Energetics of the Primary Charge Separation in Bacterial Photosynthesis

Abstract

We consider the free energy relationship for the primary electron transfer (ET) (at T = 295 K) from the electronically excited singler state of the bacteriochlorophyll dimer in the bacterial photosynthetic native reaction center (RC), some of its single-site mutants and chemically engineered RCs containing accessory 132-OH-Ni-bacteriochlorophyll (Ni-B). This analysis resulted in the reasonable value λ1 = 800±250 cm-1 for the medium reorganization energy and ΔG1(N) = -480±180 cm-1 for the energy gap of the native RC. These energetic parameters imply that ET in the native RC conresponds to (nearly) optimal activationless ET. The quantum free energy relation predicts very fast ET time for the Ni-B substituted center ΔG1 ≃ -1500 cm-1 which reflects prosthetic group(s) vibrational excitation induced by ET in the inverted region. The low negative value of ΔG1(N) implies that the dominant room temperature ET mechanism for the native RC involves sequential ET.