Statistical mechanics of solvophobic aggregation: Additive and cooperative effects

Abstract

Effects of possible non-pairwise-additive interactions on solvophobic aggregation are analyzed. A simple lattice model of binary solution with attractive solute-solute interactions is introduced to delineate the role of multiple-body effects in solute clustering and aggregation. Additive (noncooperative), cooperative, and anti-cooperative intersolute interactions are modeled by multiple-solute potentials that are respectively equal to, more favorable than, and less favorable than the sum of pairwise solute interactions. Under appropriate conditions, pairwise additive interactions and even interactions with significant anti-cooperativity can lead to aggregation and demixing. Cooperative interactions are not necessary for solute aggregation. Similarities and differences between solute aggregation and hydrophobic collapse of proteinlike heteropolymers are investigated. On average, heteropolymer collapse transitions as a function of solvophobic composition are significantly less sharp than the corresponding solute aggregation transitions. This difference is seen as a direct consequence of chain connectivity constraints.