive in nature.  High-specificity.  Capability of multielemental determination and an inherent potential for accuracy compared to the other analytical techniques. Limitations:  Needs neutron source.  Maintenance is an economical constraint.  Determination of elements forming long lived isotopes is time consuming.  NAA is insensitive to the nature of chemical species present unless preirradiation separation is carried out. The NAA opens up a wide horizon to us to deal with. To sum up it will be very important and necessary for a common man to understand what nuclear chemistry is and how it functions. We have to pass the knowledge from one generation to another generation as Richard Feynma said: “If, in some catalysm, all of scientific knowledge were to be destroyed and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis……. That all things are made of atoms. In that one sentence, there is an enormous amount of information about the world if just a little imagination and thinking are applied”. References and notes 1. Muller, H.; Zwanziger, H. W.; Flachowsky, J. Trace analysis, Ullmann‟s Encyclopedia of Industrial chemistry Vol. B-5, VCH, 1994, 96. 2. Glasstone, S. Source Book of Atomic Energy, East-West press Pvt. Ltd: New Delhi, 1967. 3. Wise, E. N. J. Chem.. Edu. 1962, 39, A771. 4. Nass, H. W.; Maddock, R. S.; Meinke, W. W. J. Chem. Edu. 1964, 41, 156. 5. Bowen, H. J. J. Chem. Edu. 1975, 52, 682. 6. Harper, W. R. Basic Principles of Fission reactor, Wiley Inter-science, New York, 1961. 7. Mapper, D. Radioactivation Analysis, Inter-science, New York, 1960. 8. Lapp, R. E.; Andrew, H. L. Nuclear Radiation Physics, Princtone Hall, Englewood Clifs, 1963. 9. Hevesy, G.; Levi, H. Det. Kgl. Danske Videnskabernes Selskab, Mathematisk-Fysiske Meddelelser, 1936, 14, 3. 10. Soete, D. De.; Gijbels, R.; Hoste J. Neutron Activation Analysis, Wiley-Interscience; John-Wiley and Sons: London, 1972. 11. Lyon, W. S. Guide to Activation Analysis, JR., Editor, Van Nostrand, Princeton; N. J., 1964. 12. Ehman, W. D.; Robertson, J. D.; Yates, S. W. Anal. Chem. 1994, 66, 229R-251R. 13. Guinn V. P. J. Radioanal. Nucl. Chem. 1992, 160, 9.

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14. Bruin, M. D. E. J. Radioanal. Nucl. Chem. 1992, 160, 31. 15. Reddy, A. V. R.; Acharya, R.N. IANCAS Bulletin. 1999, 15, 3. 16. Reddy, A. V. R. IANCAS Bulletin. 2003, 11, 108. 17. Lukens, H. R. J. Chem. Edu. 1967, 44, 668. 18. Regan, K. J. Chem. Edu. 1978, 55, 203. 19. Arnikar, H. J. Essential of Nuclear Chemistry, New Age International (P) Limited: New Delhi, 2001. 20. Sayre, E. V.; Murrenhoff, A.; Weick, C. F. Brookhaven Nat. Lab, 1958, 7, BNL-508. 21. Glascok, M.D. Meas. Sci. Technol. 2003, 14, 1516. 22. Spencer, R. P.; Mitchell, T. G.; King, E. R. J. Lab. Chim. Med. 1957, 50, 646. 23. Reiftel, L.; Stone, C. A. J. Lab. Clin. Med., 1957, 49, 286. 24. Jervis, R. E. Nuclear Activation in life Sciences, Vienna. 1976. 25. Das, H. A.; Faanhof, A.; Vandersloot, H. A. Radioanalysis in Geochemistry, Elsevier, Amesterdam, 1989. 26. Dams, R.; Robbins, J. A.; Rahn, K. A.; Winchester, J. W. Analytical Chemistry, 1970, 42, 861. 27. Lavi, N.; Alfassi, Z. B. Analyst, 1990, 817. 28. Choudhary, R. P.; Kumar, A.; Reddy, A. V. R.; Garg, A. N. J. Radioanal. Nucl. Chem. 2007, 274, 411.

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Perspective

Protein folding: understanding nature’s intelligent ergonomics Ranjeet Kumar Institute for Cell and Molecular Biology, BMC, 75124, Uppsala University Uppsala, Sweden Tel: +46 (0) 735679746 E-mail: drkumar.ranjeet@gmail.com

Introduction Proteins are the most abundant molecule in biology other than water.1 Our body is made up of more than 1,00,000 different protein that virtually govern all the crucial life processes.2 The biopolymer proteins are made up of 20 different building blocks known as amino acid which assembles in many permutations and combinations giving rise to the wide diversity. The backbone of all amino acids is made up of a carboxyl and amide group the very nature of the side chains determines whether an amino acid will be hydrophilic or hydrophobic, acidic or basic. The linear sequence of the amino acids in a protein defines its primary structure. DNA undergoes transcription to yield RNA the process mediated by RNA polymerases which is further translated to yield the building blocks of proteins. The blue print for each amino acid is laid down by sets of three letters known as codons. The linear sequence is transformed in to functional protein by virtue of its indigenously motivated assembly in to a folded entity by the process of protein folding which finally gives it a three dimensional shape. A newly synthesized polypeptide must fold in to its native (biologically active) conformation. Secondary structure refers to repeating local configuration of residues, e.g. α-helices and β-sheets, generated mainly by the need for hydrogen bonds to form between peptide bond units. They assemble denovo to form larger and more complex molecular structures known as motifs (such as helix-turn-helix motifs), which may have particular roles interacting with other cellular components. Tertiary structure refers to the overall three-dimensional configuration of a polypeptide, reflecting many different types of chemical interaction, both covalent and non-covalent, which stabilize the most energetically favorable folding conformation. It encompasses the packing together of secondary and super-secondary structures to form compact globular structure called domain. Quaternary structure refers to the arrangement of polypeptide subunits in a multimeric protein. It is still a grey area that how proteins adopt their native state given the very large number of alternatively IRSAPS Bulletin 2011, Vol. 1, Issue 1

