Biosurfactants for a Sustainable Future
Production and Applications in the Environment and Biomedicine
Edited by Hemen Sarma
Department of Botany
Nanda Nath Saika College
Titabar, Assam, India
Majeti Narasimha Vara Prasad
School of Life Sciences
University of Hyderabad (an Institution of Eminence) Hyderabad, Telangana, India
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Library of Congress Cataloging‐in‐Publication Data
Names: Sarma, Hemen, editor. | Prasad, Majeti Narasimha Vara editor.
Title: Biosurfactants for a sustainable future : production and applications in the environment and biomedicine / Hemen Sarma, Nanda Nath Saika College, Department of Botany, 785630, Titabar, India; Majeti Narasimha Vara Prasad, University of Hyderabad, School of Life Sciences, 500046 Hyderabad, India.
Description: Hoboken, NJ : Wiley, 2021. | Includes bibliographical references and index.
Identifiers: LCCN 2020051310 (print) | LCCN 2020051311 (ebook) | ISBN 9781119671008 (cloth) | ISBN 9781119671039 (adobe pdf) | ISBN 9781119671053 (epub)
Subjects: LCSH: Biosurfactants.
Classification: LCC TP248.B57 B565 2021 (print) | LCC TP248.B57 (ebook) | DDC 668/.1–dc23
LC record available at https://lccn.loc.gov/2020051310
LC ebook record available at https://lccn.loc.gov/2020051311
Cover Design: Wiley
Cover Image: @Kennia Barrantes
Set in 9.5/12.5pt STIXTwoText by SPi Global, Pondicherry, India
10 9 8 7 6 5 4 3 2 1
Contents
List of Contributors xii
Preface xvii
1 Introduction to Biosurfactants 1 José Vázquez Tato, Julio A. Seijas, M. Pilar Vázquez-Tato, Francisco Meijide, Santiago de Frutos, Aida Jover, Francisco Fraga, and Victor H. Soto
1.1 Introduction and Historical Perspective 1
1.2 Micelle Formation 5
1.3 Average Aggregation Numbers 14
1.4 Packing Properties of Amphiphiles 18
1.5 Biosurfactants 20
1.6 Sophorolipids 25
1.7 Surfactin 28
1.8 Final Comments 31
Acknowledgement 32
References 32
2 Metagenomics Approach for Selection of Biosurfactant Producing Bacteria from Oil Contaminated Soil: An Insight Into Its Technology 43 Nazim F. Islam and Hemen Sarma
2.1 Introduction 43
2.2 Metagenomics Application: A State-of-the-Art Technique 44
2.3 Hydrocarbon-Degrading Bacteria and Genes 46
2.4 Metagenomic Approaches in the Selection of Biosurfactant-Producing Microbes 47
2.5 Metagenomics with Stable Isotope Probe (SIP) Techniques 48
2.6 Screening Methods to Identify Features of Biosurfactants 50
2.7 Functional Metagenomics: Challenge and Opportunities 52
2.8 Conclusion 53
Acknowledgements 54
References 54
3 Biosurfactant Production Using Bioreactors from Industrial Byproducts 59 Arun Karnwal
3.1 Introduction 59
3.2 Significance of the Production of Biosurfactants from Industrial Products 60
3.3 Factors Affect Biosurfactant Production in Bioreactor 61
3.4 Microorganisms 61
3.5 Bacterial Growth Conditions 63
3.6 Substrate for Biosurfactant Production 65
3.7 Conclusions 71 Acknowledgement 71 References 72
4 Biosurfactants for Heavy Metal Remediation and Bioeconomics 79 Shalini Srivastava, Monoj Kumar Mondal, and Shashi Bhushan Agrawal
4.1 Introduction 80
4.2 Concept of Surfactant and Biosurfactant for Heavy Metal Remediation 81
4.3 Mechanisms of Biosurfactant–Metal Interactions 82
4.4 Substrates Used for Biosurfactant Production 82
4.5 Classification of Biosurfactants 85
4.6 Types of Biosurfactants 85
4.7 Factors Influencing Biosurfactants Production 88
4.8 Strategies for Commercial Biosurfactant Production 89
4.9 Application of Biosurfactant for Heavy Metal Remediation 90
4.10 Bioeconomics of Metal Remediation Using Biosurfactants 93
4.11 Conclusion 94 References 94
5 Application of Biosurfactants for Microbial Enhanced Oil Recovery (MEOR) 99
Jéssica Correia, Lígia R. Rodrigues, José A. Teixeira, and Eduardo J. Gudiña
5.1 Energy Demand and Fossil Fuels 99
5.2 Microbial Enhanced Oil Recovery (MEOR) 101
5.3 Mechanisms of Surfactant Flooding 102
5.4 Biosurfactants: An Alternative to Chemical Surfactants to Increase Oil Recovery 103
5.5 Biosurfactant MEOR: Laboratory Studies 104
5.6 Field Assays 112
5.7 Current State of Knowledge, Technological Advances, and Future Perspectives 113 Acknowledgements 114 References 114
6 Biosurfactant Enhanced Sustainable Remediation of Petroleum Contaminated Soil 119 Pooja Singh, Selvan Ravindran, and Yogesh Patil
6.1 Introduction 119
6.2 Microbial-Assisted Bioremediation of Petroleum Contaminated Soil 121
6.3 Hydrocarbon Degradation and Biosurfactants 122
6.4 Soil Washing Using Biosurfactants 124
6.5 Combination Strategies for Efficient Bioremediation 126
6.6 Biosurfactant Mediated Field Trials 129
6.7 Limitations, Strategies, and Considerations of Biosurfactant-Mediated Petroleum Hydrocarbon Degradation 130
6.8 Conclusion 132 References 133
7 Microbial Surfactants are Next-Generation Biomolecules for Sustainable Remediation of Polyaromatic Hydrocarbons 139
Punniyakotti Parthipan, Liang Cheng, Aruliah Rajasekar, and Subramania Angaiah
7.1 Introduction 139
7.2 Biosurfactant-Enhanced Bioremediation of PAHs 144
7.3 Microorganism’s Adaptations to Enhance Bioavailability 151
7.4 Influences of Micellization on Hydrocarbons Access 151
7.5 Accession of PAHs in Soil Texture 152
7.6 The Negative Impact of Surfactant on PAH Degradations 152
7.7 Conclusion and Future Directions 153 References 153
8 Biosurfactants for Enhanced Bioavailability of Micronutrients in Soil: A Sustainable Approach 159
Siddhartha Narayan Borah, Suparna Sen, and Kannan Pakshirajan
8.1 Introduction 159
8.2 Micronutrient Deficiency in Soil 161
8.3 Factors Affecting the Bioavailability of Micronutrients 161
8.4 Effect of Micronutrient Deficiency on the Biota 163
8.5 The Role of Surfactants in the Facilitation of Micronutrient Biosorption 166
8.6 Surfactants 166
8.7 Conclusion 173 References 174
9 Biosurfactants: Production and Role in Synthesis of Nanopar ticles for Environmental Applications 183 Ashwini N. Rane, S.J. Geetha, and Sanket J. Joshi
9.1 Nanoparticles 183
9.2 Synthesis of Nanoparticles 184
9.3 Biosurfactants 187
9.4 Biosurfactant Mediated Nanoparticles Synthesis 191
9.5 Challenges in Environmental Applications of Nanoparticles and Future Perspectives 196 Acknowledgements 197 References 197
10 Green Surfactants: Production, Properties, and Application in Advanced Medical Technologies 207 Ana María Marqués, Lourdes Pérez, Maribel Farfán, and Aurora Pinazo
10.1 Environmental Pollution and World Health 207
10.2 Amino Acid-Derived Surfactants 208
10.3 Biosurfactants 213
10.4 Antimicrobial Resistance 219
10.5 Catanionic Vesicles 223
10.6 Biosurfactant Functionalization: A Strategy to Develop Active Antimicrobial Compounds 234
10.7 Conclusions 235 References 235
11 Antiviral, Antimicrobial, and Antibiofilm Properties of Biosurfactants: Sustainable Use in Food and Pharmaceuticals 245
Kenia Barrantes, Juan José Araya, Luz Chacón, Rolando Procupez-Schtirbu, Fernanda Lugo, Gabriel Ibarra, and Víctor H. Soto
11.1 Introduction 245
11.2 Antimicrobial Properties 246
11.3 Biofilms 252
11.4 Antiviral Properties 255
11.5 Therapeutic and Pharmaceutical Applications of Biosurfactants 256
