Mechanistic Underpinnings of Phototoxicity and Photobluing: Using Organic Photochemistry and DFT to Help Solve Problems in Photomedicine and Photobiology

My research group is interested in mechanistic insights to sort out the reactive oxygen intermediates in photooxidation reactions. We have made contributions to the fields of photooxidation and oxygen-transfer processes, including singlet-oxygen disinfection priming and selective oxidations. In this seminar, one topic to be discussed is the shrinking of a molecular gap (so-to-speak), that is improving of mechanistic understanding of a phototruncation through physical organic chemistry. A photoconversion of heptamethine cyanine to trimethine cyanine will be described which involves singlet oxygen and subsequent 2-carbon and 4-carbon truncations. The latter truncation is a leapfrog strategy that we think proceeds through an allene hydroperoxide intermediate and then a downstream retro-Diels-Alder reaction for a potentially useful photobluing optical tool (∆l_em of ~200 nm). Mechanistic details of this somewhat unusual cyanine phototruncation and comments on dye photobleaching will be provided. Secondly, interfacial studies of reactive oxygen intermediates will be described in the development of a device for mass transfer of singlet oxygen from a superhydrophobic surface. Red light is transmitted through the backside of a superhydrophobic polydimethylsiloxane surface before irradiating a verteporfin sensitizer-coating facing a biofilm-covered tooth or gingival surface. The device shows promising results when applied to a Wistar rat model of periodontitis.