Population of the triplet states of bacteriorhodopsin and of related model compounds by intramolecular energy transfer.
In variance with chlorophyll-based photosynthetic pigments, the triplet states of rhodopsins, either visual or photosynthetic, have not been observed experimentally. This is due to the ultrafast crossing from S1 to S0, which effectively competes with intersystem crossing to the triplet (T1) state. In order to populate T1 indirectly, laser photolysis experiments are performed with model protonated Schiff bases of retinal in solution, in which both inter- and intramolecular energy transfer to the polyene chromophore are carried out from an appropriate triplet energy donor. The experiments are then extended to bacteriorhodopsin (bR) by detaching the native retinal chromophore from the protein-binding site and replacing it by an analogous (synthetic) protonated Schiff base polyene, attached in a nonconjugated way to a naphthone triplet donor. Pulsed laser excitation of the latter moiety led, for the first time, to the observation of the triplet state of a rhodopsin. Possible locations and roles of the T1 state in bR and in visual pigments are discussed briefly.
Friedman
N
N
Weizmann Institute of Science, Rehovot, Israel.
Sheves
M
M
Ottolenghi
M
M
D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D002734:Chlorophyll / Q000737:chemistry; D004735:Energy Transfer; D008956:Models, Chemical; D010782:Photolysis; D012545:Schiff Bases / Q000737:chemistry; D012996:Solutions
D012545:Schiff Bases; D012996:Solutions; D002734:Chlorophyll; D001436:Bacteriorhodopsins