An NMR study of 1H and 31P relaxation and molecular dynamics in polycrystalline nicotinamide adenine dinucleotide (NAD +)

Abstract

Proton spin-lattice relaxation times in the laboratory and rotating frames, dipolar relaxation time, and second moments have been measured as a function of temperature for samples of NAD + · nH 2O, where n varies between 0 and 3.6. The results show clearly that the water molecules execute twofold reorientations with activation energies varying between 11.5 and 22 kJ/mol. It seems that a model in which all crystallographically equivalent water molecules have the same correlation time is adequate in the case of three of the water molecules. The motion of the fourth water molecule is characterized by a distribution of correlation times. The twofold reorientations of the two NH 2 groups have higher activation energies. The temperature dependence of T 1(P), the phosphorus spin-lattice relaxation time in the laboratory frame, supports the interpretation of the proton spin-lattice relaxation results.