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Polyethylene terephthalate (PET) is a semi-crystalline polymer that finds broad use. Consequently, it contributes to the accumulation of plastics in the environment, warranting PET recycling technologies. Ball milling is a commonly used technique for the micronization of plastics before transformation. It has also recently been reported as an efficient mixing strategy for the enzymatic hydrolysis of plastics in moist-solid mixtures. However, the effect of milling on the microstructure of PET has not been systematically investigated. Thus, the primary objective of this study is to characterize the changes to the PET microstructure caused by various ball milling conditions. PET of different forms was examined, including pre- and post-consumer PET, as well as textiles. The material was treated to a range of milling frequencies and duration, before analysis of particle size, crystallinity by differential scanning calorimetry and powder X-ray diffraction, and morphology by scanning electron microscopy. Interestingly, our results suggest the convergence of crystallinity to ~30 % within 15 minutes of milling at 30 Hz. These results are consistent with an equilibrium between amorphous and crystalline regions of the polymer being established during ball milling. The combined data constitutes a reference guide for PET milling and recycling research., (© 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

Waste polyester textiles are not recycled due to separation challenges and partial structural degradation during use and recycling. Chemical recycling of polyethylene terephthalate (PET) textiles through depolymerization can provide a feedstock of recycled monomers to make "as-new" polymers. While enzymatic PET recycling is a more selective and more sustainable approach, methods in development, however, have thus far been limited to clean, high-quality PET feedstocks, and require an energy-intensive melt-amorphization step ahead of enzymatic treatment. Here, high-crystallinity PET in mixed PET/cotton textiles could be directly and selectively depolymerized to terephthalic acid (TPA) by using a commercial cutinase from Humicola insolens under moist-solid reaction conditions, affording up to 30±2 % yield of TPA. The process was readily combined with cotton depolymerization through simultaneous or sequential application of the cellulase enzymes CTec2®, providing up to 83±4 % yield of glucose without any negative influence on the TPA yield., (© 2022 Wiley-VCH GmbH.)

Mechanoenzymology is an emerging field in which mechanical mixing is used to sustain enzymatic reactions in low-solvent or solvent-free mixtures. Many enzymes have been reported that thrive under such conditions. Considering the central role of biopolymers and synthetic polymers in our society, this minireview highlights the use of mechanoenzymology for the synthesis or depolymerization of oligomeric or polymeric materials. In contrast to traditional in-solution reactions, solvent-free mechanoenzymology has the advantages of avoiding solubility issues, proceeding in a minimal volume, and reducing solvent waste while potentially improving the reaction efficiency and accessing new reactivity. It is expected that this strategy will continue to gain popularity and find more applications., (© 2022 Wiley-VCH GmbH.)

The activity of β-glucosidases-the enzymes responsible for the final step in the enzymatic conversion of cellulose to glucose-can be maintained and manipulated under mechanochemical conditions in the absence of bulk solvent, either through an unexpected stabilization effect of inert surfaces, or by altering the enzymatic equilibrium. The reported results illustrate unique aspects of mechanoenzymatic reactions that are not observable in conventional aqueous solutions. They also represent the first reported strategies to enhance activity and favor either direction of the reaction under mechanochemical conditions., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Chitin is not only the most abundant nitrogen-containing biopolymer on the planet, but also a renewable feedstock that is often treated as a waste. Current chemical methods to break down chitin typically employ harsh conditions, large volumes of solvent, and generate a mixture of products. Although enzymatic methods have been reported, they require a harsh chemical pretreatment of the chitinous substrate and rely on dilute solution conditions that are remote from the natural environment of microbial chitinase enzymes, which typically consists of surfaces exposed to air and moisture. We report an innovative and efficient mechanoenzymatic method to hydrolyze chitin to the N-acetylglucosamine monomer by using chitinases under the recently developed reactive aging (RAging) methodology, based on repeating cycles of brief ball-milling followed by aging, in the absence of bulk solvent. Our results demonstrate that the activity of chitinases increases several times by switching from traditional solution-based conditions of enzymatic catalysis to solventless RAging, which operates on moist solid substrates. Importantly, RAging is also highly efficient for the production of N-acetylglucosamine directly from shrimp and crab shell biomass without any other processing except for a gentle wash with aqueous acetic acid., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Pantothenamides are potent growth inhibitors of the malaria parasite Plasmodium falciparum. Their clinical use is, however, hindered due to the ubiquitous presence of pantetheinases in human serum, which rapidly degrade pantothenamides into pantothenate and the corresponding amine. We previously reported that replacement of the labile amide bond with a triazole ring not only imparts stability toward pantetheinases, but also improves activity against P. falciparum. A small library of new triazole derivatives was synthesized, and their use in establishing structure-activity relationships relevant to antiplasmodial activity of this family of compounds is discussed herein. Overall it was observed that 1,4-substitution on the triazole ring and use of an unbranched, one-carbon linker between the pantoyl group and the triazole are optimal for inhibition of intraerythrocytic P. falciparum growth. Our results imply that the triazole ring may mimic the amide bond with an orientation different from what was previously suggested for this amide bioisostere., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Mechanochemistry enables enzymatic cleavage of cellulose into glucose without bulk solvents, acids, other aggressive reagents, or substrate pre-treatment. This clean mechanoenzymatic process (coined RAging) is also directly applicable to biomass, avoids many limitations associated with the use of cellulases, and produces glucose concentrations greater than three times that obtained by conventional methods., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

As part of the development of cyanothiazolidine-based prolyl oligopeptidase inhibitors, initial metabolism studies suggested multiple sites of oxidation by P450 enzymes. Surprisingly, in-depth investigations revealed that epimerization at multiple stereogenic centers was responsible for the conversion of the single primary metabolite into a panel of secondary metabolites. The rapid isomerization of all seven detected molecules precluded the use of NMR spectroscopy or X-ray crystallography for complete structural determination, presenting an interesting structure elucidation challenge. Through a combination of LC-MS analysis, synthetic work, deuterium exchange studies, and computational predictions, we were able to characterize all metabolites and to elucidate their dynamic behavior in solution. In the context of drug development, this study reveals that cyanothiazolidine moieties are problematic due to their rapid P450-mediated oxidation and the unpredictable stability of the corresponding metabolites., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Just five steps! The synthesis of a phosphonate-linked aminoglycoside-coenzyme A derivative (see scheme) that includes a Michael addition in water has been realized in just five steps. Aminoglycoside N-6'-acetyltransferases (AAC(6')s) are important determinants of antibiotic resistance. A good mechanistic understanding of these enzymes is essential to overcome aminoglycoside resistance. We have previously reported the synthesis of amide- and sulfonamide-linked aminoglycoside-coenzyme A conjugates, which were useful mechanistic and structural probes of AAC(6')s. We report here the synthesis of a phosphonate-linked aminoglycoside-coenzyme A variant, which is expected to be a superior mimic of the tetrahedral intermediate proposed for catalysis by AAC(6')s. This synthetic target is especially challenging for a number of reasons, including the presence of multiple functional groups, the water solubility of both starting materials, and incompatibility of P(III) chemistry with water. We have overcome these challenges by adding the expensive coenzyme A in the last step by means of an elegant Michael-type addition onto a vinylphosphonate in water. Overall, a single protection step was needed. The decreased inhibitory potency of this bisubstrate compared to that of the amide-linked analogue suggests that Enterococcus faecium AAC(6')-Ii may not stabilize the proposed tetrahedral intermediate, and may act mainly through proximity catalysis.