Dioxetane Intermediates Research Articles

Modification of the photochemical reactivity of α,β-diacetoxystilbene by adsorption onto a fe 3+-doped sepiolite: Comparison with the direct and 2,4,6-triphenylpyrylium-sensitized photolyses

Photolysis of α,β-diacetoxystilbene ( 1) adsorbed onto a Fe 3+-doped sepiolite (Fe-Sp) leads to benzoic acid ( 3), 9,10-diacetoxyphenanthrene ( 5), diphenic anhydride ( 6), and benzil ( 7). While compounds 3, 5 and 6 are also observed in the direct irradiation of 1 in hexane solution, diketone 7 is formed under electron transfer conditions using 2,4,6-triphenylpyrylium tetrafluoroborate as photosensitizer. These results strongly suggest that formation of benzil ( 7) in the photolysis of 1 on Fe-Sp involves the intermediacy of 1 +, generated by single electron transfer from excited 1 to the iron active sites of the clay. In contrast to the unsubstituted stilbene, reactivity of 1 + with ground state molecular oxygen has been established by cyclic voltammetry through the current intensity decrease of the oxidation peak of 1 in the presence of oxygen. Finally, the thermodynamic feasibility of a direct electron transfer pathway between excited 1* and oxygen leading to the formation of a dioxetane intermediate is discussed.

Photosensitized Oxygenation of Lycopene

Irradiation of lycopene in an atmosphere of oxygen and in the presence of a sensitizer (methylene blue) led to the formation of 2-methyl-2-hepten-6-one and apo-6’-lycopenal. A reaction pathway via a dioxetane intermediate is proposed.

Are dioxetanes chemiluminescent intermediates in lipoperoxidation?

Ultraweak chemiluminescence arising from lipoperoxidation has been attributed by several authors to the radiative deactivation of singlet oxygen and triplet carbonyl products. The latter emitters have been suggested to come from annihilation of RO . and ROO . radicals as well as from the thermolysis of dioxetane intermediates formed by (2+2) cycloaddition of 1O 2 to polyunsaturated fatty acids. This article questions possible dioxetane intermediacy in lipoperoxidation, as the literature clearly states that addition of 1O 2 to alpha-hydrogen-containing alphatic olefins yields only the corresponding allylic hydroperoxides. These compounds may undergo dark thermal or Lewis acid-assisted decomposition to the same product obtained from dioxetane cleavage. Here, reexamining the chemiluminescence properties of dioxygenabted tetramethylethylene and linoleic acid and comparing them with those of tetraethyldioxetane, a hindered dioxetane, we corroborate the literature information that only steric hindrance leads to dioxetane formation upon singlet oxygen addition to electron-poor olefins, albeit in very low yields. Proton nuclear magnetic resonance ( 1H-NMR) analysis, quenching by dioxygen and energy transfer studies to 9,10-dibro-monanthracene, as well as gas chromatography (GC) analysis of thriphenylphosphine-treated and untreated photo- and chemically dioxygenated olefins support our final conclusion that dioxetane formation during lipoporoxidation can be safely exluded on the basis of the data presently available.

ChemInform Abstract: Dioxazole and Dioxetane Intermediates in the Thermal Rearrangement of endo‐Peroxides Obtained by Dye‐Sensitized Photooxygenation of 2‐Alkoxyoxazoles.

ChemInformVolume 21, Issue 29 Preparative Organic Chemistry ChemInform Abstract: Dioxazole and Dioxetane Intermediates in the Thermal Rearrangement of endo-Peroxides Obtained by Dye-Sensitized Photooxygenation of 2-Alkoxyoxazoles. M. L. GRAZIANO, M. L. GRAZIANO Dip. Chim. Org. Biol., Univ. "Federico II", I-80134 Napoli, ItalySearch for more papers by this authorM. R. IESCE, M. R. IESCE Dip. Chim. Org. Biol., Univ. "Federico II", I-80134 Napoli, ItalySearch for more papers by this authorG. CIMMINIELLO, G. CIMMINIELLO Dip. Chim. Org. Biol., Univ. "Federico II", I-80134 Napoli, ItalySearch for more papers by this authorR. SCARPATI, R. SCARPATI Dip. Chim. Org. Biol., Univ. "Federico II", I-80134 Napoli, ItalySearch for more papers by this authorM. PARRILLI, M. PARRILLI Dip. Chim. Org. Biol., Univ. "Federico II", I-80134 Napoli, ItalySearch for more papers by this author M. L. GRAZIANO, M. L. GRAZIANO Dip. Chim. Org. Biol., Univ. "Federico II", I-80134 Napoli, ItalySearch for more papers by this authorM. R. IESCE, M. R. IESCE Dip. Chim. Org. Biol., Univ. "Federico II", I-80134 Napoli, ItalySearch for more papers by this authorG. CIMMINIELLO, G. CIMMINIELLO Dip. Chim. Org. Biol., Univ. "Federico II", I-80134 Napoli, ItalySearch for more papers by this authorR. SCARPATI, R. SCARPATI Dip. Chim. Org. Biol., Univ. "Federico II", I-80134 Napoli, ItalySearch for more papers by this authorM. PARRILLI, M. PARRILLI Dip. Chim. Org. Biol., Univ. "Federico II", I-80134 Napoli, ItalySearch for more papers by this author First published: July 17, 1990 https://doi.org/10.1002/chin.199029070Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume21, Issue29July 17, 1990 RelatedInformation

