CONFORMATIONAL AND ENVIRONMENTAL-EFFECTS ON BACTERIOCHLOROPHYLL OPTICAL-SPECTRA - CORRELATIONS OF CALCULATED SPECTRA WITH STRUCTURAL RESULTS

Recent structural data for porphyrins and (bacterio)chlorophylls have demonstrated the skeletal flexibility of the chromophores. Experimental redox and optical results for puckered porphyrins have also established that such conformational variations can affect the highest occupied and lowest unoccupied molecular orbitals of the chromophores and thereby modulate their light-absorption properties. The concept is applied to the bacteriochlorophyll a (BChl) antenna protein complex from Prosthecochloris aestuarii, whose structure has been solved by X-ray diffraction (J. Mol. Biol. 1986, 188, 443). INDO/s calculations, based on the crystallographic data for the seven individual BChls that comprise the antenna complex, yield absorption maxima that reflect the observed conformational variations and clearly establish that skeletal differences can influence the optical properties of the chromophores. Additional effects due to axial ligands, substituent orientations, and neighboring residues are also assessed. © 1990 American Chemical Society.