A H-2 NMR spin-lattice relaxation study of -NH3+ dynamics in polycrystalline L-alanine

The H-2 spin-lattice relaxation times T-1Z and T-1Q of the -ND3+ group in polycrystalline L-alanine were measured over the temperature ranges 250-425 K and 300-425 K, respectively. The relaxation data were fitted to analytical expressions for three-fold reorientation, giving a correlation time tau(c) = 1.5 x 10-(14) s exp(40.2 kJ mol(-1)/RT), which is in good agreement with the results of a limited lineshape study. T-IZ values derived from numerical simulations, taking into consideration geometrical distortion of the -ND3+ group and experimental imperfections, are compared with values given by an analytical expression for three-fold jumps and with the experimental results. The extraction of average site quadrupolar coupling constants is discussed.