New recoupling techniques in solid-state NMR

Abstract

This thesis deals with the development of new methodology for homonuclear dipolar recoupling by symmetry-based radiofrequency pulse sequences in magic-angle-spinning solid-state nuclear magnetic resonance. The first chapters of this thesis introduce NMR spectroscopy, the basic theory of NMR and some basic elements. After these introductory chapters, the rotor-synchronized symmetry-based pulse sequences are described. Each class of symmetry-based pulse sequence is defined, introducing their selection rules and scaling factors for the recoupling of certain spin interactions. In the second part, the main topics and subjects of the thesis are analysed more deeply. First, the interference of heteronuclear dipolar decoupling in the homonuclear dipolar recoupling by symmetry-based pulse sequences is considered. These effects are studied by experiments, simulations and average Hamiltonian theory in two families of dipolar recoupling sequences belonging to the CN~ and the RN~ symmetry classes. In the final chapter, a new recoupling concept in multiple-spin systems called truncated dipolar recoupling (TDR) is presented. This new concept allows the selective determination of internuclear distances in a wide variety of homonuclear multiple-spin systems. This methodology involves a symmetry-based recoupling sequence that generates: (i) Zeroquantum (ZQ) recoupling of homonuclear dipole-dipole interactions; (ii) simultaneous recoupling of frequency-dispersing spin interactions that truncate the ZQ dipolar Hamiltonian. This truncation of the spin Hamiltonian allows the commutation of the different dipolar coupling in the multiple spin system. Two different implementations of this idea are discussed and demonstrated experimentally and by numerical simulations

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ORCID for Malcolm H. Levitt: orcid.org/0000-0001-9878-1180

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