RESONANCE RAMAN-SPECTROSCOPY OF H-2-LABELED SPHEROIDENES IN PETROLEUMETHER AND IN THE RHODOBACTER-SPHAEROIDES REACTION-CENTER

As a step towards the structural analysis of the carotenoid spheroiden e in the Rhadobacter sphaeroides reaction centre, we present the reson ance Raman spectra of 14-H-2, 15-H-2, 15-H-2, 14'-H-2, 14,15'-H-2(2), and 15,15'-H-2(2) spheroidenes in petroleum ether and, except for 14,1 5'-H-2(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. F or the all-trans spheroidenes in solution the resonance enhancement of the Raman bands is determined by the participation of carbon-carbon s tretching 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 det ermined by the participation of carbon-carbon stretching modes in the centre of the molecule, the C-9 to C-15' region. Comparison of the spe ctra in solution and in the RC reveals evidence for an out-of-plane di stortion of the RC-bound spheroidene in the central C-14 to C-14, regi on of the carotenoid. The characteristic 1240 cm(-1) band in the spect rum of the RC-bound spheroidene has been assigned to a normal mode tha t contains the coupled C-12-C-13 and C-13-C-12' stretch vibrations. (C ) 1997 Elsevier Science B.V.