Investigating FAM-N pulses for signal enhancement in MQMAS NMR of quadrupolar nuclei

• Published in: Solid state nuclear magnetic resonance Vol. 84; pp. 89 - 102
• Main Authors: Colaux, Henri, Dawson, Daniel M., Ashbrook, Sharon E.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 01.07.2017
• Subjects: Challenging systems; FAM-N pulses; Fast-amplitude modulation; MQMAS; Quadrupolar nuclei; Solid-state MAS NMR spectroscopy; MQMAS; Quadrupolar nuclei; Fast-amplitude modulation; Challenging systems; Solid-state MAS NMR spectroscopy; FAM-N pulses
• ISSN: 0926-2040; 1527-3326; 1527-3326
• DOI: 10.1016/j.ssnmr.2017.01.001

Although a popular choice for obtaining high-resolution solid-state NMR spectra of quadrupolar nuclei, the inherently low sensitivity of the multiple-quantum magic-angle spinning (MQMAS) experiment has limited its application for nuclei with low receptivity or when the available sample volume is limited. A number of methods have been introduced in the literature to attempt to address this problem. Recently, we have introduced an alternative, automated approach, based on numerical simulations, for generating amplitude-modulated pulses (termed FAM-N pulses) to enhance the efficiency of the triple- to single-quantum conversion step within MQMAS. This results in efficient pulses that can be used without experimental reoptimisation, ensuring that this method is particularly suitable for challenging nuclei and systems. In this work, we investigate the applicability of FAM-N pulses to a wider variety of systems, and their robustness under more challenging experimental conditions. These include experiments performed under fast MAS, nuclei with higher spin quantum numbers, samples with multiple distinct sites, low-γ nuclei and nuclei subject to large quadrupolar interactions. [Display omitted] •High-throughput optimisation of FAM-N pulses for MQMAS NMR of quadrupolar nuclei.•Applicability of FAM-N pulses to higher spin systems and efficiency under fast MAS.•Application of FAM-N to more challenging systems without experimental re-optimisation.•Investigation into the differences between experimental and theoretical enhancements.