title: Mechanism of Photochemical O-Atom Exchange in Nitrosamines with Molecular Oxygen.
abstract: The detection of an oxygen-atom photoexchange process of N-nitrosamines is reported. The photolysis of four nitrosamines (N-nitrosodiphenylamine 1, N-nitroso-N-methylaniline 2, N-butyl-N-(4-hydroxybutyl)nitrosamine 3, and N-nitrosodiethylamine 4) with ultraviolet light was examined in an (18)O2-enriched atmosphere in solution. HPLC/MS and HPLC-MS/MS data show that (18)O-labeled nitrosamines were generated for 1 and 2. In contrast, nitrosamines 3 and 4 do not exchange the (18)O label and instead decomposed to amines and/or imines under the conditions. For 1 and 2, the (18)O atom was found not to be introduced by moisture or by singlet oxygen [(18)((1)O2 (1)Δg)] produced thermally by (18)O-(18)O labeled endoperoxide of N,N'-di(2,3-hydroxypropyl)-1,4-naphthalene dipropanamide (DHPN(18)O2) or by visible-light sensitization. A density functional theory study of the structures and energetics of peroxy intermediates arising from reaction of nitrosamines with O2 is also presented. A reversible head-to-tail dimerization of the O-nitrooxide to the 1,2,3,5,6,7-hexaoxadiazocane (30 kcal/mol barrier) with extrusion of O═(18)O accounts for exchange of the oxygen atom label. The unimolecular cyclization of O-nitrooxide to 1,2,3,4-trioxazetidine (46 kcal/mol barrier) followed by a retro [2 + 2] reaction is an alternative, but higher energy process. Both pathways would require the photoexcitation of the nitrooxide.
authors.affiliation: †Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05508-000, São Paulo, Brazil.|‡Department of Chemistry and Graduate Center, Brooklyn College, City University of New York, Brooklyn, New York 11210, United States.
authors.forename: Marilene Silva
authors.initials: MS
authors.lastname: Oliveira
authors.affiliation: ‡Department of Chemistry and Graduate Center, Brooklyn College, City University of New York, Brooklyn, New York 11210, United States.
authors.forename: Ashwini A
authors.initials: AA
authors.lastname: Ghogare
authors.affiliation: ‡Department of Chemistry and Graduate Center, Brooklyn College, City University of New York, Brooklyn, New York 11210, United States.
authors.forename: Inna
authors.initials: I
authors.lastname: Abramova
authors.affiliation: §Department of Natural Sciences, Baruch College, City University of New York, New York, New York 10010, United States.
authors.forename: Edyta M
authors.initials: EM
authors.lastname: Greer
authors.affiliation: †Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05508-000, São Paulo, Brazil.
authors.forename: Fernanda Manso
authors.initials: FM
authors.lastname: Prado
authors.affiliation: †Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05508-000, São Paulo, Brazil.
authors.forename: Paolo
authors.initials: P
authors.lastname: Di Mascio
authors.affiliation: ‡Department of Chemistry and Graduate Center, Brooklyn College, City University of New York, Brooklyn, New York 11210, United States.
authors.forename: Alexander
authors.initials: A
authors.lastname: Greer
mesh_terms: D000588:Amines / Q000737:chemistry*; D015394:Molecular Structure; D009602:Nitrosamines / Q000737:chemistry*; D055668:Photochemical Processes; D026082:Singlet Oxygen / Q000737:chemistry*; D053719:Tandem Mass Spectrometry; D014466:Ultraviolet Rays
chemical_list: D000588:Amines; D009602:Nitrosamines; D026082:Singlet Oxygen; C014102:N-methyl-N-nitrosoaniline; C023649:N-nitrosodiphenylamine