title: N-alkoxyheterocycles as irreversible photooxidants.
abstract: Irreversible photooxidation based on N-O bond fragmentation is demonstrated for N-methoxyheterocycles in both the singlet and triplet excited state manifolds. The energetic requirements for bond fragmentation are studied in detail. Bond fragmentation in the excited singlet manifold is possible for ππ* singlet states with energies significantly larger than the N-O bond dissociation energy of ca 55 kcal mol(-1). For the nπ* triplet states, N-O bond fragmentation does not occur in the excited state for orbital overlap and energetic reasons. Irreversible photooxidation occurs in the singlet states by bond fragmentation followed by electron transfer. Irreversible photooxidation occurs in the triplet states via bimolecular electron transfer to the donor followed by bond fragmentation. Using these two sensitization schemes, donors can be irreversibly oxidized with oxidation potentials ranging from ca 1.6-2.2 V vs SCE. The corresponding N-ethylheterocycles are characterized as conventional reversible photooxidants in their triplet states. The utility of these sensitizers is demonstrated by irreversibly generating the guanosine radical cation in buffered aqueous solution.
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ.
authors.forename: Zofia M
authors.initials: ZM
authors.lastname: Wosinska
authors.forename: Faye L
authors.initials: FL
authors.lastname: Stump
authors.forename: Rajeev
authors.initials: R
authors.lastname: Ranjan
authors.forename: Edward D
authors.initials: ED
authors.lastname: Lorance
authors.forename: Genita N
authors.initials: GN
authors.lastname: Finley
authors.forename: Priya P
authors.initials: PP
authors.lastname: Patel
authors.forename: Muzamil A
authors.initials: MA
authors.lastname: Khawaja
authors.forename: Katie L
authors.initials: KL
authors.lastname: Odom
authors.forename: Wolfgang H
authors.initials: WH
authors.lastname: Kramer
authors.forename: Ian R
authors.initials: IR
authors.lastname: Gould
mesh_terms: D008401:Gas Chromatography-Mass Spectrometry; D006571:Heterocyclic Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D016877:Oxidants / Q000737:chemistry*; D055668:Photochemical Processes
chemical_list: D006571:Heterocyclic Compounds; D016877:Oxidants