(721a) Highlight: Hydration Phenomena At the Interface of Physics and Biology: A New Perspective

Water-mediated interactions (e.g., hydrophobic interactions) govern a host of biological and colloidal self-assembly phenomena from protein folding, micelle and membrane formation, to molecular recognition.  Macroscopically, hydrophobicity is often characterized by measuring a droplet contact angle on a surface. At the nanoscale, such measurements are not feasible, e.g., for surfaces of proteins or nanoparticles.  Using theory and molecular simulations, we present a new perspective that connects the behavior of water near nanoscale interfaces to their hydrophobicity/philicity. Specifically, we show that water density fluctuations (and not the average local density) provide a quantitative characterization of interfacial hydrophobicity. Density fluctuations are enhanced near hydrophobic interfaces and suppressed near hydrophilic ones. This new perspective provides a computational tool for characterizing the hydrophobicity patterns on protein surfaces, which are relevant for binding, recognition, and aggregation.  Simulations also show how the properties of water at interfaces influence binding, folding, and dynamics of flexible molecules in interfacial environments. Our current understanding of the hydration of ions, osmolytes, and solution additives, when combined with this new perspective, provides additional insights into the role of water in multicomponent biological interactions.