Abstract
Microwave energy (MWe) is, nowadays, widely used as a clean synthesis tool to improve several chemical reactions, such as drug molecule synthesis, carbohydrate conversion and biomass pyrolysis. On the other hand, its exploitation in enzymatic reactions has only been fleetingly investigated and, hence, further study of MWe is required to reach a precise understanding of its potential in this field. Starting from the authors’ experience in clean synthesis and biocatalyzed reactions, this study sheds light on the possibility of using MWe for enhancing enzyme-catalyzed polycondensation reactions and pre-polymer formation. Several systems and set ups were investigated involving bulk and organic media (solution phase) reactions, different enzymatic preparations and various starting bio-based monomers. Results show that MWe enables the biocatalyzed synthesis of polyesters and pre-polymers in a similar way to that reported using conventional heating with an oil bath, but in a few cases, notably bulk phase polycondensations under intense microwave irradiation, MWe leads to a rapid enzyme deactivation.
Highlights
The drive towards a Circular Economy will look to chemistry and biology to provide the basis of innovative products, made from renewable feedstocks and designed to be reused, recycled, or the feedstock renewed through controlled or natural processes [1]
In a first instance we investigated the effect of Microwave energy (MWe) on solvent-free reactions, as previously reported by Rejasse et al for the synthesis of butyl butyrate using both free and immobilized Candida antarctica lipase B (CaLB) [23,24]
Several reports of MWe applied to biocatalyzed reactions have been published but, to the best of our knowledge, only the reaction yield polymerizations (ROP) of ε-CL has been carried out when investigating but, to the best of our knowledge, only the ROP of ε-CL has been carried out when investigating enzymatic polymer synthesis
Summary
The drive towards a Circular Economy will look to chemistry and biology to provide the basis of innovative products, made from renewable feedstocks and designed to be reused, recycled, or the feedstock renewed through controlled or natural processes [1]. The polymer industry is under pressure to mitigate the environmental cost of using petroleum-based plastics, seeking both to source monomers from biomass and to carry out the synthesis of the polymers in a more benign fashion. Biotechnology is already contributing significantly to the gradual replacement of petroleum-based chemicals, bringing closure of the carbon circle [2]. The need now is for biotechnology to have a greater impact in developing benign polymerization processes. Several reports on enzymatic synthesis of bio-based polyesters have been presented in the last decade, leading to the production of aliphatic [3,4], aromatic [5,6] and functional [7,8] products, achieving materials otherwise unlikely obtainable via conventional chemical routes [9,10].
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