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Abstraction, hydrogen from fatty acid

Indirect initiation of lipid oxidation by ozone is similar except that it occurs via decomposition of ozonides in non-lipid molecules to form alkoxyl and peroxyl radicals that subsequently abstract hydrogens from fatty acids. Two mechanisms have been proposed, both of which yield the same hnal lipid products (186) ... [Pg.337]

Figure 17.2 Lipid peroxidation scheme. LH, a polyunsaturated fatty acid LOOM, lipid hydroperoxide LOH, lipid alcohol L, lipid radical LOO, lipid hydroperoxyl radical LO, lipid alkoxyl radical. Initiation the LH hydrogen is abstracted by reactive oxygen (e.g. lipid alkyl radical, lipid alkoxy radical, lipid hydroperoxyl radical, hydroxy radical, etc.) to produce a new lipid alkyl radical, L. Propagation the lipid alkyl, alkoxyl or hydroperoxyl radical abstracts hydrogen from the neighbouring LH to generate a new L radical. Figure 17.2 Lipid peroxidation scheme. LH, a polyunsaturated fatty acid LOOM, lipid hydroperoxide LOH, lipid alcohol L, lipid radical LOO, lipid hydroperoxyl radical LO, lipid alkoxyl radical. Initiation the LH hydrogen is abstracted by reactive oxygen (e.g. lipid alkyl radical, lipid alkoxy radical, lipid hydroperoxyl radical, hydroxy radical, etc.) to produce a new lipid alkyl radical, L. Propagation the lipid alkyl, alkoxyl or hydroperoxyl radical abstracts hydrogen from the neighbouring LH to generate a new L radical.
Example Hydroxyl radical abstracts hydrogen from a hydrocarbon side-chain of a fatty acid to initiate lipid peroxidation... [Pg.185]

It is important to note that saturated fatty acids are not immune to effects of oxidation. The strongly oxidizing radicals HO and RO abstract hydrogens at reasonable rates even from saturated fatty acids (10 for RO and 10 for HO ). The subsequent LsatOO radicals then abstract hydrogens from neighboring unsaturated fatty acids and thus can be sources of external radicals initiating radical chains in PUFA s (9, 208). [Pg.338]

Atom Transfer (hydrogen abstraction) by LOO —> Free Radical Chain Reactions Hydrogen abstraction is the heart of the classic free radical chain reaction schemes (Figure 1). Peroxyl radicals initially formed at any site on a fatty acid pass the unpaired electron to adjacent lipid molecules by abstracting hydrogens from an allylic position or a hydroperoxide, and the process repeats itself indefinitely until the chain is intercepted. [Pg.348]

D. The strength of the H—0 bond in vitamin E is weaker than the C—H from which the hydrogen is abstracted in the fatty acid primarily because,... [Pg.361]

Autoxidation is the process of oxidation at room temperature. Autoxidation of fatty acids occurs in a series of steps including the formation of free radicals. The process is very complicated and can be roughly divided into three phases initiation, propagation and termination. In the initiation phase, hydrogen is abstracted from the a-methylenic carbon of fatty acids to yield a free radical (equation (11.1)). The presence of a free radical initiator or catalyst is needed for the reaction to take place. Once a free radical is formed, it may form peroxy radicals through reaction with atmospheric oxygen (equation (11.2)). Also, these free radicals can abstract hydrogen from another unsaturated molecule to form a hydroperoxide and a new free radical (equation (11.3)). [Pg.330]

Ascorbate and a-tocopherol can repair RSSR " and RS by electron transfer, and RS have been shown to abstract hydrogen from polyunsaturated fatty acids. [124, 126] RSO have been found to be relatively stable while RSO2 abstract hydrogen atoms, though at very slow rates, and RSO2OO have been suggested to be much more reactive [127, 128], with sulfonyl peroxyl radicals from cysteine... [Pg.322]

It is easier to abstract a hydrogen atom and initiate lipid peroxidation from a fatty acid that has bis-allylic centres than from a fatty-acid side chain with only one double bond. It follows, therefore, that fatty-acid composition should influence the ability of a molecule such as LDL to act as a substrate for peroxidation. The potential... [Pg.24]

This conclusion is partly true because superoxide is unable to abstract hydrogen atom even from the most active bisallylic positions of unsaturated compounds, while perhydroxyl radical abstracts H atom from linoleic, linolenic, and arachidonic fatty acids with the rate constants of 1-3 x 1031 mol-1 s-1 [24], However, the superoxide damaging activity does not originate from hydrogen atom abstraction reactions but from one-electron reduction processes, leading to the formation of hydroxyl radicals, peroxynitrite, etc, and in these reactions perhydroxyl cannot compete with superoxide. [Pg.695]

Oxidation to CO of biodiesel results in the formation of hydroperoxides. The formation of a hydroperoxide follows a well-known peroxidation chain mechanism. Oxidative lipid modifications occur through lipid peroxidation mechanisms in which free radicals and reactive oxygen species abstract a methylene hydrogen atom from polyunsaturated fatty acids, producing a carbon-centered lipid radical. Spontaneous rearrangement of the 1,4-pentadiene yields a conjugated diene, which reacts with molecular oxygen to form a lipid peroxyl radical. [Pg.74]

The arachidonic acid cascade is a biological free radical oxidation of unsaturated fatty acids leading to formation of the prostaglandins (equation 102). Cyclization of a peroxy radical intermediate 66 leading to endoperoxide 67 was proposed as a pathway for this process, and this was demonstrated in chemical model systems, in which the peroxyl radical 66 was generated by hydrogen abstraction from the hydroperoxide corresponding to 66. [Pg.43]


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See also in sourсe #XX -- [ Pg.64 , Pg.65 ]




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Hydrogen abstraction from

Hydrogen fatty acids

Hydrogenation, fatty acids

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