Oxidation product identification procedure

Other preliminary experiments on alkali lignin included oxidations by barium peroxide and alkali (5, 6), alkali fusion, and alkali fusions in the presence of calcium peroxide, sodium borate perhydrate, and monopersulfate compound. Ether extractives and water extractives were examined, but in all cases too many of the oxidation products obtained were new and unidentifiable, and it was impossible to evaluate the experiments adequately with the available techniques. Vanillic acid appeared to be the chief oxidation product under conditions which did not demethylate further or destroy the aromatic nature of the oxidation products. Some oxidation conditions yielded p-hydroxybenzyl moieties as products, and some gave no trace of these products whatever. More detailed studies of the ether-insoluble, water-soluble components of the several oxidation mixtures were postponed until adequate procedures were developed for analytical isolation and identification. 

Oxygenated acylglycerols. Lipid peroxidation in biological tissues attracts much attention because of its possible contribution to the functional modulation of biomembranes and lipoproteins. It is believed to be involved in free-radical-mediated damage, carcinogenesis and ageing processes. Research requires specific, sensitive and reproducible procedures to quantify the lipid hydroperoxides in each lipid class as primary products and the alcohols and aldehydes as secondary products of the peroxidation reaction. The identification and quantification of lipid oxidation products is therefore of great practical and theoretical interest and MS has assumed a major role in these analyses as a result of the development of mild ionization techniques. 

The detection of products derived from the N-oxygenation of C=N functionalities presents many problems, which illustrate difficulties that are associated with the isolation, identification and quantification of small amounts of water-soluble metabolites. Spectrophotometric methods19 as well as differential pulse polarographic techniques20 previously used to determine oximes, nitrones and N-oxides frequently lack sensitivity and/or specificity. Improved analytical methods for the quantification of these N-oxy compounds include chromatographic techniques taking into account the chemical peculiarities of the individual N-oxygenated C=N functionalities. These procedures usually require the chemical synthesis of authentic material for comparison with data obtained with the isolated metabolites, and also for the construction of calibration curves. 

An alternative, or supplementary, approach is provided by oxidation with lead tetraacetate or, preferably, periodate, and possibly by identification of the products. Caution must, however, be observed in using this method, as Buchanan has shown that the compound previously designated as methyl 3-chloro-3-deoxy-a-D-gulopyranoside consumes periodic acid extremely slowly (seven days) and is, in fact, methyl 4-chloro-4-deoxy-a-D-glucopyranoside. The products of epoxide cleavage are usually completely defined by these procedures, because irans addition can be assumed, although considerable care must be exercised when there is a possibility of epoxide migration. ... 

With nitric acid, the polyols may be oxidized to the corresponding dibasic acids. This procedure provides a qualitative identification of galactitol by converting it to insoluble mucic acid, but galactose and galacturonic acid give the same product. See 106). 

---