Spinor Double-Quantum Excitation in the Solution NMR of Near-Equivalent Spin-1/2 Pairs

TL;DR

This paper introduces novel spinor-based double-quantum excitation schemes in solution NMR for near-equivalent spin-1/2 pairs, utilizing spinor behaviour and SLIC techniques to improve double-quantum coherence preparation.

Contribution

The work presents new spinor-based and SLIC methods for double-quantum excitation in solution NMR, demonstrating enhanced control over quantum coherences in near-equivalent spin pairs.

Findings

Successful demonstration with $^{19}$F NMR on diastereotopic nuclei

Comparison shows advantages over existing techniques

Introduction of a SLIC variant with improved RF field robustness

Abstract

A family of double-quantum excitation schemes is described for the solution nuclear magnetic resonance (NMR) of near-equivalent spin-1/2 pairs. These new methods exploit the spinor behaviour of 2-level systems, whose signature is the change of sign of a quantum state upon a $2\pi$ rotation. The spinor behaviour is used to manipulate the phases of single-quantum coherences, in order to prepare a double-quantum precursor state which is rapidly converted into double-quantum coherence by a straightforward $\pi/2$ rotation. One set of spinor-based methods exploits symmetry-based pulse sequences, while the other set exploits SLIC (spin-lock-induced crossing), in which the nutation frequency under a resonant radiofrequency field is matched to the spin-spin coupling. A variant of SLIC is introduced which is well-compensated for deviations in the radiofrequency field amplitude. The methods are demonstrated by performing double-quantum-filtered $^{19}$F NMR on a molecular system containing a pair of diastereotopic $^{19}$F nuclei. The new methods are compared with existing techniques.