Reactivity and Geometry in Allylic Systems. I. Stereochemistry of Photosensitized Oxygenation of Monoölefins<sup>1,2</sup>

Nickon, Alex; Bagli, Jehanbux F.

doi:10.1021/ja01467a049

Cited by 156 publications

(53 citation statements)

References 4 publications

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“…1 O 2 -mediated photooxidation (type II photoreactions) of D 5-stenols produces mainly D 6 -5a-hydroperoxides with low amounts of D 4 -6a/6b-hydroperoxides (Nickon and Bagli 1961;Kulig and Smith 1973). D 4 -6a/6b-Hydroperoxides were selected as tracers of photooxidation of D 5 -sterols because of their high specificity and relative stability (Christodoulou et al 2009;Rontani et al 2009).…”

Section: -Cismentioning

confidence: 99%

Degradation of particulate organic matter in the equatorial Pacific Ocean: Biotic or abiotic?

Rontani

Zabeti

Wakeham

2011

Limnology & Oceanography

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The behavior of organic matter (OM) in suspended and sinking particles in the equatorial Pacific Ocean was monitored by measuring lipid degradation products that are specific for biodegradation, photooxidation, and autoxidation. Photodegradation and autoxidation were significant for lipids associated with both suspended and sinking particles. Abiotically degraded terrestrial material strongly contributed to suspended particles and to sinking material in the deep ocean, probably as the result of incorporation of terrestrial particles into sinking aggregates. Analyses of degradation products of 24-methylcholesta-5,22-dien-3b-ol, 24-ethylcholest-5-en-3b-ol, and cholest-5-en-3b-ol gave diagnostic information concerning the differential behavior of phytoplanktonic, terrestrial, and zooplanktonic OM, respectively. Planktonic lipids were more susceptible to biodegradation than terrestrial lipids and biodegradation was more intense in sinking particulate organic matter (POM) than suspended POM, which we attribute to efficient transfer of singlet oxygen from suspended and senescent phytoplankton cells to associated bacteria and subsequent inhibition of heterotrophic degradation. There is a direct link between the photooxidation state of lipids of senescent phytoplankton cells in suspended particles and the apparent resistance of lipids toward biotic degradation. Terrigenous vascular plant OM, which is strongly autoxidized on land or in the atmosphere as it is transported to the remote ocean, is only weakly biodegraded during sedimentation in this open ocean setting. A significant increase in alkenone-based U K9 37 values (+0.07 equivalent to an inferred temperature change of +2uC) was observed in sinking particles with depth and the detection of epoxyalkenones further confirming the potential detrimental effect of aerobic bacterial degradation processes on the U K9 37 paleotemperature proxy.

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Section: -Cismentioning

confidence: 99%

Degradation of particulate organic matter in the equatorial Pacific Ocean: Biotic or abiotic?

Rontani

Zabeti

Wakeham

2011

Limnology & Oceanography

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“…Hence, 7-hydroperoxy-cholest-5-en-3-ol esters showed signals at the C6-olefinic proton and the C7-protons of cholesterol at 5.73 and 4.14 ppm, respectively. Although the formation mechanism of these hydroperoxides was not clear, it has been reported that 5-hydroperoxycholesterol produced by the photosensitized oxidation rearranges to 7-hydroperoxycholesterol; 21 it is therefore considered that the formation of the above 7-hydroperoxycholest-5-en-3-ol esters is a result of the rearrangement of the 5-hydroperoxycholest-6-en-3-ol esters under the reaction conditions. As evidenced, the formation of the 7-hydroperoxy isomer decreased when the reaction time was shortened.…”

Section: Photo-oxidation Of Cholesteryl Estersmentioning

confidence: 99%

Determination of Regioisomeric Hydroperoxides of Fatty Acid Cholesterol Esters Produced by Photosensitized Peroxidation Using HPLC

