title: Excited singlet molecular O₂(¹Δg) is generated enzymatically from excited carbonyls in the dark.
abstract: In mammalian tissues, ultraweak chemiluminescence arising from biomolecule oxidation has been attributed to the radiative deactivation of singlet molecular oxygen [O2 ((1)Δg)] and electronically excited triplet carbonyl products involving dioxetane intermediates. Herein, we describe evidence of the generation of O2 ((1)Δg) in aqueous solution via energy transfer from excited triplet acetone. This involves thermolysis of 3,3,4,4-tetramethyl-1,2-dioxetane, a chemical source, and horseradish peroxidase-catalyzed oxidation of 2-methylpropanal, as an enzymatic source. Both sources of excited carbonyls showed characteristic light emission at 1,270 nm, directly indicative of the monomolecular decay of O2 ((1)Δg). Indirect analysis of O2 ((1)Δg) by electron paramagnetic resonance using the chemical trap 2,2,6,6-tetramethylpiperidine showed the formation of 2,2,6,6-tetramethylpiperidine-1-oxyl. Using [(18)O]-labeled triplet, ground state molecular oxygen [(18)O2 ((3)Σg(-))], chemical trapping of (18)O2 ((1)Δg) with disodium salt of anthracene-9,10-diyldiethane-2,1-diyl disulfate yielding the corresponding double-[(18)O]-labeled 9,10-endoperoxide, was detected through mass spectrometry. This corroborates formation of O2 ((1)Δg). Altogether, photoemission and chemical trapping studies clearly demonstrate that chemically and enzymatically nascent excited carbonyl generates (18)O2 ((1)Δg) by triplet-triplet energy transfer to ground state oxygen O2 ((3)Σg(-)), and supports the long formulated hypothesis of O2 ((1)Δg) involvement in physiological and pathophysiological events that might take place in tissues in the absence of light.
authors.affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05513-970, CP 26077, São Paulo, SP, Brazil.
authors.forename: Camila M
authors.initials: CM
authors.lastname: Mano
authors.affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05513-970, CP 26077, São Paulo, SP, Brazil.
authors.forename: Fernanda M
authors.initials: FM
authors.lastname: Prado
authors.affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05513-970, CP 26077, São Paulo, SP, Brazil.
authors.forename: Júlio
authors.initials: J
authors.lastname: Massari
authors.affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05513-970, CP 26077, São Paulo, SP, Brazil.
authors.forename: Graziella E
authors.initials: GE
authors.lastname: Ronsein
authors.affiliation: Departamento de Bioquímica e Biologia Molecular, Setor de Ciências Biológicas, Universidade Federal do Paraná, Curitiba, PR, Brazil.
authors.forename: Glaucia R
authors.initials: GR
authors.lastname: Martinez
authors.affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05513-970, CP 26077, São Paulo, SP, Brazil.
authors.forename: Sayuri
authors.initials: S
authors.lastname: Miyamoto
authors.affiliation: Institut Nanosciences et Cryogénie, CEA/Grenoble, F-38054 Grenoble Cedex 9, France.
authors.forename: Jean
authors.initials: J
authors.lastname: Cadet
authors.affiliation: Institute of Biochemistry and Molecular Biology I, and Leibniz Research Institute for Environmental Medicine, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Sies
authors.affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05513-970, CP 26077, São Paulo, SP, Brazil.
authors.forename: Marisa H G
authors.initials: MH
authors.lastname: Medeiros
authors.affiliation: 1] Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05513-970, CP 26077, São Paulo, SP, Brazil [2] Departamento de Ciências Exatas e da Terra, Instituto de Ciências Ambientais, Químicas e Farmacêuticas, Universidade Federal de São Paulo, SP, Brazil.
authors.forename: Etelvino J H
authors.initials: EJ
authors.lastname: Bechara
authors.affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05513-970, CP 26077, São Paulo, SP, Brazil.
authors.forename: Paolo
authors.initials: P
authors.lastname: Di Mascio
mesh_terms: D000096:Acetone / Q000737:chemistry*; D000447:Aldehydes / Q000737:chemistry*; D003624:Darkness; D004578:Electron Spin Resonance Spectroscopy; D006571:Heterocyclic Compounds / Q000737:chemistry*; D006573:Heterocyclic Compounds, 1-Ring; D006735:Horseradish Peroxidase / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D026082:Singlet Oxygen / Q000737:chemistry*; D012996:Solutions; D013113:Spin Labels; D019097:Spin Trapping; D014867:Water / Q000737:chemistry
chemical_list: D000447:Aldehydes; D006571:Heterocyclic Compounds; D006573:Heterocyclic Compounds, 1-Ring; D012996:Solutions; D013113:Spin Labels; D014867:Water; D000096:Acetone; C079142:1,2-dioxetane; D026082:Singlet Oxygen; C017439:isobutyraldehyde; D006735:Horseradish Peroxidase; D010100:Oxygen
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