title: Cation-cation contact pairing in water: guanidinium.
abstract: The formation of like-charge guanidinium-guanidinium contact ion pairs in water is evidenced and characterized by X-ray absorption spectroscopy and first-principles spectral simulations based on molecular dynamics sampling. Observed concentration-induced nitrogen K-edge resonance shifts result from π* state mixing and the release of water molecules from each first solvation sphere as two solvated guanidinium ions associate into a stacked pair configuration. Possible biological implications of this counterintuitive cation-cation pairing are discussed.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: Orion
authors.initials: O
authors.lastname: Shih
authors.forename: Alice H
authors.initials: AH
authors.lastname: England
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Dallinger
authors.forename: Jacob W
authors.initials: JW
authors.lastname: Smith
authors.forename: Kaitlin C
authors.initials: KC
authors.lastname: Duffey
authors.forename: Ronald C
authors.initials: RC
authors.lastname: Cohen
authors.forename: David
authors.initials: D
authors.lastname: Prendergast
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Saykally
mesh_terms: D004583:Electrons; D019791:Guanidine / Q000737:chemistry*; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D011789:Quantum Theory; D012965:Sodium Chloride / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D012965:Sodium Chloride; D019791:Guanidine