Advances in double quantum and singlet nuclear magnetic resonance

Abstract

This thesis explores the experimental application of two pulse sequence families that effectively excite double-quantum coherence in near-equivalent spin-1/2 pairs in solution nuclear magnetic resonance. The established methods are inefficient in this coupling regime, leading to substantial relaxation losses.

The first procedure, GeoDQ, uses the geometric Aharonov-Anandan phase, exploiting a rotation through π about the z-axis in the zero-quantum subspace spanned by the {|S0⟩,|T0⟩} states. We combine double-quantum filtering and singlet order excitation to study the 13C2 relaxation of singlet order within a previously inaccessible molecule. This decays slower than longitudinal order, since it is protected against common relaxation mechanisms. We report pH-dependent isotope shifts due to 18O and 13C isotopic substitution. Furthermore, we use GeoDQ to investigate chiral guest binding as a symmetry-breaking mechanism between two diastereotopic 19F2 nuclei.

The second procedure, Spinor-DQ, uses the spinor behaviour of two-level quantum systems, exploiting a rotation through 2π in the single-quantum subspace spanned by the {|S0⟩,|T+1⟩} states. These are the SLIC, and PulsePol pulse sequences originally used to excite singlet order, including a SLIC variant that is well-compensated against deviations in the rf field amplitude. We apply the GeoDQ and Spinor-DQ sequences to study 13C2 and 19F2 near-equivalent spin-pairs, achieving good double-quantum filtering efficiency.

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Identifiers

ORCID for Urvashi Devi Heramun: orcid.org/0009-0007-7524-6098

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

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