Enzymatic oxidative polymerization of phenols

When a water-soluble alcohol and a buffer were used as the solvent, the product showed an improved solubility toward DMF and For instance, in 

The control of the polymer structure was achieved by solvent engineering. The ratio of phenylene and oxyphenylene units was strongly dependent on the solvent composition. In the HRP-catalyzed polymerization of phenol in a mixture of methanol and buffer, the oxyphenylene unit increased by increasing the methanol content, while the buffer pH scarcely influenced the polymer structure.  

The polymerization outcome depended on the monomer structure as well as on the enzyme origin. For instance, using HRP and p-n-alkylphenols, the 

The peroxidase-catalyzed polymerization of m-alkyl substituted phenols in aqueous methanol produced soluble phenolic polymers. The mixed ratio of buffer and methanol greatly affected the yields and the molecular weight of the polymer. The enzyme source greatly affected the polymerization pattern of m-substituted monomers. Using SBP catalyst, the polymer yield increased as a function of the bulkiness of the substituent, whereas the opposite tendency was observed when HRP was the catalyst. 

Fluorinated phenols, 3- and 4-fiuorophenols, and 2,6-difluorophenol, were subjected to peroxidase-catalyzed polymerization in an aqueous organic solvent, yielding fluorine-containing polymers. Elimination of fluorine atom partly took place during the polymerization to give polymers with complicated structures. 

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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. 

Ionic liquids are effective as co-solvents for the enzymatic oxidative polymerization of phenols [26]. In a mixture of a phosphate buffer and l-butyl-3-methylimidazolium tetrafluoroborate or 1-butyl-3-methylpyridinium tetrafluoroborate, p-cresol, 1-naphthol, 2-naphthol, and p-phenylphenol were polymerized by SBP to give polymers in good yields. 

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... 

Figure 2.14 Enzymatic oxidative polymerization of phenolic compounds.

The oxidative polymerization of phenols and anilines by enzymatic and chemical methods is an important method for synthesizing polyphenols50 and polyanilines51 in material research. Such polymerizations are often carried out in aqueous conditions. 

In the oxidative polymerization of phenols catalyzed by Cu complexes, the substrate coordinates to the Cu(II) complex and is then activated. The activated phenol couples in the next step. The Cu complex acts effectively as a catalyst at concentrations of 0.2-2 mol% compared to the substrate. The oxidation proceeds rapidly at room temperature under an air atmosphere to give poly(phenylene ether) in a quantitative yield. The polymerization follows Michaelis-Menten-type kinetics [55]. Enzymatic oxidation of phenols is an important pathway in the biosynthesis of lignin in plants [56] catalyzed by a metalloenzyme. 

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 first chapter by Reihmann and Ritter reviews the recent developments of peroxidase-catalyzed oxidative polymerization of phenol and derivatives with a phenolic OH group. The importance of enzymatic polymerization in general is emphasized. Properties of product polyphenols, characteristics of the enzyme catalysis, and significance of the process and the product are discussed. The second chapter by Uyama and Kobayashi is concerned with the oxidative polymerization of polyphenols, which are compounds containing more than two phenolic OH groups. These compounds include catechols and flavonoids... 

A bi-enzymatic system (glucose oxidase -I- HRP) was also used to catalyze the synthesis of phenolic polymers. The polymerization of phenol, albeit in moderate yield, was accomplished in the presence of glucose avoiding the addition of hydrogen peroxide (Scheme 2 ), which was formed in situ by the oxidation of glucose catalyzed by glucose oxidase. 

As described above, the enzymatic polymerization of phenols was often carried out in a mixture of a water-miscible organic solvent and a buffer. By adding 2,6-di-0-methyl-(3-cyclodextrin (DM-(3-CD), the enzymatic polymerization of water-insoluble m-substituted phenols proceeded in buffer. The water-soluble complex of the monomer and DM-(3-CD was formed and was polymerized by HRP to give a soluble polymer. In the case of phenol, the polymerization took place in the presence of 2,6-di-O-methyl-a-cyclodextrin (DM-a-CD) in a buffer. Only a catalytic amount of DM-a-CD was necessary to induce the polymerization efficiently. Coniferyl alcohol was oxidatively polymerized in the presence of a-CD in an aqueous solution. ... 

Among other in vitro enzymatic polymerizations that have been studied are the oxidative polymerizations of 2,6-disubstituted phenols to poly(p-phenylene oxide)s (Sec. 2-14b) catalyzed by horseradish peroxidase [Higashimura et al., 2000b] and the polymerization of P-cellobiosyl fluoride to cellulose catalyzed by cellulase [Kobayashi, 1999 Kobayashi et al., 2001],... 

Uyama H, Kurioka H, Kaneko I, Kobayashi S (1994) Synthesis of a new family of phenol resin by enzymatic oxidative polymerization. Chem Lett 423-426... 

Peroxidase catalyzed the oxidative polymerization of fluorinated phenols to give fluorine-containing polymers.46 During the polymerization, elimination of fluorine atom partly took place to give the polymer with a complicated structure. Antioxidant effects of the enzymatically synthesized polyphenols were evaluated.47 The autoxidation of tetralin was significantly suppressed in the presence of the polyphenols. 

New positive-type photoresist systems based on enzymatically synthesized phenolic polymers were developed [55]. The polymers from the bisphenol monomers exhibited high photosensitivity, comparable with a conventional cresol novolak. Furthermore, this photoresist showed excellent etching resistance. The oxidative polymerization of bisphenol-A proceeded by fungal peroxidase from Coprinus cinereus (CiP) in aqueous isopropanol [56]. CiP also catalyzed the oxidative... 

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. 

The enzymatic reaction kinetics on the HRP-catalyzed oxidation of p-cresol in aqueous 1,4-dioxane or methanol showed that the cataljdic turnover niunber and Michaelis constant were larger than those in water (235). Numerical and Monte Carlo simulations of the peroxidase-catalyzed polymerization of phenols were demonstrated (236). The simulations predicted the monomer reactivity and polymer molecular weight, leading to synthesis of polymers with specific molecular weight and index. In an aqueous 1,4-dioxane, the formation of monomer aggregate was observed (237), which might elucidate the specific polymerization behaviors in such a medium. 

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