Peroxy acids, detection

To isolate acidic products which were not found by gas chromatographic analysis, the crude products were treated by ordinary methods, but only small amounts of viscous brownish red liquid products were obtained, and no adipic acid was isolated. Isolation of cyclohexene oxide was unsuccessful, however gas chromatographic analysis based on the two columns showed clearly the presence of cyclohexene oxide. Gaseous products included ethylene, 1,3-butadiene, carbon dioxide, and an unidentified C4 hydrocarbon in the ratio of 12 6 3 1. Trace amounts of other gaseous hydrocarbons were also detected, and any gaseous peroxy compound was not detected. These hydrocarbons were considered to be decomposition products of activated cyclohexene. 

Chemical ionization mass spectrometric detection has been explored for the detection of methyl hydroperoxides However, fluorometry has dominated the current detection schemes for the organic peroxides. Typically, a nonfluorescent substrate is oxidized by the peroxide to generate a fluorescent product. These methods are sufficiently sensitive for accurate measurement of the peroxides in the low ppt by volume. For example, the peroxidase-catalyzed dimerization of p-hydroxyphenylacetic acid (POPHA) occurs in the presence of a peroxy group at elevated pH. The formation of the fluorescent dimer, detected by excitation at 310 nm and emission at 405 nm, is proportional to the concentration of the peroxide. The most common peroxidase catalyst used for this reaction is horseradish peroxidase (HRP). Cost and stability issues with the use of HRP led to the use of other catalysts, such as metalloporphyrins or phthalocyanine complexes. Another fluorescent reaction scheme involves the oxidation of the nonfluorescent thiamine (vitamin Bi) to the fluorescent thiochrome by the peroxide group. This reaction is catalyzed by bovine hematin. This reaction is 25-fold more sensitive for H2O2 than for the organic peroxides. 

Bulk phospholipids are relatively stable on storage (Reblova et al., 1991), but are less stable when dissolved in oils. They slowly change during storage of hpid foods. In unheated food materials, phospholipases are active so that hydrolysis occurs, accompanied by formation of phosphatidic acids. In addition to hydrolytic reactions, oxidation reactions also occur. The oxidation of PUFA, detected in phospholipids, proceeds in a way similar to the oxidation of neutral hpids, only the peroxy free radicals or the hydroperoxides formed from them can react with amine groups in a non-radical way. 

When oxygen was bubbled through a boilhig solution of colupulone in an aqueous buffer solution (pH 5-5) cohulupone (44 R = Pr ) and four new products were isolated. These were the C3 -exo and -endo epimers of tricyclo-oxycolupulone (TCOC) (54) and tricyclo-peroxycolupulone (55). These compounds, which are not bitter, accounted for 80% of the p-acid. The peroxy compounds (55) were formed first and the alcohols (54) on further heating but neither is very soluble. They were not detected in beer [44]. 

The formation and structure of a peroxy species which is converted to the acid anhydride have been discussed for a long time. In enzymatic studies, the role of the iron center has been explained by the formation of binary (ES) and ternary (ESO2) species. No doubt the low-valent iron such as Fe " is more favorable than Fe + for the activation of oxygen by coordination to iron. Based on the result that no Fe species is detected throughout the enzymatic reaction, Que et al. proposed in 1977 that the substrate... 

Guajardo and Mascharak have found that the iron complexes [Fe(PMA)] (n = 1, 2) (84, 85) shown in Fig. 23, which are synthesized as iron bleomycin analogues, promote facile lipid peroxidation in the presence of O2 or H2O2 [140]. Reaction of linoleic acid (59) with O2 catalyzed by 84 and 85 gives the 13-OOH product in the selectivity of 80 and 75%, respectively. In the reaction of arachidonic acid, (86), the 15-OOH product is also selectively formed (80%) by the two complexes. The peroxidation is also promoted by H2O2. As a possible intermediate, a low-spin (hydroperoxo)-iron(III) species, [(PMA)Fe -OOH], has been detected by X-band EPR. The EPR spectrum is identical to that of the activated bleomycin. The reaction has been explained in terms of the radical mechanism, which involves H atom abstraction from lipid (LH) by [(PMA)Fe -OOH]. Peroxidized linoleic acid (L-00 ) has been detected by UV absorption at 234 nm, and a chain propagation reaction by the peroxy radical to produce lipid hydroperoxide (L-OOH) has been proposed. 

---