possible conformations available. Many proteins can exist in alternative stable conformations which show differential activity. Switching between these states can be regulated by covalent modification or non-covalent interactions with other molecules often termed as cooperativity and allostery.3 Forces governing structure, stability and folding of proteins The major forces that maintain the structural integrity of proteins are non covalent in nature. Covalent bonds are mainly involved in putting up the backbone framework of polypeptide but essentially the intramolecular and intermolecular disulfide linkages are important stabilizing force in maintaining the tertiary and quaternary sanctity of protein molecules respectively. Covalent linkages are also predominant in binding of prosthetic groups. Whereas coordinate linkages are seen in case of metal binding proteins and metaloenzymes.4 In a protein molecule, it is thermodynamically not feasible to expose predominantly hydrophobic residues to water, therefore proteins possess a hydrophobic core serving as sequestered warehouses for these residues, and a polar or charged surface exposed to the solvent. Polar atoms generally make hydrogen bonds with water, but where this is not possible, as in the hydrophobic core of a protein, the hydrogen bonding potential must be taken up by secondary structure. The formation of secondary structures, predominantly Îą-helices and Î˛-sheets, neutralizes the polar atoms of the backbone, and polar side chains can also be neutralized by hydrogen bonding with the backbone and with each other. The hydrophobic core is further stabilized by van der Waals' interactions (hydrophobic attraction), which increase as neutral atoms approach each other until the point of contact. Protein surfaces are generally rich in polar and charged residues although nonpolar residues are also exposed. In this manner, proteins can make non-covalent contacts with other molecules using electrostatic forces, hydrogen bonds and van der Waals' interactions. Electrostatic forces are important where protein and target have opposite charges, as in the 'salt-bridge' interaction between highly basic histones and the negatively charged phosphate backbone of DNA. Van der Waals' forces are particularly important for interactions between complementary surfaces, where water is excluded and binding brings the appropriate chemical groups into close proximity.5 The term stability can be defined as the inherent tendency to maintain native conformation. A given polypeptide chain can theoretically assume countless different conformations, and as a result the unfolded state of a protein is characterized by a high degree of conformational entropy. This entropy, and the hydrogen-bonding interactions of many groups in the polypeptide chain with solvent (water), tends to maintain the unfolded state. The chemical IRSAPS Bulletin 2011, Vol. 1, Issue 1

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interactions that counteract these effects and stabilize the native conformation include disulfide bonds and the weak (non-covalent) interactions such as hydrogen bonds, and hydrophobic and ionic interactions. An appreciation of the role of these weak interactions is especially important to our understanding of how polypeptide chains fold into specific secondary and tertiary structures, and how they combine with other polypeptides to form quaternary structures. In general, the protein conformation with the lowest free energy (that is, the most stable conformation) is the one with the maximum number of weak interactions.6 This entropy term is the major thermodynamic driving force for the association of hydrophobic groups in aqueous solution. Hydrophobic amino acid side chains therefore tend to be clustered in a protein‟s interior, away from water. Under physiological conditions, the formation of hydrogen bonds and ionic interactions in a protein is driven largely by this same entropic effect.5 Studies on the stability of protein mutants in which hydrogen bonds have been removed and calorimetric analysis of the a-helix to coil transition of an alanine peptide in water appear to suggest that both hydrogen bonding and hydrophobic effect make comparable contribution to the stability of globular proteins.7 Charged residues play at least two major roles: they define solubility of the protein and they could and are used to finely modulate protein stability. 8 Recently several groups reported the experimental data that show a significant stabilization of proteins with substitutions of the surface charges.9 Heat and chemical denaturants are the most important factors that make enzymes and proteins lose their activity.10 Thermal inactivation involves considerable conformational changes in the protein molecule. Heating leads to the breakdown of various forces like hydrophobic interactions, electrostatic interactions, hydrogen bonding, van der waals interactions, etc. within the protein leading to its denaturation. Hence, strengthening of one or several of these forces within the protein should help an enzyme retain its activity under temperature stress. Protein folding peeping in to nature’s blueprint Ability for a polypeptide to select one conformation, spontaneously and usually quite rapidly, from a myriad of alternatives, has given rise to what has come to be called “The Protein Folding Problem”.11 A completely random search of conformation would require an astronomically long time, but protein usually does not take more than a few second to fold. The difference in estimated and biologically relevant timescales is called Levianthal‟s paradox. 12 Protein folding mechanism has been intellectually churned by various groups to evolve the creme de la creme by postulating the theme behind nature‟s biological wizardry. Several models have been conceptualized to answer this.13 The framework model suggests that during the initial stages of protein folding, local interactions dominate and guide the formation of secondary IRSAPS Bulletin 2011, Vol. 1, Issue 1

structural elements.14 This is followed by absolutely random diffusion–collision of these local elements of the secondary structure until stable native tertiary contacts are made. 15,

The

hydrophobic collapse model suggests that the folding of a protein is initiated by an entropically driven clustering of the hydrophobic amino acid residues.18,

The formation of a collapsed

intermediate with restricted conformational space facilitates the formation of the secondary structure and consolidation of tertiary contacts. The nucleation model is based on the formation of a local nucleus of the secondary structure by a few key residues in the polypeptide chain. The rest of the structure then propagates around the nucleus without encountering any energy barrier.20 An extension of the nucleation model, the nucleation–condensation model, envisages a more diffuse nucleus, and that the collapse of the polypeptide chain occurs in parallel with structure formation.21 This model was proposed to describe the mechanism of folding of proteins that appear to fold by a „two-state‟ mechanism, in which all physical interactions appear to develop in a concerted manner. Folding of monomeric and multimeric proteins Small monomeric proteins lacking disulfide bonds and cis-proline peptide bonds provide the simplest starting point for investigating the rules that govern protein folding. The folding of larger multidomain proteins is still more complex, and frequently there is more than one transition between native and denatured states as domains fold independently.22 The only state accessible to experimental study in a two-state reaction is the transition state. A transition state is the highest energy point in a reaction pathway. One of the characteristics of a transition state is that a molecule in its transition state structure should collapse with equal frequency to its starting materials or to its products. Intermediates have been reported to arise as a consequence of energy barrier, incorrect proline isomerisation, non disulfide bond formation, interaction with cofactor such a heme-group, non-native contacts that needs to be broken before folding proceeds. Hence most of the classical folding studies involved characterizing those intermediates e.g. CI2, Barnase, T4 lysozyme and Staphylococcus nuclease.23 Oligomeric proteins are stabilized by both the intrinsic folding energy of the subunits as well as interactions between the subunits.24 The stability of protein enhances with the ratio of buried to solvent exposed surface area and thus with their size.25 Symmetrical subunits arrangement in homo oligomers are energetically preferred.26 Folding of an oligomeric protein from its denatured and separated chains probably begins like that of single-chain proteins and proceeds until the formation of a specific binding site that can recognize another monomer. At this critical step, the folding pathway shifts from being intramolecular to intermolecular, to yield a dimeric species. This homo- or heterodimer may need further folding steps to become either a IRSAPS Bulletin 2011, Vol. 1, Issue 1

native protein or an intermediate with an adequate specific site that allows a second association step to take place. The overall folding pathway of an oligomeric protein is thus a succession of monomolecular folding steps and bimolecular association steps.22, 27 Why study protein folding? The discipline of protein folding “Foldiomics” is an endeavor to understand the diverse biological molecule called proteins (Scheme 1). Studying folding in light of sequence to delineate sequence structure relationship reaching a universal folding code, stability flexibility, diversity the involved energetics and smooth transitioning from disordered to well ordered forms is a great scientific

