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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 TBA, a simple rigid three-site model and a flexible all-atom 15-site model. In solution, the flexible TBA 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 TBA and a possible self-association of TBA due to the strong amphiphilic character of this bulky molecule. In the more concentrated solutions and for both TBA 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 TBA. The hydration structure of both models of TBA 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.

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Articles you may be interested inHydrogen bonded structure, polarity, molecular motion and frequency fluctuations at liquid-vapor interface of a water-methanol mixture: An ab initio molecular dynamics study Structure, thermodynamics, and dynamics of the liquid/vapor interface of water/dimethylsulfoxide mixtures Molecular dynamics ͑MD͒ computer simulations are carried out on liquid methylamine and on 10 and 30 wt % aqueous solutions of methylamine. The local three-dimensional structure in these liquid systems is investigated using standard one-dimensional radial distribution functions and the fully three-dimensional measure of the local structure around the molecule, spatial distribution functions. Time correlation functions for the linear and angular motion of methylamine in the molecular coordinate system are also explored. From this analysis, a detailed structural picture emerges, revealing local molecular environments in these liquids that are both complex and varied. Hydrogen bond balance is found to play a key role in determining preferred arrangements. Strong hydrogen bonds are formed around the amino group in the pure liquid and in aqueous solution. At the same time, there is a strong hydrophobic association of methyl groups. The hydration structure in aqueous solution is found to be particularly rich, where in addition to the usual H-bonding nearest neighbors in the first hydration shell of the amino group, there are bridging water molecules and a novel type of distinctly non-H-bonding neighbors. The hydration structure in aqueous methylamine solution differs substantially from that found in methanol-water liquid mixtures.

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