title: Physical and chemical properties of pyropheophorbide-a methyl ester in ethanol, phosphate buffer and aqueous dispersion of small unilamellar dimyristoyl-L-alpha-phosphatidylcholine vesicles.
abstract: The aggregation process of pyropheophorbide-a methyl ester (PPME), a second-generation photosensitizer, was investigated in various solvents. Absorption and fluorescence spectra showed that the photosensitizer was under a monomeric form in ethanol as well as in dimyristoyl-L-alpha-phosphatidylcholine liposomes while it was strongly aggregated in phosphate buffer. A quantitative determination of reactive oxygen species production by PPME in these solvents has been undertaken by electron spin resonance associated with spin trapping technique and absorption spectroscopy. In phosphate buffer, both electron spin resonance and absorption measurements led to the conclusion that singlet oxygen production was not detectable while hydroxyl radical production was very weak. In liposomes and ethanol, singlet oxygen and hydroxyl radical production increased highly; the singlet oxygen quantum yield was determined to be 0.2 in ethanol and 0.13 in liposomes. The hydroxyl radical production origin was also investigated. Singlet oxygen was formed from PPME triplet state deactivation in the presence of oxygen. Indeed, the triplet state formation quantum yield of PPME was found to be about 0.23 in ethanol, 0.15 in liposomes (too small to be measured in PBS).
authors.affiliation: Department of Physics, B5, University of Liège, B-4000, Liège, Belgium. lisiane.delanaye@ulg.ac.be
authors.forename: Lisiane
authors.initials: L
authors.lastname: Delanaye
authors.forename: Mohamed Ali
authors.initials: MA
authors.lastname: Bahri
authors.forename: Francis
authors.initials: F
authors.lastname: Tfibel
authors.forename: Marie-Pierre
authors.initials: MP
authors.lastname: Fontaine-Aupart
authors.forename: Ange
authors.initials: A
authors.lastname: Mouithys-Mickalad
authors.forename: Bélinda
authors.initials: B
authors.lastname: Heine
authors.forename: Jacques
authors.initials: J
authors.lastname: Piette
authors.forename: Maryse
authors.initials: M
authors.lastname: Hoebeke
mesh_terms: D000042:Absorption; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry* / Q000528:radiation effects; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D000431:Ethanol / Q000737:chemistry*; D017665:Hydroxyl Radical / Q000737:chemistry / Q000528:radiation effects; D007834:Lasers; D008081:Liposomes / Q000737:chemistry* / Q000528:radiation effects; D015394:Molecular Structure; D010710:Phosphates / Q000737:chemistry*; D017319:Photosensitizing Agents / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry* / Q000528:radiation effects; D011789:Quantum Theory; D017382:Reactive Oxygen Species / Q000737:chemistry / Q000528:radiation effects; D012680:Sensitivity and Specificity; D026082:Singlet Oxygen / Q000737:chemistry / Q000528:radiation effects; D013050:Spectrometry, Fluorescence / Q000379:methods; D014867:Water / Q000737:chemistry
chemical_list: D008081:Liposomes; D010710:Phosphates; D017319:Photosensitizing Agents; D011166:Porphyrins; D017382:Reactive Oxygen Species; C452939:pyropheophorbide-a methylester; D014867:Water; D026082:Singlet Oxygen; D017665:Hydroxyl Radical; D000431:Ethanol; D004134:Dimyristoylphosphatidylcholine