Fused hard sphere cavities

Figure 4 Solvent pressure on the cavity wall (a) spherical and (b) fused hard sphere cavity...

A second comparison is given in Figure 7 between I, the method for fused hard sphere cavities based on SPT (III) and the numerical and analytical (IV and V) methods for nonspherical cavities. Figure 7 shows the influence of cavity shape (Figure 8) on TCF (chain 7a sheet 7b cube 7c). For chain- and sheet-like cavities, IV and V give similar results and the difference between their values and those obtained with I and III increases with the increase in cavity volume. I gives quite close results to IV and V for chain-like cavities made up of less then twenty spheres, which explains SPT success for small nonspherical solutes. Overall, III gives the least accurate results. 

Table 4 shows a comparison between experimental and calculated solvation thermodynamics for -alkanes in water obtained by SPT, the method based on SPT for fused hard sphere cavities and the one for nonspherical cavities. Cvdw was calculated with Pierotti s method for all TCF variants. 

Claverie proposes a procedure (III) to calculate Gc for cavities made up of fused hard spheres, by summing up work contributions from individual atomic spheres which compose the nonspherical cavity. Gq required to build that part of the cavity which hosts atom i is obtained by multiplying... 

Solvent pressure is not uniform on a nonspherical cavity made of fused hard spheres, and depends on the local curvature of the cavity wall. Hence, the total force exerted by the solvent can be decomposed into components, Fjp, acting on parts of cavity surface A,- with different curvatures (Figure 4b) ... 

Figure 8 Cavity shapes made of fused hard spheres...

TCF (reversible work, enthalpy, and entropy) are quantities of considerable interest when studying interactions between molecules in fluids. TCF functions in a certain solvent vary with the size and shape of cavity and theories of statistical mechanics are generally employed to evaluate them. For example. SPT has proven a successful method for evaluation of TCF for spherical cavities in hard sphere solvents and Kihara s convex-body theory has proven an adequate method for convex-body solvents. It is interesting to remark that both theories were successful in dealing with real liquids, despite the fact that they are neither hard spheres nor convex bodies. More recent developments in liquid state theory make it possible to treat one solvent molecule as a collection of fused... 

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