11.6 Biosurfactants in the Food Industry: Quality of the Food 258
11.7 Conclusions 260
Acknowledgements 261 References 261
12 Biosurfactant-Based Antibiofilm Nano Materials 269 Sonam Gupta
12.1 Introduction 269
12.2 Emerging Biofilm Infections 270
12.3 Challenges and Recent Advancement in Antibiofilm Agent Development 272
12.4 Impact of Extracellular Matrix and Their Virulence Attributes 273
12.5 Role of Indwelling Devices in Emerging Drug Resistance 274
12.6 Role of Physiological Factors (Growth Rate, Biofilm Age, Starvation) 274
12.7 Impact of Efflux Pump in Antibiotic Resistance Development 275
12.8 Nanotechnology-Based Approaches to Combat Biofilm 276
12.9 Biosurfactants: A Promising Candidate to Synthesize Nanomedicines 277
12.10 Synthesis of Nanomaterials 278
12.11 Self-Nanoemulsifying Drug Delivery Systems (SNEDDs) 282
12.12 Biosurfactant-Based Antibiofilm Nanomaterials 283
12.13 Conclusions and Future Prospects 283
Acknowledgement 285
References 285
13 Biosurfactants from Bacteria and Fungi: Perspectives on Advanced Biomedical Applications 293 Rashmi Rekha Saikia, Suresh Deka, and Hemen Sarma
13.1 Introduction 293
13.2 Biomedical Applications of Biosurfactants: Recent Developments 295
13.3 Conclusion 307
Acknowledgements 307
References 307
14 Biosurfactant-Inspired Control of Methicillin-Resistant Staphylococcus aureus (MRSA) 317
Amy R. Nava
14.1 Staphylococcus aureus, MRSA, and Multidrug Resistance 317
14.2 Biosurfactant Types Commonly Utilized Against S. aureus and Other Pathogens 318
14.3 Properties of Efficient Biosurfactants Against MRSA and Bacterial Pathogens 319
14.4 Uses for Biosurfactants 320
14.5 Biosurfactants Illustrating Antiadhesive Properties against MRSA Biofilms 320
14.6 Biosurfactants with Antibiofilm and Antimicrobial Properties 322
14.7 Media, Microbial Source, and Culture Conditions for Antibiofilm and Antimicrobial Properties 323
14.8 Novel Synergistic Antimicrobial and Antibiofilm Strategies Against MRSA and S. aureus 326
14.9 Novel Potential Mechanisms of Antimicrobial and Antibiofilm Properties 328
14.10 Conclusion 330 References 332
15 Exploiting the Significance of Biosurfactant for the Treatment of Multidrug-Resistant Pathogenic Infections 339 Sonam Gupta and Vikas Pruthi
15.1 Introduction 339
15.2 Microbial Pathogenesis and Biosurfactants 340
15.3 Bio-Removal of Antibiotics Using Probiotics and Biosurfactants Bacteria 342
15.4 Antiproliferative, Antioxidant, and Antibiofilm Potential of Biosurfactant 343
15.5 Wound Healing Potential of Biosurfactants 344
15.6 Conclusion and Future Prospects 345 References 346
16 Biosurfactants Against Drug-Resistant Human and Plant Pathogens: Recent Advances 353 Chandana Malakar and Suresh Deka
16.1 Introduction 353
16.2 Environmental Impact of Antibiotics 354
16.3 Pathogenicity of Antibiotic-Resistant Microbes on Human and Plant Health 356
16.4 Role of Biosurfactants in Combating Antibiotic Resistance: Challenges and Prospects 360
16.5 Conclusion 364 Acknowledgements 365 References 365
17 Surfactant- and Biosurfactant-Based Therapeutics: Structure, Properties, and Recent Developments in Drug Delivery and Therapeutic Applications 373 Anand K. Kondapi
17.1 Introduction 374
17.2 Determinants and Forms of Surfactants 374
17.3 Structural Forms of Surfactants 377
17.4 Drug Delivery Systems 381
17.5 Different Types of Biosurfactants Used for Drug Delivery 384
17.6 Conclusions 391 References 392
18 The Potential Use of Biosurfactants in Cosmetics and Dermatological Products: Current Trends and Future Prospects 397
Zarith Asyikin Abdul Aziz, Siti Hamidah Mohd Setapar, Asma Khatoon, and Akil Ahmad
18.1 Introduction 397
Contents x
18.2 Properties of Biosurfactants 399
18.3 Biosurfactant Classifications and Potential Use in Cosmetic Applications 401
18.4 Dermatological Approach of Biosurfactants 406
18.5 Cosmetic Formulation with Biosurfactant 409
18.6 Safety Measurement Taken for Biosurfactant Applications in Dermatology and Cosmetics 412
18.7 Conclusion and Future Perspective 415 Acknowledgement 415 References 415
19 Cosmeceutical Applications of Biosurfactants: Challenges and Prospects 423 Káren Gercyane Oliveira Bezerra and Leonie Asfora Sarubbo
19.1 Introduction 423
19.2 Cosmeceutical Properties of Biosurfactants 424
19.3 Other Activities 429
19.4 Application Prospects 432
19.5 Biosurfactants in the Market 433
19.6 Challenges and Conclusion 434 References 436
20 Biotechnologically Derived Bioactive Molecules for Skin and Hair-Care Application 443 Suparna Sen, Siddhartha Narayan Borah, and Suresh Deka
20.1 Introduction 443
20.2 Surfactants in Cosmetic Formulation 445
20.3 Biosurfactants in Cosmetic Formulations 445
20.4 Conclusion 457 References 457
21 Biosurfactants as Biocontrol Agents Against Mycotoxigenic Fungi 465 Ana I. Rodrigues, Eduardo J. Gudiña, José A. Teixeira, and Lígia R. Rodrigues
21.1 Mycotoxins 465
21.2 Aflatoxins 466
21.3 Deoxynivalenol 467
21.4 Fumonisins 468
21.5 Ochratoxin A 468
21.6 Patulin 470
21.7 Zearalenone 470
21.8 Prevention and Control of Mycotoxins 471
21.9 Biosurfactants 472
21.10 Glycolipids 473
21.11 Lipopeptides 474
21.12 Antifungal Activity of Glycolipid Biosurfactants 474
21.13 Antifungal and Antimycotoxigenic Activity of Lipopeptide Biosurfactants 475
21.14 Opportunities and Perspectives 482
Acknowledgements 483
References 483
22 Biosurfactant-Mediated Biocontrol of Pathogenic Microbes of Crop Plants 491
Madhurankhi Goswami and Suresh Deka
22.1 Introduction 491
22.2 Biosurfactant: Properties and Types 492
22.3 Biosurfactant in Agrochemical Formulations for Sustainable Agriculture 502
22.4 Biosurfactants for a Greener and Safer Environment 503
22.5 Conclusion 503
References 504
Index 510
List of Contributors
Shashi Bhushan Agrawal
Department of Botany Institute of Science
Banaras Hindu University
Varanasi
Uttar Pradesh
India
Akil Ahmad
School of Industrial Technology
Universiti Sains Malaysia
Gelugor
Penang
Malaysia
Subramania Angaiah
Electro-Materials Research Lab
Centre for Nanoscience and Technology
Pondicherry University
Puducherry
India
Juan José Araya
Escuela de Química
Centro de Investigaciónen Electroquímica y Energía Química (CELEQ)
Universidad de Costa Rica
San José
Costa Rica
Zarith Asyikin Abdul Aziz
School of Chemical and Energy Engineering
Faculty of Engineering
University Teknologi Malaysia
Johor Bahru
Johor Malaysia
Kenia Barrantes
Nutrition and Infection Section
Health Research Institute
University of Costa Rica
San Jose
Costa Rica
Káren Gercyane Oliveira Bezerra
Northeastern Network of Biotechnology
Federal Rural University of Pernambuco
Recife
Pernambuco
Brazil
Advanced Institute of Technology and Innovation (IATI)
Recife
Pernambuco
Brazil
Catholic University of Pernambuco
Recife
Pernambuco
Brazil
Siddhartha Narayan Borah
Royal School of Biosciences
Royal Global University
Guwahati
Assam, India
Luz Chacón
Nutrition and Infection Section
Health Research Institute
University of Costa Rica
San Jose, Costa Rica
Liang Cheng
School of Environment and Safety
Engineering
Jiangsu University
Zhengjiang
China
Jéssica Correia
CEB – Centre of Biological Engineering
