Solid state NMR of multiple-spin systems

Abstract: Many nuclear magnetic resonance (NMR) experiments subject the nuclear spins to time-periodic modulations, for example, mechanical sample rotation and irradiation by periodic radio-frequency pulse sequences. An efficient simulation algorithm (COMPUTE) has been proposed for calculating NMR spectra from such systems.Computation of NMR spectra of powders involves an average over all possible crystallite orientations. It is desirable that a reasonable numerical approximation to a full powder average is obtained, using a minimum number of orientational samples. This thesis discusses methods for selecting these. Furthermore, it has been demonstrated that averaging over one of the three orientational variables may be performed within the COMPUTE framework with minimum computational effort. In many cases, these advances combine to reduce the computational time by an order of magnitude compared to previous methods.This thesis also discusses excitation and exploitation of multiple-quantum coherences in the NMR of rotating solids. A method has been developed that determines the backbone torsion angle y in peptides and proteins, by using evolution of multiple-quantum coherence under heteronuclear 13C-15N dipolar interactions. It operates under magic-angle-spinning conditions, and has been implemented in double-quantum and triple-quantum versions. The technique has been demonstrated by determining y in fragments of the tripeptides gly-gly-gly and ala-gly-gly, with an accuracy of 5o-10o.