15N-NMR Spectroscopy—New Methods and Applications [New Analytical Methods (28)]

The nitrogen nucleus is the third most important probe (after ¹H and ¹³C) for structural investigations of organic and bioorganic molecules by NMR spectroscopy. For a long time, however, the insufficient sensitivity and low natural abundance of the ¹⁵N isotope hampered detection of the ¹⁵N nucleus, and the quadrupolar ¹⁴N nucleus proved unsuitable for the study of larger molecules with several nonequivalent nitrogen atoms. The advent of new techniques, such as pulse sequences and polarization transfer, in conjunction with the use of high-field magnets and large-sample probe heads largely solved the detection problem. As a result, the last few years have seen a dramatic development of ¹⁵N-NMR spectroscopy as a versatile method for studying molecular structure, both in isotropic (liquid) and anisotropic (solid) phases. The scope of chemical applications extends from inorganic, organometallic, and organic chemistry to biochemistry and molecular biology, and includes the study of reactive intermediates, biopolymers, enzyme-inhibitor complexes, and nitrogen metabolism. Two-dimensional NMR techniques offer additional possibilities for detailed studies of biological systems.