NMR RELAXATION STUDIES IN WATER-ALCOHOL MIXTURES - THE WATER-RICH REGION

NMR proton relaxation time measurements in water-alcohol mixtures have been performed for an alcohol mole fraction X ranging from 0 to 0.1. By varying the O-17-content in water, different contributions to the proton relaxation rate could be separated and from the O-17-H dipole interaction contribution the correlation time of the OH bond in the water molecule was determined. This reorientational correlation time of water increases by addition of alcohol molecules and depends linearly on the number of proton donors and accepters. These results are compared to recent computer simulation and dielectric relaxation data. Additional oxygen-17 relaxation measurements on water yielded the quadrupole coupling constant, which shows a significant dependence on the alcohol concentration. The decreased mobility and the increased structural order of water in these mixtures can be related to the hydrophobic hydration.