Phenolics laccase-catalyzed polymerization

Lignophenols having a linear structure were obtained by the surface reaction of a native lignin and phenols in sulfuric acid. Laccase catalyzed the oxidative polymerization of lignocatechol in a mixture of ethanol and phosphate buffer to give the crosslinked polymer [92]. The product showed high affinity for bovine serum albumin and glucoamylase. 

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). 

Laccase is one of the main oxidizing enzymes responsible for polyphenol degradation. It is a copper-containing polyphenoloxidase (p-diphenoloxidase, EC 1.10.3.2) that catalyzes the oxidation of several compounds such as polyphenols, methoxy-substituted phenols, diamines, and other compounds, but that does not oxidize tyrosine (Thurston, 1994). In a classical laccase reaction, a phenol undergoes a one-electron oxidation to form a free radical. In this typical reaction the active oxygen species can be transformed in a second oxidation step into a quinone that, as the free radical product, can undergo polymerization. 

Copper-catalyzed oxidations of phenols by dioxygen have attracted considerable interest owing to their relevance to enzymic tyrosinases (which transform phenols into o-quinones equation 24) and laccases (which dimerize or polymerize diphenols),67 and owing to their importance for the synthesis of specialty polymers [poly(phenylene oxides)]599 and fine chemicals (p-benzoquinones, muconic acid). A wide variety of oxidative transformations of phenols can be accomplished in the presence of copper complexes, depending on the reaction conditions, the phenol substituents and the copper catalyst.56... 

The network structure of lignin, which is made of phenol units, coagulates the cell wall in wood tissue, which is composed of cellulose and hemicellulose. Lignin is currently a waste product because of its complicated structure [1-4], It is produced by an oxidative polymerization of coniferyl alcohol, sinapil alcohol, and cumarol alcohol (Figure 1) catalyzed by metalloenzymes such as laccase and peroxidases. Laccase is a protein whose active center contains four coppers per one subunit [5-20],... 

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. 

Some microbial pathogens can circumvent the defensive response of plants by biotransforming the antimicrobial stilbenoids in a multi-step oxidative detoxification process [106], Research has shown that the pathogenicity of B. cinerea strains is positively correlated with these fungi s production of blue-copper oxidases known as stilbene oxidases or laccases [127,128]. These enzymes are polyphenol oxidases capable of catalyzing the oxidation and polymerization of numerous phenolic substrates [129,130,131,132]. It has been shown that 1 is readily transformed in the presence of B. cinerea culture medium filtrates that contain laccases [107]. Recently, six resveratrol dimers (restrytisols A-C... 

Oxidative coupling or condensation reactions involving toxic organics are catalyzed by phenol oxidases such as laccases or peroxidases. In the oxidative coupling of phenol, for example, aryloxy or phenolate radicals are formed by removal of an electron and a proton from the hydroxyl group. The resulting phenolate radicals then couple with phenolic or other compounds to yield dimerized or polymerized products (Brown, 1967). 

Also laccases, oxidoreductases with a Cu atom in the active center, have been successfully applied to the synthesis of phenol polymers. For example, phenol and several derivatives were polymerized by laccase from Pycnoporus coccineus (PCL) in aqueous organic solvents to yield the corresponding polymers [149]. The same enzyme was used to produce PPO from syringic acid (79) and from 2,6-dimethylphenol. Laccase from Myceliophthore (MPL) was found to catalyze the polymerization of syringic acid to PPO [135-137]. Lac-... 

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. 

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