Enzymatic Oxidation Polymerization Using Peroxidase

Polyphenols. For enzymatic oxidative polymerization of phenol derivatives, peroxidase has been often used as catalyst. Catal5d ic cycle of peroxidase is shown in Figure 11. Peroxidase catalyzes decomposition of hydrogen peroxide at... 

A chemoenzymatic way to produce poly(hydroquinone) was achieved by enzymatic oxidative polymerization of 4-hydroxyphenyl benzoate, followed by alkahne hydrolysis of the resulting polymer [45]. HRP and SBP were used as enzymes. The molecular weight of the resulting poly(4-hydroxyphenyl benzoate) varied between 1100 and 2400 g/mol. The structure was said to consist of phenylene and oxyphenylene moieties, which was found by IR analysis and titration of the residual amount of phenolic groups in the polymer. Other phenol polymers have shown their potential for electronic applications as well. Besides hydroquinone, catechol has also been used as substrate for peroxidase-catalyzed polymerization. The molecular weights of the reac-... 

In the previous chapter Synthesis of Phenol Polymers Using Peroxidases , the enzymatic oxidative polymerization of monophenolic derivatives is described. This chapter deals with the enzymatic synthesis and properties of polymers from polyphenols, compounds having more than two hydroxyl groups on the aromatic ring(s). In particular, cured phenolic polymers (artificial urushi) and flavonoid polymers are examined from the standpoint of the enzymatic synthesis of functional materials. 

The peroxidase-catalyzed oxidative coupling of phenols proceeds rapidly in aqueous solution, giving rise to the formation of oligomeric compounds that, unfortunately, have not well been characterized, as most of them demonstrate a low solubility towards common organic solvents and water. In 1987, the enzymatic synthesis of a new class of phenolic polymer was first reported [15], whereby an oxidative polymerization of p-phenylphenol, using HRP as catalyst, was carried out in a mixture of water and water-miscible solvents such as 1,4-dioxane, acetone. 

One synthetic approach gaining popularity for its ecologically friendly nature and its potential biological applications is that of biomediated polymerization. Enzymatic oxidants, such as horseradish peroxidase (212,213), are commonly used for chemical oxidative polymerization. Additionally, bacteria can be used to effect chemical reactions, as in the Ballard route to PPP described above (79). 

For the last decades, enzymatic synthesis of phenolic polymers has been extensively investigated [1-10]. In living cells, various oxidoreductases play an important role in maintaining the metabolism of living systems. So far, several oxidoreductases—peroxidase, laccase, bilirubin oxidase etc.—have been reported to catalyze an oxidative polymerization of phenol derivatives, and among them, peroxidase is most often used. The enzymatically synthesized phenolic polymers are expected to become an alternative to conventional phenolic resins, which have limitations of their preparation and use due to concerns over the toxicity of formaldehyde. 

Perhaps the most well-known peroxidase-catalyzed reactions are those involving electron transfer, in which an aromatic substrate is oxidized in a mono-electronic oxidation up to its mono-radical, Eq. (1), which is capable of participating further in a variety of non-enzymatic reactions such as disproportionation, polymerization and electron transfer. These types of reactions are very common during the peroxidase-catalyzed oxidation of phenols and, in some cases, during the oxidation of alkaloids. For example, peroxidase is capable of dimerizing jatrorrhizine (IV) to 4,4 -bis-jatrorrhizine (V) in the presence of H2O2 (Scheme III) [50], Jatrorrhizine is a bioactive protoberberine alkaloid present in Colombo radix (Jatrorrhiza palmata) widely used in both oriental and western medicine. 

It is now well-established that some enzyme families, including various peroxidases and laccases, catalyze the polymerization of vinyl monomers and other redox active species such as phenol-type structures. Vinyl polymerization by these redox catalysts has recently been reviewed 93). These catalysts have been used to prepare polyanilines 94) and polyphenols 95,96). A few examples of related research are included in this book. For example. Smith et al (57) described a novel reaction catalyzed by horseradish peroxidase (HRP). In the presence of HRP and oxygen, D-glucuronic acid was polymerized to a high molecular weight (60,000) polyether. However, the authors have not yet illucidated the polyether structure. Two other oxidative biotransformations were discussed above i) the sono-enzymatic polymerization of catechol via laccase 31), and ii) the oxidation of aryl silanes via aromatic dioxygenases 30). 

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