Dye sensitised photo-oxidation of the methyl and phenyl esters of oleic and linoleic acids

An Ancient Relative of Cyclooxygenase in Cyanobacteria Is a Linoleate 10S-Dioxygenase That Works in Tandem with a Catalase-related Protein with Specific 10S-Hydroperoxide Lyase Activity

“…Racemic 10-HPODE was prepared by reaction of linoleic acid (150 mg) with singlet oxygen using methylene blue as sensitizer (1 ml of a 0.6-mg/15-ml methanol solution) and a strong source of visible light at 0°C overnight (16). After fractionation on an open-bed silica column to remove unconverted linoleic acid and the methylene blue, the HPODEs were separated by semi-preparative SP-HPLC using a Beckman 5-m silica column (25 ϫ 1 cm) and a solvent of hexane/isopropyl alcohol/glacial acetic acid (100:1:0.1 by volume).…”

“…The linoleic acid product was reduced with triphenylphosphine, hydrogenated, and converted to the methyl ester trimethylsilyl ether derivative. On GC-MS analysis, the electron ionization mass spectrum showed structural diagnostic ions at m/z 371 (2% relative abundance, M- A method for steric analysis of the C-10 hydroxyl configuration was developed, using 10-HODE purified from a singlet oxygen reaction with linoleate as a racemic standard (16,23) and 10S-HODE from an incubation of linoleate with mushroom homogenate as the standard of known chirality (24,25). The results using a Chiralpak AD column for resolution showed that the Nostoc heme peroxidase formed almost exclusively the linoleate 10S enantiomer (99.5% enantiomeric excess) (Fig.…”

A comparative study on the susceptibilities of soybean, sunflower and peanut oils to singlet molecular oxygen photooxidation

“…A similar consideration is valid for the ratios of slopes of hydroperoxide build-up, as a protection against a combined 02 (lhg)-radical mechanism. These facts can be explained by taking into account a majority contribution of the singlet molecular oxygen mechanism [between 55 and 80%, depending on the sensitizer (15)] in the photosensitized production of hydroperoxides. From the comparison of the values for each substrate in both columns of Table 2, two aspects should be emphasized: i) the similarity for each substrate between O2 (lhg) and hydroperoxides data; and ii) the identical trend for increase of protection by impurities.…”

“…It is important to emphasize that dye-sensitized photooxidation, monitored by this method, is interpreted (15) in terms of a dual mechanism involving both singlet oxygen and radical attack on the double bonds of the oxidizable substrates. It is well established (11) that a direct relationship can be obtained between the increase of absorbance at 234 nm (due to the appearance of hydroperoxides of the fatty acids) and the degree of oxidation in the early stages of dye-sensitized oxygenation of unsaturated oils (and FAME).…”

Photosensitized Peroxidation of Lipids: An Experiment Using 1H-NMR

“…HPLC separation of hydroxy derivatives has also been used to show the approximately equimolar distribution of the four isomers (6).…”