Effect of impurity compounds on ethanol hydration

The hydration of ethanol is often described as “hydrophobic hydration,” which refers to the restructuring of the water H-bond network to accommodate ethanol molecules. In the present study we investigate by molecular dynamics simulations how impurity compounds impact this water restructuring. Specifically impurity compounds found in alcoholic beverages, including acetaldehyde, ethyl acetate, methanol, and fusel oils (1-proanol, 2-methyl-1-propanol, and 2-methyl-1-butanol), are investigated by equilibrium radial distribution function (RDF) analysis of simulated water-alcohol mixtures. Impurities can increase the first peak of the RDF compared to “clean” mixtures, implying a more ordered structure. The basis of enhanced ordering is explored by MCR-ALS analysis, which resolves the solutions into four components - pure water, two ethanol hydrates, and pure ethanol. Impurities enhance the water component at the expense of the water-rich hydrate implying an enhanced hydrophobic effect. The extent of this effect depends on both the geometric and electrostatic characteristics of the impurity compound. The results suggest that impurities can induce a watery taste in alcoholic beverages.