Hydrogen bond network relaxation resolved by alcohol hydration (methanol, ethanol, and glycerol)

Abstract

Although the alcohol–water mixtures are ubiquitously important to beverage and pharmacy industries, it remains yet puzzling how the alcohols interact with water molecules and how the alcohol molecules functionalize the hydrogen bond network of liquid water and body fluid. We show spectrometrically that alcohol hydration softens both the H–O bond and the O:H nonbond through hydrogen bond cooperative relaxation and associated charge polarization. Observations suggested that each of the dangling hydroxide group :Ö:H− (interacts with :Ö or –H+) and the dangling methyl group C–H+ (with –H+ or :Ö) is equally capable of interacting with H2O molecules in the form of Ö:↔:Ö point compressor, H+↔H+ point breaker, and O:H–O hydrogen bond at the alcohol–water interface without charge sharing or new bond formation. The alcohol–water O:H–O formation enables the solubility and hydrophilicity of the alcohol; the H+↔H+ breaker embrittles the hydration network; the Ö:↔:Ö compression shortens the O:H nonbond and lengthens the H–O bond. H–O softening is associated with heat emission and depression of solution melting temperature; the O:H nonbond softening (due to polarization) lowers the critical temperatures for freezing. Copyright © 2016 John Wiley & Sons, Ltd.