Self-organized electron transfer as a possible element in the photosynthetic process

Abstract

As energy fluxes in several systems far from thermodynamic equilibrium can be largely enhanced under nonlinear conditions permitting local entropy export, this should also be possible on a more microscopic scale for biological electron transfer processes. As a precondition a molecular feedback loop must exist, which transfers a small fraction of the energy, which drives the reaction, through the surrounding medium to assist the electron transfer in a non-linear way. This can lead to microscopic self-organization, i.e. to a temporary dissipativs structure which may significantly improve electron transfer through a non-equilibrium electron distribution and a decrease of the activation barrier. The problem is theoretically modelled as a Kramers approach in which the friction term may become active. A formula for "self-organized" electron transfer is obtained which yields - for finite activation barriers - significantly higher rates than the Marcus formula. The presented model may help to explain how biological catalysts have evolved the ability of generating favourable energy barriers for multielectron transfer near the thermodynamic overall potential. © VCH Verlagsgesellschaft mbH,.