The modern understanding of hydrophobicity is thorough and sophisticated. Based on an appreciation that microscopic density fluctuations mediate hydrophobic solvation, it offers conceptual and theoretical tools that address Gaussian fluctuations at small length scales, interfacial thermodynamics at large scales, and the interplay between these behaviors at length scales characteristic of biomolecular structure. By comparison, the understanding of water’s response to charged and polar solutes is surprisingly limited. Despite a long history and a wealth of case studies, field theoretic descriptions cannot convincingly account for even the substantial difference in solvating cations and anions of the same size. The failure to capture interfacial solvation physics is more dramatic still, pointing to important interplays between density and polarization fluctuations that remain poorly understood. We are pursuing a nuanced understanding of hydrophilic solvation by studying a variety of behaviors involving the soft interfaces, strong electrostatic correlations, and geometric constraints of hydrogen bonding that make water an extremely rich but elusive environment for chemistry and biology.
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