Molecular symmetry and exciton interaction in photosynthetic primary events

Abstract

In this paper, the molecular details of the recently proposed energy upconversion theory of photosynthesis are reviewed. The primary light reactions are explained in terms of aC2 symmetrical structure of the reaction center involving a (Chl−H2O)2 adduct. It is shown that exciton interaction within the (Chl−H2O)2 complex leads to an antisymmetric triplet state which may act as an energy trap. The presence of the energy trap in the reaction center suggests that the trigger step for the photoionization of active chlorophylls may involve the summation of two red excitation photons. Under normal conditions, the steadystate one-photon-per-electron quantum requirement is obtained. The functional properties of the various molecular constituents of the Chl-a molecule, such as the Ring V β-ketoester group, the phytyl tail, the central Mg atom, and the π-system of the macrocycle are explained within the present theoretical framework. A detailed analysis is given of the postulates and the consequences of the proposed model. The ramifications of the theory are probed, and their biological consequences are suggested for future study.