Peroxide pathway, from

A variety of compounds such as hydrocarbons, alcohols, furans, aldehydes, ketones, and acid compounds are formed as secondary oxidation products and are responsible for the undesirable flavors and odors associated with rancid fat. The off-flavor properties of these compounds depend on the structure, concentration, threshold values, and the tested system. Aliphatic aldehydes are the most important volatile breakdown products because they are major contributors to unpleasant odors and flavors in food products. The peroxidation pathway from linoleic acid to various volatiles is determined in several researchs, - by using various techniques (Gas chromatography mass spectrometry, GC-MS, and electron spin resonance spectroscopy, ESR), identified the volatile aldehydes that are produced during the oxidation of sunflower oil. In both cases, hexanal was the major aldehyde product of hydroperoxide decomposition, whereas pentanal, 2-heptenal, 2-octenal, 2-nonenal, 2,4-nonadienal, and 2,4-decadienal were also identified. 

Butane-Naphtha Catalytic Liquid-Phase Oxidation. Direct Hquid-phase oxidation ofbutane and/or naphtha [8030-30-6] was once the most favored worldwide route to acetic acid because of the low cost of these hydrocarbons. Butane [106-97-8] in the presence of metallic ions, eg, cobalt, chromium, or manganese, undergoes simple air oxidation in acetic acid solvent (48). The peroxidic intermediates are decomposed by high temperature, by mechanical agitation, and by action of the metallic catalysts, to form acetic acid and a comparatively small suite of other compounds (49). Ethyl acetate and butanone are produced, and the process can be altered to provide larger quantities of these valuable materials. Ethanol is thought to be an important intermediate (50) acetone forms through a minor pathway from isobutane present in the hydrocarbon feed. Formic acid, propionic acid, and minor quantities of butyric acid are also formed. 

Fig. 28. Calculated energetic pathways from the bare active site and isolated peroxide to the 771- (left) and rf - intermediates (right) [from Cora et al. (59)].

CO is derived from a variety of feedstocks such as petroleum gas, fuel oil, coal, and biomass. The industrial scale production of PO starts from propylene, which is mainly obtained from crude oil. However, due to the high importance of this compound, many pathways from renewable sources have additionally been developed [54]. PP is converted to PO by either hydrochlorination or oxidation [55]. The use of chlorine leads to large amounts of salts as by-products, therefore oxidation methods are more important, such as the co-oxidation of PP using ethylbenzene or isobutene in the presence of air and a catalyst. However, this process is economically dependent on the market share of these by-products, thus new procedures without significant amounts of other side-products have been developed, such as the HPPO (hydrogen peroxide to propylene oxide) process in which propylene is oxidized with hydrogen peroxide to give PO and water [56, 57] (Fig. 14). 

Thromboxanes, like prostaglandins, contain a ring of five or six atoms the pathway from arachidonate to these two classes of compounds is sometimes called the cyclic pathway, to distinguish it from the linear pathway that leads from arachidonate to the leukotrienes, which are linear compounds (Fig. 21-16). Leukotriene synthesis begins with the action of several lipoxygenases that catalyze the incorporation of molecular oxygen into arachidonate. These enzymes, found in leukocytes and in heart, brain, lung, and spleen, are mixed-function oxidases that use cytochrome P-450 (Box 21-1). The various leukotrienes differ in the position of the peroxide... 

Another consequence of these findings is that the same adduct can be formed by a free radical mediated pathway from MAB following a one electron oxidation by peroxides as that formed from methylol or me thimine by a two electron oxidation catalyzed by cytochrome P450. Clearly identification of the GSH adducts of carcinogens in vivo may not distinguish both metabolic activation systems. It is also still not clear whether cytochrome P450 and peroxidases form common intermediates during N-demethylation reactions (22-24). 

JAs are derived from linolenic acid via an octadecanoid pathway consisting of several enzymatic steps (Figure 36). Multiple compartments in plant cells participate in JA synthesis. The early steps of this pathway occur in chloroplasts, where linolenic acid is converted to OPDA by means of the three enzymes lipoxygenase (LOX), allene oxide synthase (AOS), and allene oxide cyclase (AOC).867-869 Linolenic acid is oxygenated by 13-LOX producing a peroxidized fatty acid 13-hydroperoxylinolenic acid. The product is subsequently metabolized by AOS to an unstable compound allene oxide. Allene oxide is sequentially converted by AOC to produce OPDA. An alternative pathway from another trienoic fatty acid, hexadecatrienoic acid (16 3), is present in chloroplasts.870 In this pathway, dinor OPDA is produced instead of OPDA. OPDA and dinor OPDA are transported into the peroxisome. An ABC transporter involved in this transport was identified in... 

Hydrogen peroxide destruction from alternative pathways must be... 

The relative importance of the various heterogeneous oxidation pathways depends on pH. At pH values below —4.5 the hydrogen peroxide pathway typically dominates. In urban areas hydrogen peroxide may not be abundant enough to be the most important oxidant. Here transition metal catalysts can enhance the rates considerably, especially if there are alkaline materials from fly ash or ammonia to neutralize the growing acidity of droplet phases, which otherwise limits SO2 solubility. 

As observable from figures 5 and 6, the amide specific band absorptions for proteins, amide I band around 1654 cm-i and amide II band around 1541 cm" (Firth et al. 2008 Banuelos et al. 1995) are not changed when LDL was deposited on the gold support. This observation is important because it proved that the secondary structure of protein is preserved subsequent deposition therefore it can be concluded that the deposition on solid support did not affect theLDL functionality, and, consequently, that deposed LDL is expected to react with free radicals according to the same pathway as free LDL. Moreover, it should be mentioned that this argument is consistent with the data published by Paker (Paker, 1991) where it is mentioned that LDL ex vivo peroxidation pathway is similar as in vivo peroxidation pathway. 

Normally, Fe-based macrocycle catalyst such as Fe TPFPP could catalyze the ORR with a 4-electron-transfer pathway from O2 to H2O, while those of Co-based could only catalyze the process with a 2-electron-transfer pathway to produce peroxide. For example, a monolayer of cobalt(II) 1,2,3,4, 8,9,10,11, 15,16,17,18, 22,23,24,25-hexadecafluoro-29H,3 IH-phthalocyanine (abbreviated as Co HFPC) was coated on a graphite electrode by spontaneously adsorption displayed a strong electrocatalytic activity... 

Oxygen (O2) is the most abundant element in the Earth s crast. The oxygen reduetion reaetion (ORR) is also the most important reaction in life processes such as biological respiration, and in energy converting systems such as fuel cells. ORR in aqueous solutions occurs mainly by two pathways the direct 4-electron reduction pathway from O2 to H2O, and the 2-electron reduction pafliway from O2 to hydrogen peroxide (H2O2). In non-aqueous aprotic solvents and/or in alkaline solutions, the 1-electron reduction pathway from O2 to superoxide (O2 ) can also occur. 

Successful work with peroxidases requires knowledge about the possible side reactions in the catalytic cycle. The most important are shown in Scheme 5 [39]. The pathway from 18 to 21 covers the normal catalytic cycle. If the local phenol concentration is too low and/or the local concentration of hydrogen peroxide is too high, compound I is converted into an intermediate (Scheme 5, 23) [39,69]. This intermediate can follow three different paths of decomposition. First it can react back to the na-... 

Malondialdehyde (MDA) is a secondary carbonyl compound that arises from lipid peroxidation pathway. Gas chromatographic analysis of pentafluorophenyl-hydrazine derivatized carbonyl compounds was successfully used to assess antioxidant activity of vegetable oils (Stashenko et al., 1997). 

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