Singlet Oxygen Oxidation Research Articles

Effects of catechins and green tea extract on the photosensitized singlet oxygen oxidation of linoleic acid in a model system as compared with α-tocopherol

Effects of catechins and green tea extract (GTE) on the photosensitized singlet oxygen oxidation of linoleic acid were studied. Epigallocatechin gallate (EGCG) showed the highest antioxidant activity, followed by gallocatechin gallate, epigallocatechin, and epicatechin in a decreasing order. α-Tocopherol showed strong antioxidative activity at the initial oxidation stage, but its antioxidative property rapidly decreased with illumination time. EGCG showed significantly stronger antioxidative activity than α-tocopherol at the later oxidation stage (p<0.05) due to the higher stability of EGCG. Unlike α-tocopherol, GTE possessed strong antioxidative activity even at the later oxidation stage. Overall, GTE was a better antioxidant than α-tocopherol for the protection of linoleic acid from singlet oxygen oxidation. Electron spin resonance (ESR) spectroscopy and visible-spectroscopic data showed unambiguous evidences that the protective activity of GTE against the photosensitized oxidation of linoleic acid was due to the singlet oxygen quenching mechanism.

Effects of unrefined vegetable oil addition on the flavor acceptability and oil oxidation of tuna oil enriched emulsion under singlet oxygen

Addition effects of unrefined vegetable oil on the fishy flavor and singlet oxygen oxidation of tuna oil enriched O/W emulsion were studied by sensory evaluation and determining hydroperoxide contents and headspace oxygen consumption. Emulsion consisted of canola and tuna oil (2:1, w/w), acetic acid, egg yolk, and with/without unrefined oil (olive, sesame, mustard, or perilla oil). Singlet oxygen was produced by chlorophyll b under 1,700 lx. Addition of sesame oil inverted negative response on the flavor of tuna oil enriched emulsion to positive one, and addition of perilla or mustard oil decreased unacceptability on the emulsion flavor. Oxidative stability of oil under singlet oxygen was the highest in the emulsion added with mustard oil, but olive oil addition decreased it. Therefore, health-beneficial tuna oil enriched emulsion with acceptable flavor and oxidative stability could be made by addition of good-flavored unrefined sesame and mustard oils with high amount of natural antioxidants.

Effects of phospholipids on the antioxidant activity of α-tocopherol in the singlet oxygen oxidation of canola oil

This study evaluated the effects of phosphatidylcholine (PC) or phosphatidylethanolamine (PE) on the antioxidative activity of α-tocopherol during oxidation of canola oil by singlet oxygen at 10°C for seven hours. Singlet oxygen was produced by chlorophyll b (4 ppm) under 1,700 lux. The oxidation of oil was evaluated by headspace oxygen consumption by gas chromatography and peroxide values (POVs). Concentrations of PC, PE, chlorophyll, and α-tocopherol were determined by HPLC. PC and PE protected chlorophyll from degradation, but they accelerated the degradation of α-tocopherol under singlet oxygen. Contents of PC and PE did not change for seven hours under singlet oxygen. α-Tocopherol significantly lowered POV and headspace oxygen consumption of canola oil under singlet oxygen, and its antioxidant activity was increased by the co-presence of PC and PE. PC and PE increased chemical quenching of singlet oxygen by tocopherol in decreasing the oil oxidation.

Interaction of Phosphatidylcholine and α‐Tocopherol on the Oxidation of Sunflower Oil and Content Changes of Phosphatidylcholine and Tocopherol in the Emulsion under Singlet Oxygen

Interaction of phosphatidylcholine (PC) and α-tocopherol (α-Toc) on the oxidation of oil in the emulsion consisting of sunflower oil and water under singlet oxygen at 25 °C was studied by determining peroxide value (PV) and conjugated dienoic acid (CDA) contents. Singlet oxygen was produced by chlorophyll b under 1700 lux. Single addition of PC or α-Toc decreased the values of peroxides and CDAs of oil in the emulsion via singlet oxygen quenching. PC and α-Toc showed simply additive interaction in decreasing the singlet oxygen oxidation of oil in the emulsion. α-Toc was a physical quencher of singlet oxygen in the emulsion, but PC involved chemical quenching in the antioxidant action. Chlorophyll and PC contents were decreased in the emulsion under singlet oxygen, while α-Toc was not. α-Toc protected chlorophyll and PC from degradation, and was a more important component than PC in the oil oxidation under singlet oxygen in the emulsion.