University of Minho
Braga
Portugal
Suresh Deka
Environmental Biotechnology Laboratory
Resource Management and Environment
Section
Life Sciences Division
Institute of Advanced Study in Science and Technology (IASST)
Guwahati
Assam
India
Santiago de Frutos
Departamento de Química Física
Facultad de Ciencias
Universidad de Santiago de Compostela
Lugo
Spain
Maribel Farfán
Department of Biology
Healthcare and the Environment
Section of Microbiology
University of Barcelona
Barcelona
Spain
Francisco Fraga
Departamento de Física Aplicada
Facultad de Ciencias
Universidad de Santiago de Compostela
Lugo
Spain
List of Contributors xiii
S. J. Geetha
Department of Biology College of Science
Sultan Qaboos University
Muscat
Oman
Madhurankhi Goswami
Environmental Biotechnology Laboratory
Resource Management and Environment Section
Life Sciences Division
Institute of Advanced Study in Science and Technology (IASST)
Guwahati
Assam
India
Eduardo J. Gudiña
CEB – Centre of Biological Engineering
University of Minho
Braga
Portugal
Sonam Gupta
Department of Biotechnology
National Institute of Technology, Raipur
Chhattisgarh
India
Gabriel Ibarra
Department of Public Health Sciences College of Health Sciences
University of Texas at El Paso
El Paso
TX
USA
Nazim F. Islam
Department of Botany N N Saikia College
Assam
India
List of Contributors
Sanket J. Joshi
Oil & Gas Research Center
Central Analytical and Applied Research Unit
Sultan Qaboos University
Muscat
Oman
Aida Jover
Departamento de Química Física
Facultad de Ciencias
Universidad de Santiago de Compostela
Lugo
Spain
Arun Karnwal
Department of Microbiology
School of Bioengineering and Biosciences
Lovely Professional University
Phagwara
Punjab
India
Asma Khatoon
Centre of Lipids Engineering and Applied Research (CLEAR)
Universiti Teknologi Malaysia
Johor Bahru
Johor
Malaysia
Anand K. Kondapi
Laboratory for Molecular Therapeutics
Department of Biotechnology and Bioinformatics
School of Life Sciences, University of Hyderabad
Hyderabad
India
Current address: Department of Microbiology
Immunology and Pathology
Colorado State University
Fort Collins
CO
USA
Fernanda Lugo
Department of Public Health Sciences
College of Health Sciences
University of Texas at El Paso
El Paso
TX, USA
Chandana Malakar
Institute of Advanced Study in Science and Technology (IASST)
Garchuk
Assam
India
Ana María Marqués
Department of Biology
Healthcare and the Environment
Section of Microbiology
University of Barcelona
Barcelona
Spain
Francisco Meijide
Departamento de Química Física
Facultad de Ciencias
Universidad de Santiago de Compostela
Lugo
Spain
Monoj Kumar Mondal
Department of Chemical Engineering and Technology
Indian Institute of Technology (Banaras Hindu University)
Varanasi
Uttar Pradesh
India
Amy R. Nava
Department of Interdisciplinary Health Sciences
College of Health Sciences
University of Texas
El Paso
TX, USA
Kannan Pakshirajan
Department of Biosciences and Bioengineering
Indian Institute of Technology Guwahati
Guwahati
Assam
India
Punniyakotti Parthipan
Electro-Materials Research Lab
Centre for Nanoscience and Technology
Pondicherry University
Puducherry
India
Yogesh Patil
Symbiosis Centre for Research and Innovation
Symbiosis International University
Pune Maharashtra
India
Lourdes Pérez
Department of Surfactant and Nanobiotechnology
IQAC, CSIC
Barcelona
Spain
Aurora Pinazo
Department of Surfactant and Nanobiotechnology
IQAC, CSIC
Barcelona
Spain
Rolando Procupez-Schtirbu
General Chemistry
Department of Chemistry
University of Costa Rica
San Jose
Costa Rica
Vikas Pruthi
Department of Biotechnology
Indian Institute of Technology Roorkee
Roorkee
Uttarakhand
India
List of Contributors
Aruliah Rajasekar
Environmental Molecular Microbiology
Research Laboratory
Department of Biotechnology
Thiruvalluvar University
Vellore
Tamilnadu
India
Ashwini N. Rane
Department of Environmental Science
Savitribai Phule Pune University
Pune
Maharashtra
India
Selvan Ravindran
Symbiosis School of Biological Sciences
Symbiosis International University
Pune
Maharashtra
India
Ana I. Rodrigues
CEB – Centre of Biological Engineering
University of Minho
Braga
Portugal
Lígia R. Rodrigues
CEB – Centre of Biological Engineering
University of Minho
Braga
Portugal
Rashmi Rekha Saikia
Department of Zoology
Jagannath Barooah College
Jorhat
Assam
India
Hemen Sarma
Department of Botany
N N Saikia College
Titabar
Assam
India
List of Contributors
Leonie Asfora Sarubbo
Advanced Institute of Technology and Innovation (AITI)
Recife
Pernambuco
Brazil
Catholic University of Pernambuco
Recife
Pernambuco
Brazil
Julio A. Seijas
Departamento de Química Orgánica
Facultad de Ciencias
Universidad de Santiago de Compostela
Lugo
Spain
Suparna Sen
Environmental Biotechnology Laboratory
Resource Management and Environment Section
Life Sciences Division
Institute of Advanced Study in Science and Technology
Guwahati
Assam
India
Siti Hamidah Mohd Setapar
School of Chemical and Energy Engineering
Faculty of Engineering, Universiti Teknologi
Malaysia
Johor Bahru
Johor
Malaysia;
Department of Chemical Processes
Malaysia-Japan
International Institute of Technology
University Teknologi Malaysia
Skudai
Johor
Malaysia
SHE Empire Sdn., Jalan Pulai Ria
Bandar Baru Kangkar Pulai
Skudai
Johor
Malaysia
Pooja Singh
Symbiosis School of Biological Sciences
Symbiosis International University
Pune
Maharashtra
India
Victor H. Soto
School of Chemistry
Research Center in Electrochemistry and Chemical Energy (CELEQ)
University of Costa Rica
Costa Rica
Shalini Srivastava
Department of Botany
Institute of Science
Banaras Hindu University
Varanasi
Uttar Pradesh
India
José A. Teixeira
CEB – Centre of Biological Engineering
University of Minho
Braga
Portugal
José Vázquez-Tato
Departamento de Química Física
Facultad de Ciencias
Universidad de Santiago de Compostela
Lugo
Spain
M. Pilar Vázquez-Tato
Departamento de Química Orgánica
Facultad de Ciencias
Universidad de Santiago de Compostela
Lugo
Spain
Preface
This book is useful for the petrochemical industry (enhanced oil recovery from sludge), the pharmaceutical industry (developed technology for controlling multidrug-resistant pathogens), and the agro-industry (using byproducts), as well as environmental scientists and engineers (developing sustainable remediation technologies). As bioremediation is becoming green and a sustainable approach to environmental pollution control, the articles in this book will be relevant for future research that could benefit our stakeholders. The chapters in this reference book may be a unique collection that has been covered by most of the recent studies and provides systematic material produced by contemporary experts in the field. Focusing on research and development over the last 10 years, the study highlights relevant developments in the field. We hope that this book will support researchers by adding a new dimension to environmental studies and the remediation of emerging pollutants. A further benefit would be the understanding of the processes involved from the production to the sustainable use of biosurfactants in the environment and biomedicine.
