title: Gas phase H/D exchange of sodiated amino acids: why do we see zwitterions?
abstract: The gas-phase interaction of sodiated amino acids and sodiated amino acid methyl esters with various deuterium donors is investigated by combining results of H/D exchange reactions with those from density functional theory and molecular dynamics calculations. Discrepancy between experimentally and theoretically obtained structures for sodium cationized amino acids is explained by deuterium donor caused perturbation of the most stable amino acid conformation. Detailed study of H/D exchange mechanism on sodiated amino acids shows that the H/D exchange reaction is preceded by a multistep quasi-isoenergetic transition (perturbation) from a charge solvated to zwitterionic structure in the amino acid. Although the computation refers to the system AlaNa(+) and D(2)O, these mechanisms apply to all amino acids, except those where a functional side-chain group takes part in the perturbation process. The suggested perturbation mechanism applies also for other deuterium donors such as CD(3)OD or even ND(3) and indicates that a single water molecule suffices to convert the sodiated amino acid from charge solvated to zwitterionic form.
authors.affiliation: Laboratory for Chemical Kinetics and Atmospheric Chemistry, Ruđer Bošković Institute, Bijenička 54, HR-10002, Zagreb, Croatia.|Laboratory for Chemical Kinetics and Atmospheric Chemistry, Croatia.
authors.forename: Marko
authors.initials: M
authors.lastname: Rožman
authors.affiliation: Laboratory for Chemical Kinetics and Atmospheric Chemistry, Ruđer Bošković Institute, Bijenička 54, HR-10002, Zagreb, Croatia.|Laboratory of Chemical and Biological Crystallography, Croatia.
authors.forename: Branimir
authors.initials: B
authors.lastname: Bertoša
authors.affiliation: Laboratory for Chemical Kinetics and Atmospheric Chemistry, Ruđer Bošković Institute, Bijenička 54, HR-10002, Zagreb, Croatia.|Laboratory for Chemical Kinetics and Atmospheric Chemistry, Croatia.
authors.forename: Leo
authors.initials: L
authors.lastname: Klasinc
authors.affiliation: Laboratory for Chemical Kinetics and Atmospheric Chemistry, Ruđer Bošković Institute, Bijenička 54, HR-10002, Zagreb, Croatia. andrew.emili@utoronto.ca.|Laboratory for Chemical Kinetics and Atmospheric Chemistry, Croatia. andrew.emili@utoronto.ca.
authors.forename: Dunja
authors.initials: D
authors.lastname: Srzić
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D003198:Computer Simulation; D003903:Deuterium / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D012964:Sodium / Q000737:chemistry*; D012984:Software; D014867:Water / Q000737:chemistry
chemical_list: D000596:Amino Acids; D014867:Water; D012964:Sodium; D003903:Deuterium