Scheme 1. Various arenas to endeavor protein folding.

pursuit and scintillating academic challenge. The range of human diseases associated with protein misfolding and aggregation which results in cellular malfunctioning are focus of contemporary quest.28-30 Defects in protein folding have been linked to a number of pathologies where aggregates (amyloids) are observed, including neuro-degenerative conditions such as Parkinson‟s, Alzheimer‟s and Huntington‟s diseases.31 Protein engineering has been put to great use for designing new proteins and enzymes with improved, novel properties with potential application in biotechnology. Localized perturbation in the structure that are required for the analysis of structure-function relationships and that can sometimes lead to the dramatic changes in the usual properties of protein.32 Fersht and coworkers improved the specificity of subtilisin BPN‟ towards substrates with large hydrophobic residues by single amino acid replacement at two positions.33 Perham and IRSAPS Bulletin 2011, Vol. 1, Issue 1

coworkers altered the coenzyme specificity of glutathione reductase from NADP+ to NAD+ by introducing mutations at specific sites without altering its substrate specificity.34 In vivo Protein Folding The cellular environment in which proteins fold following synthesis on ribosomes is of course extremely complex compared to that associated with most experiments conducted in vitro. It is so densely packed with all the molecular components that are needed for its survival and replication that the macromolecular concentration can exceed 350 mg/ml. 35, 36

Figure 1: Chaperones assisted protein folding.37

While the molecules within a cell have evolved, remarkably, to be able to function correctly and often independently within such an environment, this degree of molecular crowding means that incompletely or improperly folded molecules will undoubtedly aggregate with each other or associate improperly with other cellular components. To avoid such problems, a series of auxiliary proteins have evolved to assist proteins to fold efficiently and without such complications.38, 39 This efficient fine tuning is brought about by molecular catalyst Chaperones (Figure 1). Protein misfolding and disease Protein folding and unfolding within the cell is a crucial biological process it is inevitable that mistakes in folding will translate to the malfunctioning of bioprocesses and hence to disease. In some disorders, such as cystic fibrosis, the ability of a protein to fold correctly is reduced by familial mutations (in this case, in the gene encoding a membrane protein involved in chloride ion transport) resulting in a reduction in the level, or in some cases the complete IRSAPS Bulletin 2011, Vol. 1, Issue 1

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absence of a key functional species. In other cases, such as the amyloid diseases, failure to fold or to remain correctly folded results in the aggregation and deposition of proteins in one or more types of tissue.40,

Symptoms can result from a „„gain of toxic function‟‟ associated with the

aggregates; this latter situation is thought to be the primary origin of several neurodegenerative disorders, notably Alzheimers and Parkinsons diseases.40,

42, 43

In principle, protein-folding

diseases can be divided into two groups. In the group of diseases known as amyloidoses, large quantities of wrongly folded proteins undergo aggregation destroying brain cells and other tissues. Such disorders include Alzheimer‟s disease, Parkinson‟s disease, transmissible spongiform encephalopathies, familial amyloid polyneuropathy, Huntington‟s disease, type II diabetes, among several other well-known diseases. In the other group, a small genetic error, usually affecting a single amino acid residue, leads to a misfolded conformation, which either affects its function or makes it extremely susceptible to cellular proteases. These latter diseases include cystic fibrosis, inherited emphysema, and some types of cancer. Most human cancers (50%) result from mutations in the p53 protein, mainly at its core domain (p53/DBD), affecting the DNA binding ability or the protein stability. In some of these diseases, both aggregation and lack of function may contribute to its pathogenesis. In the case of prions, the remarkable additional property is that they are infectious; they cause transmissible spongiform encephalopathies, such as the mad cow disease and its human counterpart, new-variant Creutzfeldt-Jakob disease. A unified view of protein folding dynamics The dynamic personalities of protein have always been an exciting area of research. A nascent polypeptide may reach to its native form traversing many folding intermediates. Its fate may further be governed by its propensity to undergo aggregation and degradation. Another intriguing feature that these aggregate can adopt is to form structured fibrilar topology leading to amyloid fibers. The populations and interconversions of the various states are determined by their relative thermodynamic and kinetic stabilities under any given conditions. In living systems, however, transitions between the different states are highly regulated by control of the environment, and by the presence of molecular chaperones, proteolytic enzymes, and other factors. Failure of such regulatory mechanisms is likely to be a major factor in the onset of misfolding diseases. 44 References and notes: 1. Dobson, C. M. Semin Cell Dev Biol 2004, 15, 3. 2. Branden C, T. J. in Introduction to protein structure, 2nd ed ed., Garland Publishing 1999.

