Photosynthesis and negative entropy production

The widely held view that the maximum efficiency of a photosynthetic pigment system is given by the Carnot cycle expression (1 − T/ T r) for energy transfer from a hot bath (radiation at temperature T r) to a cold bath (pigment system at temperature T) is critically examined and demonstrated to be i...

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Bibliographic Details
Published in:Biochimica et biophysica acta 2005-09, Vol.1709 (3), p.251-255
Main Authors: Jennings, Robert C., Engelmann, Enrico, Garlaschi, Flavio, Casazza, Anna Paola, Zucchelli, Giuseppe
Format: Article
Language:English
Subjects:
Carnot cycle
energy metabolism
Energy Transfer - physiology
Entropy
Fluorescence
Fluorescence lifetime
Photosynthesis
Photosynthesis - physiology
Photosystem I core
Photosystem I Protein Complex - metabolism
Photosystem I Protein Complex - physiology
Photosystem II core
Photosystem II Protein Complex - metabolism
Photosystem II Protein Complex - physiology
Temperature
Thermodynamics
Zea mays - physiology
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Summary:The widely held view that the maximum efficiency of a photosynthetic pigment system is given by the Carnot cycle expression (1 − T/ T r) for energy transfer from a hot bath (radiation at temperature T r) to a cold bath (pigment system at temperature T) is critically examined and demonstrated to be inaccurate when the entropy changes associated with the microscopic process of photon absorption and photochemistry at the level of single photosystems are considered. This is because entropy losses due to excited state generation and relaxation are extremely small (Δ S ≪ T/ T r) and are essentially associated with the absorption-fluorescence Stokes shift. Total entropy changes associated with primary photochemistry for single photosystems are shown to depend critically on the thermodynamic efficiency of the process. This principle is applied to the case of primary photochemistry of the isolated core of higher plant photosystem I and photosystem II, which are demonstrated to have maximal thermodynamic efficiencies of ξ > 0.98 and ξ > 0.92 respectively, and which, in principle, function with negative entropy production. It is demonstrated that for the case of ξ > (1 − T/ T r) entropy production is always negative and only becomes positive when ξ < (1 − T/ T r).
ISSN:0005-2728
0006-3002
1879-2650
DOI:10.1016/j.bbabio.2005.08.004