Magnetisation transfer

Figure 5.1.6 Stop-flow 2D WET-TOCSY data of ruberoside A. Magnetisation transfer from the methyl groups A-H3-21 and A-H3-26/27 to a resonance at 3.67ppm indicates a hydroxy function in the aglycone side-chain...

Potts, J.R., Hounslow, A.M., Kuchel, P.W. (1990). Exchange of fluorinated glucose across the red cell membrane measured by 19F n.m.r. magnetisation transfer. Biochem. J. 266,925-928. 

To enhance the sensitivity of 13C solid state NMR, polarisation (magnetisation) transfer from the abundant proton spins to the rare carbon spins is applied. This technique is called cross polarisation (CP). This is achieved by first exciting the proton resonance and then simultaneously turning on the 13C and aH radio frequency fields. The so called Hartmann-Hahn condition should then be satisfied ... 

Cross-polarisation To avoid long relaxation delays Magnetisation transferred from... 

Dynamic nuclear polarisation (DNP) To increase sensitivity Magnetisation transferred from unpaired electrons to 13C spins via 1H spins if required. Sensitivity improvement of about 100-fold... 

The dipolar coupling is also central to many schemes for magnetisation transfer between nuclei using double resonance techniques such as cross-polarisation. The data become more difficult to unravel when a nucleus experiences numerous different dipolar interactions at the same time. Even an increase to just three spins causes the lineshape... 

The above analysis is usually applied to spin- /2 systems but there is no reason why magnetisation transfer cannot be applied to quadrupole systems. If Xq is small the theory is identical to that given above, but if xq becomes significant the Hartmann-Hahn condition is modified to... 

Spectrometers now often come equipped with at least two channels (designated X and Y) and often three lower frequency channels. This allows polarisation transfer experiments between X and Y nuclei. Examples of X—>Y magnetisation transfer are rapidly increasing and some examples are given in Table 3.9. 

Table 3.9. Some examples of X- Y magnetisation transfer used in NMR investigations of inorganic solids.

Figure 5.16. Coupling evolution during ti produces in-phase and antiphase magnetisation components. Only the antiphase component contributes to magnetisation transfer and hence to crosspeaks in the 2D spectrum.

Similarly incoherent magnetisation transfer due to chemical exchange is also not part of the current version of NMR-SIM. Only chemical shift and coupling evolution that... 

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