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3. Twyman, R. M. in Advanced Molecular Biology: A Concise Reference, Springer Verlag 1998. 4. Stryer, L. in Biochemistry, W. H. Freeman and Company 1995. 5. David L Nelson, M. M. C. in Lehninger Principles of Biochemistry Fifth ed., W H Freeman 2009. 6. Udgaonkar, J. B. Annu Rev Biophys 2008, 37, 489. 7. Takano, K.; Funahashi, J.; Yamagata, Y.; Fujii, S.; Yutani, K. Journal of molecular biology 1997, 274, 132. 8. Loladze, V. V.; Makhatadze, G. I. Protein Sci. 2002, 11, 174. 9. Pace, C. N. Nat Struct Biol 2000, 7, 345-346. 10. Gianfreda, L.; Scarfi, M. R. Mol Cell Biochem 1991, 100, 97. 11. Protein: A Comprehensive Treatise, Vol. 2, JAI Press Inc. 1999. 12. Levinthal, C. J. Chim. Phys. 1968, 65, 44. 13. Fersht, A. in Structure and Mechanism in Protein Science, First ed., W.H. Freeman 1999. 14. Udgaonkar, J. B.; Baldwin, R. L. Nature 1988, 335, 694. 15. Karplus, M.; Weaver, D. L. Nature 1976, 260, 404. 16. Bashford, D.; Cohen, F. E.; Karplus, M.; Kuntz, I. D.; Weaver, D. L. Proteins 1988, 4, 211. 17. Cohen, F. E.; Sternberg, M. J.; Phillips, D. C.; Kuntz, I. D.; Kollman, P. A. Nature 1980, 286, 632. 18. Dill, K. A. Biochemistry 1985, 24, 1501. 19. Gutin, A. M.; Abkevich, V. I.; Shakhnovich, E. I. Biochemistry 1995, 34, 3066. 20. Wetlaufer, D. B. Proceedings of the National Academy of Sciences of the United States of America 1973, 70, 697. 21. Fersht, A. R. Proceedings of the National Academy of Sciences of the United States of America 2000, 97, 14121. 22. Jaenicke, R. Prog. Biophys Mol. Biol. 1987, 49, 117. 23. Li, L.; Shakhnovich, E. I. Proceedings of the National Academy of Sciences of the United States of America 2001, 98, 13014. 24. Shriver, J. W.; Edmondson, S. P. Methods in molecular biology Clifton, N. J 2009, 490, 57. 25. Vogt, G.; Woell, S.; Argos, P. Journal of molecular biology 1997, 269, 631. 26. Pain, R. H. Mechanisms of Protein Folding, Oxford University Press 2000. 27. Dautry-Varsat, A.; Garel, J. R. Biochemistry 1981, 20, 1396. 28. Thomas, P. J.; Qu, B. H.; Pedersen, P. L. Trends Biochem. Sci. 1995, 20, 456. 29. Carrell, R. W.; Gooptu, B. Curr. Opin. Struct. Biol. 1998, 8, 799. 30 Rochet, J. C.; Lansbury, P. T., Jr. Curr. Opin. Struct. Biol. 2000, 10, 60. 31. Kurt, N.; Cavagnero, S. J. Am. Chem. Soc. 2005, 127, 15690. 32. Fersht, A.; Winter, G. Trends Biochem. Sci. 1992, 17, 292. 33. Eder, J.; Rheinnecker, M.; Fersht, A. R. Biochemistry 1993, 32, 18. 34. Scrutton, N. S.; Berry, A.; Deonarain, M. P.; Perham, R. N. Proc. Biol. Sci. 1990, 242, 217. 35. Ellis, R. J. Trends Biochem. Sci. 2001, 26, 597. 36. Ellis, R. J. Curr. Opin. Struct. Biol. 2001, 11, 114. 37. Harvey Lodish, A. B.; Matsudaira, P.; Kaiser, C. A.; Krieger, M.; Scott, M. P.; Zipursky, L.; Darnell, J. Molecular Cell Biology, Fifth Ed. 38. Gething, M. J., Sambrook, J. Nature 1992, 355, 33. 39. Hartl, F. U., Hayer-Hartl, M. Science 2002, 295, 1852. 40. Selkoe, D. J. Nature 2003, 426, 900.

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41. Koo, E. H.; Lansbury, P. T. Jr.; Kelly, J. W. Proceedings of the National Academy of Sciences of the United States of America 1999, 96, 9989. 42. Caughey, B.; Kocisko, D. A.; Raymond, G. J.; Lansbury, P. T. Jr. Chem. Biol. 1995, 2, 807-817. 43. Selkoe, D. J. Nature 1999, 399, A23. 44. Dobson, C. M. Methods 2004, 34, 4.

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Highlight

The science behind ocular dietary supplements: lutein and zeaxanthin Prakash Bhosale Senior Scientist, Indianapolis, USA Tel: 801-349-6458 E-mail: prakashbhosale1@gmail.com

Carotenoids like lutein and zeaxanthin that are found abundantly in dark-green leafy vegetables. These carotenoids are also found in human eyes mainly in retina and lens. Research studies indicate dietary consumption of lutein and zeaxanthin can reduce developing symptoms of eye diseases such as age-related macular degeneration (AMD) and cataract. The research work has supported million dollar market for lutein and zeaxathin supplements originating from natural sources such as marigold petals. In this work, we present you the slice of the basic science relating lutein and zeaxanthin to healthy eyes.

Introduction Lutein and zeaxanthin are two major oily pigments found in dark green vegetables such as spinach, kale, broccoli and collard greens, as well as yellow-red fruits such as corn, oranges, peaches, mangoes, and tangerines, and in egg yolks.1,

Experimental and epidemiological

evidence suggest that on dietary consumption carotenoids predominate in the human eyes, where they are play vital role as an antioxidant and light filter.3-5 They act as an antioxidant by quenching singlet oxygen, reactive oxygen species, and free radicals the major by-products of metabolic processes in cells or from environmental pollutants.6 There are several major research reports suggesting beneficial roles of lutein and zeaxanthin in the prevention of age related macular degeneration, cataract, and other blinding disorders.7, 8 These ocular disorders are a major cause of concern in the developed and undeveloped world, as millions are suffering from these diseases. In this article, we review the distribution of carotenoids in the human eyes, the measurement of macular carotenoids in vivo, evidence for the causal link between oxidative IRSAPS Bulletin 2011, Vol. 1, Issue 1

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stress and these diseases, and the potential protective and toxic effects of dietary and nutraceutical lutein and zeaxanthin. Carotenoids in human eyes: We have several dietary sources of carotenoids and we consume over 25 different dietary carotenoids that are detectable in human blood but only lutein and zeaxanthin and their metabolites are found to any substantial extent in the retina.9 Human retina and lens are highly enriched with lutein and zeaxanthin, and the macular region of the human retina which falls at the center of retina contains by far the highest concentrations of these two carotenoids relative to any other tissue in the body. Among two carotenoids, zeaxanthin is the dominant component in the macular area, while lutein distributes more evenly throughout the retina (Figure 1). The lutein: zeaxanthin ratio is 1:2 for macula, and 2:1 for the peripheral retina. The scientific findings suggest that macular zeaxanthin actually exists as two isomeric

forms,

namely

dietary

(3R,3‟R)-zeaxanthin

and

non-dietary

(3R,3‟S-meso)-

zeaxanthin.9, 10 (3R,3‟S meso)-zeaxanthin is believed to originate from dietary lutein. In addition to meso-zeaxanthin , significant amounts of 3‟-epilutein and 3‟-oxolutein, non-dietary oxidative metabolites of lutein and zeaxanthin, have also been detected in human retina. They are proposed to form by a series of light-induced or enzymatically-mediated oxidation-reduction and double-bond isomerization reactions from dietary lutein and/or zeaxanthin.11 Biochemistry of selectivity in eyes: Highly selective uptake and deposition lutein and zeaxanthin is likely to be mediated by specific binding proteins. Carotenoid-binding proteins have been described in plants, microorganisms, and invertebrates, but relatively little information has been available about specific carotenoid-binding proteins in any vertebrate system. Several mammalian proteins such as tubulin, high-density lipoprotein (HDL), lowdensity lipoprotein (LDL), albumin, and beta-lactoglobulin can act as carrier proteins for carotenoids, although there is no evidence that they do so with high specificity or affinity. A recent study identified that a pi isoform of glutathione S-transferase (GSTP1) is a specific zeaxanthin-binding protein in the human macula.12 It protects the bound carotenoids from degradation, enhancing their antioxidant functions.13 Immunolocalization on a human parafoveal section revealed that GSTP1 is especially concentrated in the outer plexiform layer (also known as the Henle Fiber layer) and the inner plexiform layer. The observation of high levels of GSTP1 in the macular plexiform layers correlates well with the pigment distribution of the macular carotenoids reported using light microscopy.14 Lutein Binding protein was later identified as binding protein (CBP) belonging to the steroidogenic acute regulatory (StAR) protein family with significant homology to many human StAR proteins.15 Immunolocalization with antibodies IRSAPS Bulletin 2011, Vol. 1, Issue 1

