Computer simulation study of tert-butyl alcohol.: 2.: Structure in aqueous solution

MD simulations of tert-butyl alcohol (TBA), dissolved in water, are carried out. Two aqueous alcohol solutions are studied, a dilute 2 mol % and a more concentrated, 8 mol % solution. Two new potential models are used for TEA, a simple rigid three-site model and a flexible all-atom 15-site model. In solution, the flexible TEA model is dissolved with flexible SPC water molecules, while the rigid tert-butyl alcohol is simulated in rigid SPC/E water. This study principally focuses on the hydration structure around TEA and a possible self-association of TEA due to the strong amphiphilic character of this bulky molecule. In the more concentrated solutions and for both TEA models, small aggregates of a few alcohol molecules are formed spontaneously, persisting several tens of picoseconds. Tail-to-tail pairwise configurations of alcohols are preferred. In the dilute solution, little tendency to aggregation is observed during the simulation. The diffusion of the alcohols is reduced considerably as the concentration of the solution increases. Water structure is significantly enhanced upon the addition of TEA. The hydration structure of both models of TEA is markedly different from that of methanol, indicating that the steric bulk of a tert-butyl group can have large, though indirect, effect on hydrogen bonding.