Oxidative degradation peroxidation chain

Another aspect of polysorbates is that they are inherently susceptible to oxidative degradation. Often, as raw materials, they contain sufficient quantities of peroxides to cause oxidation of protein residue side chains, especially methionine (59). The potential for oxidative damage arising from the addition of stabilizer emphasizes the point that the lowest effective concentrations of excipients should be used in formulations. For surfactants, the effective concentration for a given protein will depend on the mechanism of stabilization. It has been postulated that if the mechanism of surfactant stabilization is related to preventing surface-denaturation, the effective concentration will be around the detergent s critical micellar concentration. Conversely, if the mechanism of stabilization is associated with specific protein-detergent interactions, the effective surfactant concentration will be related to the protein concentration and the stoichiometry of the interaction (39). 

The oxidative degradation represented by the foregoing reactions is referred to as peroxidation. Peroxidation can lead to rapid development of rancidity in fats and oils. However, the presence of a small amount of tocopherol inhibits this decomposition, presumably by trapping the intermediate radicals in the form of the more stable tocopherol radicals (Eq. 15-54), which may dimerize or react with other radicals to terminate the chain. 

Many metals or ions of metals are catalysts of oxidative degradation of plastics. The conversion of peroxides (RiOO ) to hydroperoxides (RiOOH) via abstraction of hydrogen from an adjacent polymer molecule (R2H) is typically the rate-limiting step for the propagating chain reaction of oxidation... 

Oxidative degradative reactions can occur to the side chains of sulfur-containing methionine (Met) and cysteine (Cys) residues and the aromatic amino acid residues histidine (His), tryptophan (Trp), and tyrosine (Tyr) in proteins during their isolation and storage. The weakly nucleophilic thioether group of Met (R-S-CH3) can be oxidized at low pH by hydrogen peroxide as well as by oxygen in the air to the sulfoxide (R-SO-CH3) and the sulfone (R-SO2-CH3). The thiol... 

Antioxidant A chemical substance capable of inhibiting oxidation or oxidative degradation of another substance such as plastic in which it is incorporated. Antioxidants act by terminating chain-propagating free radicals or by decomposing peroxides, formed during oxidation, into stable products. The first group of antioxidants include... 

Experiments on the oxidative degradation of PVA with potassium permanganate [103], potassium dichromate [104], hydrogen peroxide [105], and ozone [106] were carried out in detail. It was observed that a random scission of the PVA chain occurs. The scission product was fractionated, and the determination of the DP and end groups was carried out. It was found that the main end groups formed by the scission are either carbonyls or carboxyls. Radiation-induced oxidative degradation has also been studied [107]. 

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