● This book explains how various methods can be used to recognize and classify microorganismproducing biosurfactants in the environment. In addition, the various aspects of biosurfactants, including structural characteristics, developments, production, bioeconomics and their sustainable use in the environment, and biomedicine, are addressed. It presents metagenomic strategies to facilitate the discovery of novel biosurfactants (mechanistic understanding and future prospects) for the sustainable remediation of emerging pollutants.
● The use of microbes for human well-being is a prospective challenge, as they have developed novel chemicals and their metabolic pathway could be altered through omics approaches to the production of high-value chemicals (HVCs), including biosurfactants. These chemicals may be used in sustainable remediation techniques such as the regulation of the antibiotic resistance gene (AGR) and microbe-enhanced oil recovery (MEOR). We continue to face new and difficult challenges in the restoration of the environment, because current methods of remediation require so many chemicals that have again polluted the environment. There is a need to turn to more efficient alternative approaches and to find environmentally friendly chemicals for sustainability. As a result, the microbial world has the option of offering a replacement for green high-value chemicals to replace certain hazardous compounds already used in environmental reclamation.
This book opens a window on the rapid development of microbiology sciences by explaining how microbes and their products are used in advanced medical technology and in the sustainable remediation of emerging environmental contaminants. The authors concentrate on the environment as well as the biomedical field and highlight the role of microbes in the real world. This book will be updated to reflect current knowledge, the latest developments in the field of biosurfactants,
sustainable remediation applications, and applied medical sciences, and the biotechnological strategies being developed to improve production processes. The most important goal of writing this book will be to communicate current advances and challenges in biosurfactant research. This will allow the reader to understand the dynamics of applied science that underlie microbially derived surfactants, called biosurfactants, and their use in sustainable remediation technology. The basic aim is to include updated content throughout in order to keep pace with this advancing field.
Key features:
● Addresses the applications of biosurfactants in sustainable remediation technology, for example, as agents to form emulsions and biofilm formation for desorption of hydrophobic pollutants.
● Discusses the current state of understanding of the different microbial surfactants, their classifications, properties, how to achieve higher yields, and new applications.
● There is a substantial research result on biosurfactants that envisages our capacity to build a consolidated framework for further development of applications. Biosurfactants for sustainable remediation technology should fill this need, covering the latest trend on biosurfactant research and their applications.
The book was contributed by 56 authors from leading surfactants research groups from Brazil, Costa Rica, China, India, Malaysia, Oman, Portugal, Spain, and the United States, comprising 22 chapters.
1) Introduction to Biosurfactants
2) Metagenomics Approach for Selection of Biosurfactant Producing Bacteria from Oil Contaminated Soils: An Insight into Its Technology
3) Biosurfactant Production Using Bioreactors from Industrial Byproducts
4) Biosurfactants for Heavy Metal Remediation and Bioeconomics
5) Application of Biosurfactants for Microbial Enhanced Oil Recovery (MEOR)
6) Biosurfactant Enhanced Sustainable Remediation of Petroleum Contaminated Soil
7) Microbial Surfactants Are Next-Generation Biomolecules for Sustainable Remediation of Polyaromatic Hydrocarbons
8) Biosurfactants for Enhanced Bioavailability of Micronutrients in Soil: A Sustainable Approach
9) Biosurfactants: Production and Role in Synthesis of Nanoparticles for Environmental Applications
10) Green Surfactants: Production, Properties, and Application in Advanced Medical Technologies
11) Antiviral, Antimicrobial, and Antibiofilm Properties of Biosurfactants: Sustainable Use in Food and Pharmaceuticals
12) Biosurfactant-Based Antibiofilm Nano Materials
13) Biosurfactants from Bacteria and Fungi: Perspectives on Advanced Biomedical Applications
14) Biosurfactant-Inspired Control of Methicillin-Resistant Staphylococcus aureus (MRSA)
15) Exploiting the Significance of Biosurfactant for the Treatment of Multidrug-Resistant Pathogenic Infections
16) Biosurfactants Against Drug-Resistant Human and Plant Pathogens: Recent Advances
17) Surfactant- and Biosurfactant-based Therapeutics: Structures, Properties, and Recent Developments in Drug Delivery and Therapeutic Applications
18) The Potential Use of Biosurfactants in Cosmetics and Dermatological Products: Current Trends and Future Prospects
19) Cosmeceutical Applications of Biosurfactants: Challenges and Perspectives
20) Biotechnologically Derived Bioactive Molecules for Skin and Hair-Care Application
21) Biosurfactants as Biocontrol Agents Against Mycotoxigenic Fungi
22) Biosurfactant-Mediated Biocontrol of Pathogenic Microbes of Crop Plants
The book explores how these twenty-first century multifunctional biomolecules improve or replace chemically synthesized surface-active agents with the aid of the industrial application of biosurfactant production based on renewable resources. This book is also useful for scholars, academicians in bioengineering and biomedical sciences, undergraduate and graduate students in microbiology, environmental biotechnology, health, clinical, and pharmaceutical sciences.
1
Introduction to Biosurfactants
José Vázquez Tato1, Julio A. Seijas2, M. Pilar Vázquez-Tato2, Francisco Meijide1, Santiago de Frutos1, Aida Jover1, Francisco Fraga3, and Victor H. Soto4
1 Departamento de Química Física, Facultad de Ciencias, Universidad de Santiago de Compostela, Avda, Lugo, Spain
2 Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Santiago de Compostela, Avda, Lugo, Spain
3 Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Santiago de Compostela, Avda, Lugo, Spain
4 Escuela de Química, Centro de Investigación en Electroquímica y Energía Química (CELEQ), Universidad de Costa Rica, San José, Costa Rica
CHAPTER MENU
1.1 Introduction and Historical Perspective, 1
1.2 Micelle Formation, 5
1.3 Average Aggregation Numbers, 14
1.4 Packing Properties of Amphiphiles, 18
1.5 Biosurfactants, 20
1.6 Sophorolipids, 25
1.7 Surfactin, 28
1.8 Final Comments, 31 Acknowledgement, 32 References, 32
1.1 Introduction and Historical Perspective
Surface tension is a property that involves the common frontier (boundary surface) between two media or phases. Strictly speaking, the surface tension of a liquid should mean the surface tension of the liquid in contact and equilibrium with its own vapor. However, as the gas phase has normally a small influence on the surface, the term is generally applied to the liquid–air boundary. The phases can also be two liquids (interfacial tension) or a liquid and solid. According to IUPAC, the surface tension is the work required to increase a surface area divided by that area [1]. This is the reversible work required to carry the molecules or ions from the bulk phase into the surface implying its enlargement and corresponds to the increase in Gibbs free energy (G) of the system per unit surface area (A),
Biosurfactants for a Sustainable Future: Production and Applications in the Environment and Biomedicine, First Edition. Edited by Hemen Sarma and Majeti Narasimha Vara Prasad. © 2021 John Wiley & Sons Ltd. Published 2021 by John Wiley & Sons Ltd.
where γ is the interfacial tension. Therefore, the units of γ are J/m2 or N/m, but it is normally recorded in mN/m (because it coincides with the value in dyn/cm of the cgs system). In 1944, Taylor and Alexander [2] collected some representative published (1885–1939) values for the surface tension of water at 20 °C. Their own value was 72.70 ± 0.07 mN/m (calculated by extrapolation) in agreement with more recent determinations, the accepted value being 71.99 ± 0.36 mN/m at 25 °C [3]. This is a rather high value when it is compared with those of other common solvents as ethanol (22.39 ± 0.06 mN/m), acetic acid (27.59 ± 0.09 mN/m), or acetone (29.26 ± 0.05 mN/m) (values from [4]) at 20 °C.