Dioxazole and dioxetane intermediates in the thermal rearrangement of endo-peroxides obtained by dye-sensitized photo-oxygenation of 2-alkoxyoxazoles

Singlet oxygen reacts with 2-alkoxyoxazoles (2c,d) leading to endo-peroxides (1c,d), which easily rearrange into dioxazoles (3c,d) and dioxetanes (4c,d). Both give carbamates (5c,d)via imino anhydrides (7c,d). When the reaction is carried out in alcohols at –60 °C only the dioxetanes (4c,d) are obtained. These compounds, which are the first examples of a bicyclic system of this type, at higher temperatures add methanol to give 2,5-dihydro-oxazoles (9c,d) and already at –60 °C react with diethyl sulphide to give the imines (10c,d).

Characterization of the oxidant generation by inflammatory cells lavaged from rat lungs following acute exposure to ozone

Following exposure to 2 ppm ozone for 4 hr, two distinct effects on rat lung inflammatory cell oxidant generation were observed. TPA- and opsonized zymosan-stimulated O 2 • production by the inflammatory cell population was found to be maximally inhibited 24 hr following ozone exposure. In contrast, luminol-amplified chemiluminescence increased 24 hr following ozone exposure, coinciding with an increase in the percentage of neutrophils and myeloperoxidase in the inflammatory cell population. Supporting the involvement of myeloperoxidase in the enhanced oxidant-generating status of these cells, the luminol-amplified chemiluminescence was found to be azide-, but not superoxide dismutase-inhibitable. Additionally, this cell populatioån was found to generate taurine chloramines, a myeloperoxidase-dependent function which was absent prior to the ozone exposure and also demonstrated enhanced activation of benzo[ a]pyrene-7,8-dihydrodiol to its light-emitting dioxetane intermediate. Addition of myeloperoxidase to control alveolar macrophages resulted in enhanced luminol-amplified chemiluminescence, taurine chloramine generation, and enhanced chemiluminescence from benzo[ a]pyrene-7,8-dihydrodiol demonstrating that, in the presence of myeloperoxidase, alveolar macrophages are capable of supporting myeloperoxidase-dependent reactions. The possibility of such an interaction occurring in vivo is suggested by the detection of myeloperoxidase activity in the cell-free lavagates of ozone-exposed rats. These studies suggest that neutrophils recruited to ozone-exposed lungs alter the oxidant-generating capabilities in the lung which could further contribute to lung injury or to the metabolism of inhaled xenobiotics.

Photochemistry and photobiology without light.

Abstract— This review covers the literature since 1980 on chemically and enzymatically generated electronically excited species. The emphasis lies on triplet states of carbonyl products that are derived from dioxetanes and dioxetanones as precursors or from suitable enzymatic oxygenations. Singlet oxygen, an important excited state species in biological processes, is not explicitly treated. The utilization of triplet excited carbonyl products to promote photochemical and photobiological transformations by energy transfer are of primordial interest and not the photomechanistic behavior, photophysical properties and inherent photochemical reactions of such excited state species. Thus, the coverage concentrates on photodamage of DNA and RNA, the photochemistry of flavins, vitamin D, tryptophan, arachidonic acid, chlorophyll, lipid peroxidation, urocanase activation, excitation of chlorophlasts, and the aerobic oxidation of Schiff bases derived from amino acids and proteins. The potential perspectives of employing authentic dioxetanes and enzymatically generated dioxetane intermediates as effective photon equivalents in photochemotherapy, phototoxicity, photoaffinity labeling and photogenotoxicity are pointed out, in the hope of stimulating more intensive activity in this emerging and novel bioorganic and photobiological field.

The Reaction of Psoralens and Related Benzofurans with Singlet Oxygen An Account of Current Research

AbstractRecent work dealing with the role of singlet oxygen in the biological activity of the psoralens has been reviewed. The reaction of singlet oxygen with benzofurans gives products which result from initially formed dioxetanes. Evidence for dioxetane intermediates was obtained from experiments using diphenyl sulfide as a trapping agent. Psoralen derivatives which contain alkyl or aryl groups on the furan double bond react readily with singlet oxygen to give dioxetane cleavage‐type products. Psoralens which lack furan substituents but possess powerful electrondonating groups in the 5‐ and 8‐positions give rise to peroxidic intermediates which are stable only at low temperature.

A new source of carbon oxides in biochemical systems. Implications regarding dioxetane intermediates

The peroxidase catalyzed aerobic oxidation of aromatic pyruvates produces the aromatic aldehyde, oxalate, CO and CO 2 and a weak light emission. This indicates the preliminary formation of a peroxy anion which can cyclizes to a four-membered ring dioxetane and to a five membered ring α-keto-β-peroxylactone intermediates. The possible importance of this new source of carbon oxides in biological systems is pointed out. The results considerably strengthen the view that a dioxetane is formed in side chain of the plant hormone indoleacetic acid during the oxidation catalyzed by peroxidase.