TOWARDS A VIBRATIONAL ANALYSIS OF SPHEROIDENE - RESONANCE RAMAN-SPECTROSCOPY OF C-13-LABELED SPHEROIDENES IN PETROLEUM ETHER AND IN THE RHODOBACTER-SPHAEROIDES REACTION-CENTER

We report resonance Raman spectra of the carotenoid spheroidene and it s 14'-C-13 and 15'-C-13 substituted analogues in petroleum ether and b ound to the reaction centre of Rhodobacter sphaeroides R26. The spectr a in petroleum ether correspond to planar all-trans spheroidene while those of the reaction centres are consistent with a nonplanar 15,15'-c is spheroidene. The effect of C-13 labelling is largest in the carbon- carbon double-bond stretching region. The 15'-C-13 substitution of the reaction centre bound spheroidene, however, hardly changes the C=C ba nd as compared to that for the natural abundance spheroidene apart fro m a new weak band at 1508 cm(-1). This observation has been interprete d as a decoupling of the C-15 = C-15' stretch from the other double-bo nd stretches in combination with a small intrinsic Raman intensity of this local mode for 15,15'-cis spheroidene.