title: Water confined in the local field of ions.
abstract: Interionic distances are shorter in concentrated ionic solutions, thus instigating the interaction and overlap of hydration shells, as ions become separated by only one or two layers of water molecules. The simultaneous interaction of water with two oppositely charged ions has, so far, only been investigated by computer simulation studies, because the isolated vibrational spectroscopic signature of these molecules remains undetected. Our combined near-infrared spectroscopic and molecular dynamics simulation studies of alkali halide solutions present a distinct spectral feature, which is highly responsive to depletion of bulk water and merging of hydration shells. The analysis of this spectral feature demonstrates that absorption trends are in good agreement with the law of matching affinities, thus providing the first successful vibrational spectroscopic treatment of this topic. Combined with commonly observed near-infrared bands, this feature provides a spectral pattern that describes some relevant aspects of ionic hydration.
authors.affiliation: Center for Medical Genetics, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582 (Japan); Department of Pharmacology and Neuroscience, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582 (Japan). dkojic@z8.keio.jp.
authors.forename: Dušan
authors.initials: D
authors.lastname: Kojić
authors.forename: Roumiana
authors.initials: R
authors.lastname: Tsenkova
authors.forename: Katsufumi
authors.initials: K
authors.lastname: Tomobe
authors.forename: Kenji
authors.initials: K
authors.lastname: Yasuoka
authors.forename: Masato
authors.initials: M
authors.lastname: Yasui
mesh_terms: D006860:Hydrogen Bonding; D007477:Ions / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D019265:Spectroscopy, Near-Infrared; D014867:Water / Q000737:chemistry*
chemical_list: D007477:Ions; D014867:Water
keywords: hydrogen bonds; ion pairs; molecular dynamics; near-infrared spectroscopy; water chemistry