Quantitative analysis of 14N quadrupolar coupling using 1H detected 14N solid-state NMR

Abstract

Magic-angle spinning solid-state NMR is increasingly utilized to study the naturally abundant, spin-1 nucleus ¹⁴N, providing insights into the structure and dynamics of biological and organic molecules. In particular, the characterisation of ¹⁴N sites using indirect detection has proven useful for complex molecules, where the ‘spy’ nucleus provides enhanced sensitivity and resolution. Here we exploit the sensitivity of proton detection, to indirectly characterise ¹⁴N sites using a moderate rf field to generate coherence between the ¹H and ¹⁴N at moderate and fast-magic-angle spinning frequencies. Efficient numerical simulations have been developed that have allowed us to quantitatively analyse the resulting ¹⁴N lineshapes to determine both the size and asymmetry of the quadrupolar interaction. Exploiting only naturally occurring abundant isotopes will aid the analysis of materials with the need to resort to isotope labelling, whilst providing additional insights into the structure and dynamics that the characterisation of the quadrupolar interaction affords.