title: Aqueous Mg2+ and Ca2+ ligand exchange mechanisms identified with 2DIR spectroscopy.
abstract: Biological systems must discriminate between calcium and magnesium for these ions to perform their distinct biological functions, but the mechanism for distinguishing aqueous ions has yet to be determined. Ionic recognition depends upon the rate and mechanism by which ligands enter and leave the first solvation shell surrounding these cations. We present a time-resolved vibrational spectroscopy study of these ligand exchange dynamics in aqueous solution. The sensitivity of the CN-stretch frequency of NCS(-) to ion pair formation has been utilized to investigate the mechanism and dynamics of ligand exchange into and out of the first solvation shell of aqueous magnesium and calcium ions with multidimensional vibrational (2DIR) spectroscopy. We have determined that anion exchange follows a dissociative mechanism for Mg(2+) and an associative mechanism for Ca(2+).
authors.affiliation: PULSE Institute, SLAC National Accelerator Laboratory, Stanford University , Stanford, California 94305, United States.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Sun
authors.forename: Wenkai
authors.initials: W
authors.lastname: Zhang
authors.forename: Minbiao
authors.initials: M
authors.lastname: Ji
authors.forename: Robert
authors.initials: R
authors.lastname: Hartsock
authors.forename: Kelly J
authors.initials: KJ
authors.lastname: Gaffney
mesh_terms: D002118:Calcium / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D007700:Kinetics; D008024:Ligands; D008274:Magnesium / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D013055:Spectrophotometry, Infrared; D014867:Water / Q000737:chemistry
chemical_list: D007477:Ions; D008024:Ligands; D014867:Water; D008274:Magnesium; D002118:Calcium