title: Transient phenomena in the pulse radiolysis of oxoisoaporphine derivatives in acetonitrile.
abstract: The absorption-spectral and kinetic behavior of radical ions and triplet states of two oxoisoaporphine derivatives, 2,3-dihydrooxoisoaporphine (2,3-DHOA) and 5-methoxy-2,3-dihydrooxoisoaporphine (5-MeO-2,3-DHOA), have been studied by UV-vis spectrophotometric pulse radiolysis in a neat acetonitrile saturated with argon and oxygen at room temperature. The radical anions of 2,3-DHOA and 5-MeO-2,3-DHOA are characterized by intense absorption maxima located at lambda max = 605 and 590 nm, with molar absorption coefficients 605 = 5600 M (-1) cm (-1) and 590 = 4900 M (-1) cm (-1), respectively. Both radical anions decay via first-order kinetics with the rate constants in the range (1.5-2.6) x 10 (5) s (-1), predominantly through protonation by adventitious water forming neutral-hydrogenated radicals. Oxygen insensitive, the radical cations of 2,3-DHOA are characterized by a strong nondescript absorption band with no distinct lambda max in the range 350-450 nm. On the other hand, the radical cations of 5-MeO-2,3-DHOA are characterized by the distinctive absorption band with lambda max = 420 nm. The experimental spectra of the neutral-hydrogenated radicals and the triplet excited states derived from 2,3-DHOA and 5-MeO-2,3-DHOA are in accordance with the spectra observed previously during laser flash photolysis ( De la Fuente, J. R. ; et al. J. Phys. Chem. 2005, 109, 5897 ). Most of the transient spectra generated radiolytically are adequately reproduced by quantum mechanical semiempirical PM3 and ZINDO/S methods.
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: 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: D000097:Acetonitriles / Q000737:chemistry*; D001060:Aporphines / Q000138:chemical synthesis / Q000737:chemistry*; D001128:Argon / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry; D007700:Kinetics; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry; D011675:Pulse Radiolysis / Q000379:methods; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D012996:Solutions / Q000737:chemistry; D014315:Triterpenes
chemical_list: C468596:2,3-dihydroxy-24-nor-4(23),12-oleanadien-28-oic acid; C533474:5-methoxy-2,3-dihydrooxoisoaporphine; D000097:Acetonitriles; D001060:Aporphines; D005609:Free Radicals; D012996:Solutions; D014315:Triterpenes; D001128:Argon; D010100:Oxygen; C032159:acetonitrile