Recent Advances in the Enzymatic Synthesis of Polyester

Screening assay for polyester hydrolyzing microorganisms using fluorescence-labeled poly(butylene adipate)

Despite recent advances, there is still a demand for more efficient enzymes hydrolyzing synthetic polymers. Automated high throughput screening strategies of microorganisms from different environments could yield novel enzymes but require specific methods for detection of polymer hydrolysis in complex matrices. Here, 5-carboxy-fluorescein (5-FAM) was covalently coupled to poly(butylene adipate) (PBA) and blended at 1 %, 5 % and 10 % w/w concentrations with non-labeled PBA. Hydrolysis of PBA by the Thc_Cut1 cutinase from Thermobifida cellulosilytica was confirmed via quantification of the released monomers 1,4-butanediol and adipic acid, weight loss and FTIR analysis. Upon incubation with Thc_Cut1, hydrolysis of all three fluorescent labeled PBA blends lead to a clear fluorescence increase of up to 4000 RFU while no signal change was detected for the blank and for heat-inactivated enzyme (signal below 500 RFU). In a next step, as a model organism Pichia pastoris expressing the identical cutinase was cultivated in the presences of labeled PBA. Despite the complex matrix, a fluorescence increase of up to 500 RFU was observed for P. pastoris expressing the enzyme while no significant signal change was seen for the control strain (lacking Thc_Cut1 expression). Likewise, extracellular enzymes from the fungi Fusarium solani and Alternaria alternata hydrolyzed labeled PBA leading to fluorescence increases of 1328 and 1187 RFU. This indicates that 5-FAM covalently coupled to polymers could be used for development of simple and high throughput screening platforms to identify polymer decomposing microorganisms and enzymes.

Enzymatically Covalent and Noncovalent Weaving toward Highly Efficient Synthesis of 2D Monolayered Molecular Fabrics

Molecular fabrics with fascinating physical characteristics, such as structural flexibility and single-layered thinness, have attracted much attention. Chemists worldwide have been working on building unique molecularly woven structures in two dimensions. However, the synthesis of two-dimensional molecular weaving remains a challenging task, especially in water. Herein, we propose a straightforward and practical method to construct 2D molecular fabrics by enzymatically covalent and noncovalent syntheses in water. In particular, aromatic helical pentamers with two-terminal tyrosine residues (Penta-Tyr) can spontaneously dimerize via π-π interactions into double-helical interlocking structure, and the two-terminal tyrosine moieties of Penta-Tyr can undergo oxidative polymerization catalyzed by horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) for effective covalent cross-linking. The 2D monolayered molecular fabrics can be readily prepared by the catalysis of HRP and H2O2 under mild conditions, which exhibit concentration-dependent weaving behavior. This work not only demonstrates an enzyme-catalyzed approach for the highly efficient synthesis of 2D monolayered molecular fabrics for the first time but also will promote the controllable preparation and application of water-soluble 2D molecular fabrics.

Enzymatic synthesis of aromatic biobased polymers in green, low-boiling solvents

Given the urge to accelerate the substitution of petrol-derived solvents not only in more traditional fields like pharmaceuticals, personal care, or electronics but also in innovative research processes, this work focuses on the utilisation of four biobased solvents as media for the enzymatic synthesis of aliphatic-aromatic polyesters. As building blocks, the lignin-derived diethyl-2,4-pyridinedicarboxylate was selected as the potentially biobased, aromatic component while more classical diols such as 1,4-butanediol and 1,8-octanediol were used as the aliphatic portion. Results show that among the tested green solvents (cyclohexanone, phenetole, anisole and eucalyptol), the most suitable medium for lipase B from Candida antarctica-catalysed polycondensation reactions was eucalyptol that allowed reach monomer conversions >95 % and number average molecular weights up to 3500 g·mol-1. On the other hand, cyclohexanone led to the lowest monomer conversions (<80 %) and molecular weights (Mn<500 g·mol-1) confirming once again the unsuitability of ketone-containing solvents for enzymatic esterification and transesterification reactions. The lipase could be used up to three times, in eucalyptol as a solvent, without a significant decrease in monomer conversion or molecular weight.