directed against either CBP or GSTP1 showed specific labeling of rod and cone inner segments, especially in the mitochondria-rich ellipsoid region.

Figure 1. Structure of Lutein (upper part) and zeaxanthin (lower part).

Measurement of carotenoid in human eyes: Several methodologies exist to quantify levels of lutein and zeaxanthin non-invasively in the tissue of interest, the living human macula, with high reliability.16-19 Heterochromatic flicker photometry (HFP) has been the most commonly used test to quantify macular pigment in the human eyes.20-22 It is a psychophysical test requiring an attentive subject with good visual acuity, and it has been used to measure macular pigment in long-term supplementation studies.23-25 Resonance Raman spectroscopy is newest technology used for measurement of macular pigments.26 It has proven to be sensitive and very specific, and it is well suited to large-scale screening of clinic populations.27-29 As an objective measurement method, it was validated against high-pressure liquid chromatography (HPLC) analysis in human cadaver eyes and in living monkey eyes.18,

19, 30

Using this method, it was

demonstrated recently that average levels of lutein and zeaxanthin are 32% lower in AMD eyes versus normal elderly control eyes, consistent with the hypothesis that low levels of lutein and zeaxanthin in the human macula may represent a pathogenic risk factor for AMD. Carotenoids depletion and ocular disorders There are several age related ocular disorders that are associated with depletion of carotenoids. The two major ones are cataract and age related macular degeneration. Cataract: Age-related cataract, the most common form of cataract, is an opacification of the lens that causes decreased visual acuity and can lead to blindness if left untreated. It is believed to be a multifactorial disease that may be initiated or promoted by oxidative damage because IRSAPS Bulletin 2011, Vol. 1, Issue 1

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with aging, lens constituents sustain extensive photooxidative damage.31 Nursesâ&#x20AC;&#x; Health Study cohort found that consumption of spinach and other greens at least five times per week compared to less than once a month resulted in a 47% lower risk (RR: 0.53; 95% CI 0.38-0.73; p- trend = 0.001) for cataract extraction during up to 8 years of follow-up.32 After up to 12 years of follow-up on 77,466 US women â&#x2030;Ľ 45 years of age by the same group, Chasan-Taber et al. 1999 reported that those with the highest intake of lutein and zeaxanthin had a 22% decreased risk of cataract extraction compared with those in the lowest quintile (relative risk: 0.78; 95% CI: 0.63, 0.95; P for trend = 0.04), after age, smoking, and other potential cataract risk factors were controlled for.33 A prospective cohort study of US male health professionals (n = 36,644) with 8 years of follow-up reported that men with the highest intakes of lutein plus zeaxanthin had a 19% lower risk of cataract extraction compared to those in the lowest quintile (RR 0.81: 95% CI: 0.65-1.01; P-trend = 0.03).34 These prospective findings suggest that lutein and zeaxanthin may provide the greatest protection against cataracts. Age-related macular degeneration (AMD): Age-related macular degeneration (AMD) is a devastating disease of the elderly that is the leading cause of irreversible blindness in the developed world. It is the primary cause of vision loss and legal blindness in adults over 60 in the U.S.35 Because of the limited treatments for both the wet and the dry forms of AMD, there is increasing interest among clinicians and patients to identify modifiable risk factors so that interventions can be instituted at an early stage before significant irreversible damage has occurred. Among the nutritional dietary factors that may protect against AMD, the carotenoids lutein and zeaxanthin have received considerable attention in the recent years.36-39 The Eye Disease Case-Control Study (1993) reported that high serum carotenoid levels and high dietary intakes of lutein and zeaxanthin are associated with lower relative risk of age-related macular degeneration (AMD).7,

More recently, a cross-sectional study of 380 subjects aged 66 to 75

years found a statistically significant inverse trend between plasma concentrations of zeaxanthin and risk of age-related macular degeneration (AMD), after adjustment for age and other risk factors.40 Since the report was based on a cross-sectional study, the sequence of cause and effect cannot usually be determined, and the levels of macular carotenoids were never measured. On the other hand, a retrospective study of the Beaver Dam Eye Study cohort found no significant association between lutein and zeaxanthin intake 10 years prior to study enrollment and AMD.41 Further studies on the relationship of lutein and zeaxanthin in the diet and serum to photographic evidence of early and late age-related maculopathy (ARM) among persons over age 40 years have been conducted. This study by Mares-Perlman et al. demonstrated no overall relationship of lutein and zeaxanthin in the diet and serum to ARM in IRSAPS Bulletin 2011, Vol. 1, Issue 1

