Abstract
As a step towards the structural analysis of the carotenoid spheroidene in the Rhodobacter sphaeroides reaction centre, we present the resonance Raman spectra of 14- 2H, 15- 2H, 15′- 2H, 14′- 2H, 14,15′- 2H 2, and 15,15′- 2H 2 spheroidenes in petroleum ether and, except for 14,15′- 2H 2 spheroidene, in the Rb. sphaeroides R26 reaction center (RC). Analysis of the spectral changes upon isotopic substitution allows a qualitative assignment of most of the vibrational bands to be made. For the all- trans spheroidenes in solution the resonance enhancement of the Raman bands is determined by the participation of carbon-carbon stretching modes in the centre of the conjugated chain, the C 9 to C 15′ region. For the RC-bound 15,15′- cis spheroidenes, enhancement is determined by the participation of carbon-carbon stretching modes in the centre of the molecule, the C 13 to C 13′ region. Comparison of the spectra in solution and in the RC reveals evidence for an out-of-plane distortion of the RC-bound spheroidene in the central C 14 to C 14′ region of the carotenoid. The characteristic 1240 cm −1 band in the spectrum of the RC-bound spheroidene has been assigned to a normal mode that contains the coupled C 12C 13 and C 13′C 12′ stretch vibrations.
Published Version
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