title: Thermodynamics of anion-π interactions in aqueous solution.
abstract: Thermodynamic parameters (ΔG°, ΔH°, TΔS°), obtained by means of potentiometric and isothermal titration calorimetry (ITC) methods, for the binding equilibria involving anions of high negative charge, like SO(4)(2-), SeO(4)(2-), S(2)O(3)(2-) and Co(CN)(6)(3-), and nitroso-amino-pyrimidine receptors in water suggested that anion-π interactions furnish a stabilization of about -10 kJ/mol to the free energy of association. These anion-π interactions are almost athermic and favored by large entropic contributions which are likely due to the reduced hydrophobic pyrimidine surface exposed to water after anion aggregation, and the consequent reduced disruptive effect on the dynamic water structure. The crystal structure of the {H(4)L[Co(CN)(6)]}·2H(2)O complex showed strong anion-π interactions between Co(CN)(6)(3-) and the protonated H(4)L(3+) receptor. The CN···centroid distance (2.786(3) Å), occurring with a cyanide N atom located almost above the centroid of the pyrimidine ring, is the shortest distance till now reported for the interaction between CN(-) ions and heteroaromatic rings.
authors.affiliation: Department of Inorganic and Organic Chemistry, University of Jaen, 23071, Jaen, Spain.
authors.forename: Paloma
authors.initials: P
authors.lastname: Arranz-Mascarós
authors.forename: Carla
authors.initials: C
authors.lastname: Bazzicalupi
authors.forename: Antonio
authors.initials: A
authors.lastname: Bianchi
authors.forename: Claudia
authors.initials: C
authors.lastname: Giorgi
authors.forename: Maria-Luz
authors.initials: ML
authors.lastname: Godino-Salido
authors.forename: Maria-Dolores
authors.initials: MD
authors.lastname: Gutiérrez-Valero
authors.forename: Rafael
authors.initials: R
authors.lastname: Lopez-Garzón
authors.forename: Matteo
authors.initials: M
authors.lastname: Savastano
mesh_terms: D000838:Anions / Q000737:chemistry; D002151:Calorimetry; D012996:Solutions; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D000838:Anions; D012996:Solutions; D014867:Water