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the third National Health and Nutrition Examination Survey (NHANES III) sample.42 Using a noninvasive laser optical method, resonance Raman spectroscopy, Bernstein et al. reported that carotenoid Raman signal intensity declined with age in normal eyes (P < 0.001).28 The average levels of the lutein and zeaxanthin were 32% lower in AMD eyes versus normal elderly control eyes as long as the subjects were not consuming high-dose lutein supplements (P = 0.001). Patients who had begun to consume supplements containing high doses of lutein (≥ 4 mg/day) regularly after their initial diagnosis of AMD had average macular pigment levels that were in the normal range for age (P = 0.829) and that were significantly higher than in AMD patients not consuming these supplements (P = 0.038). These findings are consistent with the hypothesis that low levels of lutein and zeaxanthin in the human macula may represent a pathogenic risk factor for the development of AMD. Ocular carotenoid supplementation studies Lutein and zeaxanthin can be obtained from the diet in two major that includes supplements and functional foods. Unesterifed carotenoids are usually found in crystalline supplements and in some dietary sources such as green leafy vegetables, and are expected to get absorbed easily, whereas esterified carotenoids commonly found in fruits, flowers, and some microorganisms require prior de-esterification by intestinal enzymes to enter the blood stream. Both forms seem to have excellent serum bioavailability, especially when consumed along with fat. Landrum et al., 1997a reported two subjects study wherein they consumed lutein esters, equivalent to 30 mg of free lutein per day, for a period of 140 days.23 Macular pigment optical density was determined by heterochromatic flicker photometry before, during, and after the supplementation period. Serum lutein concentration was also obtained through the analysis of blood samples by high-performance liquid chromatography. 20 to 40 days after the subjects commenced taking the lutein supplement, their macular pigment optical density began to increase uniformly at an average rate of 1.13+/-0.12 milliabsorbance units/day. During this same period, the serum concentration of lutein increased roughly tenfold, approaching a steady state plateau. Berendschot et al. reported that a daily dose of 10 mg lutein supplementation induced an increase in mean plasma lutein by a factor of 5 and a linear 4-week increase in relative MP density of 4% to 5% by using two different reflectance methods.43 In a double-blind placebo-controlled study, individuals were randomly assigned to 20 mg/day of lutein or to placebo for 120 days.30 Results demonstrated rises in the serum carotenoid and macular pigment levels in the lutein supplementation group. The 25% “nonresponder” rate was similar to the previous studies.21, 44 It is possible that specific binding sites for xanthophyll carotenoids in the macula were already saturated at the beginning of the supplementation period in these IRSAPS Bulletin 2011, Vol. 1, Issue 1

individuals. The existence and possible functional role of these binding proteins is well documented.45,

While lutein and zeaxanthin supplementation studies have shown widely

varying responses of macular pigment levels, it has proven even more elusive to demonstrate functional effects. Only two studies have shown significantly improved visual function in an AMD population, and the improvements were quite subtle.46 Prospective studies to prove a benefit for lutein and/or zeaxanthin supplementation in the prevention of AMD will require large populations followed for many years to provide definitive results. The ongoing AREDS II study sponsored by the National Eye Institute will probably answer some of the queries related to carotenoids supplementation.47, 48 Safety of ocular carotenoids Unlike beta-carotene, Lutein and zeaxanthin have never been linked to elevated risk of human diseases such as cancer, and they generally seem to have a very wide margin of safety. Several animal toxicology studies have established their safety as dietary supplements. One study conducted on rats using crystalline lutein extracted from marigold flowers showed that amounts averaging several milligrams had no negative effect on growth, hematology and other parameters.49 Further primate studies conducted in Europe by Roche Vitamins (now DSM) confirmed the safety of pharmacological doses of lutein and zeaxanthin over one hundred times the amount consumed in the average American diet (1-2 mg). At necropsy, the monkeysâ&#x20AC;&#x; eyes showed no evidence of ocular damage or crystal deposition. These studies have led to the classification of lutein as a generally recognized as safe (GRAS) compound in the United States, and in Europe the upper limit of consumption for humans has been set at an extraordinarily high level of 150 mg/day for an average weight individual. The GRAS status of lutein allows its addition in several food and beverage applications in the United States at 0.3 to 2.0 mg/serving. Continuously growing evidence suggests that lutein and zeaxanthin may contribute to the protection against several age-related ocular diseases, including cataract and AMD. In vivo assessment of macular pigment levels will be useful in future studies as a biomarker of lutein and zeaxanthin bioavailability for AMD. The ability to raise macular pigment levels in at least some

AMD

patients

and

normal

subjects

via

dietary

manipulation

antioxidant

supplementation will facilitate the further investigation of the association of macular carotenoids pigment with visual functions in AMD patients. Due to the multifactorial nature of the age-related cataract and AMD, it is essential to develop a complete understanding of the etiology of these

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diseases, including further studies on the role of genetics and environmental conditions that might be involved in their development. References and notes 1. Khachik, F.; Beecher, G. R.; Goli, M. B.; Lusby, W. R. Methods Enzymol. 1992, 213, 347. 2. Bhosale, P.; Ermakov, I. V.; Ermakova, M. R., Gellermann, W.; Bernstein, P. S. J. Agric. Food Chem. 2004, 52, 3281. 3. Bone, R. A.; Landrum, J. T.; Fernandez, L.; Tarsis, S. L. Invest. Ophthalmol Vis. Sci. 1988, 29, 843. 4. Junghans, A.; Sies, H.; Stahl, W. Arch. Biochem. Biophys. 2001, 391,160. 5. Krinsky, N. I.; Landrum, J. T.; Bone, R. A. Annu. Rev. Nutr. 2003, 23, 171. 6. Edge, R.; McGarvey, D. J.; Truscott, T. G. J. Photochem. Photobiol. B 1997, 41, 189. 7. Eye Disease Case-Control Study Group. Antioxidant status and neovascular age-related macular degeneration. Arch. Ophthalmol. 1993, 111, 104. 8. Seddon, J. M.; Ajani, U. A.; Sperduto, R. D.; Hiller, R.; Blair, N.; Burton, T. C.; Farber, M. D.; Gragoudas, E. S.; Haller, J.; Miller, D. T.; Yannuzzi, L. A.; Willett, W. J. Am. Med. Assoc. 1994, 272, 1413. 9. Bone, R. A.; Landrum, J. T.; Hime, G. W.; Cains, A.; Zamor, J. Invest. Ophthalmol. Vis. Sci. 1993, 34, 2033. 10. Bone, R. A.; Landrum, J. T.; Friedes, L. M.; Gomez, C. M.; Kilburn, M. D.; Menendez, E.; Vidal, I.; Wang, W. Exp. Eye. Res. 1997, 64, 211. 11. Khachik, F.; de Moura, F. F.; Zhao, D-Y.; Aebischer, C-P.; Bernstein, P. S. Invest. Ophthamol. Vis. Sci. 2002, 43, 3383-3392. 12. Bhosale, P.; Larson, A. J.; Frederick, J. M.; Southwick, K.; Thulin, C. D.; Bernstein, P. S. J. Biol. Chem. 2004, 279, 49447-49454. 13. Bhosale, P., Bernstein, P. S. Biochim. Biophys. Acta. 2005, 1740,116. 14. Snodderly, D. M.; Auran, J. D.; Delori, F. C. Invest. Ophthalmol. Vis. Sci. 1984, 25, 674.