et al. 2000

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It has been widely known that lipid hydroperoxidation has a pathogenic effect for atherosclerosis, 1,2 and possibly contributes to both cancer and aging. [3][4][5][6][7] The oxidation of lipids proceeds via a free-radical chain mechanism. Singlet O2 is one of the reactive species for initiating the above oxidation process, and lipid hydroperoxides are believed to be produced as primary oxidative products. The hydroperoxidation of unsaturated fatty acids has also been reported to produce regioisomeric hydroperoxides by photosensitized singlet O2 oxidation or autooxidation. [8][9][10][11] Kritharides et al. showed the initial formation of lipid hydroperoxides by the oxidation of low-density lipoprotein (LDL) using HPLC analysis. 12 It is considered that the three lipid groups (cholesteryl esters, triglycelides and phospholipids) are to be oxidized in biological fluids. Several sensitive methods for detecting and identifying the hydroperoxides of three lipid groups have been reported. [13][14][15][16][17][18] However, the formation of regioisomeric hydroperoxides from each of the above-mentioned lipid group and their prosperity and decay has not yet been sufficiently clarified. To understand the lipid oxidation mechanism in tissue or blood, it would be desirable to clarify the possible regioisomers of each oxidized lipid group. The purpose of this work was to clarify the components of hydroperoxides produced from cholesteryl oleate (C18-1), cholesteryl linoleate (C18-2) and cholesteryl linolenate (C18-3) by photosensitized peroxidation. Experimental MaterialsOleic, linoleic and linolenic acids and their methyl esters were purchased from Kanto Chemical Co., and were purified by SiO2 column chromatography (hexane/ethyl acetate = 3/1 for acids and 20/1 for methyl esters, v/v) before use. The purities of the fatty acids and their methyl esters were over 95%; this was confirmed by 1 H-NMR analysis. They were also shown by GLC to be free from other isomers. Cholesterol was purchased from Wako Pure Chemical Inc., and used after SiO2 column chromatography (hexane/ethyl acetate = 5/1) and recrystallization. All of the solvents and reagents used were of analytical grade. InstrumentationHPLC was performed by the LC-6A system (Shimadzu Co.) including the Rheodyne 7125 injector, and the SPD-10A UV-VIS detector (Shimadzu Co.). An analytical column used was Mightysil Si 60 (4.5 × 250 mm, 5 µm, Kanto Chemical Co.); the mobile phase was a mixture of hexane/2-propanol (100/1 or 250/1, v/v). The flow rate was 1 ml/min and the temperature was ambient. The detection wavelengths were 210 and 233 nm. Mass spectra were taken using a JEOL Automass under the following conditions: column, DB-1, 30 m × 0.25 mm (J & W Co.); column temperature, 80˚C to 280˚C at a rate of 20 ˚C/min; carrier gas, helium (60 ml/min); ion source temperature, 250˚C; separator temperature, 250˚C; ionization energy, 70 eV.1 H-NMR was taken with a JEOL JNM EX-400 at 400 MHz with tetramethylsilane as an internal standard. Japan In order to examine the process of th...

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“…These processes mainly produce 6 -5-hydroperoxides (8) and to a lesser extent  4 -6/6-hydroperoxides (9 and 10) ( Fig. 3) (Nickon and Bagli, 1961;Kulig and Smith, 1973).  6 -5-hydroperoxysterols (8) are relatively unstable and may undergo allylic rearrangement to  5 -7-hydroperoxysterols (11), which in turn epimerize to the corresponding 7-hydroperoxides (12) (Fig.…”

Section: Carotenoidsmentioning

confidence: 99%

Photo- and Free Radical-Mediated Oxidation of Lipid Components During the Senescence of Phototrophic Organisms

Rontani¹

2012

Senescence

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Reactivity and Geometry in Allylic Systems. I. Stereochemistry of Photosensitized Oxygenation of Monoölefins^1,2

Cited by 156 publications

References 4 publications

Degradation of particulate organic matter in the equatorial Pacific Ocean: Biotic or abiotic?

Degradation of particulate organic matter in the equatorial Pacific Ocean: Biotic or abiotic?

Determination of Regioisomeric Hydroperoxides of Fatty Acid Cholesterol Esters Produced by Photosensitized Peroxidation Using HPLC

Photo- and Free Radical-Mediated Oxidation of Lipid Components During the Senescence of Phototrophic Organisms

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Reactivity and Geometry in Allylic Systems. I. Stereochemistry of Photosensitized Oxygenation of Monoölefins1,2

Cited by 156 publications

References 4 publications

Degradation of particulate organic matter in the equatorial Pacific Ocean: Biotic or abiotic?

Degradation of particulate organic matter in the equatorial Pacific Ocean: Biotic or abiotic?

Determination of Regioisomeric Hydroperoxides of Fatty Acid Cholesterol Esters Produced by Photosensitized Peroxidation Using HPLC

Photo- and Free Radical-Mediated Oxidation of Lipid Components During the Senescence of Phototrophic Organisms

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Reactivity and Geometry in Allylic Systems. I. Stereochemistry of Photosensitized Oxygenation of Monoölefins^1,2