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RESEARCH PRODUCT

Physical Origin and Biological Significance of Solvent Induced Forces

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The notion of solvent-induced forces (SIFs), as distinct from solute-solute forces acting through the solvent, is illustrated in terms of: i) the microscopic space-and time-resolved view provided by Molecular Dynamics Simulations; ii) the standard statistical-mechanical formulation, and iii) the inherent structures of water. It is shown that the origin of SIFs is in the non-additivity of the effects of solute-perturbation on the H-bond network in the solvent. This nonadditivity does not require non-additivity of water-water and solute-water interaction potentials. Two experimental studies, illustrating different aspects of SIFs are discussed in detail. One is the case of Human Adult Hemoglobin, where the SIFs contribution to the functional conformational transition has been quantitatively determined. In this case, SIFs have the localized and specific character required for biomolecular stability and function. The large number of water molecules involved in these SIFs provides the additional and philosophically important result of a great expansion of the phase space relevant to the thermodynamic probability of functional conformations. Another case is the gelation of Bovine Serum Albumin. Here SIFs have a mean-field behaviour, and contribute to the first break of symmetry in the sol, towards self-assembly. In this way SIFs contribute establishing solute-solute correlations and generating preferential paths, which channel the percolation of crosslinks along polymer-rich regions. By this symmetry-breaking mechanism, SIFs can allow gelation at very low polymer concentrations and, more in general, they can be highly relevant to morphogenesis. Experiments on non-additivity of effects of solvent perturbation promoted by alcohols and by osmolytes are also presented. Results allow tracing the origin of the effects of cosolutes in modulating SIFs and solvent-mediated interactions.