Anilines peroxidase-catalyzed oxidation

These peaks may also be comprised of imine nitrogens arising from 1,2-addition of aniline to quinones formed from the peroxidase catalyzed oxidative decarboxylation... 

A new class of polyaromatics was synthesized by peroxidase-catalyzed oxidative copolymerization of phenol derivatives with anilines. In the case of a combination of phenol and o-pheneylenediamine, FT-IR analysis showed the formation of the corresponding copolymer.75... 

In some methods, the final mixture is acidified slightly to stop the reaction, and the intensity of the yellow chro-mophore is measured at 400 nm. In stronger acid solution, the color becomes pink, with maximum absorbance at 540 nm, and both sensitivity and stability are improved. Other approaches to measurement of the H2O2 produced include the peroxide-mediated oxidative coupMng of 3-methyl 2-benzothia2olinone hydrazone (MBTH) with N,N-dimethyl-aniline (DMA) catalyzed by peroxidase or the oxidative coupHng of p-aminophenazone (PAP) to phenoi. Both procedures have been automated. The... 

Other peroxidases such as HRP or CPO were also able to perform such reactions. Another approach to the production of nitroarenes with peroxidases is based on the CPO (or bromoperoxidase)-catalyzed oxidation of arylamines. Table 16.3-10 gives a selection of peroxidase-catalyzed conversions of aniline derivatives to corresponding nitroarenes. 

In some cases, quinone-imine formation requires an initial hydroxylation step as illustrated with the nonsteroidal anti-inflammatory drug and idiosyncratic hepatotoxin diclofenac. Thus, CYP-catalyzed aromatic hydroxylation para to the aniline nitrogen affords thepara-hydroxydiclofenac isomers, which can then undergo CYP or peroxidase-mediated oxidation to the quinone-imines amenable to trapping with GSH (Scheme 6) (Tang et al., 1999 Miyamoto et al., 1997). The aniline nitrogen in quinone-imine derivatives can also be part of a heterocyclic... 

Besides participating in quinone-imine formation, primary anilines can also undergo an alternate CYP- or peroxidase-catalyzed bioactivation pathway that involves an initial Y-hydroxylation on the aniline nitrogen to afford the Y-hydroxylamine metabolite followed by further oxidation to a reactive nitroso species, which, in some cases, can be trapped with GSH (Scheme 10)... 

A molar equivalent of hydrogen peroxide to monomer and horseradish peroxidase is a well-known redox system that catalyzes the free radical polymerization of phenol, anilines, and their derivatives [6-14]. Horseradish peroxidase-mediated polymerization of styrene and methyl methacrylate, with a monomer (styrene or methyl methacrylate) to hydrogen peroxide ratio of 40 1, did not occur in the absence of 2,4-pentanedione. Therefore, it is likely that this compound is involved in the initiation of free radical formation. A reasonable hypothesis for the horseradish peroxidase-catalyzed polymerization of vinyl monomers is that the enzyme is oxidized by hydrogen peroxide and passes from its native state through two catalytically active forms (Ez and Ezz). Each of these active forms oxidizes the initiator (b-diketone, 2,4-pentanedione) while the enzyme returns to the native form. The Ezz state of enzyme is oxidized by hydrogen peroxide to produce inactive enzyme, Ezzz, which spontaneously reverts to the native form of enzyme. The free radicals produced from the initiator generate radicals in the vinyl monomer to form polymer (Fig. 2). 

Similarly to Mb, Hb is also active in the catalytic oxidation of substrates by hydrogen peroxide, with rates and general behavior comparable with those of Mb. In particular, a number of research reports showed that Hb exhibits oxidizing activities and can be used as a mimetic peroxidase to catalyze the oxidation reactions of aromatic compounds [180-182], aniline [183, 184], lipids [185], styrene [186], and sulfides [187]. Again, although the activity of Hb is not comparable with... 

HRP catalyzes the oxidative dehydrogenation of a wide range of electron-rich aromatic compounds. The result of this radical formation pathway is dimerization and subsequent oligomerization of the substrates [76-78]. Peroxidases have been used to catalyze polymerizations of phenols (e.g. p-cresol and guaiacol) and aromatic amines (e.g. aniline, and o-phenyldiamine) [79, 80]. N- and O-dealkylations are also useful electron transfer reactions catalyzed by peroxidases. These reactions are used in industrial wastewater treatment and may have synthetic applications [81]. 

Cytochrome c peroxidase (CCP) catalyzes the oxidation of ferrocytochrome c (cyt c). Many site-directed mutagenesis studies have been performed on this enzyme in efforts to better understand and rationally engineer heme peroxidase function [149 -156], Various studies indicate that the large protein substrate cyt c binds to CCP in a different region than smaller substrates [155, 157]. Whereas small substrates such as phenol and aniline are believed to approach the heme from its distal side and bind at the heme edge, cyt c lies much further from the heme, and electron transfer seems to occur from the proximal side [158], The low activity and selectivity exhibited by CCP compared to HRP and CPO is attributed to the limited access by small substrates to the heme [159]. 

Manganese dioxides operate in a manner similar to the phenoloxidase enzymes by promoting the one electron oxidation of anilines and phenols with the concomitant reductive dissolution of the manganese dioxide (Mn IV) to soluble manganese (Mn II) (21). In their work with guaiacol and 4-chloroaniline, Simmons et al. (19) reported that peroxidase, laccase, tyrosinase, and manganese dioxide all catalyzed formation of the same five co-oligomers as initial reaction products. 

Aniline and its derivatives were oxidatively polymerized by peroxidase catalyst. HRP catalyzed the polymerization of aniline in aqueous organic solvents to produce the polymer with a complicated structure in low yields.65 The resulting polymer showed good third-order nonlinear optical properties.66... 

Another advantage of this enzyme-catalyzed route to colloidal PAn salts is the considerably higher pH that can be employed compared to the previous chemical and electrochemical polymerization methods. Horseradish peroxidase immobilized on chitosan powder as a solid support has also been found to catalyze the H202 oxidation of aniline to a similar PAn/PSS product, opening up the prospect of enzyme reuse and the design of enzyme reactors for PAn synthesis.104... 

One of the most interesting applications is the development of an enzyme transistor [79], The idea is based on the DET between HRP and a poly(aniline) film, which loses electrical conductivity due to its oxidation by H2O2 catalyzed by the enzyme. As mentioned by the authors, the enzyme transistor can form the basis for a new generation of devices distinctly different from usual amperomet-ric electrodes however, a number of limitations still need to be overcome, such as fast reproducible switching of the transistor and inactivation of peroxidase. The last limitation might not be a problem in the format of a disposable sensor. 

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