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

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 X 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 approximate to 2600 cm(-1) [J. Breton, E. Nabedryk, W.W. Parson, Biochemistry, 31 (1992) 7503-7510] is confirmed. (C) 1999 Elsevier Science B.V. All rights reserved.