Nmr Spectroscopy Nmr Spectroscopy Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a research technique that exploits the magnetic properties of certain atomic nuclei to determine physical and chemical properties of atoms or the molecules in which they are contained. It relies on the phenomenon of nuclear magnetic resonance and can provide detailed information about the structure, dynamics, reaction state, and chemical environment of molecules. Most frequently, NMR spectroscopy is used by chemists and biochemists to investigate the properties of organic molecules, though it is applicable to any kind of sample that contains nuclei possessing spin. Suitable samples range from small compounds analyzed with 1-dimensional proton or carbon13 NMR spectroscopy to large proteins or nucleic acids using 3 or 4-dimensional techniques. The impact of NMR spectroscopy on the sciences has been substantial because of the range of information and the diversity of samples, including solutions and solids.
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Shielding in H-NMR :The structural factors are the factors which cause the change in resonance frequency and then the chemical shift due to alter the value of magnetic field by nucleus. Thus the different protons show the different chemical shifts. This is the basic for the structure determination of the compounds. This includes the electro negativity, magnetic anisotropy, and hydrogen bonding. 1. Electronegativity :The isolated protons show the resonance at lower value of magnetic field strength than the covalently bonded hydrogen. The protons are surrounded by negatively charged particles. When the external magnetic field (Bo) is applied then these charged particles move and a secondary magnetic field is produced. This secondary field is very stronger than applied external field. Thus the protons are shielded by electrons. Protein NMR Spectroscopy :Proteins play a very important role in living organism for skeleton support, movement of muscles, digestion system; defend for infection etc. they are in various shapes like round shape in hemoglobin, long shape collagen, strong spectrin-c etc. Proteins are made with amino acids which gives the specific character to protein. The protein folding state is a stable state than the unfolded state of protein. In both the states, they form various hydrogen bonds and non-ionic interactions. The folding state is more ordered and compact containing the long range interactions among the different chains of proteins.
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The protein folding process is quite complex because it is very difficult to know that how protein folds into correct structural forms with in tiny of seconds. So the important techniques were found to know about the complex process. One is X-ray crystallography and another is nuclear magnetic resonance spectroscopy (NMR). It is based on the identification of the observed signals in the spectra. These observed signals are correlated with the amino acid protons which gives the signals. Tertiary Structure The computer calculations is used to detect the distance- and torsion-angle data into a visible structure but this information is not sufficient for the proper determination of protein structure. So the determination of randomly folded starting is done by the known amino acid sequence. Then the computer program folds the structure in order to compensate the observed inter proton distance with calculated structures. The energy potential is given by known parameters. The protein molecule have tendency to take various conformation due to free rotation in chemical bonds. All the possible conformations are known as conformational space. So for determination of structure of protein by the NMR, the conformation space should be restricted. Especially computer programmes are based on two programmes for calculating a protein structure in solution which are as below;
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