title: Detection and identification of 1-methylethyl and methyl radicals generated by irradiating tea tree (Melaleuca alternifolia) oil with visible light (436 nm) in the presence of flavin mononucleotide and ferrous ion.
abstract: Here, we determined the electron spin resonance (ESR) spectra of standard reaction mixtures (I) containing 25 μM flavin mononucleotide (FMN), 0.018% tea tree (Melaleuca alternifolia) oil, 1.9 M acetonitrile, 20 mM phosphate buffer (pH 7.4), 0.1 M α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN), and 1.0 mM FeSO₄(NH₄)₂SO₄ irradiated with 436 nm visible light (7.8 J/cm²). Prominent ESR signals (αN = 1.58 mT and αHβ = 0.26 mT) were detected, suggesting that free radicals form in the standard reaction. In order to know whether singlet oxygen (¹O₂) is involved in the radical formation or not, ESR measurement was performed for the standard D₂O reaction mixture (I) which contained 25 μM FMN, 0.0036% tea tree oil, 1.9 M acetonitrile-d3, 20 mM phosphate buffer (pH 7.4), 0.1 M 4-POBN and 1.0 mM FeSO₄ in D₂O. The ESR peak height of the standard D₂O reaction increased to 169 ± 24% of the control. Thus, ¹O₂ seems to be involved in the formation of the radicals because D₂O increases the lifetime of singlet oxygen. High-performance liquid chromatography-ESR-mass spectrometry analyses detected 1-methylethyl and methyl radicals in the standard reaction. The radicals appear to form through the reaction of ferrous ion with α-terpinene endoperoxide (ascaridole), which generated from the reaction of α-terpinene with ¹O₂. The 1-methylethyl and methyl radicals may exert a pro-oxidant effect under these conditions.
authors.affiliation: Department of Chemistry, Wakayama Medical University, Wakayama, Japan.
authors.forename: H-M
authors.initials: HM
authors.lastname: Mori
authors.forename: H
authors.initials: H
authors.lastname: Iwahashi
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D005296:Ferrous Compounds / Q000737:chemistry*; D005486:Flavin Mononucleotide / Q000737:chemistry*; D005609:Free Radicals / Q000032:analysis* / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D008027:Light; D011407:Propane / Q000032:analysis* / Q000737:chemistry*; D020947:Tea Tree Oil / Q000737:chemistry* / Q000528:radiation effects*
chemical_list: D005296:Ferrous Compounds; D005609:Free Radicals; D007477:Ions; D020947:Tea Tree Oil; D005486:Flavin Mononucleotide; D011407:Propane