Lipase-catalyzed solvent-free synthesis of monoglycerides from biodiesel-derived crude glycerol: Optimized using response surface methodology

The growth of the biodiesel industry has resulted in significant quantity of crude glycerol. It is necessary to explore the synthesis of high-value-added products from crude glycerol. In this study, the enzymatic synthesis of monoglycerides under solvent-free conditions, employing crude glycerol as the primary feedstock, had been investigated. The analysis showed that the highest yield of monoglycerides was obtained after 12 h, and Novozym 435 showed the highest monoglyceride yield of 18.41 % among the three lipases tested, followed by Lipozyme TL IM and Lipozyme RM IM. Monoglycerides were synthesized from biodiesel-derived crude glycerol using Novozym 435 as the catalyst under solvent-free conditions at different parameters, which were catalyst concentration, substrate molar ratio, and temperature. The yield of monoglycerides was examined in single-factor experiments. Response surface methodology (RSM) was subsequently employed to optimize the synthesis conditions based on the single-factor experimental results. The optimal conditions were at an enzyme concentration of 12.7 wt% and a molar ratio of crude glycerol:oil of 5.7:1 at a reaction temperature of 65.2 °C. The experimental yield of monoglycerides under the optimal conditions was 28.93 %, which is close to the value predicted from the RSM model (29.02 %).

Recyclable and (Bio)degradable Polyesters in a Circular Plastics Economy

Polyesters carrying polar main-chain ester linkages exhibit distinct material properties for diverse applications and thus play an important role in today's plastics economy. It is anticipated that they will play an even greater role in tomorrow's circular plastics economy that focuses on sustainability, thanks to the abundant availability of their biosourced building blocks and the presence of the main-chain ester bonds that can be chemically or biologically cleaved on demand by multiple methods and thus bring about more desired end-of-life plastic waste management options. Because of this potential and promise, there have been intense research activities directed at addressing recycling, upcycling or biodegradation of existing legacy polyesters, designing their biorenewable alternatives, and redesigning future polyesters with intrinsic chemical recyclability and tailored performance that can rival today's commodity plastics that are either petroleum based and/or hard to recycle. This review captures these exciting recent developments and outlines future challenges and opportunities. Case studies on the legacy polyesters, poly(lactic acid), poly(3-hydroxyalkanoate)s, poly(ethylene terephthalate), poly(butylene succinate), and poly(butylene-adipate terephthalate), are presented, and emerging chemically recyclable polyesters are comprehensively reviewed.

A systematic review on utilization of biodiesel-derived crude glycerol in sustainable polymers preparation

With the rapid development of biodiesel, biodiesel-derived glycerol has become a promising renewable bioresource. The key to utilizing this bioresource lies in the value-added conversion of crude glycerol. While purifying crude glycerol into a pure form allows for diverse applications, the intricate nature of this process renders it costly and environmentally stressful. Consequently, technology facilitating the direct utilization of unpurified crude glycerol holds significant importance. It has been reported that crude glycerol can be bio-transformed or chemically converted into high-value polymers. These technologies provide cost-effective alternatives for polymer production while contributing to a more sustainable biodiesel industry. This review article describes the global production and quality characteristics of biodiesel-derived glycerol and investigates the influencing factors and treatment of the composition of crude glycerol including water, methanol, soap, matter organic non-glycerol, and ash. Additionally, this review also focused on the advantages and challenges of various technologies for converting crude glycerol into polymers, considering factors such as the compatibility of crude glycerol and the control of unfavorable factors. Lastly, the application prospect and value of crude glycerol conversion were discussed from the aspects of economy and environmental protection. The development of new technologies for the increased use of crude glycerol as a renewable feedstock for polymer production will be facilitated by the findings of this review, while promoting mass market applications.