Chemical degradation method

In addition to the above techniques, inverse gas chromatography, swelling experiments, tensile tests, mechanical analyses, and small-angle neutron scattering have been used to determine the cross-link density of cured networks (240—245). Si soHd-state nmr and chemical degradation methods have been used to characterize cured networks stmcturaHy (246). H- and H-nmr and spin echo experiments have been used to study the dynamics of cured sihcone networks (247—250). 

The availability of these novel enzymes, next to the known pectic enzymes, offer new opportunities to use them as analytical tools in revealing the structure of oligo- and polysaccharides [31,32]. In contrast with frequently used chemical degradation methods, which usually have a poor selectivity, these enzymes act in a deflned way. To be able to recognize different structural units within the polymer, endo-acting types of enzyme are preferred, although accessory enzymes might be essential as well [30]. 

Beltran, FJ. Ozone-UV radiation-hydrogen peroxide oxidation technologies. In Tarr MA, editor. Chemical degradation methods for wastes and pollutants - environmental and industrial applications. New York Marcel Dekker 2003 1-75. 

Chemical Degradation Methods for Wastes and Pollutants Environmental and Industrial Applications, edited by Matthew A. Tarr... 

The reactivity of initial products will have a dramatic effect on their buildup during oxidation. Those that react rapidly (e.g., benzoquinones) will be seen only in minor amounts, whereas less reactive initial or subsequent products will tend to accumulate. One weakness of in situ remediation applications, using Fenton or other biochemical or chemical degradation methods, is a failure to monitor potentially harmful degradation products. 

The thin-layer gel system used for resolving the different fragments produced by the chemical degradation method is essentially that of Sanger, Nicklen and Coulson (1977) as described in Chapter 4. An 8% polyacrylamide gel is usually used though for special purposes a 10 or 12% gel can give an improved resolution of the smallest fragments. For the standard 8% gel the polymerization mixture contains 7.6% (wt/vol) acrylamide, 0.4% (wt/vol) bisacrylamide, 50% (wt/vol) urea, 100 mM Tris-borate, pH 8.3, 2mM EDTA, 0.07% (wt/vol) ammonium persulphate and TEMED catalyst. This solution is poured or injected into a 0.4 x 200 x 400 mm mold to form a gel slab. 

The structure of aspidospermine (II) was practically solved by chemical degradative methods (see formula CCCCXXXIII, Volume VII, p. 131) but the final location of the ethyl side chain and the relative stereochemistry only became known after the single crystal X-ray study of its methiodide (22, 11) which was shown to have structure X.1 Extensive degradative work, the results of which appeared side by side with those of the X-ray determination, had shown the nature of the structure around both nitrogen atoms and established the size of rings D and E (24, 12). 

Although the periodate oxidation and aminolysis methods provide quantitative data on the frequency with which of phenolic hydroxyl groups occur in lignin, they do not reveal the structural environment in which they occur. Such information may be obtained by other means, e.g., UV spectroscopic or chemical degradation methods (Adler 1977). 

The structure elucidation, mainly by chemical degradation methods, has been extensively dealt with by Battersby and Openshaw (/). There remained the problems of stereochemistry that were solved mostly in the years following the review just mentioned. They are described in Section III,D. 

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