Degradation products/kinetic

The bromine atoms in the addition product can be completely replaced by phenyl groups by reaction with PhMgBr (Kathan 1977), as indicated by the subsequent metathetical degradation products. Kinetic studies show that double bonds adjacent to M2 groups react rather more slowly than those adjacent to Mj groups (Hummel 1977c). 

An example is poly(bis(p-carboxyphenoxy)propane) (PCPP) which has been prepared as a copolymer with various levels of sebacic anhydride (SA). Injection molded samples of poly (anhydride) / dmg mixtures display 2ero-order kinetics in both polymer erosion and dmg release. Degradation of these polymers simply releases the dicarboxyhc acid monomers (54). Preliminary toxicological evaluations showed that the polymers and degradation products had acceptable biocompatibiUty and did not exhibit cytotoxicity or mutagenicity (55). 

Studies of chlorophyll degradation in heated broccoli juices over the 80 to 120°C range revealed that chlorophylls degrade first to their respective pheophytins and then to other degradation products in what can therefore be described as a two-step process. Both chlorophyll and pheophytin conversions followed a first-order kinetics, but chlorophyll a was more heat sensitive and degraded at a rate approximately twice that of chlorophyll This feature had been observed by other authors. Temperature dependence of the degradation rate could adequately be described by the Arrhenius equation. ... 

Therefore no trustworthy results for kinetic analysis conld be obtained from the UV-vis absorption spectra due to the formation of bixin isomers and degradation products at different rate constants. " ... 

Scotter, M.J., Castle, L., and Appleton, G.P., Kinetics and yields for the formation of colonred and aromatic thermal degradation products of annatto in foods, Food Chem., 74, 365, 2001. 

Acero JL, K Stemmier, U van Gunten (2000) Degradation kinetics of atrazine and its degradation products with ozone and OH radicals a predictive tool for drinking water treatment. Environ Sci Technol 34 591-597. 

It is important to distinguish between erosion and degradation. Erosion is mass loss from a bioerodible polymer and may be a consequence of polymer dissolution or degradation of the polymer backbone, followed by dissolution of the degradation products. Degradation typically occurs by hydrolysis of the polymer backbone, the kinetics of which is a function of the polymer chemistry. Thus, erosion is the sum of several elementary processes, one of which may be polymer degradation. 

Erosion is typically characterized by either occurring on the surface or in the bulk. Surface erosion is controlled by the chemical reaction and/or dissolution kinetics, while bulk erosion is controlled by diffusion and transport processes such as polymer swelling, diffusion of water through the polymer matrix, and the diffusion of degradation products from the swollen polymer matrix. The processes of surface and bulk erosion are compared schematically in Fig. 1. These two processes are idealized descriptions. In real systems, the tendency towards surface versus bulk erosion behavior is a function of the particular chemistry and device geometry (Tamada and Langer, 1993). Surface erosion may permit the... 

During early phase development there is limited knowledge about the chemistry of the new chemical entity (NCE) with respect to synthetic impurities and degradation pathways and kinetics. It is, therefore, desirable to develop an array of methods that show applicability to a broad range of potential impurities, degradation products, and excipients. The methods are intended to provide the information necessary to guide the improvement of a synthesis route or a new drug formulation. 

The reactions of A-phenyl a-r-butyl nitrone (PEN) with maleimides, maleic anhydride, and diethyl maleate have been studied by EPR and two types of spin adduct detected. They arise from the reductive addition of PEN to the alkenes and the degradation product of DEN (2-methyl-2-nitropropane). The deuterium and muonium kinetic isotope effects for the addition of the hydrogen atom to a variety of alkenes have been determined experimentally and theoretically. ... 

Qin-Tao L, Williams HE (2007) Kinetics and degradation products for direct photolysis of P-blockers in water. Environ Sci Technol 41(3) 803-810... 

One advantage of HPLC is that the analysis of unstable pesticides may be performed directly in aqueous medium without the extraction step or following extraction and concentration. Although the direct approach is quite useful for formulations or for kinetic studies to monitor the parent compounds in the presence of degradation products, its usefulness is limited in the case of environmental samples, where the concentration is usually in the parts-per-billion range (31). 

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