title: Incomplete mixing versus clathrate-like structures: a molecular view on hydrophobicity in methanol-water mixtures.
abstract: The underlying molecular mechanisms of macroscopic excess properties were studied by molecular dynamics simulations for different compositions of methanol-water mixtures. Structural data (nearest neighbor relationships, clustering analysis) and dynamic data (hydrogen bond lifetimes, rotational autocorrelation, translational diffusion) were evaluated. Nearest neighbor relationships provide quantitative evidence and a pictorial description of incomplete mixing at the molecular level as a source for mixture anomalies, while a comparative study of water surrounding methyl moieties versus water in the bulk-like environment provides evidence against the hydrophobicity model of clathrate-like hydration. Furthermore, the formation or breakdown of the system-wide hydrogen bonding network at a critical threshold of approximately equimolar mixture is perceived to separate the mixture system into two hydrogen bonding regimes: hydrogen-bonded water clusters embedded in methanol for mixtures with low water content and methanol molecules within a system-wide hydrogen-bonded water network for mixtures with high water content.
authors.affiliation: Institute of Technical Biochemistry, University of Stuttgart, Allmandring 31, 70569 Stuttgart, Germany.
authors.forename: Sven P
authors.initials: SP
authors.lastname: Benson
authors.forename: Jürgen
authors.initials: J
authors.lastname: Pleiss
mesh_terms: D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D000432:Methanol / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D000432:Methanol