Infrared Difference Spectroscopy of Electro-chemically Generated Redox States in Bacterial Reaction Centers

Abstract

In bacterial photosynthetic reaction centers (RC), about 40% of the energy of the absorbed photon or trapped exciton are stored in a charge-separated state, whose free energy can be used by secondary redox reactions. This charge-separated state is created in a sequence of steps; i.e. an electron is transferred from the primary electron donor P (a bacteriochlorophyll dimer, BChl2) via a monomeric bacteriochlorophyll B to an intermediary electron acceptor H (a bacteriopheophytin, BPheo), and from there to a primary and secondary quinone acceptor QA and QB, thus creating a P+Q− state (for a review, see [1]). The free energy stored in this state can be expressed as the sum of the energy needed to shift the redox poise of P/P+ and of Q/Q− from the quiescent state of the RC, where both P and Q are neutral, to an accumulation of the charged radicalic species.