On the origin of microheterogeneity: A mass spectrometric study of dimethyl sulfoxide-water binary mixture

We have studied the microscopic solvent structure of dimethyl sulfoxide-wat er mixtures and its influence on the solvation structure of solute from a c lustering point of view, by means of a specially designed mass spectrometri c system. It was observed that the propensity to the cluster formation is n onlinearly dependent on the solvent composition, exhibiting the existence o f a critical value of mixing ratios where drastic changes in the microscopi c solvent structure occur. It was also demonstrated that in such a solvent mixture the solvation structure of solutes such as 2-butanol, cyclopentanol , cyclohexanol, and phenol is greatly related to the microscopic solvent st ructures, implying that solute species interact with already established so lvent clusters, rather than with individual solvent molecules.