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EXPERIMENTAL and THEORETICAL STUDIES OF SCHIFF BASE CHLOROPHYLLS
Author(s) -
Maggiora Linda L.,
Petke James D.,
Gopal Dama,
Iwamoto Reynold T.,
Maggiora Gerald M.
Publication year - 1985
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1985.tb03549.x
Subject(s) - bathochromic shift , hypsochromic shift , protonation , chemistry , p680 , schiff base , photochemistry , moiety , crystallography , stereochemistry , fluorescence , organic chemistry , ion , photosystem i , photosystem ii , biochemistry , physics , photosynthesis , quantum mechanics
— A protonated Schiff base of Ni (II)‐pyrochlorophyll a has been synthesized which exhibits a reversible bathochromic shift of 504 cm ‐1 relative to Ni (II)‐pyrochlorophyll a. The magnitude of this shift lies between those observed for P700 and P680, the photoactive pigments of photosystems I and II in plants. Cyclic voltammetric measurements show that the protonated Schiff base is about 0.2 V more difficult to oxidize than its unprotonated form. These results suggest that a protonated Schiff base may be a better model for P680 than, as was originally assumed, for P700. In addition, the results of solvent and counterion effect studies show that microenvironmental perturbations in the neighborhood of the protonated Schiff base moiety are unlikely to induce further spectral shifts. Ab initio quantum mechanical calculations show a small hypsochromic shift rather than the observed bathochromic one, and the reasons for this discrepancy are discussed.