ORGN 233 |
| Colleen C. Trevithick-Sutton, Department of Chemistry and Biochemistry, University of California at Los Angeles, 607 Charles E Young Dr. East, Los Angeles, CA 90095 and Christopher S. Foote, Department of Chemistry and Biochemistry, University of California, Los Angeles, 607 Charles E. Young Drive East, Box 951569, Los Angeles, CA CA90095. |
| Hypericin is a photosensitizing agent found in various plants, including St. John's Wort, and is currently under investigation in cancer and HIV therapy. Hypericin causes hypericism, a photosensitivity characterized by cellular damage (from singlet oxygen) in light-exposed areas. Darkly pigmented animals do not suffer this damage; eumelanin, a brown to black pigment, protects against hypericism. Pheomelanin, the yellow to red pigment of blondes and redheads, does not protect against hypericism. Our investigations elucidate the photochemical and photophysical mechanisms that lead to this difference in protection. Our experiments show that eumelanin screens light and quenches both the triplet excited state of hypericin and singlet oxygen itself. This multi-pronged defense against damage from light-activated hypericin suggests how dark-skinned animals can ingest hypericin without noticeable harm. Pheomelanins screen light and quench triplet hypericin and singlet oxygen much less than eumelanin. Results from biosynthesized and extracted pheomelanins will be discussed. |
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Physical Organic Chemistry: Calculations, Mechanisms, Photochemistry, and High-Energy Species
8:00 AM-12:00 PM, Tuesday, March 30, 2004 Anaheim Convention Center -- 303A, Oral
Division of Organic Chemistry |