Temperature Dependences of T1 and T2 of Residual Water in D2O Determined at 400 MHz 1H-NMR

T1 and T2 relaxation times in D2O were investigated at various temperatures with 400 MHz NMR. It is well known that D2O is a solvent for investigation of chemical molecules with NMR. Likewise, many biological molecules, particularly proteins and enzymes are studied in D2O. T1 was measured at different temperatures by Inversion Recovery Method, while T2 was measured for the same temperatures by CPMG Method. T1 relaxation times were found longer than T2 relaxation times. The rotational correlation time and activation energy values were found as 0.71 ps, 3.93 kcal. mol-1 for T1 and 2 ns, 3.38 kcal. mol-1 for T2, respectively. In conclusion, chemical exchange between protons and deuterons and dipolar coupling may be dominant process for the transverse relaxation mechanism, whereas tumbling reorientation process may dominates the longitudinal relaxation in D2O. This suggests that, with respect to reorientation dynamics, two distinct molecular species exist in liquid water. In addition, our results are coherent with low frequency studies of D2O.