The decrease in the surface tension of water has been traditionally achieved by using soaps or soap-like compounds. According to IUPAC a “soap is a salt of a fatty acid, saturated or unsaturated, containing at least eight carbon atoms or a mixture of such salts. A neat soap is a lamellar structure containing much (e.g. 75%) soap and little (e.g. 25%) water. Soaps have the property of reducing the surface tension of water when they are dissolved in soap-like compounds in water.” This reduction facilitates personal care, washing of clothes and other fabrics, etc. The early documents with descriptions of soaps and their uses are typically related with medicinal aspects, and nowadays there is almost a specific type of soap for each requirement. Levey [5] has reviewed the early history of “soaps” used in medicine, cleansing, and personal care. For instance, he mentions that “in a prescription of the seventh century bc, soap made from castor oil (source of ricinoleic [12-hydroxy9-cis-octadecenoic] acid) and horned alkali is used. . . as a mouth cleanser, in enemata, and also to wash the head.” However, Levey concludes that a true soap using caustic alkali was probably not produced in antiquity but “evidence has been adduced to indicate that salting out was in use in early Sumerian times.” In his Naturalis Historia, Pliny the Elder [6] refers to soap (sapo) as prodest et sapo, Galliarum hoc inventum rutilandis capillis. fit ex sebo et cinere, optimus fagino et caprino, duobus modis, spissus ac liquidus, uterque apud Germanos maiore in usu viris quam feminis, which may be translated as “There is also soap, an invention of the Gauls for making their hair shiny (or glossy). It is made from suet and ashes, the best from beechwood ash and goat suet, and exists in two forms, thick and liquid, both being used among the Germans, more by men than by women.” Hunt [7] indicates that centers of soap production by the end of the first millennium were in Marseilles (France) and Savona (Italy), while in Britain some references appear in the literature around 1000 ad. For instance, in 1192 the monk Richard of Devizes referred to the number of “soap makers in Bristol and the unpleasant smells which their activities produced.” Hunt also resumed other aspects as the chemistry of soap, the British alkali industry, the expansion of soap production, soap manufacturers, and manufacturing methods. As early as 1858, Campbell presented a USA patent [8] for the production of soaps. He described the process as consisting in “the use of powdered carbonate of soda for saponifying the fatty acids generally, and more particularly the red oil or ‘red (oleic) acid oil’ and converting them, by direct combination, into soap in open pans or kettles, at temperatures between 32 and 500 °F.” Mitchell [9] revised the Jabón de Castilla or Castile soap (named from the central region of Spain), probably the first white hard soap. It was an olive oil-based soap and soaps with this name can still be bought today. Traditional recipes and videos can be easily found on the Internet. In the paper “Literature of Soaps and Synthetic Detergents”, Schulze [10] recorded the literature (including books, periodicals, abstracts, indexes, information services, patent publications, association publications, conference proceedings) on soaps, surfactants, and synthetic detergents up to 1966.
Nowadays descriptions for soap-making from fats and oils are frequent for teaching purposes. For instance, Phanstiel et al. [11] have described the saponification process (basic hydrolysis of fats). It involves heating either animal fat or vegetable oil in an alkaline solution. The alkaline solution hydrolyses the triglyceride into glycerol and salts of the long-chain carboxylic acids (Scheme 1.1).
To overcome the shortcomings of the carboxylic group of soaps, during the first decades of the twentieth century, new surface-active agents were obtained in chemistry laboratories. Kastens and Ayo [12] and Kosswig [13] reviewed the main achievements of these decades. The first result of this search was Nekal, an alkyl naphthalene sulfonate, although it probably was a mixture of various homologs [14]. Other pioneer compounds were Avirol series (sulfuric acid esters of butyl ricinoleic acid), Igepon A series (fatty acid esters of hydroxyethanesulfonic acid), Igepon T series (amide-derivatives of taurine). All these products represented different approaches to the elimination of the carboxylic group of soaps. IUPAC defines a surfactant as a substance that lowers the surface tension of the medium in which it is dissolved and/or the interfacial tension with other phases, and, accordingly, is positively adsorbed at the liquid/vapor and/or at other interfaces. By detergent, IUPAC refers to a surfactant (or a mixture containing one or more surfactants) having cleaning properties in dilute solutions. Thus, soaps are surfactants and detergents.
It is not easy to whom the use of the word surfactant should be ascribed for the first time. A search in SciFinder® suggests that the word was first used by Bellon and LeTellier in a French patent (1943) [15]. The SciFinder abstract of this patent indicates that “Surfactants such as wetting agents, detergents, emulsifiers, and stickers are prepared by treating by-product materials containing starches, cellulose, amino acids, and smaller quantities of inedible fats with NaOH and neutralizing the reaction product.”
Because of their physicochemical properties, surfactants have found applications in almost any kind of industry. A list of the relevant ISO and DIN regulations for a utility evaluation of surfactants has been provided by Kosswig [13]. For instance, in 1950 Lucas and Brown [16] measured the wetting power of 13 surfactants to find a wetting agent that would enable sulfuric acid to wet peaches quickly and uniformly so as to permit acid peeling. Anionic, cationic, and neutral surfactants were tested. In the Application Guide appendix of the book Chemistry and Technology of Surfactants [17] there is a list that illustrates the variety of surfactants and their versatility in a wide range of applications. Among others the following are mentioned: Agrochemical formulations, Civil engineering, Cosmetics and toiletries, Detergents, Household products, Miscellaneous industrial applications, Leather, Metal and engineering, Paints, inks, coatings, and adhesives, Paper and pulp, Petroleum and oil, Plastics, rubber, and resins, and Textiles and fibers. For instance, their wetting properties have been early used in food technology. We have already mentioned the early connection of soap and medicine and correspondingly the use of surfactants in pharmacy in the formulation (as emulsifying agents, solubilizers, dispersants, for suspensions) and as wetting agents, which cannot be a surprise [18]. Nursing care makes a continuous use of surface-active agents.
The soaps of Scheme 1.1 show the most important structural characteristic of surfactants: the coexistence of one lyophilic group (alkyl chain) and one lyophobic group (carboxylate ion). In aqueous solutions, it is more frequent to use the terms hydrophilic and hydrophobic. A graphical representation head–tail (hydrophobic group–hydrophilic group) is widely used, the alkyl chain
Scheme 1.1 Alkaline hydrolysis of a triglyceride to obtain soaps.
being the tail and the carboxylate group the head (Figure 1.1). This structure gives the amphiphile character to surfactant compounds.
More generally, the head can be any polar group and the tail any apolar group, leading to a wide range of structures and types of surfactants. Among anionic heads, typical groups are carboxylate, sulfate, sulfonate, and phosphate, while the most frequent counterions are monovalent and divalent cations. Polycharged heads are also common, EDTA derivatives being well-known examples [19]. Cyclopeptides constitute another important group [20]. Among cationic heads, typical groups are tetralkylammonium, N,N-dialkylimidazolinium and N-alkylpyridinium ions, while chloride and bromide are the most common counterions. Among neutral heads, polyethylene glycol ethers, polyglycol ethers, and carbohydrates can be mentioned. Zwitterionic heads are very important as phospholipids belong to this group, as well as sulfobetaines and trialkylamine oxides. Many examples can be found elsewhere [13].
However, the structures of surfactants may be more complex than the head–tail model suggests. For instance, the number of polar and non-polar groups can be higher than one, the phospholipid phosphatidylcholine with two alkyl–allyl chains and a zwitterion as the head being an example. Gemini surfactants are dimeric surfactants [21] carrying two charged groups and two alkyl groups. The two amphiphilic moieties are connected at the level of the head groups, which are separated by a spacer group. They are characterized by critical micelle concentrations that are one to two orders of magnitude lower than those corresponding to conventional (monomeric) surfactants [22].
