Light-induced FTIR difference spectroscopy of photosynthetic charge separation between 9000 and 250 cm −1

Abstract

The light-induced FTIR difference spectrum corresponding to photosynthetic charge separation between the dimeric bacteriochlorophyll primary donor (P) and the quinone Q A in the reaction center of the photosynthetic bacterium Rhodobacter sphaeroides has been measured in the frequency range between 9000 and 250 cm −1 using a DTGS detector. Upon extensive signal averaging, the noise level is reduced below 2×10 −5 absorbance unit. The positive bands of the difference spectrum contribute much more than the negative ones over the whole frequency range investigated. In the region below 650 cm −1, a number of bands of small amplitude are observed for the first time. The presence of a tail extending between 6000 and 3600 cm −1 on the high-energy side of the electronic transition of P + peaking at ≈2600 cm −1 [J. Breton, E. Nabedryk, W.W. Parson, Biochemistry, 31 (1992) 7503–7510] is confirmed.