Thermodynamics of Reactions Affected by Medium Reorganization

Journal Article · Tue Dec 04 00:00:00 EST 2018 · Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry

DOI:https://doi.org/10.1021/acs.jpcb.8b08865· OSTI ID:1492769

Matyushov, Dmitry V. ^[1]; Newton, Marshall D. ^[2]

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1. Arizona State Univ., Tempe, AZ (United States)
2. Brookhaven National Lab. (BNL), Upton, NY (United States)

We present a thermodynamic analysis of the activation barrier for reactions which can be monitored through the difference in the energies of reactants and products defined as the reaction coordinate (electron and atom transfer, enzyme catalysis, etc). The free-energy surfaces along the reaction coordinate are separated into the enthalpy and entropy surfaces. For the Gaussian statistics of the reaction coordinate, the free-energy surfaces are parabolas, and the entropy surface is an inverted parabola. Its maximum coincides with the transition state for reactions with zero value of the reaction free energy. Maximum entropic depression of the activation barrier, anticipated by the concept of transition-state ensembles, can be achieved for such reactions. From Onsager’s reversibility, the entropy of equilibrium fluctuations encodes the entropic component of the activation barrier. The reorganization entropy thus becomes the critical parameter of the theory reducing the problem of activation entropy to the problem of reorganization entropy. Standard solvation theories do not provide reorganization entropy sufficient for the barrier depression. Complex media, characterized by many relaxation processes, need to be involved and proteins provide several routes for achieving large entropic effects related to incomplete (nonergodic) sampling of the complex energy landscape and active role of water in the reaction mechanism.

• Research Organization: Brookhaven National Lab. (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: SC0012704
• OSTI ID: 1492769
• Report Number(s): BNL--210911-2019-JAAM
• Journal Information: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry, Journal Name: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry Journal Issue: 51 Vol. 122; ISSN 1520-6106
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

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