Bolaamphiphilic molecules contain a hydrophobic skeleton (e.g. one, two, or three alkyl chains, a steroid, or a porphyrin) and two water-soluble groups on both ends [23]. They can be symmetric or asymmetric [24, 25]. Recent examples of bolaamphiphilic, Y-shaped and divalent surfactants have been published by Baccile et al. [26] (Figure 1.1).
Some surfactants, instead of the mentioned head–tail structure, present a bifacial polarity with the hydrophilic and hydrophobic characteristics at two opposite sides of the molecule. The bestknown examples are bile salts (see Figure 1.2) [27, 28]. Many membrane-active compounds are facial amphiphiles including cationic peptide antibiotics [29]. The facial amphiphilic conformation adopted by these peptides is a consequence of their secondary and tertiary structures, allowing
Hydrophilic head
Hydrophobic tail
ClassicBolaamphiphileGeminiPhospholipid Diva lent Y-shaped Hybrid
Figure 1.1 Schematic representation of the structure of some surfactants.
Figure 1.2 Bifacial structure of cholic acid.
that one face of the molecule presents cationic groups (protonated amines or guanidines) and the other face contains hydrophobic groups. An example may be magainin I [30]. Among other surfactant structures, diblock copolymers and polymeric surfactants, fluorosurfactants and siliconebased surfactants can be mentioned [13].
1.2 Micelle Formation
The necessity of a quantitative measurement of the surface tension of soap solutions was soon evident. By the time that I. Traube published his earliest paper in 1884, significant theories of capillarity from La Place, Poisson, or Gauss were known [31]. Early measurements of the surface tension only imply inorganic salts, acids, and bases. In 1864 Guthrie [32, 33] measured some organic liquids. At the same time, Musculus [34] studied the capillarity of aqueous solution of alcohol observing that “the capillarity of the water decreases considerably with the addition of the least amount of alcohol, in the beginning, much faster than in the presence of more alcohol.” He also noticed that “all derivatives of ethyl alcohol which are soluble in water (as acetic acid) behave like this, and probably this is also the case with the other alcohols,” but substances such as “sugars, and salts if they are not present in a great amount, almost do not influence the capillarity of water.” He proposed the use of capillarity for measuring the concentration of alcohol and acetic acid in water, among other reasons, because “it offers the advantage that one needs only very little fluid for analysis, one drop being enough.” He continued that, as “the animal fluids, such as blood serum, urine, have a capillarity which is equal to that of water, it is possible to detect and quantify substances in the urine,” making reference, for instance, to bile.
Traube started the measurement of the influence of many organic substances on the surface tension of water in the period 1884–1885 [31] and observed that “the surface tension of capillaryactive compounds belonging to one homologous series decreased with each additional CH2 group in a constant ratio which is approximately 3:1,” leading him to propose Traube’s Rule.
A nice historical paper was published by Traube [31] in 1940, in which he mentioned previous works related to the investigation of aqueous solutions of inorganic salts, acids, and bases, employing the method of capillary tubes, and, particularly, the dropping method applied by Quinke. Traube developed this method and designed a simple instrument, the stalagmometer – together with the stagonometer – which found general application in science and industry. In the mentioned paper, Traube refers mainly to his publications that appeared in the period 1886–1887. By 1906, the measurement of the surface tension by the capillary rise was so important that it was included in the book Practical Physical Chemistry by A. Findlay. The use of Traube’s stalagmometer for such a purpose was proposed in the 3rd edition of the book, published in 1915. The experiment is still proposed in recent textbooks on practical Physical Chemistry [35].
Seventeen of the more important methods of measuring surface tension were described in 1926 by Dorsey [36]. According to his own words, “The list of references does not pretend to be complete but is intended merely to direct the reader to one or more of the sources from which the required information can be obtained most satisfactorily.” Even so, the number of cited papers was greater than 110, while the number of citations corresponding to the nineteenth century was 63 (56%). Eminent scientists such as Bohr, Rayleigh, Thomson, Kelvin, Maxwell, Laplace, and Poisson were among them. Tate [37] published his famous law in 1864 and Wilhelmy in 1863.
Even at low concentrations, surfactants reduce the surface tension of water due to its tendency to migrate toward the air–water interface, forming a monolayer. This was first suggested in 1907 by Milner [38] and, previously, Marangoni in 1871 “suggested that this capability [local variation in the tension of its surface] is due to the presence on the surface of the film of a pellicle, composed of
matter having a smaller capillary tension than that of water.” Milner clearly established that “in several organic solutions the surface tension is less than that of water, and there is consequently an excess of solute in the surface.” Later, Langmuir [39] indicated that “the -COOH, -CO, and –OH groups have more affinity for water than for hydrocarbons. . . [and] when an oil is placed on water, the –COO– groups combine with the water, while the hydrocarbon chains remain combined with each other.” In other words, the tail of a surfactant (the hydrocarbon chain) must be located at the air interface, with the tail upwards oriented and the head (hydrophilic groups) at the water interface. Rising the surfactant concentration, the surface concentration increases as well until the full coverage of the interface by the molecules or ions. If the interface is completely covered, further increment of the surfactant concentration does not (almost) modify the surface tension. Furthermore, the additional surfactant molecules (or ions) have to remain in the bulk solution, and following Langmuir “hydrocarbon chains remain combined with each other, thus forming micelles” (or other aggregates).
The term micelle was commonly used by the first years of the twentieth century [40, 41] in relation to colloid solutions (frequently inorganic gels). In 1920 McBain and Salmon [42] (see also [43]) described a brief résumé of previous work, citing, for instance, Krafft’s work. From the summary of this paper we extract the following sentences:
• 3. These colloidal electrolytes are salts in which one of the ions has been replaced by an ionic micelle.
• 5. This is exemplified by any one of the higher soaps simply on change of concentration. Thus, in concentrated solution there is little else present than colloid plus cation, whereas in dilute solution both undissociated and dissociated soap are crystalloids of simple molecular weight.
• 8. The ionic micelle in the case of soaps exhibits an equivalent conductivity quite equal to that of potassium ion. Its formula may correspond to PmHO n n . 2 but more probably it is NaPP mH O x n n 2 , where P is the anion of the fatty acid in question.
Therefore, the essential definition of the present concept of a micelle was established. IUPAC indicates that “Surfactants in solution are often association colloids, that is, they tend to form aggregates of colloidal dimensions, which exist in equilibrium with the molecules or ions from which they are formed. Such aggregates are termed micelles.”
In 1922, McBain and Jenkins [44] studied solutions of sodium oleate and potassium laurate by ultrafiltration, using this technique for separating the ionic micelle from the neutral colloid. For both surfactants they showed that the proportion (simple potassium laurate or sodium oleate)/ (ionic micelle) increases fast at low concentrations and reached a plateau at high concentrations (see graphs of the paper). They also concluded that the diameter of the ionic micelle is only a few times the length of the molecule and “the particles of sodium oleate are about ten times larger than those of potassium laurate.”