15. Bhosale, P.; Li, B.; Sharifzadeh, M.; Gellermann, W.; Frederick, J. M.; Tsuchida, K.; Bernstein, P. S. Biochemistry. 2009, 48, 4798. 16. Hammond, B. R.; Wooten, B. R.; Snodderly, D. M. J. Opt. Soc. Am. A 1997, 14, 1187. 17. Delori, F. C.; Goger, D. G.; Dorey, C. K. Invest. Ophthalmol. Vis. Sci. 2001, 42, 1855. 18. Gellermann, W.; Ermakov, I. V.; Ermakova, M. A.; McClane, R. W.; Zhao, D-Y.; Bernstein, P. S. J. Opt. Soc. Am. A 2002, 19, 1172. 19. Gellermann, W.; Ermakov, I. V.; McClane, R. W.; Bernstein, P. S. Optics Letters 2002, 27, 833. 20. Beatty, S.; Koh, H-H.; Carden, D.; Murray, I. J. Ophthalm. Phys. Optics 2000, 20, 105. 21. Bone, R. A.; Landrum, J. T.; Guerra, L. H.; Ruiz, C. A. J. Nutr. 2003, 133, 992. 22. Snodderly, D. M.; Mares, J. A.; Wooten, B. R.; Oxton, L.; Gruber, M.; Ficek, T. Invest. Ophthalmol. Vis. Sci. 2004, 45, 531. 23. Landrum, J. T.; Bone, R. A.; Joa, H.; Kilburn, M. D.; Moore, L. L.; Sprague, K. E. Exp. Eye. Res. 1997, 65, 57. 24. Tang, C. Y.; Yip, H. S.; Poon, M. Y.; Yau, W. L.; Yap, M. K. Ophthalmic Physiol. Opt. 2004, 24, 586. 25. Ciulla, T. A.; Hammond, B. R. Am. J. Ophthalmol. 2004, 138, 582.

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26. Bernstein, P. S.; Yoshida, M. D.; Katz, N. B.; McClane, R. W.; Gellermann, W. Invest. Ophthalmol. Vis. Sci. 1998, 39, 2003. 27. Bernstein, P. S. Pure Appl. Chem. 2002, 74, 1419. 28. Bernstein, P. S.; Zhao, D. Y.; Wintch, S. W.; Ermakov, I. V.; McClane, R. W.; Gellermann, W. Ophthalmology 2002, 109, 1780. 29. Neelam, K., O'Gorman, N., Nolan, J., O'Donovan, O., Wong, H.B., Au Eong, K.G., Beatty, S. Invest. Ophthalmol. Vis. Sci. 2005, 46, 1023. 30. Bernstein, P. S.; Zhao, D. Y.; Sharifzadeh, M.; Ermakov, I. V.; Gellermann, W. Arch. Biochem. Biophys. 2004, 430,163. 31. Berman, E. R. Biochemistry of the eyes. New York, Plenum Press, 1991. 32. Hankinson, S. E.; Willett, W. C.; Colditz, G. A.; Seddon, J. M.; Rosner, B.; Speizer, F. E.; Stampfer, M. J. JAMA. 1992, 268, 994. 33. Chasan-Taber, L.; Willett, W. C.; Seddon, J. M.; Stampfer, M. J.; Rosner, B.; Colditz, G. A.; Hankinson, S. E. Epidemiology 1999, 10, 679. 34. Brown, L.; Rimm, E. B.; Seddon, J. M.; Giovannucci, E. L.; Chasan-Taber, L.; Spiegelman, D.; Willett, W. C.; Hankinson, S. E. Am. J. Clin. Nutr. 1999, 70, 517. 35. Bernstein, P. S. in Age-Related Macular Degeneration. by Berger, J. W.; Fine, S. L.; Maguire, M. G. Macular Biology. St. Louis: Mosby, 1999, 1. 36. Beatty, S.; Boulton, M. E.; Henson, D. B.; Hui-Hiang, K.; Murray, I. J. Br. J. Ophthalmol. 1999, 83, 867. 37. Beatty, S.; Koh, H-H.; Henson, D.; Boulton, M. Surv. Ophthalmol. 2000, 45, 115. 38. Landrum, J. T.; Bone, R. A.; Kilburn, M. D. Adv. Pharmacol. 1997, 38, 537. 39. Landrum, J. T.; Bone, R. A. Arch. Biochem. Biophys. 2001, 385, 28. 40. Gale, C. R.; Hall, N. F.; Phillips, D. I.; Martyn, C. N. Invest. Ophthalmol. Vis. Sci. 2003, 44, 2461. 41. Mares-Perlman, J. A.; Klein, R.; Klein, B. E.; Greger, J. L.; Brady, W. E.; Palta, M.; Ritter, L. L. Arch. Ophthalmol. 1996, 114, 991. 42. Mares-Perlman, J. A.; Fisher, A. I.; Klein R.; Palta, M.; Block, G.; Millen, A. E.; Wirght, J. D. Am. J. Epidemiol. 2001, 153, 424. 43. Berendschot, T. T.; Goldbohm, R. A.; Klopping, W. A.; van de Kraats, J.; van Norel, J.; van Norren, D. Invest. Ophthalmol. Vis. Sci. 2000, 41, 3322. 44. Hammond, B. R.; Johnson, E. J.; Russell, R. M.; Krinsky, N. I.; Yeum, K-J.; Edwards, R. B.; Snodderly, D. M. Invest. Ophthalmol. Vis. Sci. 1997, 38, 1798-1801. 45. Yemelyanov, A. Y.; Katz, N. B.; Bernstein, P. S. Exp. Eye. Res. 2001, 72, 381. 46. Falsini, B.; Piccardi, M.; Iarossi, G.; Fadda, A.; Merendino, E.; Valentini, P. Ophthalmology 2003, 110,

51. 47. Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, -carotene, and zinc for age-related macular degeneration and vision loss: AREDS report No. 8. Arch. Ophthalmol. 2001, 119, 1417. 48. Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E and carotene for age-related cataract and vision loss: AREDS report No. 9. Arch. Ophthalmol. 2001, 119, 1439. 49. Kruger, C. L.; Murphy, M.; DeFreitas, Z.; Pfannkuch, F.; Heimbach, J. Food. Chem. Toxicol. 2002, 40, 1535.

