Photosynthetic glow peaks and their relationship with the free energy changes |
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Authors: | Don DeVault Govindjee |
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Institution: | (1) Biophysics Division, University of Illinois at Urbana-Champaign, 156 Davenport Hall, 607 S. Mathews, 61801 Urbana, IL, USA |
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Abstract: | This paper is concerned with relating thermoluminescence to the total free-energy change, G, involved in detrapping a particular electron-hole pair as a photosynthetic sample is warmed from an initial low temperature. It extends a mathematical discussion of four possible mechanisms introduced in an earlier paper DeVault, Govindjee and Arnold, Proc Nat'l Acad Sci USA 80: 983–987 (1983)]; here, particular attention is paid to the dependence of the absolute temperature of the maximum of a glow-peak, T
m
, on the total free-energy change, G. The conclusion from the cases studied is that T
m
=G/(k
B
W) where G is evaluated at T
m
, W is a complicated function of temperature and of thermodynamic parameters in the steps of the mechanism, and k
B
is the Boltzmann constant. If the rate limiting step in the mechanism of detrapping is not preceded by any step in which G is appreciably negative, W is likely to have a value of about 33 and T
m
is approximately proportional to G. Otherwise W can become much smaller and more strongly dependent on temperature and T
m
is no longer proportional to G. These conclusions are of significance in lending theoretical support to the practice of inferring redox midpoint potential changes from shifts in T
m
. |
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Keywords: | Thermoluminescence delayed light reversed electron flow electron and hole traps free-energy dependence |
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