By the end of the twenties and the beginning of thirties of the twentieth century, the research activity on micelle-forming substances experienced an extraordinary blooming spring. The paper by Grindley and Bury [45] is a landmark on the subject, being particularly illustrative for the purposes of this review. They represented the formation of micelles by butyric acid in solution by the equation nC HCOH CH CO H n 37 23 72 (1.2) where n is “the number of simple molecules in a micelle” or aggregation number (which is a relatively large number) and write the equilibrium constant as Ks m nn n / (1.3)
where s and m are the concentrations of butyric acid as monomers and as micelles, respectively. The previous equation can be written as
m sK n n() / (1.4) from which they deduced that if s/K is appreciably smaller than unity, the concentration of micelles will be negligible. Only when s approaches the value K does the concentration of micelles become appreciable, and “will rapidly increase as the total concentration increases.” From this analysis they conclude that “if any physical property of aqueous butyric acid solutions be plotted against the concentration, the slope of the curve will change abruptly near this point.” A few months later, Davies and Bury [46] named that concentration as the critical concentration for micelles
Previous analysis constitutes the basis of all experimental techniques so far used for determining the critical concentration for micelles (from here cmc). For instance, the association of monomers in micelles reduces the number of particles in the solution and, consequently, colligative properties (freezing point, vapor pressure. . .) also drastically change at this concentration. Other properties such as solubilization of solutes as dyes or the conductivity of the solution also change significantly. As an example, we shall mention the paper by Powney and Addison [47] who measured the surface tension of aqueous solutions of sodium dodecyl, tetradecyl, hexadecyl, and octadecyl sulfates and plotted the results in the form of vs log (concentration), as we do nowadays. The curves showed breaks at critical concentrations, which correspond to transitions from single ions to micelles, these single ions constituting the surface-active species. Figure 1.3 shows a typical plot for an unspecified surfactant. Powney and Addison noticed that the magnitude of the surface activity and the critical concentration for micelles were governed by chain length, temperature, and the valency of the added cation.
In 1895, Krafft and Wiglow [48] observed the formation of crystals at 60°, 45°, 31.5°, 11°, 35°, and 0° with hot aqueous solutions (1%) of stearate, palmitate, myristate, laurate, and elaidate sodium salts, respectively. Each of these temperatures is now known as the Krafft point (Tk). IUPAC defines it as the temperature (more precisely, narrow temperature range) above which the solubility of a surfactant rises sharply. At this temperature the solubility of the surfactant becomes equal to the cmc
In 1955, Hutchinson et al. [49] published the paper “A new interpretation of the properties of colloidal electrolyte solutions” in which “the formation of micelles was treated as a phase separation rather than as an association governed by the law of mass action.” Seven years later, Shinoda and Hutchinson [50] used this model to interpret the Krafft point, associated to the micellization process. These authors proposed micellization as a “similar phase separation, with the important distinction that micellization does not lead to an effectively infinite aggregation number, such as corresponds to true phase separation.” If correct, the model requires that the activity of
/(mN/m)
Figure 1.3 Typical surface tension vs ln (surfactant) plot showing the break point corresponding to cmc
micelle-forming compounds should be practically constant above the cmc. Among others, the authors invoke Nilsson results [51] with radiotracers as evidence for their proposition. In a frequently reproduced graph, Shinoda and Hutchinson [50] plotted the concentration vs temperature for sodium decyl sulfonate near the Krafft point. The plot resembles the phase diagram of water near its triple point. If micelles are considered as a phase, by the phase rule, the system should become invariant at constant temperature and pressure [49, 50]. In other words, “the equilibrium hydrated solid monomers micelles is univariant, so that at a given pressure the point is fixed.” As temperature increases, the solubility also increases until Tk where the cmc is reached. Above this temperature, the surfactant is dissolved in the form of micelles.
Let us go back to 1915. In this year, Allen [52] published a paper in which he showed the use of the surface tension measurement for the determination of bile salts in urine. In the introduction of his paper, Allen refers to Hay’s method of testing the presence of bile salts in the urine. That method consists in “shaking flowers of sulphur upon the surface of the urine. . . When the surface tension of the urine is lowered [by bile salts] the powdered sulphur sinks to the bottom, and the lower the surface tension the more rapidly this takes place. [But] The method is very unsatisfactory. . . and if possible, a quantitative method, would be very desirable.” Thus Allen proposed a very accurate measurement of the surface tension of a solution by the stalagmometric method “to determine the feasibility of estimating the amount of bile salts present in pathological urines from measurements of the surface tension taken with a portable Traube stalagmometer.” He computed the surface tension value of a solution in per cent of that of distilled water according to the formula
Number ofdropsofdistillided water
Number ofdropsofsoluution specific gravity of thesolution (1.5)
The method relies on the fact that bile salts possess the property of lowering the surface tension of a solution very markedly, even when present in small concentrations. Table I of his paper shows some results for sodium glycocholate (NaGC) in distilled water. In a reanalysis of these data by plotting the surface tension vs ln(concentration), it is possible to determine a value of 0.0117 M for the cmc of NaGC, a value in perfect agreement with recent measurements. From the Reis et al. [53] compilation, an average value of (1.04 ± 0.29) × 10−2 M may be estimated for the cmc of this bile salt.
The “excess of solute [surfactant] in the surface” indicated by Milner has traditionally been analyzed through the Gibbs equation [54]
where Γ is the surface excess, ( γ/ ln c) is the slope of the dependence of γ with the logarithm of the concentration of the surfactant (frequently being linear), R is the ideal gas constant, T the temperature, and n a factor that depends on the nature of the surfactant. The equation allows the determination of the area occupied per molecule at the interface, which is the inverse of the surface excess, i.e.
where NA is Avogadro’s number.
Recently Menger et al. [55] have questioned the validity of the Gibbs equation on the basis that in the region of concentration where the equation is applied the adsorption at the interface does not generally reach saturation. This criticism has been supported by measurements from a radioactive surfactant [56], results that suggest that the γ-ln c linearity is not indicative of surface saturation, a hypothesis required for the deduction of the Gibbs equation. Neutron reflection
measurements also support the fact that there are serious limitations in applying the Gibbs equation accurately to surface tension data [57, 58].
In the late nineteen thirties, other important papers were published. Wright and co-workers [59–61] measured the conductivity, density, viscosity, and solubility of several sodium alkyl (decyl, dodecyl, and hexadecyl) sulfonates at several temperatures. In all cases breaks at the curves or linear dependences of the property with the sulfonate concentration were observed. They also reported that the addition of sodium chloride to solutions of sodium dodecyl sulfonate lowered the cmc and that the lowering becomes less marked with a rise in temperature. Hartley [62] demonstrated that paraffin chain salts behave as strong electrolytes at low concentrations. For cetane sulfonic acid, a value of about 0.008 N in water at 60 °C was given for cmc and that it increased by about 2% per degree. This is an important question since the formation (or not) of premicellar aggregates is still under debate.
By the end of this decade Hartley [63] reviewed (36 references) the subject, the title of the paper being Ion aggregation in solutions of salts with long paraffin chains. In the abstracts we can read about the structure of micelles which are “aggregates of paraffin-chain ions with some adsorbed opposite ions,” micelles are spherical with a radius equal to the length of a completely stretched paraffin-chain and have a liquid interior and the strong dependence of cmc with the length of the hydrocarbon chain and nature of the ionized terminal groups and opposite ions (counterions), and with temperature (in less extension). He also affirmed that “the spherical micelle is more stable than ion pairs.”
Thus, by this time, the essential parameters that define a micelle were introduced or established: change of properties at the cmc, variables that influence the cmc, shape and size, internal and peripheral structures, and the essential thermodynamics (mass action law).
In the period 1946–1947, immediately after the Second World War, the activity on surfactant research experiences an important enhancement.
Corrin and Harkins [64] proposed the equation log(cmc) = A × log(counterion±) B to relate the dependence of the cmc with the concentration of added salts (the sign at the superscript of the counterion is opposite to that of the surfactant ion). Table 1.1 resumes the values for the constants A and B for several surfactants. They also noticed that urea has a negligible effect in lowering the cmc.
Three years later, Lange [65] applied the mass action law to ionic micelles and wrote the equilibrium of formation of the micelle as
where K is the counterion, A the surfactant ion, and p and q the stoichiometric coefficients. Although Lange considered the activity coefficients of the different species, for simplicity we will ignore them and write the equilibrium constant as
(1.9)
Table 1.1 Parameters A and B of the Corrin–Harkins equation. The number of figures on the values of A and B has been reduced.
Surfactant
Source: Corrin and Harkins [64], p. 683.
Writing [A] = ck and [K] = ck + N, where N is the equivalent concentration of added salt, it is finally found that
where L = [KpAq]. Thus with logck as ordinate and log(ck + N) as abscissa, this is the equation of a straight line with the slope –p/q, which corresponds to the empirical one found by Corrin and Harkins. This point has been discussed in detail by Hall [66] in his theory for dilute solutions of polyelectrolytes and of ionic surfactants.
