Covalently linked chlorophyll a dimer: A biomimetic model of special pair chlorophyll

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Abstract
The synthesis of a covalent dimer of chlorophyll a which possesses properties strikingly similar to those exhibited by P700 special pair chlorophyll in vivo was described. The covalent dimer is characterized by several spectroscopic techniques. H-bonding nucleophiles, such as H2O, primary alcohols and primary thiols, are effective in generating a species from solutions of 10 .mu.M covalent dimer in hydrophobic solvents which absorbs light near 700 nm. Formation of this in vitro special pair is a rapid, spontaneous process at room temperature. The range of nucleophiles which promote this process suggests that amino acid residues may function in a similar fashion to form P700 in chlorophyll-protein complexes. The photochemical properties of this in vitro special pair mimic those of in vivo P700 species. The 697 nm absorption of the in vitro special pair undergoes photo-bleaching rapidly in the presence of iodine that results in the production of a cation radical which exhibits an ESR signal similar to that of oxidized P700 observed in Chlorella vulgaris.