title: Photogeneration of singlet oxygen (1O2) and free radicals (Sen*-, O2*-) by tetra-brominated hypocrellin B derivative.
abstract: To improve photodynamic activity of the parent hypocrellin B (HB), a tetra-brominated HB derivative (compound 1) was synthesized in high yield. Compared with HB, compound 1 has enhanced red absorption and high molar extinction coefficients. The photodynamic action of compound 1, especially the generation mechanism and efficiencies of active species (Sens*-, O2*- and 1O2) were studied using electron paramagnetic resonance (EPR) and spectrophotometric methods. In the deoxygenated DMSO solution of compound 1, the semiquinone anion radical of compound 1 is photogenerated via the self-electron transfer between the excited and ground state species. The presence of electron donor significantly promotes the reduction of compound 1. When oxygen is present, superoxide anion radical (O2*-) is formed via the electron transfer from Sens*- to the ground state molecular oxygen. The efficiencies of Sens*- and O2*- generation by compound 1 are about three and two times as much as that of HB, respectively. Singlet oxygen (1O2) can be produced via the energy transfer from triplet compound 1 to ground state oxygen molecules. The quantum yield of singlet oxygen (1O2) is 0.54 in CHCl3 similar to that of HB. Furthermore, it was found that the accumulation of Sens*- would replace that of O2*- or 1O2 with the depletion of oxygen in the sealed system.
authors.affiliation: Centerfor Molecular Science, Institute of Chemistry, The Chinese Academy of Sciences, Beijing, People's Republic of China. jhma2@yahoo.com
authors.forename: J
authors.initials: J
authors.lastname: Ma
authors.forename: L
authors.initials: L
authors.lastname: Jiang
mesh_terms: D016227:Benzoquinones / Q000737:chemistry; D001966:Bromine / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry*; D008027:Light; D010569:Perylene / Q000031:analogs & derivatives* / Q000737:chemistry*; D017319:Photosensitizing Agents / Q000737:chemistry*; D011809:Quinones / Q000737:chemistry*; D026082:Singlet Oxygen / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013481:Superoxides / Q000737:chemistry; D013997:Time Factors
chemical_list: D016227:Benzoquinones; D005609:Free Radicals; D017319:Photosensitizing Agents; D011809:Quinones; D013481:Superoxides; D026082:Singlet Oxygen; C025232:semiquinone radicals; D010569:Perylene; D001966:Bromine; C064522:hypocrellin B