The effects of solvents (alkyl alcohols CnH2n+1OH, n = 1–4; HOCH2CH2OH, glycerol, 1,4-dioxane, and heptanol) on the critical concentration for micelle formation of cationic soaps was studied by Corrin and Harkins [67], Herzfeld et al. [68], and Reichenberg [69]. Klevens [70] found that increasing the temperature causes an apparent decrease in the cmc, as determined by spectral changes in various dyes. However, this same author found the opposite effect when the micelles formation was determined by refraction [71].
Simultaneously, other experimental techniques, mainly spectroscopic ones, were introduced for the determination of the cmc. After a paper published by Sheppard and Geddes [72], in which the authors reported that by the addition of cetyl pyridinium chloride, the absorption spectrum of aqueous pinacyanol chloride was shifted from that exhibited in aqueous solutions to that in non-polar solvents, Corrin et al. [73] used this property to determine the cmc of laurate and myristate potassium salts, giving values of 6 × 10−3 M and 0.023–0.024 M, respectively. The concentration of soap at which this spectral change occurs was taken as the cmc, proposing that the dye is solubilized in a non-polar environment within the micelle. Klevens [74] performed a similar work by studying the changes in the spectrum of pinacyanol chloride in solutions of myristate, laurate, caprate and caprylate potassium salts, and sodium lauryl sulfate. These studies were extended to other surfactants [75] and other dyes as p-dimethylaminoazobenzene [76]. By using suitable dyes (Rhodamine 6G, Fluorescein, Acridine Orange, Acridine Yellow, Acriflavine, and Dichlorofluorescein) fluorescence spectroscopy was soon adopted [77, 78].
In 1950, Klevens [79] studied the solubility of some polycyclic hydrocarbons in water and in solutions of potassium laurate (at 25 °C). For all the polycyclic hydrocarbons, he showed that by increasing the concentration of the surfactant, their solubility also increased. Particularly, for pyrene he measured solubilities of 0.77 × 10−6 and 2.24 × 10−3 M in water and potassium laurate (0.50 M), respectively.
One year later, Ekwall [80] studied the sodium cholate association by measuring the fluorescence intensity, and determined that the lowest concentration at which polycyclic hydrocarbons (3,4-benzopyrene included) are solubilized is 0.018 M. This corresponds to the beginning of the micelle formation, although “at first relatively small amounts of cholate ion aggregates and the actual micelle formation occurs at about 0.040 to 0.044 M.” Foerster and Selinger [81] observed that in micelles of cetyldimethylbenzylammonium chloride, pyrene forms dimers in excited states (excimers).
In the period 1971–1980, the number of papers on solubilized pyrene in micelle solutions increased very quickly. The fluorescence decay of the excited state of pyrene received an important attention. The aggregation number and microviscosities of the micellar interior [82], the permeability of these micelles with respect to nonionic and ionic quenchers [83], oxygen penetration of micelles [84], or the environmental effects on the vibronic band intensities in pyrene monomer fluorescence in micellar systems [85, 86] were published. Kalyanasundaram and Thomas carefully analyzed the lifetime of the monomer fluorescence and the ratio I3/I1 of the third and first vibronic
band intensities of pyrene in sodium lauryl sulfate as a function of its concentration. Both curves have a sigmoidal shape (see Figure 1.3 of the paper). A value of 8 × 10−3 M for the cmc of the surfactant was given.
However, Nakajima [86] plotted the ratio I1/I3 and accepted the cmc as the concentration at which the first break is observed (point A in Figure 1.4). At low concentrations of the surfactants the values of the I1/I3 ratio are high, typical of a hydrophilic environment for pyrene, the value in water being 1.96 [87] while at high surfactant concentrations the I1/I3 ratio tend to typical values of non-polar solvents. For instance, at high surfactant concentrations of sodium cholate and sodium deoxycholate, the I1/I3 ratio is around 0.7 [88] while the value in cyclohexane is 0.61 [89]. This suggests that the polarity of the microenvironment of pyrene is a lipophilic one. Andersson and Olofsson [90], when performing a calorimetric study of nonionic surfactants, also made use of Nakajima’s approach. Other authors have proposed the inflection point of the curve (point B) as cmc [91]. As such it fulfills the condition
where φ would be the I1/I3 ratio. The expression is also valid for any other property that exhibits a sigmoidal behavior as the obtained enthalpograms from isothermal titration calorimetry (ITC) [92]. The plot of (dφ/dSt) vs St is shown in Figure 1.4 (right) and the cmc is easily obtained from the peak. Aguiar et al. [93] have analyzed both points (A and B) for several surfactants and proposed an approach for choosing between one or the other point. Occasionally, both A and C points have been accepted as an indication that the system has two cmc values. We consider that this is not correct. These different points of view introduce an important question related to the determination of the cmc from sigmoidal curves, which are frequently found when using some experimental techniques. By now, some different approaches to determine the cmc have already been introduced. Rusanov [94] has reviewed the definitions of cmc based on the application of the mass action law to the aggregation process in surfactant solutions. Among them, we must mention the definition given by the equation
Figure 1.4 Typical plot of a sigmoidal curve. Example φ = I1/I3 (ratio of the intensities of the first and third vibronic peaks of pyrene) vs increasing concentration of a surfactant (left) and its first derivative (right). The shape of curves from isothermal titration calorimetry are similar in shape (see below for a description).
which was proposed by Phillips [95] in 1955 for determining the cmc for an ideal measured property (φ)-concentration (St) relationship. Phillips pretended that Eq. (1.12) corresponds to the point of maximum curvature, but this is not the case. Nakajima’s approach fulfills this condition as well as the methodology proposed by Olesen et al. [96] for determining the aggregation number of aggregates from ITC curves. However, the definition of cmc as corresponding to the inflection point in the φ vs St curve has been recommended [97] for the determination of the cmc from ITC curves. For large absolute values of the slope at the inflection point (= (φC φA)/(SC SA)) in previous sigmoidal curves, the difference in the values obtained from any of the two previous equations may be considered negligible for practical purposes. If the cmc is fairly sharp, Hall [98] has proposed that it can be regarded approximately as a second order phase transition.
Among the other definitions for cmc analyzed by Rusanov we would like to remark on the following one. The focus is on a system in which micelles are composed of a single sort of particle. For further details and the analysis of more complex systems, the two papers by Rusanov [94] are recommended.
Let us redefine the Grindley and Bury [45] equilibrium constant as
The equilibrium constant Ko would correspond to a hypothetical single step in which a virtual aggregate mj is formed by the binding of an additional monomer to a virtual aggregate of size mj-1 according to
its equilibrium constant being Km ms jj j / 1
The isodesmic model accepts that all Kj constants are equal to Ko. The difference with the Grindley and Bury equilibrium constant comes from the fact that only (n – 1) steps are required to form a micelle with n monomers. Interestingly, in 1935 Goodeve [99] have pointed out that forming micelles of, say, about 20 molecules must pass through all the intermediate stages of association. The formation of the micelles from the monomer in one stage is, of course, highly improbable as it requires “a collision of 20 molecules at one time.” Goodeve presented Eq. (1.14) as representing the equilibrium according to this point of view.
Equation (1.13) is better understood in the form
m s Ks n o n 1 (1.16)
where Ko and s are both positive, n is usually large, and, independently of the value of n, for Ko × s = 1, the concentration of micelles and monomers are the same. Deviations of the product Ko × s from that value lead to either mn < s or mn > s. For instance, for n = 50, the ratio mn/s changes by a factor 1.86 × 104 when Ko × s varies from 0.9 to 1.1. This is in fact the analysis by Grindley and Bury [45].
This suggests a definition of cmc by the condition
sKcmco 1 (1.17) and from the conservation of material (St = s + n × mn) it follows that at cmc St,cmc = (n + 1)scmc = (n + 1)mn
