ENZYMATIC POLYMERIZATION OF PHENOLS IN ROOM TEMPERATURE IONIC LIQUIDS

Antioxidant Activity of Synthetic Polymers of Phenolic Compounds

In recent years, developing potent antioxidants has been a very active area of research. In this context, phenolic compounds have been evaluated for their antioxidant activity. However, the use of phenolic compounds has also been limited by poor antioxidant activity in several in vivo studies. Polymeric phenols have received much attention owing to their potent antioxidant properties and increased stability in aqueous systems. To be truly effective in biological applications, it is important that these polymers be synthesized using benign methods. In this context, enzyme catalyzed synthesis of polymeric phenols has been explored as an environmentally friendly and safer approach. This review summarizes work in enzymatic syntheses of polymers of phenols. Several assays have been developed to determine the antioxidant potency of these polymeric phenols. These assays are discussed in detail along with structure-property relationships. A deeper understanding of factors affecting antioxidant activity would provide an opportunity for the design of versatile, high performing polymers with enhanced antioxidant activity.

Development of a Surfactant-Containing Process to Improve the Removal Efficiency of Phenol and Control the Molecular Weight of Synthetic Phenolic Polymers Using Horseradish Peroxidase in an Aqueous System

To reduce phenolic pollutants in the environment, many countries have imposed firm restrictions on industrial wastewater discharge. In addition, the current industrial process of phenolic resin production uses phenol and formaldehyde as the reactants to perform a polycondensation reaction. Due to the toxicity of formaldehyde and phenolic pollutants, the main purpose of this research was to design a green process using horseradish peroxidase (HRP) enzymatic polymerization to remove phenols and to produce formaldehyde-free phenolic polymers. In this study, the optimal reaction conditions, such as reaction temperature, pH, initial phenol concentration and initial ratio of phenol, and H₂O₂, were examined. Then, the parameters of the enzyme kinetics were determined. To solve the restriction of enzyme inactivation, several nonionic surfactants were selected to improve the phenol removal efficiency, and the optimal operation conditions in a surfactant-containing system were also confirmed. Importantly, the molecular weight of the synthetic phenolic polymers could be controlled by adjusting the ratio of phenol and H₂O_2. The content of biphenols in the products was almost undetectable. Collectively, a green chemistry process was proposed in this study and would benefit the treatment of phenol-containing wastewater and the production of formaldehyde-free phenolic resin in the future.

Peroxidases-assisted removal of environmentally-related hazardous pollutants with reference to the reaction mechanisms of industrial dyes

Environmental protection is one of the most important challenges for the humankind. Increasing number of emerging pollutants resulting from industrial/human-made activities represents a serious menace to the ecological and environmental equilibrium. Industrial dyes, endocrine disrupters, pesticides, phenols and halogenated phenols, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and other xenobiotics are among the top priority environmental pollutants. Some classical remediation approaches including physical, chemical and biological are being employed, but are ineffective in cleaning the environment. Enzyme-catalyzed transformation reactions are gearing accelerating attention in this context as potential alternatives to classical chemical methods. Peroxidases are catalysts able to decontaminate an array of toxic compounds by a free radical mechanism resulting in oxidized or depolymerized products along with a significant toxicity reduction. Admittedly, enzymatic catalysis offers the hallmark of high chemo-, regio-, and enantioselectivity and superior catalytic efficiency under given reaction environment. Moreover, enzymes are considered more benign, socially acceptable and greener production routes since derived from the renewable and sustainable feedstock. Regardless of their versatility and potential use in environmental processes, several limitations, such as heterologous production, catalytic stability, and redox potential should be overcome to implement peroxidases at large-scale transformation and bio-elimination of recalcitrant pollutants. In this article, a critical review of the transformation of different types of hazardous pollutants by peroxidases, with special reference to the proposed reaction mechanisms of several dyes is presented. Following that major challenges for industrial and environmental applications of peroxidases are also discussed. Towards the end, the information is also given on miscellaneous applications of peroxidases, concluding remarks and outlook.

