title: Water-Mediated Ion Pairing: Occurrence and Relevance.
abstract: We present an overview of the studies of ion pairing in aqueous media of the past decade. In these studies, interactions between ions, and between ions and water, are investigated with relatively novel approaches, including dielectric relaxation spectroscopy, far-infrared (terahertz) absorption spectroscopy, femtosecond mid-infrared spectroscopy, and X-ray spectroscopy and scattering, as well as molecular dynamics simulation methods. With these methods, it is found that ion pairing is not a rare phenomenon only occurring for very particular, strongly interacting cations and anions. Instead, for many salt solutions and their interfaces, the measured and calculated structure and dynamics reveal the presence of a distinct concentration of contact ion pairs (CIPs), solvent shared ion pairs (SIPs), and solvent-separated ion pairs (2SIPs). We discuss the importance of specific ion-pairing interactions between cations like Li(+) and Na(+) and anionic carboxylate and phosphate groups for the structure and functioning of large (bio)molecular systems.
authors.affiliation: Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt , Alarich-Weiss-Strasse 10, 64287 Darmstadt, Germany.
authors.forename: Nico F A
authors.initials: NF
authors.lastname: van der Vegt
authors.affiliation: Physics Department, NEXMAP Section, Technical University of Denmark , Fysikvej 307, 2800 Kongens Lyngby, Denmark.
authors.forename: Kristoffer
authors.initials: K
authors.lastname: Haldrup
authors.affiliation: Laboratory for Fundamental BioPhotonics, Institute of Bioengineering, and Institute of Materials Science, School of Engineering, and Lausanne Centre for Ultrafast Science, École Polytechnique Fédérale de Lausanne , CH-1015 Lausanne, Switzerland.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Roke
authors.affiliation: College of Chemistry and Molecular Engineering, Beijing National Laboratory for Molecular Sciences, Peking University , Beijing 100871, China.|Department of Chemistry, Rice University , 6100 Main Street, Houston, Texas 77005-1892, United States.
authors.forename: Junrong
authors.initials: J
authors.lastname: Zheng
authors.affiliation: Division of Theoretical Chemistry, Department of Chemistry, Lund University , SE-22100 Lund, Sweden.
authors.forename: Mikael
authors.initials: M
authors.lastname: Lund
authors.affiliation: FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors.forename: Huib J
authors.initials: HJ
authors.lastname: Bakker