Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session T7: Physics, Chemistry and Biology of the Hydrophobic Effect |
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Sponsoring Units: DBP Chair: Chao Tang, University of California, San Francisco Room: Baltimore Convention Center 307 |
Wednesday, March 15, 2006 5:45PM - 6:21PM |
T7.00001: The Hydrophobic Effect ab initio Invited Speaker: We employ fully quantum-mechanical molecular-dynamics simulations to evaluate the force between two methanes dissolved in water, as a model for hydrophobic association. A stable configuration is found near the methane-methane contact separation, while a shallow second potential minimum occurs for the solvent-separated configuration. The strength and shape of the potential of mean force are in conflict with earlier classical-force-field simulations but agree well with a simple hydrophobic burial model which is based on solubility experiments. Examination of solvent dynamics reveals stable water cages at several specific methane-methane separations. [Preview Abstract] |
Wednesday, March 15, 2006 6:21PM - 6:57PM |
T7.00002: Hydrophobic Effects as Seen in Lattice Models Invited Speaker: A class of lattice models incorporating the thermodynamic mechanism of hydrophobicity is defined and its properties derived. The models are equivalent to Ising models in a field. The solvent-mediated part of the potential of mean force between a pair of hydrophobic solute molecules is obtained from the pair correlation function of the underlying one-component lattice gas. The models yield a testable relation between the strength of the hydrophobic attraction between solute molecules and the free energy of solvation of a single one. The properties of the models are obtainable analytically in Bethe-Guggenheim approximation. The local energy density in the solvent is obtained as a function of the distance from an inserted solute. As a consistency check, this energy density, when summed over the lattice, is found to satisfy the required thermodynamic relation between the total energy change due to the solute molecule and the temperature dependence of the solubility. [Preview Abstract] |
Wednesday, March 15, 2006 6:57PM - 7:33PM |
T7.00003: Hydrophobicity at small and large length scales Invited Speaker: This lecture is about the statistics of density fluctuations for liquids at thermodynamic states close to liquid-vapor coexistence. Theoretical and simulation results on the length scale dependence of this statistics will be described and used to explain hydrophobic solvation, hydrophobic forces of assembly and kinetics of hydrophobic collapse. Several issues concerning so-called ``drying'' near extended hydrophobic surfaces will be addressed, and biophysical implications will be discussed. [Preview Abstract] |
Wednesday, March 15, 2006 7:33PM - 8:09PM |
T7.00004: Modeling water, hydrophobic interactions, and polymer collapse Invited Speaker: Small and large nonpolar solutes exhibit qualitatively different hydration thermodynamics. The former are naturally accommodated into bulk water via equilibrium density fluctuations, while the latter require the formation of a macroscopic solute-water interface. Although there has been significant progress on the theory of lengthscale-dependent hydration, there are still many open questions concerning how various thermodynamic parameters (e.g., pressure, additive concentration, and pH) impact the crossover between small and large solute behavior. Similarly, there is confusion over whether hydration of small, intermediate, or large lengthscales dominate in various biological self-assembly processes. In this talk, I discuss recent theoretical progress on understanding how solution conditions affect the crossover between small and large solute hydration phenomena and how simulation/theory of the collapse of hydrophobic polymers can provide new insights into the relevance of hydrophobic interactions at different lengthscales. [Preview Abstract] |
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