title: Effects of carboxylate anions on the molecular organization of H2O as probed by 1-propanol.
abstract: We characterized the effects of carboxylate anions, formate (OFm(-)), acetate (OAc(-)), and propionate (OPr(-)), on the molecular organization of liquid H(2)O by the 1-propanol (1P) probing methodology. The latter thermodynamic methodology provides two indices: one pertaining to the hydration number, n(H), and the other being related to the net increase/decrease of the entropy-volume cross fluctuation of the system. The results indicated that OFm(-) is a hydration center with n(H) = 1.2 ± 0.5 and leaves the bulk H(2)O away from the hydration shell unperturbed. We suggest that this single H(2)O hydrates preferentially one of the O's in the COO(-) group, showing the hydration center character. The values of n(H) for OAc(-) and OPr(-) were found to be 3.7 ± 0.8 and 9 ± 2, respectively, out of which one H(2)O molecule is used for hydrating the COO(-) side and the remaining 2.7 and 8 H(2)O molecules hydrate the respective alkyl group. Hence, OPr(-) is more hydrophobic than OAc(-) in terms of the hydration number. However, both alkyl moieties seem to equally retard the hydrogen bond probability of bulk H(2)O away from hydration shells around nonpolar sites, as much as the probing 1P does.
authors.affiliation: Research Center for Structural Thermodynamics, Graduate School of Sciences, Osaka University, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Takemi
authors.initials: T
authors.lastname: Kondo
authors.forename: Yuji
authors.initials: Y
authors.lastname: Miyazaki
authors.forename: Akira
authors.initials: A
authors.lastname: Inaba
authors.forename: Yoshikata
authors.initials: Y
authors.lastname: Koga