Phenoxy species

The phenoxy species is released from the cluster with no activation energy barrier to overcome but a constant increase in energy to a Wheland complex from which shift isomerization transition state takes place. With respect to physisorbed toluene, the activation energy to achieve this transition state is act = + 282 kJ/mol. In the transition state, the shifting methyl group occupies an intermediate position between the aromatic ring carbon atom it was connected to, and the carbon atom it will connect to. The shift methyl... 

FIGURE 8. A functional model for galactose oxidase based on a di-copper/di-phenoxy species (Chaudhuri et al., 1998). 

The next two examples illustrate more complex surface reaction chemistry that brings about the covalent immobilization of bioactive species such as enzymes and catecholamines. Poly [bis (phenoxy)-phosphazene] (compound 1 ) can be used to coat particles of porous alumina with a high-surface-area film of the polymer (23). A scanning electron micrograph of the surface of a coated particle is shown in Fig. 3. The polymer surface is then nitrated and the arylnitro groups reduced to arylamino units. These then provided reactive sites for the immobilization of enzymes, as shown in Scheme III. 

The capability to detect such species by ESR spectroscopy provides a means to analyse the mechanisms of polymer breakdown under irradiation (17.19). In addition, certain compounds used to photostabilize polymers against UV radiation act by scavenging the reactive radicals to form more stable radical species (e.g., hindered phenoxy radicals) and thus the performance of these stabilizers can be assessed by ESR methods (12) ... 

This group of pesticides comprises different families of chemicals with her-bicidal action including substituted phenols, chlorinated aliphatic acids, chloro-phenoxy alkanoic acids, and substituted benzoic acids, which possess carboxyl or phenolic functional groups capable of ionization in aqueous media to yield anionic species [47,151,168-170]. 

An ESR spectrum of the electrolysis solution of 2,4,6-tri-t-butylphenol showed the formation of phenoxy radical which was accumulated in the solution with the supplied current amount. The active species of polymerization reaction was assumed to be a phenoxy radical formed by the electrolysis. 

Phenoxy radical species were believed to be present on the fibre surface, and superoxide was also identified in a cytochrome c assay. However, the presence of superoxide... 

Kinetic study of this reaction usually requires sampling the polymerizing mixture and analyzing for the concentrations of the various reaction species at different polymerization times. Vofsi and Tobolsky in 1965 reported the use of radioactively tagged initiator (10), while Saegusa amd coworkers in 1968 developed a "phenoxy end-capping" method in which the oxonium ion is trapped with sodium phenoxide and the derived phenyl ether at the polymer chain end quantitatively determined by UV spectrophotometry (11). 

Attachment of Hydroxycinnamic Acids to Structural Cell Wall Polymers. Peroxidase mediation may also result in binding the hydroxycinnamic acids to the plant cell wall polymers (66,67). For example, it was reported that peroxidases isolated from the cell walls of Pinus elliottii catalyze the formation of alkali-stable linkages between [2-14C] ferulic acid 1 and pine cell walls (66). Presumably this is a consequence of free-radical coupling of the phenoxy radical species (from ferulic acid 1) with other free-radical moieties on the lignin polymer. There is some additional indirect support for this hypothesis, since we have established that E-ferulic acid 1 is a good substrate for horseradish peroxidase with an apparent Km (77 /tM), which is approximately one fifth of that for E-coniferyl alcohol (400 /iM) (unpublished data). 

A subsequent study examined phenylperoxy radical in greater detail. Fadden et identified five possible unimolecular decomposition pathways for phenylperoxy radical (Fig. 10) via oxygen atom loss to form phenoxy radical (Fig. 10, route A), via a dioxiranyl radical species (Fig. 10, route B), via a dioxetanyl radical... 

The overall pathways of benzene oxidation and the decompositions of possible intermediates have been well characterized via theoretical methods. Thus far, we have discussed these species mainly in the context of their oxidation mechanisms, but phenylperoxy and phenoxy radicals have also been investigated as individual experimental targets. 

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