title: Osmolyte depletion viewed in terms of the dividing membrane and its work of expansion against osmotic pressure.
abstract: How osmolytes enhance the folding, binding, and self-assembly of biological macromolecules at a microscopic scale has long been a matter of debate. Ambiguities persist on the key interpretive concepts, such as the "effective membrane" (which marks the boundary of the volume from which osmolytes are excluded) and the "free energy of exclusion" of osmolytes from biomolecular surfaces. In this paper, we formulate these elusive concepts based upon chemical thermodynamics and rigorous statistical thermodynamics (the Kirkwood-Buff theory). Positioning of the membrane at the osmotic dividing surface is crucial in order not to affect the thermodynamics of solvation. The notion of the free energy (work) of excluding osmolytes is refined to the expansion work against the osmotic pressure, which indeed describes the change of solvation free energy at dilute osmolyte concentrations.
authors.affiliation: York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom. Electronic address: seishi.shimizu@york.ac.uk.
authors.forename: Seishi
authors.initials: S
authors.lastname: Shimizu
authors.affiliation: Division of Chemical Engineering, Graduate School of Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan; Elements Strategy Initiative for Catalysts and Batteries, Kyoto University, Katsura, Kyoto 615-8520, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Matubayasi
mesh_terms: D008051:Lipid Bilayers / Q000737:chemistry*; D009997:Osmotic Pressure; D012997:Solvents / Q000737:chemistry; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D008051:Lipid Bilayers; D012997:Solvents; D014867:Water