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09:42
Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes
Published on: January 16, 2016
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How fast can a proton-transfer reaction be beyond the solvent-control limit?
Ron Simkovitch1, Shay Shomer, Rinat Gepshtein
1Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University , Tel Aviv 69978, Israel.
The Journal of Physical Chemistry. B
|August 1, 2014
Summary
This review categorizes photoacids by strength, revealing excited-state proton transfer (ESPT) rates from nanoseconds to femtoseconds. The strongest photoacids achieve ESPT rates limited by intermolecular vibrations, not solvent dynamics.
Area of Science:
- Photochemistry
- Physical Chemistry
- Chemical Kinetics
Background:
- Photoacids undergo excited-state proton transfer (ESPT) to solvents.
- ESPT rates vary significantly based on photoacid strength and solvent properties.
Purpose of the Study:
- To review and categorize photoacids based on their proton transfer capabilities.
- To elucidate the factors governing ESPT rates across different photoacid strength regimes.
Main Methods:
- Classification of photoacids into four strength regimes based on pKa* values.
- Analysis of ESPT rate constants (kPT) and their relationship to solvent dynamics and intermolecular vibrations.
Main Results:
- Identified four regimes of photoacid strength, with ESPT rates ranging from nanoseconds to 100 femtoseconds (fs).
- Demonstrated that for the strongest photoacids, ESPT is limited by intermolecular vibrations, not solvent orientational time.
- Established a new time limit for ESPT (100 fs) attributed to vibrational assistance.
Conclusions:
- Photoacid strength dictates ESPT rates and solvent interactions.
- Intermolecular vibrations play a crucial role in accelerating ESPT for the strongest photoacids, surpassing solvent control limits.
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