Nitrogen-14 NMR Studies of Biological Systems

Abstract

In spite of its significant isotopic abundance and the importance of nitrogen as an element, nitrogen-14 has often been viewed as a rather unfavorable nucleus for NMR spectroscopy. In recent years, however, experimental difficulties in observing high-resolution 14N magic angle spinning (MAS) NMR spectra of powdered materials have been overcome by the use of indirect methods of detection. Hence, HMQC-like indirect detection of the nitrogen-14 nuclei via “spy” S = ½ nuclei, such as 1H or 13C, can yield highly resolved 14N NMR spectra under MAS conditions. This review focuses on the description of the HMQC, HSQC-like experiments for 14N indirect detection of spinning solids, and shows how crucial information about the structure and dynamic properties of nitrogen-containing solids can be obtained. Moreover, the review briefly discusses S = ½ NMR spectra of compounds that exhibit dipolar-quadrupolar interaction effects and TRAPDOR experiments that exploit these. Much study remains to be done to apply these indirect detection methods to biomolecules such as proteins or nucleic acids. Keywords: nitrogen-14; quadrupolar nucleus; indirect detection; HMQC; HSQC