(354c) A Water Density Fluctuation-Based Perspective on the Hydration of Van Der Waals Solutes

When hydrophobic solutes are solvated in water, they perturb the strong inherent interactions between the nearby water molecules in a manner that depends on the size and shape of the solute. The association of two such hydrophobic solutes is dictated by the extent of this perturbation, rather than the relatively weak direct interactions between the solutes. A quantitative characterization of this perturbation in the water structure is provided by the fluctuations in water density in the vicinity of the solute, with the fluctuations being enhanced near extended hydrophobic solutes. In this work, we exploit a detailed understanding of these density fluctuations in uniform and non-uniform environments to better understand the thermodynamics of hydrophobic interactions. Additionally, we show that the influence of van der Waals attractions on hydrophobic effects can also be understood from the perspective of water density fluctuations, specifically through how these fluctuations are coupled in neighboring regions of space. Our findings suggest novel strategies for accurately quantifying hydration thermodynamics.