Photodynamics of the bacteriochlorophyll-carotenoid system. 1. Bacteriochlorophyll-photosensitized oxygenation of beta-carotene in acetone

Carotenoids are well-known physical quenchers of chlorophyll excited states and reactive oxygen species both in vivo and in vitro. They may also be in volved in chemical quenching undergoing, e.g, isomerizations or oxidations. We have found that p-carotene (Car) in aerobic acetone is rapidly oxygenat ed under strong illumination with red light (lambda (exc) greater than or e qual to 630 nm) in the presence of bacteriopheophytin a. At the same time t he photosensitizer undergoes only slight (< 10%) photodegradation, By prepa rative high-performance liquid chromatography as many as seven major produc ts of oxygen attachment to Car have been isolated. Their molecular masses s how that Car sequentially accumulates up to six oxygen atoms while its C-40 -skeleton remains intact.