Model Systems for Observing Photoredox Reactions of Carotenoids

F. FUNGO, L. OTERO, J. J. SILBER AND L. SERENO, A. MOORE, T. MOORE AND D. GUST G. STEINBERG-YFRANCH, P. A. LIDELL, S. C. HUNG, H. IMAHORI, S. CARDOSO, D. TATMAN, A. N. MACPHERSON

PURE AND APPLIED CHEMISTRY

INT UNION PURE APPLIED CHEMISTRY

Año: 1997 vol. 69 p. 2111 - 2120

0033-4545

Abstract: Two approaches to eliciting photoelectrochemical reactions from carotenoids are beingpursued. One uses LB films of amphipathic carotenoids deposited on semiconductingelectrodes which are immersed in electrolytes containing electron donors or acceptors.Photocurrents are observed and their action spectra implicate the excited carotenoid pigment,possibly in an aggregated form, as the photoactive species. An example of the second approachis a molecular dyad consisting of a carotenoid covalently linked to Gjo. Excitation of thecarotenoid moiety generates a charge-separated species in high yield. More complex systemsinclude a molecular mad (C-P-Q) containing a porphyrin moiety (P) linked to a quinone (Q) andto a carotenoid (C). Triads of this type have been incorporated unidirectionally into lipid bilayermembranes. Time-resolved fluorescence experiments reveal that excitation of C-P-Q in themembrane leads to electron transfer from 1P to give C-P´+-Q". A subsequent electron transferfrom C to P" yields C´+-P-Q´-. In this species the carotenoid pigment acts as a molecular wireto conduct charge across the membrane. In the presence of appropriate cofactors, this systemtranslocates protons across the bilayer lipid membrane and generates proton motive force