Hypothesis explaining the activated complex in primary photosynthetic electron transfer as a dissipative structure

• Published in: Journal of physical chemistry (1952) 1993-10, Vol.97 (43), p.11318-11323
• Main Authors: Pohlmann, Ludwig, Tributsch, Helmut
• Format: Article
• Language: English
• Subjects: 140505 > Solar Energy Conversion-- Photochemical, Photobiological, & Thermochemical Conversion-- (1980-); ACTIVATION ENERGY; BACTERIA; Biological and medical sciences; CARBOXYLIC ACIDS; CHEMICAL ACTIVATION; CHEMICAL REACTION KINETICS; CHEMICAL REACTIONS; CHLOROPHYLL; COMPLEXES; ELECTRON TRANSFER; ENERGY; Fundamental and applied biological sciences. Psychology; HETEROCYCLIC ACIDS; HETEROCYCLIC COMPOUNDS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; KINETICS; MATHEMATICAL MODELS; Mechanisms. Catalysis. Electron transfer. Models; MICROORGANISMS; Molecular biophysics; ORGANIC ACIDS; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; PARTICLE MODELS; PHOTOCHEMICAL REACTIONS; PHOTOSYNTHESIS; Physical chemistry in biology; PHYTOCHROMES; PIGMENTS; PORPHYRINS; PROTEINS; REACTION KINETICS; SOLAR ENERGY; STATISTICAL MODELS; SYNTHESIS 400201 > Chemical & Physicochemical Properties; THERMODYNAMIC MODEL
• ISSN: 0022-3654; 1541-5740
• DOI: 10.1021/j100145a033

A far from equilibrium thermodynamic kinetic model treatment of the kinetics of primary electron transfer considering autocatalytic feedback reveals relevant mechanistic properties: a small portion of the excitation energy is used to build up microscopic order in an activated complex which thus facilitates efficient electron transfer and capture. On the molecular basis, monomeric bacteriochlorophyll energetically activated by the excited bacteriochlorophyll pair and inducing nonlinear feedback via the protein environment is assumed to play a key role. A negative effective activation energy, for a given temperature range, is obtained -- in agreement with experimental data. Formally the system may be understood as exhibiting a negative reorganization energy with the energy for the activated complex provided by the reaction itself. The model also explains why the rate of electron transfer can be extremely fast and why the rate of forward reaction largely exceeds the rate of reverse reaction. The concept of activated complexes as dissipative structures may lead to a more general new approach in understanding efficient irreversible mechanisms. 32 refs., 7 figs.