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IRSAPS as an Organization

List of advisory board members* 1. Dr. Sourav Pal FNA, FASc, FNASc Director, National Chemical Laboratory (NCL) J. C. Bose National Fellow Pune 411 008, India 2. Prof. K. Muralidhar Dept of Zoology University of Delhi Delhi 110 007

3. Dr. Chandra Verma Head of The Division, Biomolecular Modelling and Design Bioinformatics Institute, A member of A*STAR's Biomedical Sciences Institutes 30 Biopolis Street, Singapore URL: http://www.bii.astar.edu.sg/research/bmad/bmad.php

Vanderbilt University, Nashville, TN, 37235 USA 10. Prof. Amit K. Chattopadhyay School of Engineering and Applied Sciences Mathematics (NCRG) Aston University Birmingham B4 7ET, UK 11. Dr. Manish Chandra Pathak Department of Biochemistry Emory University School of Medicine 1510 Clifton Road NE, Atlanta, GA 30322 USA 12. Dr. Amit Kumar National Laboratory of Intense Magnetic Fields National Institute of Applied Sciences, 143, avenue de Rangueil, F-31400 Toulouse, France

4. Dr. Ashlesha A Deshpande School of Medicine The University of Alabama at Birmingham 1025,18th Ave South, Room 146 Birmingham, Alabama 35294 USA

5. Dr. Vijaylakshmi Gupta University of Kansas Medical Center, Kansas city, Kansas-66160 USA 6. Dr. Prakash Bhosale Scientist, Indianapolis, USA 7. Dr. Jadab Sharma NanoSciences Group CEMES CNRS UPR 8011 B.P. 94347, 29 rue Jeanne Marvig 31055 Toulouse Cedex 4 - France

8. Prof. Bhaskar Sathe Department of Chemistry Dr. Babasaheb Ambedkar Marathwada University, Maharshtra India 9. Dr. Mukesh Gupta Department of Biomedical Engineering,

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State wise list of coordinators* S. No. 1

State

Name

Subject

E-mail ID

Address

West Bengal

Prof. Muklesur Rahman

Physics

rahman.con@gmail.com

Department of Physics Aliah University, WB, India

Uttarakhand

Vikas Shukla

Embedded Systems

vikasshuklait@gmail.com

Thésard CNRS-LAAS,Groupe-ISI Bureau -126 7, Avenue de colonel roche , 31000 Toulouse France

Uttar Pradesh

Dr. Amit Kumar

Physics

amitnsc@gmail.com

National Institute of Applied Sciences, France

Dr. Sanjeev Malik

Mathematics

malikdma@gmail.com

Assistant Professor, IIT Roorkee, India

Dr. Manish Chandra Pathak

Biology

pcmanish@gmail.com

Emory University School of Medicine, USA

Dr. Samipillai Marivel

Chemistry

smvelu@gmail.com

Dr. Mallika Veeramalai

Bioinformatics

mallikaveeramalai@gmail. com

Dept. of Inorganic Chemistry Indian Association for the Cultivation of Science Kolata - 700032 The University of Kansas, USA

Sikkim

Prof. Nayan Kamal Bhattacharyya

Chemistry

nkamalbhatt@gmail.com

Sikkim Manipal Institute of Technology, Sikkim

Rajasthan

Dr. Mukesh Gupta

Chemistry

zealmukesh@gmail.com

Vanderbilt University, USA

Orissa

Prof. Abhijit Datta Banik

Mathematics

banikad@gmail.com

Dr. Satyabrata Si

Chemistry

satyabrata.si@gmail.com

Asst. Prof. School of Basic Sciences IIT, Bhubaneswar CPMOH - Univ. Bordeaux 1, France

Dr. Ganapati Sahoo

Physics

ganapatisahoo@gmail.com

Assistant Professor School of Applied Sciences KIIT University Bhubaneswar- 751024, INDIA

Prof. Thangjam Robert Singh

Biology

robertthangjam@gmail.co m

Department of Biotechnology Mizoram University Aizawl – 796 009, Mizoram, INDIA

2 3 4 5

6 7 8 9

12 13

Tamil Nadu

15 16 17 18 19 20 21 22 23 24 25

28 29

Mizoram

IRSAPS Bulletin 2011, Vol. 1, Issue 1

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30 31 32 33

Andhra Pradesh

Dr. Lakshmi Swarna Mukhi Pidugu Dr. M.Buchi Suresh

Biology

plsmukhi@gmail.com

Physics

mbsuri74@gmail.com

Dr. Santosh B. Chavan

Biology

sbchavan23@gmail.com

Jay Biotech, Pune, India

Dr. Bhalchandra A. Kakade

Chemistry

bhalchandrakakade@gmail .com

Tokyo Institute of Technology, Chemical Resources Laboratory, R1-17, 4259 Nagatsuta, Midori-Ku, Yokohama 226-8503, JAPAN

Madya Pradesh

Dr. Sandeep K. Shrivastava

Biology

sskpgi@gmail.com

Basic and Clinical Immunology of Parasitic Diseases CIIL - Center for Infection and Immunity of Lille University Lille Nord de France Institut Pasteur de Lille 1 rue du Professeur Calmette 59019 Lille Cedex, France

Kerala

Mr. Vivek J. P.

Chemistry

jpvivekjp@gmail.com

Canada

Dr. T. R. Anish

Biology

anishtr.78@gmail.com

Baylor College of Medicine, USA

Dr. Vasanthakumar Ganga Ramu Dr. K. S. Shashidhara

Chemistry

gangaramuvk@gmail.com

RUB, Germany

Biology

shashi2k4@gmail.com

Bangalore, India

Dr. Gurpreet Singh

Chemistry

NCL, Pune, India

Dr. Ravibhushan Singh

Biology

gurpreetsingh147@gmail.c om ravibhushan.singh@gmail. com

Dr. Hardeep Sehgal

Physics

mail2hsehgal@gmail.com

IIT, Delhi

Dr. Manoj Panchal

Biology

mpanchal1976@gmail.co m

Research Associate, ICGEB International Centre for Genetic Engineering and Biotechnology New Delhi

5277 Rivendell lane Columbia MD-21044, USA Scientist Center for ceramic processing international Advanced research institute for powder metallurgy and material processing(ARCI) Balapur, Hyderabad A.P -500005, India

35 36 37

Maharashtra

39 40 41

42 43 44 45 46 47 48 49

Karnataka

50 51 52 53

Jharkhand

201-4990 McGeer Street Vancouver, BC, Canada V5R 6C1

55 56 57 58

Delhi

59 60

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Bihar

Dr. Brajesh Kumar

Biology

krbrajesh@gmail.com

Post-Doctoral Researcher UT Southwestern Medical Center Dallas, USA

Assam

Md. Harunar Rashid

Nanotechnology

mhriacs@gmail.com

Cornell University, USA

62 63 64 65 66 67 68

National Board Members 1

Assam

Prof. Utpal Bora

Chemistry

utpal06@gmail.com

Assistant Professor Department of Chemistry Dibrugarh University Dibrugarh, Assam, India Pin: 786 004

Orissa

Dr. Suman Sahoo

Chemistry

Maharashtra

Prof. Bhaskar Sathe

Chemistry

sumansahoo@gmail.co m bhaskarsathe@gmail.c om

Assistant Professor, Department of Chemistry, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad- 431 004, India

*List is incomplete.

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B. iv

Science cartoons by Sumanta Baruah (Contact: sumanta.baruah@gmail.com)

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