Search

The spectral deconvolution of the bacteriochlorophyll Qx band serves to estimate thermodynamic parameters of Chl-ligand interactions in solution and to disclose differences between the R and S diastereoisomeric forms of the pigment in coordination properties. The steric control of ligation relates well to the partial diastereoselectivity of chlorophyll self-assembly and the very high diastereoselectivity of the ligation of chlorophylls in photosynthetic proteins.

A simple reconstitution technique is developed and then applied to prepare a series of light-harvesting antenna 1 (LH1) complexes with a programmed carotenoid composition, not available from native photosynthetic membranes. The reconstituted LH1 complexes resemble the native antenna, isolated from wild-type rhodospirillum rubrum, but their coloration is entirely determined by carotenoid.

Research has been conducted on the replacement of the central Mg in chlorophylls by Ni. The substitution method of the native bacteriochlorophyll a by Ni-bacteriochlorophyll a in the light harvesting antenna from the purple bacteria Rhodobacter sphaeroides core complex is described.

Research has been conducted on the purple photosynthetic bacterium Rhodobacter sphaeroides. The identification of the genes that have been involved in the terminal bacteriochlorophyll biosynthesis esterification stage is described.

The preparation and spectral identification of metal-substituted bacteriochlorophylls (BChl) were explained and correlated to the properties and characteristics of the central metal. BChl and their free bases, bacteriopheophytins (BPhe), are vital to photosynthesis and utilized as photosensitizers in tumor phototherapy. Copper, zinc and cadmium ions can be introduced into the BChl and BPhe through transmetalation. The metal-substituted BChl produced spectroscopic information not usually obtained from porphyrin and chlorins.

The redox potentials (RP) and electronic transition energies (TE) of metal-substituted bacteriochlorophylls (BChl) were studied through transmetalation of bacteriopheophytin (BPhe). Different metal ions were inserted into BPhe and its derivatives. Alterations in RP and TE of metal-substituted BChls resulted to changes in the electronegativity and covalent radius of the central metal. The alterations were induced by electrostatic interactions between the efficient charge in the molecule's center and the electron densities in the frontier molecular orbitals.

A study was conducted to investigate the pigment coordination state in bacterial photosynthetic antenna LH1 by applying the correlation of the Q(sub X) transition energy with the coordination state of the central metal in bacteriochlorophyll. The deconvolution of the Q(sub X) envelop in LH1 reveals that the band is the sum of two transitions showing that a significant fraction of hexacoordinated bacteriochloroplyll is present in the complex.

The chapter gives an overview about chlorophylls involved in oxygenic photosynthesis and summarizes the most recent findings about these key photosynthetic pigments. First, a general description of structural, stereochemical and photophysical features of chlorophylls is given, as this is relevant to their functioning. Next, the details of the electronic structure and the mechanisms contributing to fine tuning of chlorophylls in photosynthetic apparatus are discussed, including the roles of conservative structural elements of these molecules. Briefly, also the use and results of quantum chemical approaches are described. Further, the biosynthesis and biodegradation of chlorophylls is shortly reviewed, followed by a survey of the photosensitizing and photoprotective functions of chlorophylls, the commercial and therapeutic applications of the pigments and their impact on animal organisms. [ABSTRACT FROM AUTHOR]