Intermolecular hydrogen bonding between carotenoid and bacteriochlorophyllin LH2

We ha c e studied van der Waals contacts of the carotenoid rhodopin glucosi de (RG) with the bacteriochlorophyll pigments absorbing at 800 nm (B800) in the crystal structure of Rhodopseudomonas acidophila. and the hydrogen pos itions were determined from quantum chemical calculations at the Hartree-Fo ck (6-31G) Level, We have found strong evidence for hydrogen bonding betwee n the B800 BCh1 and the RG from neighboring protomer units. The binding ene rgy was estimated to be about 2 kcal/mol (700 cm(-1)). CI-singles approach and time-dependent density functional theory calculations of the B800-RG di mer indicate a red-shift (ca 2 nm) of the B800 Q(y) transition, along with a substantial increase of its oscillator strength, probably due to the hydr ogen bonding, (C) 2001 Published by Elsevier Science B,V, on behalf of the Federation of European Biochemical Societies.