Sequential Proton Transfer Through Water Bridges in Acid-Base Reactions

The proton transfer mechanism between aqueous Brønsted acids and bases, forming an encounter pair, has been studied in real time with ultrafast infrared spectroscopy. The transient intermediacy of a hydrated proton, formed by ultrafast dissociation from an optically triggered photoacid proton donor ROH, is implicated by the appearance of an infrared absorption marker band before protonation of the base, B–. Thus, proton exchange between an acid and a base in aqueous solution is shown to proceed by a sequential, von Grotthuss–type, proton-hopping mechanism through water bridges. The spectra suggest a hydronium cation H3O+ structure for the intermediate, stabilized in the Eigen configuration in the ionic complex RO–···H3O+···B–.

[1]  P. Matousek,et al.  Observation of excited-state proton transfer in green fluorescent protein using ultrafast vibrational spectroscopy. , 2005, Journal of the American Chemical Society.

[2]  H Luecke,et al.  Proton transfer pathways in bacteriorhodopsin at 2.3 angstrom resolution. , 1998, Science.

[3]  J. Hynes.  Physical chemistry: The protean proton in water , 1999, Nature.

[4]  Asuka Fujii,et al.  Infrared Spectroscopic Evidence for Protonated Water Clusters Forming Nanoscale Cages , 2004, Science.

[5]  M. Parrinello,et al.  The nature of the hydrated excess proton in water , 1999, Nature.

[6]  B. Ault,et al.  Infrared spectrum of the water-hydrochloric acid complex in solid nitrogen , 1973 .

[7]  Mark A. Johnson,et al.  Predissociation spectroscopy of the argon-solvated H5O2+ "zundel" cation in the 1000-1900 cm(-1) region. , 2004, The Journal of chemical physics.

[8]  C. Dellago,et al.  Autoionization in Liquid Water , 2001, Science.

[9]  Evgeniy M. Myshakin,et al.  Spectral Signatures of Hydrated Proton Vibrations in Water Clusters , 2005, Science.

[10]  Assigning protonation patterns in water networks in bacteriorhodopsin based on computed IR spectra. , 2004, Angewandte Chemie.

[11]  K. Ando,et al.  Molecular Mechanism of HF Acid Ionization in Water: An Electronic Structure−Monte Carlo Study , 1999 .

[12]  N. Agmon,et al.  The Grotthuss mechanism , 1995 .

[13]  T. D. Fridgen,et al.  Infrared Spectrum of the Protonated Water Dimer in the Gas Phase , 2004 .

[14]  S. Corcelli,et al.  Infrared and Raman line shapes of dilute HOD in liquid H2O and D2O from 10 to 90 °C , 2005 .

[15]  Hadas Lapid,et al.  A bond-order analysis of the mechanism for hydrated proton mobility in liquid water. , 2005, The Journal of chemical physics.

[16]  M. Zimmer,et al.  Green fluorescent protein (GFP): applications, structure, and related photophysical behavior. , 2002, Chemical reviews.

[17]  Daniel Borgis,et al.  Transport and spectroscopy of the hydrated proton: A molecular dynamics study , 1999 .

[18]  K. Jordan,et al.  Infrared Signature of Structures Associated with the H+(H2O)n (n = 6 to 27) Clusters , 2004, Science.

[19]  L. Delzeit,et al.  Infrared spectra of hydrogen chloride complexed/ionized in amorphous hydrates and at ice surfaces in the 15-90 K range , 1993 .

[20]  Joachim Sauer,et al.  The infrared spectrum of the O⋯H⋯O fragment of H5O2+: Ab initio classical molecular dynamics and quantum 4D model calculations , 2001 .

[21]  Matteo Rini,et al.  Real-Time Observation of Bimodal Proton Transfer in Acid-Base Pairs in Water , 2003, Science.

[22]  D. Pines,et al.  Bimodal proton transfer in acid-base reactions in water. , 2004, The Journal of chemical physics.

[23]  Jeongho Kim,et al.  The vibrational spectrum of the hydrated proton: Comparison of experiment, simulation, and normal mode analysis , 2002 .

[24]  N. Agmon,et al.  Geminate recombination in excited-state proton-transfer reactions: Numerical solution of the Debye-Smoluchowski equation with backreaction and comparison with experimental results , 1988 .

[25]  O. Mohammed,et al.  Solvent-dependent photoacidity state of pyranine monitored by transient mid-infrared spectroscopy. , 2005, Chemphyschem : a European journal of chemical physics and physical chemistry.

[26]  J. Hynes,et al.  Molecular Mechanism of HCl Acid Ionization in Water: Ab Initio Potential Energy Surfaces and Monte Carlo Simulations , 1997 .

[27]  Ludger Wöste,et al.  Gas-Phase Infrared Spectrum of the Protonated Water Dimer , 2003, Science.

[28]  Mitchio Okumura,et al.  Infrared spectra of the solvated hydronium ion: Vibrational predissociation spectroscopy of mass-selected H3O+.cntdot.(H2O)n.cntdot.(H2)m , 1990 .

[29]  Manfred Eigen,et al.  Proton Transfer, Acid-Base Catalysis, and Enzymatic Hydrolysis. Part I: ELEMENTARY PROCESSES†‡ , 1964 .

[30]  T. DeCoursey.  Voltage-gated proton channels and other proton transfer pathways. , 2003, Physiological reviews.

[31]  S. Meiboom,et al.  NUCLEAR MAGNETIC RESONANCE STUDY OF THE PROTON TRANSFER IN WATER , 1961 .

[32]  W. Kühlbrandt,et al.  Bacteriorhodopsin — the movie , 2000, Nature.