Formation of Diaryl Telluroxides and Tellurones by Photosensitized Oxygenation of Diaryl Tellurides

Aerobic oxygenation of diaryl tellurides under photosensitized conditions is investigated. Unlike Ph(2)S and Ph(2)Se, reaction of diaryl tellurides with singlet oxygen proceeds smoothly to yield diaryl telluroxides and the corresponding tellurones. The product distribution is largely affected by the substrate and the reaction conditions. In particular, the photooxygenation of bulky diaryl tellurides principally produces tellurones. The results of a series of trapping experiments suggest that the diaryl telluroxides can capture transient intermediates such as Me(2)S(+)OO(-) and Ar(2)Te(+)OO(-), generated in the singlet oxygen oxidation of chalcogenides, to yield diaryl tellurones, and therefore it may be the most potent precursors of the tellurones.

ChemInform Abstract: Singlet Oxygen Oxidation of Substituted Furans to 5-Hydroxy-2(5H)- furanone.

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ChemInform Abstract: Spongiabutenolides A-D: Minor γ-Hydroxybutenolide Diterpenoids from a Philippines Spongia sp.

Abstract Four novel diterpenoids, spongiabutenolides A – D (2–5), all of which contain a γ-hydroxybutenolide moiety, have been isolated from a Philippines marine sponge of the genus Spongia. The structures of spongiabutenolides A – D (2–5) and the methyl esters 6 and 7 were elucidated by interpretation of spectral data. Spongiabuteonolide A (2) was synthesized from spongia-13(16),14-diene-19-oic acid (1) by singlet oxygen oxidation.

Development of [60] fullerene supported on silica catalysts for the photo-oxidation of alkenes

Simple or successive incipient wetness impregnation followed by heating at 180 °C is proved an efficient preparation method for dispersing effectively onto the silica surface various amounts of C 60 in the range 1–4% (w/w). BET, XRD, DRS, TGA, microelectrophoresis and photoluminescence have been used to characterize the photocatalysts prepared. A high dispersion was obtained for the quite stable supported C 60 phase, comprised mainly from relatively small or medium size C 60 clusters/aggregates. The photocatalytic activity was assessed in the singlet oxygen oxidation of alkenes by examining the photo-oxygenation of 2-methyl-2-heptene as a probe reaction. The catalytic tests were carried out at 0–5 °C in CH 3CN, under oxygen atmosphere and using a 300 W xenon lamp as the light source. The heterogeneous catalysts obtained were proved to be active in the photocatalytic oxidation of olefins via a 1O 2 ene reaction. The catalysts exhibited significant conversion, turnover number and turnover frequency values, substantially higher than those achieved over the unsupported C 60. The conversion increases with the amount of the supported C 60 up to a value equal to 3% (w/w) and then it decreases whereas turnover number and turnover frequency decreases monotonically as the amount of the supported C 60 increases. The easy separation of these solid catalysts from the reaction mixture, the high activity and stability as well as the retained activity in subsequent catalytic cycles, make these supported catalysts suitable for a small-scale synthesis of fine chemicals.

