NMR pulse sequence:
MQ-CP followed by MQ-MAS




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Multiple Quantum Cross Polarization MQ-MAS

MQ-CP experiments allow editing of high-resolution spectrum.

Lim and Grey investigated MQ-CP experiment, in which S-spin MQ coherences are created directly by cross-polarization from the fluor and then correlated with single-quantum coherences in a 2D MQMAS experiment.

MQ CP with two-pulse sequence

This figure represents the 3Q-CP with (amplitude-modulated) two-pulse experiment, which should not generate pure absorption 2D lineshape because the coherence transfer pathways are not symmetric.

ACQUISITION: Hyper-complex or TPPI

Shearing transformation is required to obtain 2D isotropic (in F1 dimension) anisotropic (in the F2 dimension) correlation spectrum.


Ashbrook and coworkers proposed various methods for MQ-CP experiments, in which S-spin MQ coherences are created directly by cross-polarization from the proton and then correlated with single-quantum coherences in a 2D MQMAS experiment.

First method

MQ CP with z-filter sequence

This figure represents 3Q-CP with (amplitude-modulated) z-filter experiment where p = 3 coherences are excited from the p = 0 coherence created by the cross-polarization.

The 'flip-back' pulse aids the recovery of the proton equilibrium magnetization.

Amplitude-modulated experiment should generate pure absorption 2D lineshape.

ACQUISITION: Hyper-complex or TPPI

Shearing transformation is required to obtain 2D isotropic (in F1 dimension) anisotropic (in the F2 dimension) correlation spectrum.

Second method

3Q CP with split-t1 sequence and anti-echo signal

This figure represents the phase-modulated split-t1 experiment where p = +3 coherence is excited from the p = 0 coherence created by the cross-polarization.

Phase cycling ensures that only the p = +3 coherence is selected after the spin-locking period.

The 'flip-back' pulse aids the recovery of the proton equilibrium magnetization.

The single-quantum k'*t1 evolution period is before the final pulse. The anti-echo signal is detected. This is the case for the triple-quantum coherence of a spin I = 3/2 nucleus.

ACQUISITION: F1-QF

Shearing transformation is avoided.

Third method

3Q CP with split-t1 sequence and echo signal

This figure represents the phase-modulated split-t1 experiment where p = +3 coherence is excited from the p = 0 coherence created by the cross-polarization.

Phase cycling ensures that only the p = +3 coherence is selected after the spin-locking period.

The 'flip-back' pulse aids the recovery of the proton equilibrium magnetization.

The single-quantum k'*t1 evolution period is after the final pulse. The echo signal is detected. This is the case for the triple-quantum coherence of a spin I = 5/2, 7/2 or 9/2 nucleus.

ACQUISITION: F1-QF

Shearing transformation is avoided.

 

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