Abstract
Biomass-derived phenols have recently arisen as an attractive alternative for building blocks to be used in synthetic applications, due to their widespread availability as an abundant renewable resource. In the present paper, commercial laccase from the thermophilic fungus Myceliophthora thermophila was used to bioconvert phenol monomers, namely catechol, pyrogallol and gallic acid in water. The resulting products from catechol and gallic acid were polymers that were partially characterized in respect to their optical and thermal properties, and their average molecular weight was estimated via solution viscosity measurements and GPC. FT-IR and 1H-NMR data suggest that phenol monomers are connected with ether or C–C bonds depending on the starting monomer, while the achieved molecular weight of polycatechol is found higher than the corresponding poly(gallic acid). On the other hand, under the same condition, pyrogallol was dimerized in a pure red crystalline compound and its structure was confirmed by 1H-NMR as purpurogallin. The herein studied green synthesis of enzymatically synthesized phenol polymers or biological active compounds could be exploited as an alternative synthetic route targeting a variety of applications.
Highlights
Phenol polymers have attracted increasing attention as novel materials with various useful properties and applications
In order to find the functional conditions where the enzyme catalyzes the oxidative bioconversion of various phenols, we studied the effect of pH and temperature for the polymerization of catechol and pyrogallol dimerization
The best conditions for M. thermophila laccase reactions were found similar in pH, while in both reactions 30 ̋ C was found as the optimal temperature, despite the thermophilic nature of the biocatalyst (Figure 1)
Summary
Phenol polymers have attracted increasing attention as novel materials with various useful properties and applications. Research efforts are mainly focusing on the manufacture of novel polyphenols as an alternative to phenol-formaldehyde resins, widely used as adhesives, electric coatings and composites [1]. Despite their numerous applications, the present phenol-formaldehyde resin manufacturing processes pose many issues. The present phenol-formaldehyde resin manufacturing processes pose many issues Chemical synthesis of such products requires the use of inorganic catalysts, often of high cost and toxicity, and is usually carried out under extreme conditions of pressure, temperature and pH [2]. Oxidoreductive enzymes, such as laccases [3], peroxidases [4,5], tyrosinases [6] or bilirubin oxidases [7] oxidize a variety of phenols, producing free radicals that are further subject to spontaneous polymerization
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