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 (Delta 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 xi > 0.98 and xi > 0.92 respectively, and which, in principle, function with negative entropy production. It is demonstrated that for the case of xi >(1 - T/T-r) entropy production is always negative and only becomes positive when xi <(1 - T/T-r).
Photosynthesis and negative entropy production / R.C. Jennings, E. Engelmann, F. Garlaschi, A.P. Casazza, G. Zucchelli. - In: BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS. - ISSN 0005-2728. - 1709:3(2005), pp. 251-255.
|Titolo:||Photosynthesis and negative entropy production|
JENNINGS, ROBERT CHARLES (Primo)
ENGELMANN, ENRICO CLETO MARIA (Secondo)
CASAZZA, ANNA PAOLA (Penultimo)
|Parole Chiave:||Carnot cycle ; entropy ; fluorescence lifetime ; photosynthesis ; photosystem I core ; photosystem II core|
|Settore Scientifico Disciplinare:||Settore BIO/04 - Fisiologia Vegetale|
|Data di pubblicazione:||2005|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1016/j.bbabio.2005.08.004|
|Appare nelle tipologie:||01 - Articolo su periodico|