Abstract
In relation to the development of environmentally-friendly processing technologies for the continuously growing market of plastics, enzymes play an important role as green and sustainable biocatalysts. The present study reports the use of heterogeneous immobilized biocatalysts in solvent-free systems for the synthesis of aliphatic oligoesters with Mws and monomer conversions up to 1500 Da and 74%, respectively. To improve the accessibility of hydrophilic and hydrophobic substrates to the surface of the biocatalyst and improve the reaction kinetic and the chain elongation, two different binding modules were fused on the surface of cutinase 1 from Thermobifida cellulosilytica. The fusion enzymes were successfully immobilized (>99% of bound protein) via covalent bonding onto epoxy-activated beads. To the best of our knowledge, this is the first example where fused enzymes are used to catalyze transesterification reactions for polymer synthesis purposes.
Highlights
The present study reports the use of heterogeneous immobilized biocatalysts in solventfree systems for the synthesis of aliphatic oligoesters with Mws and monomer conversions up to 1500 Da and 74%, respectively
In this research article we propose the utilization of Thc_Cut1 fused with different binding modules—from cellobiohydrolase I from Hypocrea jecorina (CBM) and an Alcaligenes faecalis poly(hydroxy alkanoate) depolymerase (PBM)—for the tuning of biocatalyzed polycondensation of aliphatic polyesters
The negligible differences in terms of hydrophilic and hydrophobic properties of the modules are in line with the similar behaviour and specificity observed for the two fused cutinases
Summary
When compared with classical chemical catalysis, enzymes frequently prevail in terms of selectivity and impact on the environment [1]. One of the current most growing fields of interest is, without a doubt, the application of biocatalysts for the processing of natural and synthetic polymers, in particular polyesters [3,4] These environmentally friendly catalysts can work under mild conditions, enabling both the surface functionalization of the polymer and its decomposition to constitutive monomers, which could in turn be used for a subsequent re-polymerization closing the carbon cycle. For such purposes, one of the most investigated enzyme class is cutinases, serine-hydrolytic enzymes that show activity on their natural substrate cutin and on man-made polyesters [3]. The synthetic capabilities of cutinases were exploited: HiC was demonstrated to be active in the synthesis of linear polyesters and ring opening polymerization of several lactones [10,11] while cutinase 1 from Thermobifida cellulosilytica (Thc_Cut1) was reported as an interesting biocatalyst for the polycondensation of aliphatic oligoesters under solvent-free conditions [12]
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