Step-Scan FT-IR Spectroscopy of Electron Transfer in the Photosynthetic Bacterial Reaction Center

Abstract

Step-scan light-induced FT-IR difference spectra (1800–1200 cm⁻¹) of Rhodobacter sphaeroides photosynthetic bacterial reaction centers at low temperature and with a 10-μs time resolution are presented. The molecular changes and relaxation processes accompanying the photoxidation of the primary electron donor (P) are already present 10 μs after excitation. The photoconversion of P to the triplet state gives rise to characteristic IR absorption changes which decay with a half-time of 130 μs. A negative band at 1695 cm⁻¹ and a positive one at 1670 cm⁻¹ are assigned to the 9-keto carbonyl of bacteriochlorophyll in the states P and ³P, respectively.