Solid state NMR – Part 2 · 2013-04-10 · then connected to the input pulley of the NMR probe as...
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Solid state NMR – Part 2 - Chapter 14, on web site: http://www.chem.ubc.ca/faculty/straus/c518_09.html A) Averaging – Magic angle sample spinning B) Polarization transfer - CP
Transcript of Solid state NMR – Part 2 · 2013-04-10 · then connected to the input pulley of the NMR probe as...
Solid state NMR –Part 2
- Chapter 14, on web site: http://www.chem.ubc.ca/faculty/straus/c518_09.html
A) Averaging – Magic angle sample spinning
B) Polarization transfer - CP
Interactions in solid state
Chemical shift:
Spherical tensor notation:
where
Dipolar interaction:
How averaging of CSA works under MAS:
average A20
In the LAB frame:
Or rewritten in a different way:
FT
signal at isotropic chemical shift, with sidebands due to theterm
e.g. 13C spectrum ofalanine
Alternative methods: Magic angle hopping and Magic angle turning
MAS continuous rotation, averaging over a full rotation
Given
Final result:
= 0
How is this achieved experimentally?
Analogous approach: magic angle turning
rotor is synchronized so that signal is detected at the appropriate angles (120° apart) requires slow spinning
A quick look at MAS and quadrupolar nuclei:
To average the P4 term completely dynamic angle spinning (DAS) ordouble rotation (DOR)
B) Cross-polarization
Why use it? To enhance sensitivity (analogous to INEPT in solution state)
oscillations proportional todipolar coupling constant
Dipolar oscillations PISEMA