A novel, efficient and sustainable strategy for the synthesis of α-glycoconjugates by combination of a α-galactosynthase and a green solvent

Synthesis of glycoconjugates using an α-galactosynthase in green solvents.

Biocatalysis for biobased chemicals

The design and development of greener processes that are safe and friendly is an irreversible trend that is driven by sustainable and economic issues. The use of Biocatalysis as part of a manufacturing process fits well in this trend as enzymes are themselves biodegradable, require mild conditions to work and are highly specific and well suited to carry out complex reactions in a simple way. The growth of computational capabilities in the last decades has allowed Biocatalysis to develop sophisticated tools to understand better enzymatic phenomena and to have the power to control not only process conditions but also the enzyme's own nature. Nowadays, Biocatalysis is behind some important products in the pharmaceutical, cosmetic, food and bulk chemicals industry. In this review we want to present some of the most representative examples of industrial chemicals produced in vitro through enzymatic catalysis.

Synthesis and chemical properties of polyphenols with oligoaniline pendant groups

Horseradish peroxidaze (HRP)- or N, N′-bis(salicylidene)ethylenediamineiron(III)-catalyzed polymerizations of 4-(4-phenylaminophenylamino)phenol (monomer-1) and 4-[4-(4-phenylaminophenylamino)phenylamino]phenol (monomer-2) caused oxidative coupling at the hydroxyphenyl group to yield polyphenols (PPs) with pendant oligoaniline (OAN) groups. UV-vis measurements suggested that the OAN pendant groups of the polymers were oxidized in air, resulting in the formation of quinoid structures, which were converted into benzonoid structures by treatment with hydrazine monohydrate. The polymers were electrochemically oxidized in solution.

Valuable chemicals by the enzymatic modification of molecules of natural origin: terpenoids, steroids, phenolics and related compounds

A renewed interest for using natural organic molecules for the production of valuable chemicals is observed in current organic processes. Natural compounds provide the access to natural grade chemicals when submitted to physical treatments or biotechnological processes. Dealing with structurally complex molecules, they can provide complex core structures for hemisynthesis purposes, and in many instances they offer the advantage of providing sustainable processes when using renewable resources. These assets could be synergistic with the assets of biocatalytic processes, to end-up with efficient and sustainable processes in the organic synthesis of valuable products. In this review, we have gathered a selection of examples on the use of enzymes for the modification of molecules of natural origin being either purified compounds (terpenoids, steroids, phenolics) or mixtures (essential oils, natural extracts) to access fine chemicals or organic polymers.

Activation and stabilization of enzymes in ionic liquids

As environmentally benign "green" solvents, room temperature ionic liquids (ILs) have been used as solvents or (co)solvents in biocatalytic reactions and processes for a decade. The technological utility of enzymes can be enhanced greatly by their use in ionic liquids (ILs) rather than in conventional organic solvents or in their natural aqueous reaction media. In fact, the combination of green properties and unique tailor-made physicochemical properties make ILs excellent non-aqueous solvents for enzymatic catalysis with numerous advantages over other solvents, including high conversion rates, high selectivity, better enzyme stability, as well as better recoverability and recyclability. However, in many cases, particularly in hydrophilic ILs, enzymes show relative instability and/or lower activity compared with conventional solvents. To improve the enzyme activity as well as stability in ILs, various attempts have been made by modifying the form of the enzymes. Examples are enzyme immobilization onto support materials via adsorption or multipoint attachment, lyophilization in the presence of stabilizing agents, chemical modification with stabilizing agents, formation of cross-linked enzyme aggregates, pretreatment with polar organic solvents or enzymes combined with suitable surfactants to form microemulsions. The use of these enzyme preparations in ILs can dramatically increase the solvent tolerance, enhance activity as well as stability, and improve enantioselectivity. This perspective highlights a number of pronounced strategies being used successfully for activation and stabilization of enzymes in non-aqueous ILs media. This review is not intended to be comprehensive, but rather to present a general overview of the potential approaches to activate enzymes for diverse enzymatic processes and biotransformations in ILs.