Changes of Headspace Volatiles in Milk with Riboflavin Photosensitization

Effects of fluorescent light, riboflavin, ascorbic acid, sodium azide, and butylated hydroxyanisole (BHA) on the volatiles in milk at 4 degrees C were determined using a combination of headspace-solid phase microextraction (HS-SPME), gas chromatography (GC), and mass spectrometry (MS). Pentanal, hexanal, heptanal, and dimethyl disulfide were formed only in the milk stored under light and increased significantly as the duration of light exposure increased from 0 to 8 h and the concentration of added riboflavin increased from 5 to 50 ppm (P < 0.05). As fat content in milk increased, peak areas of pentanal, hexanal, and heptanal increased significantly (P < 0.05) while those of dimethyl disulfide did not change significantly (P > 0.05). Sodium azide prevented the formation of dimethyl disulfide in milk, implying that dimethyl disulfide can be formed through singlet oxygen oxidation (type II pathway). Addition of ascorbic acid and BHA reduced the formation of hexanal, heptanal, and dimethyl disulfide significantly (P < 0.05). Generation mechanisms of pentanal seem to be different from those of hexanal and heptanal in milk. Both singlet oxygen oxidation (type II pathway) and free radicals (type I pathway) play important roles in the formation of light-induced volatiles in milk.

Effects of Trolox and ascorbic acid on the riboflavin photosensitised oxidation of aromatic amino acids

Abstract The effects of 0, 100, 250, 500, 750 or 1000 ppm Trolox and ascorbic acid on the singlet oxygen oxidation of aromatic amino acids viz. phenylalanine, tryptophan, tyrosine in the presence of 25 ppm riboflavin were determined by measuring depleted headspace oxygen by gas chromatography and aromatic amino acid content by high performance liquid chromatography. The coefficients of variations (CVs) for headspace oxygen analysis and HPLC analysis of aromatic amino acids were 1.4% and 4.7%, respectively. Samples were stored under light (1000 lux) at 30 °C for 10 h. Both Trolox and ascorbic acid acted as antioxidants. As the concentration of Trolox and ascorbic increased from 0 to 1000 ppm, the head space oxygen depletion increased. This was due to the oxidation of Trolox and ascorbic acid along with amino acids in the presence of riboflavin. High performance liquid chromatography analysis of the samples clearly indicated that both Trolox and ascorbic acid minimised the degradation of phenylalanine, tryptophan, tyrosine significantly ( p

Biomimetic Total Synthesis of (±)‐Pallavicinolide A

Piecing it together: The first total synthesis of naturally occurring diterpene pallavicinolide A was achieved. Notable features are highlighted by three key biomimetic transformations: a base-promoted Grob fragmentation, a singlet oxygen oxidation, and an intramolecular Diels-Alder cycloaddition.

Quenching Mechanisms and Kinetics of Trolox and Ascorbic Acid on the Riboflavin-Photosensitized Oxidation of Tryptophan and Tyrosine

The effects of 0, 0.3, 0.6, and 0.9 mM Trolox and ascorbic acid on the singlet oxygen oxidation of tryptophan and tyrosine containing 25 ppm of riboflavin were determined by measuring tryptophan and tyrosine concentration by high-performance liquid chromatography analysis. The samples were stored in the a 1000 lx light storage box for 4 h at 30 degrees C. As the concentration of Trolox and ascorbic acid increased, the degradation of tryptophan and tyrosine decreased significantly at p < 0.05. Trolox reduced tryptophan and tyrosine degradation by quenching both singlet oxygen and excited triplet riboflavin, whereas ascorbic acid quenched singlet oxygen only. The total singlet oxygen quenchings of Trolox in the presence of tryptophan and tyrosine were 1.55 x 10(7) and 1.32 x 10(7) M(-1) s(-1), respectively. The total singlet oxygen quenchings of ascorbic acid in the presence of tryptophan and tyrosine were 1.16 x 10(7) and 1.10 x 10(7) M(-1) s(-1), respectively. Trolox was more effective than ascorbic acid in preventing the degradation of tryptophan and tyrosine.

Regioselective Synthesis and Structural Studies of Substituted γ-Hydroxybutenolides with Use of a Tandem Baylis−Hillman/Singlet Oxygenation Reaction

The scope and limitations of a regioselective synthesis of either alpha- or beta-substituted gamma-hydroxybutenolides from 3-furfural and enones are described. The sequence features a Baylis-Hillman reaction followed by singlet oxygen oxidation with use of either an amine base or TBAF as the regioselectivity switches. Structural studies in solution on some of the resulting gamma-hydroxybutenolides are also reported.

