title: Photoreduction of oxoisoaporphines by amines: laser flash and steady-state photolysis, pulse radiolysis, and TD-DFT studies.
abstract: Photoreduction of oxoisoaporphine (OIA) (1-aza-benzo-[de]anthracen-7-one) and its 5-methoxy (5-MeO-OIA) derivative by selected amines (two non-alpha-hydrogen-donating amines (1,4-diaza[2.2.2]-bicyclooctane (DABCO) and 2,2,6,6-tetramethylpiperidine (TMP)) and three alpha-hydrogen-donating amines (triethylamine (TEA), diethylmethylamine (DEMA), and dimethylethylamine (DMEA))) has been studied in deaerated neat acetonitrile solutions using laser flash and steady-state photolysis. The triplet excited states of OIA and 5-MeO-OIA are characterized by intense absorption maxima located at lambda(max) = 450 nm and lifetimes of 34.7 +/- 0.5 and 44.6 +/- 0.4 micros, respectively. In the presence of tertiary amines, both triplets are quenched with a rate constant that varies from the near diffusion limit (>10(9) M(-1) s(-1)) to a rather low value (approximately 10(7) M(-1) s(-1)) and shows the expected dependence on the reduction potential for one-electron-transfer reactions. The transient absorption spectra observed after quenching of the respective triplet states are characterized by distinct absorption maxima located at lambda(max) = 480 and 490 nm (for OIA and 5-MeO-OIA, respectively) and accompanied by broad shoulders in the range of 510-560 nm. They were assigned to either solvent-separated radical ion pairs and/or isolated radical anions. In the presence of alpha-hydrogen-donating amines these species undergo protonation that leads to the formation of neutral hydrogenated radicals A1H(*)/A2H(*) with two possible sites of protonation, N and O atoms. Pulse radiolysis and molecular modeling together with TD-DFT calculations were used to support the conclusions about the origin of transients.
authors.affiliation: Departamento de Química Orgánica y Fisicoquímica, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Casilla 223, Santiago 1, Chile. jrfuente@ciq.uchile.cl
authors.forename: Julio R
authors.initials: JR
authors.lastname: De la Fuente
authors.forename: Christian
authors.initials: C
authors.lastname: Aliaga
authors.forename: Cristian
authors.initials: C
authors.lastname: Poblete
authors.forename: Gerald
authors.initials: G
authors.lastname: Zapata
authors.forename: Carolina
authors.initials: C
authors.lastname: Jullian
authors.forename: Claudio
authors.initials: C
authors.lastname: Saitz
authors.forename: Alvaro
authors.initials: A
authors.lastname: Cañete
authors.forename: Gabriel
authors.initials: G
authors.lastname: Kciuk
authors.forename: Eduardo
authors.initials: E
authors.lastname: Sobarzo-Sanchez
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Bobrowski
mesh_terms: D000042:Absorption; D000588:Amines / Q000737:chemistry*; D001060:Aporphines / Q000737:chemistry*; D004579:Electron Transport; D005609:Free Radicals / Q000737:chemistry; D006865:Hydrogenation; D007700:Kinetics; D007834:Lasers; D009682:Magnetic Resonance Spectroscopy; D010782:Photolysis; D011675:Pulse Radiolysis; D011789:Quantum Theory; D012717:Sesquiterpenes; D013729:Terpenes / Q000737:chemistry; D000094162:Phytoalexins
chemical_list: D000588:Amines; D001060:Aporphines; D005609:Free Radicals; D012717:Sesquiterpenes; D013729:Terpenes; C081279:aporphine; D000094162:Phytoalexins