Regensburg 2019 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 60: Statistical Physics in Biological Systems III

DY 60.1: Talk

Friday, April 5, 2019, 10:00–10:15, H3

Charting the hydrophobic effect: Computing spatially resolved absolute hydration shell entropies — •Leonard Heinz and Helmut Grubmüller — Department of Theoretical and Computational Biophysics, Max Planck Institute for Biophysical Chemistry, Göttingen

Biophysical systems are governed by their free energy and thus depend on a fine-tuned interplay between enthalpy and entropy. E.g. for protein folding, the solvation contributions are crucial, as they give rise to the hydrophobic effect. A quantitative understanding of the thermodynamics of solvation, and in particular the associated entropies, is therefore essential. While a variety of methods allow assessing the solute entropy, solvation shell entropies are notoriously difficult to obtain from computer simulations, because the shallow energy landscape requires sampling of an extremely large configuration space. Here we solve the sampling problem by exploiting the permutation symmetry of the solvent particles which reduces the configuration space that needs to be sampled by the Gibbs factor 1/N!, leaving the physics of the system unchanged. We perform a mutual information expansion to obtain translational and rotational solvent entropy values from the permutationally reduced trajectory. The expansion yields entropy contributions of individual solvent particles as well as of groups of particles, such as different solvation shells, thereby providing spatial resolution. We tested our method by assessing the solvation of small molecules, such as n-alkanes and small peptides and obtained agreement with other methods and experimental values.