title: [Mechanism of quenching of hematoporphyrin and mono-L-aspartyl chlorine e6 triplet states by metronidazole].
abstract: The quenching of the triplet state of hematopophyrin (3HP.) and mono-L-aspartyl chlorine e6, (3MACE.) by metrotlidazole (METRO) ground state, has been investigated in binary mixtures of water and aliphatic alcohol by means of 532 nm laser flash. In water, both 3HP. and 3MACE. quenched by METRO with at rate: kQw = 1.9 x 10(9) M-1.s-1. The quenching is accompanied by the appearance of a transient absorbance near 690 nm. This transient absorbance corresponds to the tetrapyrrole radical-cation formation in result of an electron transfer between 3HP. or 3MACE. and METRO. In neat alcohol, the electron transfer was not observed. In binary mixtures the quenching constant is reduced as the molar fraction of water is decreased. In water, the activation barrier of the quenching is 5.9 kcal/mol for HP and 3.9 kcal/mol for MACE. In going from water to water-alcohol mixtures the energy of activation is practically unchanged. Based on flash photolysis data, and analysis of absorption spectra of METRO we conclude that the electron-acceptor ability of metronidazole essentially depends on the intermolecular interaction with nearby solvent molecules. The mechanism of the quenching is discussed.
authors.affiliation: Laboratoite de Photobiologie, INSERM U312, Museum National d'Histoire Naturelle, Paris, France.
authors.forename: S V
authors.initials: SV
authors.lastname: Kuznetsov
authors.forename: M
authors.initials: M
authors.lastname: Bazin
authors.forename: K M
authors.initials: KM
authors.lastname: L'vov
authors.forename: R
authors.initials: R
authors.lastname: Santus
mesh_terms: D004579:Electron Transport; D006415:Hematoporphyrins / Q000737:chemistry*; D007834:Lasers; D008795:Metronidazole / Q000737:chemistry*; D017319:Photosensitizing Agents / Q000737:chemistry* / Q000494:pharmacology; D010789:Phototherapy; D011166:Porphyrins / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D006415:Hematoporphyrins; D017319:Photosensitizing Agents; D011166:Porphyrins; D008795:Metronidazole; C053434:Talaporfin
vernacular_title: O mekhanizme tusheniia tripletno-vozbuzhdennogo sostoianiia gematoporphirina i mono-L-aspartil khlorina e6 metronidazonom.