title: Polar solvent fluctuations drive proton transfer in hydrogen bonded complexes of carboxylic acid with pyridines: NMR, IR and ab initio MD study.
abstract: We study a series of intermolecular hydrogen-bonded 1 : 1 complexes formed by chloroacetic acid with 19 substituted pyridines and one aliphatic amine dissolved in CD2Cl2at low temperature by1H and13C NMR and FTIR spectroscopy. The hydrogen bond geometries in these complexes vary from molecular (O-HN) to zwitterionic (O-H-N+) ones, while NMR spectra show the formation of short strong hydrogen bonds in intermediate cases. Analysis of C[double bond, length as m-dash]O stretching and asymmetric CO2-stretching bands in FTIR spectra reveal the presence of proton tautomerism. On the basis of these data, we construct the overall proton transfer pathway. In addition to that, we also study by use of ab initio molecular dynamics the complex formed by chloroacetic acid with 2-methylpyridine, surrounded by 71 CD2Cl2molecules, revealing a dual-maximum distribution of hydrogen bond geometries in solution. The analysis of the calculated trajectory shows that the proton jumps between molecular and zwitterionic forms are indeed driven by dipole-dipole solvent-solute interactions, but the primary cause of the jumps is the formation/breaking of weak CHO bonds from solvent molecules to oxygen atoms of the carboxylate group.
authors.affiliation: Department of Chemistry, Humboldt-Universität zu Berlin, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Koeppe
authors.affiliation: Institute of Chemistry, Martin-Luther Universität Halle-Wittenberg, Germany. daniel.sebastiani@chemie.uni-halle.de.
authors.forename: S A
authors.initials: SA
authors.lastname: Pylaeva
authors.affiliation: Institute of Chemistry, Martin-Luther Universität Halle-Wittenberg, Germany. daniel.sebastiani@chemie.uni-halle.de.
authors.forename: C
authors.initials: C
authors.lastname: Allolio
authors.affiliation: Institute of Chemistry, Martin-Luther Universität Halle-Wittenberg, Germany. daniel.sebastiani@chemie.uni-halle.de.
authors.forename: D
authors.initials: D
authors.lastname: Sebastiani
authors.affiliation: Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Berlin, Germany. nibberin@mbi-berlin.de.
authors.forename: E T J
authors.initials: ET
authors.lastname: Nibbering
authors.affiliation: Department of Physics, St.Petersburg State University, Russia.
authors.forename: G S
authors.initials: GS
authors.lastname: Denisov
authors.affiliation: Institute of Chemistry and Biochemistry, Freie Universität Berlin, Germany.
authors.forename: H-H
authors.initials: HH
authors.lastname: Limbach
authors.affiliation: Center for Magnetic Resonance, St. Petersburg State University, Russia. peter.tolstoy@spbu.ru.
authors.forename: P M
authors.identifier: http://orcid.org/0000-0002-8426-3988
authors.initials: PM
authors.lastname: Tolstoy