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A theory-experiment conundrum for proton transfer
1Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, USA. Kevin.Peters@Colorado.Edu
Accounts of Chemical Research
|September 11, 2008
Summary
A new model challenges traditional transition state theory for proton transfer, suggesting solvent fluctuations drive the process. Experimental data on nonadiabatic proton transfer reveals discrepancies with current theories, highlighting gaps in understanding.
Area of Science:
- Physical Chemistry
- Chemical Kinetics
- Theoretical Chemistry
Background:
- Transition state theory (TST) has been the dominant framework for understanding proton transfer kinetics for 60 years.
- TST, with Bell tunneling correction, is the standard model for analyzing proton, hydrogen atom, and hydride transfer.
- A novel theoretical model proposes that the transition state occurs within the solvent coordinate, not the proton transfer coordinate.
Purpose of the Study:
- To discuss the core principles of the new theoretical model of proton transfer.
- To contrast the new model with the established transition state theory.
- To present experimental discrepancies between nonadiabatic systems and current proton transfer understanding.
Main Methods:
- Theoretical analysis of transition state theory and a new solvent-coordinate-based model.
- Experimental studies on weakly hydrogen-bonded complexes to investigate proton transfer mechanisms.
- Correlation of rate constants with driving force to identify normal and inverted regions in proton transfer.
Main Results:
- The new model suggests proton transfer is initiated by solvent fluctuations, leading to resonance between reactant and product states.
- Proton transfer can proceed adiabatically or nonadiabatically within the new theoretical framework.
- Experimental data for nonadiabatic proton transfer in weakly hydrogen-bonded complexes shows kinetic behavior inconsistent with current theoretical formulations.
Conclusions:
- The findings question deductions derived from the standard transition state theory regarding proton transfer processes.
- Experimental observations highlight a significant gap in the collective understanding of nonadiabatic proton transfer phenomena.
- Further theoretical and experimental work is needed to reconcile observed kinetics with proposed models of proton transfer.
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