15N nuclear magnetic resonance investigations on amino acids

15N nuclear magnetic resonance investigations of some amino acids were carried out in order 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 had temperature.