Polymerization of Phenol Derivatives

Polymer-Copper Catalysts for Oxidative Polymerization of Phenol Derivatives... 

The Cu-complex-catalyzed oxidative polymerization of phenol derivatives has been selected here as a model reaction in which a polymer-metal complex acts as a catalyst. The catalytic cycle is illustrated in Scheme 3, the example used being the oxidative... 

Oxidative polymerization of phenol derivatives is also important pathway in vivo, and one example is the formation of melanin from tyrosine catalyzed by the Cu enzyme, tyrosinase. The pathway from tyrosine to melanin is described by Raper (7) and Mason (8) as Scheme 8 the oxygenation of tyrosine to 4-(3,4-dihydro-xyphenyl)-L-alanin (dopa), its subsequent oxidation to dopaqui-none, its oxidative cyclization to dopachrome and succeeding decarboxylation to 5,6-dihydroxyindole, and the oxidative coupling of the products leads to the melanin polymer. The oxidation of dopa to melanin was attempted here by using Cu as the catalyst. 

Reverse micellar systems were used for the polymerization of phenol derivatives. HRP-catalyzed polymerization of p-ethylphenol in the ternary system composed of a bis(2-ethylhexyl) sodium sulfosuccinate (AOT)—water—isooctane system produced spherical polyphenol particles having 0.1—2 /tm diameters quantitatively.21 Similar particles were obtained by pouring the solution of enzymatically prepared polyphenol into a nonsolvent containing AOT.22... 

FIGURE 12. Oxidative polymerization of phenol derivatives involving amino sugar units (modified after Martin et al., 1975). 

So far, several oxidoreductases, peroxidase, laccase, polyphenol oxidase (tyrosinase), and so on have been reported to catalyze oxidative polymerization of phenol derivatives among which peroxidase is most often used [165,166]. Peroxidase is an enzyme that catalyzes the oxidation of a donor to an oxidized donor by the action of hydrogen peroxide, liberating two water molecules. Horseradish peroxidase (HRP) is a single-chain p-type hemoprotein that catalyzes the decomposition of hydrogen peroxide at the expense of aromatic proton donors. 

In living cells, various oxidoreductases play an important role in maintaining the metabolism of living systems. Most of oxidoreductases contain low valent metals as their catalytic center. In vitro enzymatic oxidoreductions have afforded functional organic materials. Some oxidoreductases such as peroxidase, laccase, and polyphenol oxidase have received much attention as catalysts for oxidative polymerizations of phenol derivatives to produce novel polyaromatics [1-10], This chapter deals with enzymatic oxidative polymerization of phenolic compounds. 

Ayyagari, M.S., Marx, K.A., Tripathy, S.K., Akkara, ).A., and Kaplan, D.L. (1995) Controlled free-radical polymerization of phenol derivatives by enzyme-catalyzed reactions in organic solvents. Macromolecules, 28 (15), 5192-5197. 

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... 

Enzymatic polymerization of phenol derivatives in a monolayer form was demonstrated (241,244,245). A monolayer was formed fromp-tetradecylox5q)henol and phenol at the air-water interface in a Langmuir trough, which was polymerized by HRP catalyst in the subphase. The polymerized film could be deposited on silicon wafer with a transfer ratio of 100% for the Y-type film. The monolayer thickness determined by Eppipsometric and AFM was 27.8 A. 

The expression polyphenol is assigned in organic chemistry to an aromatic compound with two or more hydroxyl fimctions, such as a flavonoid compound. In contrast, in publications deahng with the enzyme-catalyzed polymerization of phenol derivatives, this term is often used to name the polymeric products. Although this expression is not incorrect for these materials, its use can lead to confusion, especially if polymers made from flavonoid compounds are discussed, hi order to avoid misunderstanding, in this article the expression phenol polymer is used instead of polyphenol to name all polymers produced from phenols by peroxidase catalysis. 

It is expected that new types of functional phenol polymers with interesting properties in terms of thermal stabiUty or optical and electronic properties will be presented in the next few years. New examples of phenol polymers from natural resources will hopefully broaden the interest for this type of polymerization from a commercial point of view. In this connection, the finding of suitable highly active model complexes could be of increasing interest in reducing the cost of the oxidative polymerization of phenol derivatives. 

In the enzymatic polymerization of phenol derivatives, a mixture of hy-drophihc organic solvent and buffer is often used as a medium for the efficient production of polymers [45-47]. The HRP-catalyzed polymerization of catechin was carried out in an equivolume mixture of 1,4-dioxane and buffer (pH 7) to give a polymer with a molecular weight of 3.0 x 10 in 30% yield [48]. Using methanol as cosolvent improved the polymer yield and molecular weight [49]. 

Fig.1 Chemoselective polymerization of phenol derivative by horseradish peroxidase...

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