New Tools in Bio-NMR: Indirect Detection of Nitrogen-14 in Solids

This paper presents an overview of recently developed methods for the indirect detection of N-14 nuclei (spin I = 1) in spinning solids by nuclear magnetic resonance spectroscopy. These methods exploit the transfer of coherence from a neighboring 'spy' nucleus with spin S = (1)/(2), such as 130 or H-1, to single- or double-quantum transitions of 14N nuclei. The two-dimensional correlation methods presented here are closely related to the well-known heteronuclear single- and multiple-quantum correlation (HSQC and HMQC, respectively) experiments, already widely used for the investigation of molecules in liquids. Nitrogen-14 NMR spectra exhibit powder patterns characterized by second- and third-order quadrupolar couplings which can provide important information about structure and dynamics of molecules in powder samples.