The Magic of NMR: Magic Angle Spinning NMR

The application of NMR in studying different types of samples is a proven fact, but still it finds some limitations in analyzing some samples. NMR scientists have always been looking for the discoveries of new techniques for better results. Magic Angle Spinning (MAS) NMR is one such magical technique.

 
The magic angle (54.7^o) is derived from a mathematical equation

                                     θm=arccos⁡1/(√3)=arcctan√2≈54.7°

 
The basic principle of MAS NMR is that the nuclei are being spun at an angle (magic angle) to the direction of the applied magnetic field. 

NMR experiments usually experience certain types of interactions such as dipolar couplings, chemical shift anisotropy (CSA), and magnetic susceptibilities. These interactions cause the line width in NMR spectrum to increase, thus leading to poor resolution. In addition, the distribution of the magnetic susceptibilities may modify the already homogenous magnetic field. These dipolar interactions are a result of the combination of the macroscopic and microscopic dipoles. MAS NMR helps to remove the dipolar interactions, CSA, and the magnetic susceptibility effects, leading to enhanced resolutions and a clearer spectrum.

When oriented at the magic angle, the z components of the dipolar field almost vanish.

MAS PROBE

MAS experiments need a special, standard bore probe. A solenoid is used as the RF coil. The probe can be triply (¹H/¹³C/²H) or quadruply tuned (¹H/¹³C/²H/³¹P). The gradient coil is oriented/tilted at the magic angle. The probe is also provided with 4 mm rotors.

APPLICATIONS

1.  Heterogeneous samples

High resolution MAS techniques may be utilized to study heterogeneous samples such as oil present inside the rocks.

    2. Solid Phase Synthesis

Molecules bound to the solid support in solid phase synthesis can be directly studied with this technique

3.    Human tissues and intact animals 

1H HR-MAS has been utilized for metabolic profiling of intact tissues which may provide information about their molecular makeup. A study on the live drosophila flies helped determining their metabolic profile by using this technique.

    4. Viral assemblies

MAS experiments have been applied to study complex viral assemblies and intact virus particles to investigate the structure and dynamics of HIV and Pf1 viral systems.

 5. MRI

HR MAS NMR has also found its application in Magnetic Resonance Imaging (MRI).

Besides this MAS NMR has been applied to study polymers, soil contaminants, food items, and animal cells

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