Propagation, oxidation

Traces as low as parts per million of certain transition metals, notably copper, manganese, cobalt and iron, which may have been introduced as catalysts, are able to propagate oxidation. Metal deactivators serve to reduce these effects. 

Antioxidants for fats and oils function by interfering in the formation of the free radicals that initiate and propagate oxidation. Knowledge of the mechanism of antioxidant performance reinforces several important aspects of antioxidant usage. 

All these radical cations are fairly strong oxidants. For example, the monomeric methionine radical cation is likely to propagate oxidative damage in peptides (Rauk et al. 2000). Yet in cellular systems, thiourea has radiation-protective properties (Bacq 1965). This may be accounted for considering that the oxidative power of its dimeric radical is not high enough to oxidize even G it reacts only reasonably fast when G is deprotonated (Schuchmann et al. 2000), and this is a non-relevant situation in DNA. 

The oxidative power of peroxyl radicals, although sometimes increased by electron withdrawal, is smaller than that of RO radicals, but thanks to their longer lifetime [48], peroxyl radicals are ideal candidates for propagating oxidative chain reactions in biological membranes of aerobic cells, as discussed below. Traces of unprotected iron will therefore be sufficient to maintain a substantial free radical production from pre-formed hydroperoxides, even in the absence of important reductant concentrations [49]. 

In 1942, soon after demobilization from the army, he had defended his PhD thesis on the theme, Oxidation of Hydrogen Sulphide . He generalized this research in the book Intermediate Products of Complex Reactions in Gaseous Phase (Moscow-Leningrad, Publishing house AS USSR, 1946) where, for the first time, it has been shown that such intermediate products as sulfur oxide possess properties of free radicals and can propagate oxidation. It was an important scientific benchmark. 

One such application of RSEs, or their constituent bond dissociation energies, is in the study of radical-mediated degradation mechanisms. For example, based on an examination of the relevant C-H and S-H bond dissociation energies in model peptides. Rank et al. postulated a mechanism for generating and propagating oxidative damage via a Met residue of the Ap peptide of Alzheimer s disease or the prion peptide of Creutzfeldt-Jakob disease. In a similar manner, Li et al. used C-H BDE calculations to identify the most vulnerable sites for radical-mediated damage in... 

The polymerization itself proceeds almost exclusively in the /3-cleavage manner. The results of end-group analysis showed that the addition of methoxide ion to propylene oxide preferred the /3-cleavage but in a less-specific way than that of the propagating oxide anion.95... 

As already mentioned, the estimation presented here applies to the rather unrealistic assumption, that each H00- radical leaving a pair of recombining primary peroxy radicals would be able to initiate a propagating oxidative chain. In reality, this might... 

AB aggregation stimulates ROS production, which may lead to cyclic or self-propagating oxidative damage. The DHA metabolite neuroprotectin D1 promoted neuronal survival and anti-apoptotic pathways that attenuated AB42 neurotoxicity (Lukiw et al., 2005). AD and mild cognitive disorder subjects also showed lower levels of antioxidant defense systems. 

Figure 8.24. Propagating oxidation waves the Belousov-Zhabotinsky reaction.

The pictures from left to right (Figure 8. 24) show propagating oxidation waves in an unstirred layer of the ferroin-malonic acid BZ reaction. When the wave is broken at a certain point (for example by a gentle airflow through a pipette) a pair of spiral waves develop at this point. 

The ability to measure spatial distribution of in situ oxidation can also be used to study the advancement of a propagating oxidation front in polymer films under different conditions. Oxidation of stabilised PP films has been initiated by unstabilised PP particles that were kept in direct contact with the film surface [614]. Figure 5.19 shows the induction time and advancement at 150°C in air of the oxidation fronts in PP film stabilised with Irganox... 

First, vitamin E scavenges free radicals propagating oxidation. It is hence not surprising to observe that it significantly reduces the post irradiation effects observed in UHMWPE. Kinetic curves in post irradiation phase always display the same characteristic shape with a maximal increase rate at the beginning of post irradiation (Figure 3.13). 

Fig. 9.29 Propagating oxidation waves in the Beiousov-Zhabotinsky reaction. (From http //www. trinitas.ru/rus/doc/0235/005a/pic/1134/03stathgif).

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