Campus Units

Chemistry

Document Type

Article

Publication Version

Published Version

Publication Date

2-17-1999

Journal or Book Title

Journal of Physical Chemistry B

Volume

103

Issue

9

First Page

1581

Last Page

1585

DOI

10.1021/jp982728w

Abstract

The excited-state intramolecular proton-transfer reactions of hypericin and hypocrellin A are measured as a function of temperature in an ethanol/methanol mixture. The data yield activation energies of 0.044 ± 0.008 and 2.12 ± 0.070 kcal/mol for hypericin and hypocrellin A, respectively. The negligible activation energy of hypericin is consistent with previous suggestions that the proton-transfer reaction is adiabatic (K. Das et al., J. Phys. Chem. 1997,101A, 3241.) and that a very low-amplitude displacement in at least one other coordinate be taken into account in order to describe the reaction dynamics. The proton transfer for hypocrellin is also considered to occur in the adiabatic regime, but the significant activation energy suggests that a larger amplitude motion than that for the case of hypericin comprises part of the reaction coordinate. Much of the barrier cited above for hypocrellin A results from the temperature dependence of the viscosity of the solvent mixture. The viscosity independent part of the activation barrier is 0.41 ± 0.088 kcal/mol.

Comments

Reprinted (adapted) with permission from Journal of Physical Chemistry B 103 (1999): 1581, doi: 10.1021/jp982728w. Copyright 1999 American Chemical Society.

Copyright Owner

American Chemical Society

Language

en

File Format

application/pdf

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