title: Reaction Mechanism for Direct Proton Transfer from Carbonic Acid to a Strong Base in Aqueous Solution I: Acid and Base Coordinate and Charge Dynamics.
abstract: Protonation by carbonic acid H2CO3 of the strong base methylamine CH3NH2 in a neutral contact pair in aqueous solution is followed via Car-Parrinello molecular dynamics simulations. Proton transfer (PT) occurs to form an aqueous solvent-stabilized contact ion pair within 100 fs, a fast time scale associated with the compression of the acid-base hydrogen-bond (H-bond), a key reaction coordinate. This rapid barrierless PT is consistent with the carbonic acid-protonated base pKa difference that considerably favors the PT, and supports the view of intact carbonic acid as potentially important proton donor in assorted biological and environmental contexts. The charge redistribution within the H-bonded complex during PT supports a Mulliken picture of charge transfer from the nitrogen base to carbonic acid without altering the transferring hydrogen's charge from approximately midway between that of a hydrogen atom and that of a proton.
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado , Boulder, Colorado 80309-0215, United States.
authors.forename: Snehasis
authors.initials: S
authors.lastname: Daschakraborty
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado , Boulder, Colorado 80309-0215, United States.
authors.forename: Philip M
authors.initials: PM
authors.lastname: Kiefer
authors.affiliation: Department of Chemistry, Ben-Gurion University of the Negev , P.O. Box 653, Beer-Sheva 84105, Israel.
authors.forename: Yifat
authors.initials: Y
authors.lastname: Miller
authors.affiliation: Department of Chemistry, Ben-Gurion University of the Negev , P.O. Box 653, Beer-Sheva 84105, Israel.
authors.forename: Yair
authors.initials: Y
authors.lastname: Motro
authors.affiliation: Department of Chemistry, Ben-Gurion University of the Negev , P.O. Box 653, Beer-Sheva 84105, Israel.
authors.forename: Dina
authors.initials: D
authors.lastname: Pines
authors.affiliation: Department of Chemistry, Ben-Gurion University of the Negev , P.O. Box 653, Beer-Sheva 84105, Israel.
authors.forename: Ehud
authors.initials: E
authors.lastname: Pines
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado , Boulder, Colorado 80309-0215, United States.|Ecole Normale Supérieure-PSL Research University, Chemistry Department, Sorbonne Universités-UPMC University Paris 06, CNRS UMR 8640 Pasteur, 24 rue Lhomond, 75005 Paris, France.
authors.forename: James T
authors.initials: JT
authors.lastname: Hynes
mesh_terms: D002255:Carbonic Acid / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D011522:Protons; D012996:Solutions; D014867:Water / Q000737:chemistry
chemical_list: D011522:Protons; D012996:Solutions; D014867:Water; D002255:Carbonic Acid