Theory and Simulation of Multicomponent Osmotic Systems.

Most cellular processes occur in systems containing a variety of components many of which are open to material exchange. However, computer simulations of biological systems are almost exclusively performed in systems closed to material exchange. In principle, the behavior of biomolecules in open and closed systems will be different.

A Kirkwood-Buff Derived Force Field for Aqueous Alkali Halides.

A classical nonpolarizable force field is presented for the simulation of aqueous alkali halide solutions (MX), where M = Li(+), Na(+), K(+), Rb(+), Cs(+) and X = F(-), Cl(-), Br(-), I(-), and their interactions with biomolecules. The models are specifically designed to reproduce the experimental Kirkwood-Buff integrals, and thereby the solution salt activities, as a function of salt concentration. Additionally, we demonstrate that these models reasonably reproduce other experimental properties including ion diffusion constants, dielectric decrements, and the excess heats of mixing.

Kirkwood-Buff theory of molecular and protein association, aggregation, and cellular crowding.

An analysis of the effect of a cosolvent on the association of a solute in solution using the Kirkwood-Buff theory of solutions is presented. The approach builds on the previous results of Ben-Naim by extending the range of applicability to include any number of components at finite concentrations in both closed and semiopen systems. The derived expressions, which are exact, provide a foundation for the analysis and rationalization of cosolvent effects on molecular and biomolecular equilibria including protein association, aggregation, and cellular crowding.