Degradation of hydroxyl

Moeder M, Martin C, Koeller G (2004) Degradation of hydroxylated compounds using laccase and horseradish peroxidase immobilized on microporous polypropylene hollow fiber membranes. J Memb Sci 245(1) 183-190... 

PI. Pacifici, R. E., Kono, Y., and Davies, K. J., Hydrophobicity as the signal for selective degradation of hydroxyl radical-modified hemoglobin by the multicatalytic proteinase complex, proteasome. J. Biol. Chem. 268, 15405—15411 (1993). 

The CL analysis applied on the degradation of hydroxyl-terminated polybutadiene based polyurethane elastomers illustrates the effect of previous energetic treatment to which samples were subjected. The increase in the initial CL intensity and the shift of maximum CL intensity upon the shorter time are the effects of the initiation of oxidation by molecular scissions and, respectively, the reactions of free radicals with oxygen that leads to decrease in the material durability (Fig. 61) [06C1]. Another proof for the beginning of degradation by prior processing is the increased CL-emission at the start of the CL measurements. (Fig. 62). 

Broadband Dielectric Spectroscopic Characterization of the Hydrolytic Degradation of Hydroxyl-Terminated Poly(D,L-lactide) Materials... 

This chapter reports the use of modem broadband dielectric spectroscopy as a novel approach in the study of the degradation of hydroxyl-terminated poly(D,L-lactide) materials from the perspective of modified macromolecular motions. As this technique is largely unfamiliar to the community engaged in the pursuit of biodegradable materials, fundamental explanations are provided where needed in this chapter. The analysis outlined here can be considered as useful in a broader context of materials that are degraded in similar ways, such as proton exchange membranes that are exposed to generated peroxide in fuel cells. 

Oxidative Reactions. The majority of pesticides, or pesticide products, are susceptible to some form of attack by oxidative enzymes. For more persistent pesticides, oxidation is frequently the primary mode of metaboHsm, although there are important exceptions, eg, DDT. For less persistent pesticides, oxidation may play a relatively minor role, or be the first reaction ia a metaboHc pathway. Oxidation generally results ia degradation of the parent molecule. However, attack by certain oxidative enzymes (phenol oxidases) can result ia the condensation or polymerization of the parent molecules this phenomenon is referred to as oxidative coupling (16). Examples of some important oxidative reactions are ether cleavage, alkyl-hydroxylation, aryl-hydroxylation, AJ-dealkylation, and sulfoxidation. 

Figure 9.3 The figure shows the degradation of the side chain of sterols which have substitutions at C-19. Removal of the C-19 methyl group (eg 19 norchoiesta-1,3,5 (10) triene-3-ol) also prevents ring breakdown. Note, however, hydroxylation of C-19 does not prevent all ring modifications.

Polyether-based thermoplastic copolyesters show a tendency toward oxidative degradation and hydrolysis at elevated temperature, which makes the use of stabilizer necessary. The problem could be overcome by incorporation of polyolehnic soft segments in PBT-based copolyesters [31,32]. Schmalz et al. [33] have proposed recently a more useful technique to incorporate nonpolar segments in PBT-based copolyesters. This involves a conventional two-step melt polycondensation of hydroxyl-terminated PEO-PEB-PEO (synthesized by chain extension of hydroxyl-terminated hydrogenated polybutadienes with ethylene oxide) and PBT-based copolyesters. 

Nomiyama K, T Tanizaki, H Ishibashi, K Arizono, R Shinohara (2005) Production mechanism of hydroxylated PCBs by oxidative degradation of selected PCBs using TiOj in water and estrogenic activity of their intermediates. Environ Sci Technol 39 8762-8769. 

Spadaro JT, L Isabelle, V Renganathan (1994) Hydroxyl radical mediated degradation of azo dyes evidence for benzene generation. Environ Sci Technol 28 1389-1393. 

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