Immobilised porphyrins in monoterpene photooxidations

Porphyrins were covalently linked to modified Merrifield polymers by chlorosulphonation activation of the porphyrin nucleus. These supported porphyrins were used as photosensitizers to promote singlet oxygen oxidation of monoterpenes with an efficiency that depends on porphyrin structure and the spacer used to link it to the polymer structure. The performance of these photosensitizers was studied. Citronellol and α-terpinene gave the expected singlet oxygen ene addition products. α-Pinene and β-pinene also gave products from non-ene reactions, which is explained by the existence of an alternative radical pathway.

Synthesis of (+)-Zerumin B Using a Regioselective Singlet Oxygen Furan Oxidation

A short and efficient synthesis of the antitumor diterpenoid (+)-zerumin B has been accomplished starting from (+)-sclareolide. At the heart of the synthetic strategy lies the regioselective formation of the alpha-substituted gamma-hydroxybutenolide moiety of zerumin B. This was achieved by means of a [1,4] O-->C triisopropylsilyl migration followed by singlet oxygen (1 O 2) oxidation of the resulting 2-triisopropylsilyl-3-(alpha-hydroxy)alkylfuran.

DNA−Protein Cross-links between Guanine and Lysine Depend on the Mechanism of Oxidation for Formation of C5 Vs C8 Guanosine Adducts

The reaction between N(alpha)-acetyllysine methyl ester (Lys) and 2'-deoxyguanosine (dGuo) was used to study structural aspects of DNA-protein cross-link (DPC) formation. The precise structure of DPCs depended on the nature of the oxidant and cross-linking reactions in which a series of different oxidation conditions generated a distribution of adducts, principally spirodiiminodihydantoins with lysine appended at the purine position of C5 (5-Lys-Sp), C8 (8-Lys-Sp), or both C5 and C8 (5,8-diLys-Sp). Singlet oxygen oxidation of dGuo produced 5-Lys-Sp exclusively when Rose Bengal or methylene blue was used to photochemically generate (1)O2 in the presence of Lys, whereas riboflavin or benzophenone-mediated photochemistry generated lysine radicals and led to C8 adduct formation, yielding 8-Lys-Sp and 5,8-diLys-Sp. Notably, the yield of dGuo modifications from riboflavin photooxidation increased dramatically in the presence of lysine. Oxidation of deoxyguanosine/lysine mixtures with Na2IrCl6 or sulfate radicals produced both 5-Lys-Sp and 8-Lys-Sp. The same adducts were formed in single and double-stranded oligodeoxynucleotides, and these could be analyzed after nuclease digestion. Adduct formation in duplex DNA was somewhat dependent on the accessibility of lysine to C5 vs C8 of the purine. No adduct formation was detected between lysine and the other nucleobases T, C, or A. Overall, the precise location of adduct formation at C5 vs C8 of guanine appears to be diagnostic of the oxidation pathway.

Fluoride‐Assisted Regioselective Conversion of Functionalized Furans to α‐Substituted γ‐Hydroxybutenolides Using Singlet Oxygen.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Fluoride-Assisted Regioselective Conversion of Functionalized Furans to α-Substituted γ-Hydroxybutenolides Using Singlet Oxygen

A facile synthesis of alpha-substituted gamma-hydroxybutenolides from 3-furfural was achieved using a Baylis-Hillman reaction followed by singlet oxygen oxidation. The regioselectivity of this conversion was controlled by using TBAF.

The Singlet Oxygen Oxidation of Chlorpromazine and Some Phenothiazine Derivatives. Products and Reaction Mechanisms

A kinetic and product study of the reactions of chlorpromazine 1, N-methylphenothiazine 2, and N-ethylphenothiazine 3 with singlet oxygen was carried out in MeOH and MeCN. 1 undergoes exclusive side-chain cleavage, whereas the reactions of 2 and 3, in MeOH, afforded only the corresponding sulfoxides. A mechanism for the reaction of 1 is proposed where the first step involves an interaction between singlet oxygen and the side-chain dimethylamino nitrogen. This explains why no side-chain cleavage is observed for 2 and 3.

Base‐Assisted Regio‐ and Diastereoselective Conversion of Functionalized Furans to Butenolides Using Singlet Oxygen.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.