DYNAMICS OF HYDRATION OF ALCOHOLS AND DIOLS IN AQUEOUS-SOLUTIONS

The O-17 NMR spin-lattice relaxation times, T-1, of the solvent water in aqueous solutions of nine alcohols and five diols have been determi ned as a function of the concentration at 25 degrees C. For the alcoho l solutions, the concentration dependence of T-1 has been determined i n the temperature range from 1 to 50 degrees C. The value of n(h)[(tau (c)(h)/tau(c)(0))-1] which has been obtained from the concentration de pendence of T-1 has been defined as the dynamic hydration number (n(DH N)). The values of the coordination numbers n(h), have been estimated on the basis of the water-accessible surface areas (ASA) of the solute molecules. The rotational correlation times, tau(c)(h), of water mole cules around the solute molecules have been estimated and compared wit h that of pure water tau(c)(0). The value of tau(c)(h)/tau(c)(0) = 2.2 2 for (BuOH)-O-t at 25 degrees C is the largest among the solutes inve stigated. The tau(c)(h)/tau(c)(0) values of the n-alcohols and diols i ncrease with increasing ASA and become almost constant. The tau(c)(h)/ tau(c)(0) values decrease with increasing temperature and approach con stant value above 40 degrees C. The temperature dependence of tau(c)(h )/tau(c)(0) for (BuOH)-O-t is the largest. The activation energy of ta u(c)(h) for n-alcohols has the maximum value at ASA approximate to 240 Angstrom(2). These results are discussed bg considering the molecular sizes. The tau(c)(h)/tau(c)(0) value for a diol was smaller than that of the corresponding n-alcohol. This result supports the concept that hydrophobic hydration is distributed by the OH groups of the solute m olecules. The thermodynamic properties of hydration for n-alcohols, bu tanol isomers and diols are linearly dependent on their n(DHN).