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Excess chemical potential of small solutes across water--membrane and water--hexane interfacesThe excess chemical potentials of five small, structurally related solutes, CH4, CH3F, CH2F2, CHF3, and CF4, across the water-glycerol 1-monooleate bilayer and water-hexane interfaces were calculated at 300, 310, and 340 K using the particle insertion method. The excess chemical potentials of nonpolar molecules (CH4 and CF4) decrease monotonically or nearly monotonically from water to a nonpolar phase. In contrast, for molecules that possess permanent dipole moments (CH3F, CH2F, and CHF3), the excess chemical potentials exhibit an interfacial minimum that arises from superposition of two monotonically and oppositely changing contributions: electrostatic and nonelectrostatic. The nonelectrostatic term, dominated by the reversible work of creating a cavity that accommodates the solute, decreases, whereas the electrostatic term increases across the interface from water to the membrane interior. In water, the dependence of this term on the dipole moment is accurately described by second order perturbation theory. To achieve the same accuracy at the interface, third order terms must also be included. In the interfacial region, the molecular structure of the solvent influences both the excess chemical potential and solute orientations. The excess chemical potential across the interface increases with temperature, but this effect is rather small. Our analysis indicates that a broad range of small, moderately polar molecules should be surface active at the water-membrane and water-oil interfaces. The biological and medical significance of this result, especially in relation to the mechanism of anesthetic action, is discussed.
Document ID
20040089729
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Pohorille, A.
(University of California San Francisco 94143, United States)
Wilson, M. A.
Date Acquired
August 21, 2013
Publication Date
March 8, 1996
Publication Information
Publication: The Journal of chemical physics
Volume: 104
Issue: 10
ISSN: 0021-9606
Subject Category
Exobiology
Funding Number(s)
CONTRACT_GRANT: NCC2-772
CONTRACT_GRANT: GM47818-01
Distribution Limits
Public
Copyright
Other
Keywords
NASA Center ARC
NASA Program Exobiology
NASA Discipline Number 52-20
NASA Discipline Exobiology

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