Development of Pure Shift NMR Spectroscopy Techniques Through Novel Acquisition Schemes

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Modern NMR Spectroscopy relies not just upon sophisticated hardware but also upon complex pulse sequences that often trade sensitivity for selectivity or vice versa. Pure shift NMR Spectroscopy allows collection of broadband homodecoupled spectra, but such techniques cause losses in sensitivity. The MSE (Multiple Spin Echo) pure shift methodology in this thesis provides a sensitivity increase of around 10% for pure shift spectra acquired using the “Zangger Sterk” refocussing technique, though this varies substantially based on experimental parameters and the molecule under study. This is achieved without introducing significant artefacts or line broadening. The repeated refocussing of the MSE method also offers significant advantages with regard to pulse miscalibration. However, even in optimal cases MSE pure shift provides less absolute signal-to-noise than the PSYCHE approach (which it is incompatible with). It does, however, represent an enticing “something for nothing” approach to signal acquisition which may have implications for other NMR techniques where acquisition is limited to short data chunks.

In contrast, the SHARPER experiment trades selectivity for sensitivity in reaction monitoring methods. The originally reported SHARPER experiment provides a significant boost in signal-to-noise and magnetic field inhomogeneity compensation, but only one resonance at a time can be studied and the frequency of this resonance must remain stationary throughout the experiment.

The mobile-SHARPER and MR-SHARPER (Multiple Resonance SHARPER) methodologies presented here alleviate the extreme selectivity by allowing significant frequency changes to occur with no loss in spectral quality and multiple signals to be recorded simultaneously. The methodology used to do so is demonstrated on up to three signals, though in principle could be further extended. Adding such capability to SHARPER is ideal for its role as a sequence for chemical reaction monitoring as it allows simultaneous monitoring of signals relating to products, reactants and intermediates.
Date of Award24 Jun 2021
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorCraig P Butts (Supervisor)

Keywords

  • NMR
  • pure shift
  • SHARPER

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