15N nuclear magnetic resonance investigations on amino acids.

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Abstract
15N NMR investigations of some amino acids were carried out to check the applicability of this method to biological problems. Because the natural abundance of the 15N isotope is not sufficient to get readable spectra in a reasonable time, 95% 15N isotope-enriched samples were used for the measurements. Besides the chemical shift values, the line widths and the nuclear Overhauser enhancement factors, spin lattice relaxation times of the correspondent 15N resonances were measured as functions of pH and temperature. The functional groups that bear the 15N nucleus reveal characteristic differences in the measured quantities. The exchange behavior of protons attached to the 15N with protons of the solvent water permits certain insights into the mechanism of these processes. The various contributions to spin lattice relaxation of the investigated 15N resonances are discussed.