Optically Detected Magnetic Resonance of Porphyrin Complexes in the Bacterium Rhodopseudomonas sphaeroides

Abstract

By ODMR in zero-field the porphyrins of the BChl-biosynthesis in whole cells of Rhodopseudomonas sphaeroides R-26 are investigated. In the optical emission spectrum 11 pigments could be identified using ODMR in combination with emission and excitation spectroscopy. The properties of these pigments were analyzed in respect to their interactions with the surrounding molecules. An energy transferfrom the triplet state of Zn-protoporphyrin to the antenna pigment singlet system was proved by DE-ODMR. The wavelength dependence of the zfs parameters within the individual emission band is explained by a model of selective spin-orbit-coupling. In the case of the precursors chlorophyllide a and pheophorbide a, for example, we could show that the pigments are bound to proteins via a hydrogen bond to the ketocarbonylgroup of ring V and that porphyrins with a central Mg-atom have an additional bond via a Fifth ligand of the Mg. © 1983, Walter de Gruyter. All rights reserved.