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Published on: July 19, 2019
Long-range proton transfer in aqueous Acid-base reactions
B J Siwick1, M J Cox, H J Bakker
1FOM Institute AMOLF, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands.
The Journal of Physical Chemistry. B
|December 11, 2007
Summary
Proton transfer in aqueous reactions occurs via diverse hydrogen-bound complexes. Solvent fluctuations and distance-dependent rates govern this essential chemical process, with tunneling playing a minor role.
Area of Science:
- Physical Chemistry
- Chemical Kinetics
- Spectroscopy
Background:
- Proton transfer (PT) is fundamental to many chemical and biological processes.
- Understanding PT mechanisms in solution is crucial for various scientific disciplines.
Purpose of the Study:
- To elucidate the mechanism of proton transfer in the aqueous reaction between 8-hydroxy-1,3,6-pyrenetrisulfonic acid (HPTS) and acetate.
- To investigate the role of solvent and reaction complex structure in proton transfer kinetics.
Main Methods:
- Femtosecond mid-infrared laser spectroscopy to probe vibrational resonances.
- Analysis of kinetic isotope effects to determine the contribution of tunneling.
- Characterization of reaction complexes with varying numbers of intervening water molecules.
Main Results:
- Proton transfer occurs within a distribution of hydrogen-bound complexes with 0-5 water molecules separating the acid and base.
- A strongly distance-dependent proton transfer rate explains nonexponential kinetics.
- A kinetic isotope effect of 1.5 indicates minimal proton tunneling.
Conclusions:
- The proton transfer mechanism is best described by the adiabatic picture, emphasizing the role of solvent fluctuations.
- Solvent reorganization and hydrogen-bond dynamics are critical for facilitating proton transfer.
- The study provides detailed insights into the molecular-level dynamics of proton transfer in solution.
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