Chapter Four - The D-HMQC MAS-NMR Technique: An Efficient Tool for the Editing of Through-Space Correlation Spectra Between Quadrupolar and Spin-1/2 (31P, 29Si, 1H, 13C) Nuclei

Abstract

The D-HMQC (dipolar heteronuclear multiple-quantum coherence) technique is a recently developed NMR pulse sequence particularly suitable for the investigation of spatial proximity between quadrupolar and spin-1/2 nuclei. Compared to the cross-polarisation magic-angle spinning technique applied to a quadrupolar nucleus, D-HMQC does not require time-consuming optimisations and exhibits on the quadrupolar spin a better robustness to irradiation offset and to Cq values and radiofrequency field. Furthermore, the high robustness to irradiation offset makes of the D-HMQC sequence the technique of choice for the structural characterisation of materials especially at high magnetic field. We show here how the D-HMQC can be easily implemented and optimised to give access to the structural analysis of silicate-, phosphate-, carbon- and proton-containing materials. An emphasis will be on describing the most popular dipolar recoupling schemes that can be used in that sequence and providing their advantages and drawbacks.