Degradation mechanism, viii

Figure VIII-M-3. OH-initiated degradation mechanism of peroxymethacrilic nitric anhydride (Orlando et al., 2002).

Table VIII lists a variety of substances that are known chemotaxins. Chemotaxins attract white blood cells, primarily neutrophils, eosinophils and macrophages, to a specific site by causing directed movement. Once these cells arrive they phagocytize and degrade invading microorganisms, and/or release hydrolytic enzymes which can cause subsequent tissue injury. These cells also release bronchoconstrictors, which provides another mechanism worthy of consideration.

Consideration of reasonable mechanisms for producing formic acid from an aldose led to the hypothesis that the sugar forms an addition product with the hydroperoxide anion, comparable with an aldehyde sulfite or the addition product of aldoses with chlorous acid (52). The intermediate product (12) could decompose by a free-radical or an ionic mechanism. In the absence of a free-radical catalyst, the ionic mechanism of Scheme VIII seems probable. By either mechanism the products are formic acid and the next lower sugar. The lower sugar then repeats the process, with the result that the aldose is degraded stepwise to formic acid. Addition of the hydroperoxide anion to the carbonyl carbon is in accord with its strong nucleophilic character (53) and with certain reaction mechanisms suggested in the literature (54) for related substances. 

The discovery by Kuhn and Low13 that picrocrocin (VIII) is degraded by aqueous alkali to D-glucose and safranal (IX) indicated a mechanism for the alkaline decomposition of this class of glycoside. 

Table VIII lists oligosaccharides which have been degraded in alkali, some of the products of this degradation, and some conditions which bring about the reaction. The products, which may vary with the conditions used, are complex and because of this it is difficult to determine the mechanisms by which the decomposition occurs. However, the degradation is certainly dependent on the presence of a free reducing group. A general effect of alkalis on reducing sugars is to bring about isomerization of the...

At the time, model reactions for (VIII) were known, but no simple analogy for (VII) had been discovered. Schoberl and Wagner (1956), however, showed that the treatment of uncombined cystine with alkali leads to the formation of some lanthionine and, hence, the reaction with the protein was not unique. There has been considerable discussion about the extent to which the lanthionine reaction can account quantitatively for the alkaline degradation of the cystine of keratins and about the mechanism of the reaction. 

The ESR spectra of PIB irradiated at low temperature consists of a broad doublet with a hyperfine coupling constant of 2 mT, attributed to either radical VIII (182) or a combination of contributions from radicals VII and VIII (183, 184). The primary radicals V and VI (Fig. 2) have not been observed by ESR spectroscopy. Despite extensive studies of the radiochemical changes in PIB by ESR, volatile product analysis, and UV and IR spectroscopy, the mechanism of degradation had been imcertain imtil the advent of high resolution NMR methods. In a comprehensive study, Bremner and co-workers (185) and Hill and... 

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