title: Ion pairing in aqueous electrolyte solutions with biologically relevant anions.
abstract: We performed molecular simulations to study ion pairing in aqueous solutions. Our results indicate that ion specific interactions of Li(+), Na(+), and K(+) with the dimethyl phosphate anion are solvent-mediated. The same mechanism applies to carboxylate ions, as has been illustrated in earlier simulations of aqueous alkali acetate solutions. Contact ion pairs play only a minor role--or no role at all--in determining the solution structure and ion specific thermodynamics of these systems. On the basis of the Kirkwood-Buff theory of solution we furthermore show that the well-known reversal of the Hofmeister series of salt activity coefficients, comparing chloride or bromide with dimethyl phosphate or acetate, is caused by changing from a contact pairing mechanism in the former system to a solvent-mediated interaction mechanism in the latter system.
authors.affiliation: Center of Smart Interfaces, Technische Universität Darmstadt, 64287 Darmstadt, Germany.
authors.forename: Pritam
authors.initials: P
authors.lastname: Ganguly
authors.forename: Pim
authors.initials: P
authors.lastname: Schravendijk
authors.forename: Berk
authors.initials: B
authors.lastname: Hess
authors.forename: Nico F A
authors.initials: NF
authors.lastname: van der Vegt
mesh_terms: D000838:Anions / Q000737:chemistry; D004573:Electrolytes / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D009943:Organophosphorus Compounds / Q000737:chemistry; D011188:Potassium / Q000737:chemistry; D011312:Pressure; D012964:Sodium / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D000838:Anions; D004573:Electrolytes; D007477:Ions; D009943:Organophosphorus Compounds; D012996:Solutions; D014867:Water; D008094:Lithium; D012964:Sodium; C007477:dimethyl phosphate; D011188:Potassium