NMR (NUCLEAR MAGNETIC RESONANCE)

NMR (NUCLEAR MAGNETIC RESONANCE)

21.      NMR (NUCLEAR MAGNETIC RESONANCE)

It is a physical phenomenon in which nuclei absorb electromagnetic radiations in presence of a magnetic field and then re-emit them. This technique used in biochemical studies with several isotopes like 1H, 13C, 15N and 31P. 
This technique is based on the resonating frequency of molecules between the ground state and excited energy state and the magnetism arises by the spinning motion of charged particles. 


The two possible energy states exists in the presence of the external magnetic field. First, low-energy state, the spinning of charged particles generates the magnetic field which is parallel to the external field and second, high energy state, the spinning of charged particles generates the magnetic field which is antiparallel to the external field.
The angular momentum of the spin is described by the quantum spin number I. If I is an integral number (I = 0, 1, 2, etc.), then there is no net spin and no NMR signal because electrons cancel each others effect where as if I is half-integral than it gives a resultant direction of field and this magnetic induction is measured in Tesla (T) which is directly proportional to the strength of the applied magnetic field.
Ta Strength of Applied magnetic field
Modern NMR instruments maintains a constant radio-frequency and also induce small changes in the magnetic field so a perfect NMR image is obtained. One-dimensional NMR is used for structural analysis of small molecule but for proteins and other complex biopolymers multidimensional NMR (2-D, 3-D, 4-D is used which generates overlapping line spectra).
21.1.    Application 
-    It is used in advanced medical imaging techniques, like in magnetic resonance imaging (MRI). 
-    Several radio isotopes like 1H and 13C, although nuclei from isotopes of many 2H, 6Li, 10B, 11B, 14N, 15N, 17O, 19F etc. are studied.
-     It is used in chemical studies with several variants of NMR such as proton NMR, carbon-13 NMR, deuterium NMR and phosphorus-31 NMR.
-    Study of living tissue like brain tumors with the technique in vivo with the help of magnetic resonance spectroscopy.
    Circular Dichroism (CD) is a spectroscopic technique widely used for the evaluation of the conformation and stability of proteins in several environmental conditions like temperature, ionic strength, and presence of solutes or small molecules.
This technique is based on circularly polarized light. Basically, linearly polarised light is light whose oscillations are confined into a single plane polarised light is the sum of two linearly polarised states at right angles to each other which are vertically and horizontally polarised light.
    If one of the polarised states is out of phase with the other by a quarter?wave, the resultant will be a helix and is known as circularly polarised light (CPL). 
Interaction of polarised light with chiral molecules and the majority of biological molecules such as protein and DNA, determine the structure of molecules.
Circular dichroism determines secondary structural elements of proteins such as the α?helix and the β sheet.
 


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