Peroxidase-Initiated Polymerizations

Peroxidase-catalyzed radical formation is by far the most popular and best characterized initiation reaction for enzymatic polymerizations. Particularly horseradish peroxidase (HRP) has been used for a variety of polymerization reactions. 

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Gross and coworkers examined the influence of surfactants on the peroxidase-initiated polymerization of acrylamide [21]. Irrespective of the nature of surfactant (cationic, anionic, neutral), they found a significant rate acceleration,... 

Enzyme immobilization is an attractive method to stabilize the enzyme against denaturating reaction conditions and to make the biocatalyst recyclable [34-37]. In combination with peroxidase-initiated polymerizations, this has been reported recently by Zhao et al. [38]. Incorporation of HRP into a hydrogel increased both storage and thermal stability of the enzyme also resistance against H202 was increased to some extent. Furthermore, the immobilized enzyme preparation could be reused at least four times, albeit with significant activity losses after each cycle. 

One of the most used systems involves use of horseradish peroxidase, a 3-diketone (mosl commonly 2,4-pentandione), and hydrogen peroxide." " " Since these enzymes contain iron(II), initiation may involve decomposition of hydrogen peroxide by a redox reaction with formation of hydroxy radicals. However, the proposed initiation mechanism- involves a catalytic cycle with enzyme activation by hydrogen peroxide and oxidation of the [3-diketone to give a species which initiates polymerization. Some influence of the enzyme on tacticity and molecular... 

Foumand, D. Cathala, B. Lapierre, C. Initial steps of the peroxidase-catalyzed polymerization of coniferyl alcohol and/or sinapyl aldehyde capillary zone electrophoresis study of pH effect. Phytochemistry 2003, 62, 139-146. 

The lignols are synthesized within cells and are thought to move out into cell walls, possibly as phenolic glycosides.19°C/195 Cell wall peroxidases or laccas-es initiate polymerization.173 The previously discussed lignans do not tend to polymerize, but other dimeric... 

Peroxidase-Catalyzed Polymerization of p-Cresol. Large scale polymerizations were carried out in a volume of 250 mL in a 500 mL round bottom flask at 25°C with stirring at ca. 250 rpm. p-Cresol (688 mg, 25 mM) was dissolved in 213 mL dioxane and 37 mL aqueous buffer, pH 7 (0.01 M phosphate) added to give a solution consisting of 85% (v/v) dioxane. Horseradish peroxidase (25 mg, free powder) was added and the reaction was initiated by the addition of 0.28 mL of 30% H2O2 (10 mM). The suspension (peroxidase is insoluble in 85% dioxane) immediately turned yellow and the reaction was allowed to proceed 15 min. The concentrations of p-cresol and reaction products were determined by high performance liquid chromatography (HPLC) with a Ci8-reverse phase column (Waters Associates, Milford, MA). The isocratic solvent used was acetonitrile water (56 44) with... 

The influence of [02], [laccase] on the performance of the laccase-initiated polymerization of vinyl monomers is essentially the same as observed with peroxidases (6.3.2) [69], Thus, the polymer characteristics are inversely correlated with [laccase] and [monomer], [Acac] exceeds only in minor effect on the polymer weight with the exception of very low [Acac] [69], Here, no polymerization was observed unless the [02] was reduced significantly. This indicates an 02-dependent irreversible inactivation mechanism of the Acac radical. The mechanism of this inactivation however remains to be elucidated. On the other hand, [02] may be an efficient handle to control the average molecular weight of the resulting... 

Horseradish peroxidase. These radicals then of Chemistry), initiate polymerization in the presence of... 

Typically, peroxidase-catalyzed polymerization of phenol is carried out in the presence of H2O2, which acts as an oxidizing agent. The free radicals of monomers (substrates) formed initially undergo coupling to produce dimers, and successive oxidation and coupling eventually results in the formation of polymers. The peroxidase-catalyzed polymerization of phenols and substituted phenols usually produce the polymer with complicated structures. The main structure was estimated to be of phenylene units or a mixture of phenylene and oxyphenylene units (5). 

The peroxidase-catalyzed polymerizations of phenols involve the formation of phenoxy radicals as an initial step. These radicals may either condense with each other or may be added to unsaturated compounds forming irregular high molecular polymers (see the biosynthesis of lignin, D 22.2.3). 

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). 

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