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Encyclopedia > Magic angle spinning

In physics, magic angle spinning (MAS) is a technique often used to perform solid-state NMR experiments. The willingness to question previously held truths and search for new answers resulted in a period of major scientific advancements, now known as the Scientific Revolution. ... Brief Nuclear magnetic resonance (NMR) spectroscopy characterized by the appearance of anisotropic interactions is referred to as solid-state NMR (SSNMR) spectroscopy. ...


By spinning the sample (1-40 kHz) at an angle θ of ca. 54.7 degrees (cos2θ=1/3) with respect to the direction of the magnetic field, the normally wide lines, narrow, therefore increasing the resolution for better identification and analysis of the spectrum. Current flowing through a wire produces a magnetic field (M) around the wire. ...


In any condensed phase, a nuclear spin experiences a great number of interactions. The main three interactions (dipolar, chemical shift anisotropy, quadrupolar) often lead to very broad and featureless lines. However, these three interactions in solids are time-dependent and can be averaged by MAS. The nuclear dipole-dipole interaction, between magnetic moments of nuclei averages to zero. The chemical shift anisotropy, a nuclear-electron interaction, averages to a non-zero value. And the quadrpolar interaction is only partially averaged by MAS leaving a residual secondary quadrupolar interaction. In liquids, e.g. a solution of an organic compound, most of these interactions will average out because of the rapid time-averaged molecular motion that occurs. This orientational averaging in solution is mimicked by MAS of a solid. This causes the signal to become much narrower giving rise to the isotropic value which is of interest for structural determination of solid materials and compounds. Link titleAn organic compound is any member of a large class of chemical compounds whose molecules contain carbon, with exception of carbides, carbonates and carbon oxides. ...


Solid-state NMR spectroscopy has been slower to develop than solution state NMR spectroscopy becuase of the difficulty of mitigating these line broadening interactions present in the solid state. Brief Nuclear magnetic resonance (NMR) spectroscopy characterized by the appearance of anisotropic interactions is referred to as solid-state NMR (SSNMR) spectroscopy. ... Spectroscopy is the study of spectra, that is, the dependence of physical quantities on frequency. ...


  Results from FactBites:
 
David Doty's Explanation of Magic Angle Spinning (MAS) and Nuclear Magnetic Resonance (NMR) (1084 words)
It so happens that when the angle between any two molecules with respect to the external magnetic field is a certain value, the so-called “Magic Angle”, or 54.7°, the magnetic interactions between those molecules vanish.
Solid (rigid) samples must be spun at the magic angle at incredible speeds in NMR so that all the molecules in the sample sing in the same key.
The faster we want to spin, the smaller the spinner must be, as the surface speeds must be limited to approximately the speed of sound or the sample will heat up too much and the stresses will cause the spinner to explode.
  More results at FactBites »

 
 

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