A New Colorimetric Test for Accurate Determination of Plastic Biodegradation.

As plastic waste is accumulating in both controlled waste management settings and natural settings, much research is devoted to search for solutions, also in the field of biodegradation. However, determining the biodegradability of plastics in natural environments remains a big challenge due to the often very low biodegradation rates. Many standardised test methods for biodegradation in natural environments exist.

Sustainable Polythioesters via Thio(no)lactones: Monomer Synthesis, Ring-Opening Polymerization, End-of-Life Considerations, and Industrial Perspectives.

As the environmental effects of plastics are of ever greater concern, the industry is driven towards more sustainable polymers. Besides sustainability, our fast-developing society imposes the need for highly versatile materials. Whereas aliphatic polyesters (PEs) are widely adopted and studied as next-generation biobased and (bio)degradable materials, their sulfur-containing analogs, polythioesters (PTEs), only recently gained attention.

Radical Formation in Sugar-Derived Acetals under Solvent-Free Conditions.

The degradation of acetal derivatives of the diethylester of galactarate (GalX) was investigated by electron paramagnetic resonance (EPR) spectroscopy in the context of solvent-free, high-temperature reactions like polycondensations. It was demonstrated that less substituted cyclic acetals are prone to undergo radical degradation at higher temperatures as a result of hydrogen abstraction. The EPR observations were supported by the synthesis of GalX based polyamides via ester-amide exchange-type polycondensations in solvent-free conditions at high temperatures in the presence and in the absence of radical inhibitors.

Chemoselective formation of cyclo-aliphatic and cyclo-olefinic 1,3-diols pressure hydrogenation of potentially biobased platform molecules using Knölker-type catalysts.

The hydrogenative conversions of the biobased platform molecules 4-hydroxycyclopent-2-enone and cyclopentane-1,3-dione to their corresponding 1,3-diols are established using a pre-activated Knölker-type iron catalyst. The catalyst exhibits a high selectivity for ketone reduction, and does not induce dehydration. Moreover, by using different substituents of the ligand, the cis-trans ratio of the products can be affected substantially.

Hydrogenation of Cyclic 1,3-Diones to Their 1,3-Diols Using Heterogeneous Catalysts: Toward a Facile, Robust, Scalable, and Potentially Bio-Based Route.

Cyclopentane-1,3-diol () has gained renewed attention as a potential building block for polymers and fuels because its synthesis from hemicellulose-derived 4-hydroxycyclopent-2-enone () was recently disclosed. However, cyclopentane-1,3-dione (), which is a constitutional isomer of , possesses a higher chemical stability and can therefore afford higher carbon mass balances and higher yields of in the hydrogenation reaction under more concentrated conditions. In this work, the hydrogenation of into over a commercial Ru/C catalyst was systematically investigated on a bench scale through kinetic studies and variation of reaction conditions.

The Forgotten Pyrazines: Exploring the Dakin-West Reaction.

Pyrazines are an underreported class of N-heterocycles available from nitrogen-rich biomass presenting an interesting functional alternative for current aromatics. In this work, access to pyrazines obtained from amino acids by using the 90 year old Dakin-West reaction was explored. After a qualitative screening several functional proteinogenic amino acids proved good substrates for this reaction, which were successfully scaled to multigram scale synthesis of the corresponding intermediate α-acetamido ketones.

Towards High-performance Materials Based on Carbohydrate-Derived Polyamide Blends.

A bio-derived monomer called 2,3:4,5-di--isopropylidene-galactarate acid/ester (GalXMe) has great potential in polymer production. The unique properties of this molecule, such as its rigidity and bulkiness, contribute to the good thermal properties and appealing transparency of the material. The main problem, however, is that like other biobased materials, the polymers derived thereof are very brittle.

A Prospective Life Cycle Assessment (LCA) of Monomer Synthesis: Comparison of Biocatalytic and Oxidative Chemistry.

Biotechnological processes are typically perceived to be greener than chemical processes. A life cycle assessment (LCA) was performed to compare the chemical and biochemical synthesis of lactones obtained by Baeyer-Villiger oxidation. The LCA is prospective (based on experiments at a small scale with primary data) because the process is at an early stage.

Solvent-Free Method for the Copolymerization of Labile Sugar-Derived Building Blocks into Polyamides.

This research focuses on the preparation of biobased copolyamides containing biacetalized galactaric acid (GalX), namely, 2,3:4,5-di--isopropylidene-galactaric acid (GalXMe) and 2,3:4,5-di--methylene-galactaric acid (GalXH), in bulk by melt polycondensation of salt monomers. In order to allow the incorporation of temperature-sensitive sugar-derived building blocks into copolyamides at temperatures below the degradation temperature of the monomers and below their melting temperatures, a clever selection of salt monomers is required, such that the sugar-derived salt monomer dissolves in the other salt monomers. The polymerization was investigated by temperature dependent FT-IR and optical microscopy.

Application of a thermostable Baeyer-Villiger monooxygenase for the synthesis of branched polyester precursors.

Background: It is widely accepted that the poor thermostability of Baeyer-Villiger monooxygenases limits their use as biocatalysts for applied biocatalysis in industrial applications. The goal of this study was to investigate the biocatalytic oxidation of 3,3,5-trimethylcyclohexanone using a thermostable cyclohexanone monooxygenase from Thermocrispum municipale (TmCHMO) for the synthesis of branched ϵ-caprolactone derivatives as building blocks for tuned polymeric backbones. In this multi-enzymatic reaction, the thermostable cyclohexanone monooxygenase was fused to a phosphite dehydrogenase (PTDH) in order to ensure co-factor regeneration.

Structure-Property Relations in New Cyclic Galactaric Acid Derived Monomers and Polymers Therefrom: Possibilities and Challenges.

In order to fully exploit the potential of carbohydrate-based monomers, different (and some new) functionalities are introduced on galactaric acid via acetalization, and subsequently, partially-biobased polyamides are prepared therefrom via polycondensation in the melt. Compared to nonsubstituted linear monomer, faster advancement of the reaction is observed for the different biacetal derivatives of galactaric acid. This kinetic observation is of great significance since it allows conducting a polymerization reaction at lower temperatures than normally expected for polyamides, which allows overcoming typical challenges (e.

Exploring the Substrate Scope of Baeyer-Villiger Monooxygenases with Branched Lactones as Entry towards Polyesters.

Baeyer-Villiger monooxygenases (BVMOs) are biocatalysts that are able to convert cyclic ketones into lactones by the insertion of oxygen. The aim of this study was to explore the substrate scope of several BVMOs with (biobased) cyclic ketones as precursors for the synthesis of branched polyesters. The product structure and the degree of conversion of several biotransformations were determined after conversions by using self-sufficient BVMOs.

Metabolic Engineering toward Sustainable Production of Nylon-6.

Nylon-6 is a bulk polymer used for many applications. It consists of the non-natural building block 6-aminocaproic acid, the linear form of caprolactam. Via a retro-synthetic approach, two synthetic pathways were identified for the fermentative production of 6-aminocaproic acid.

Metabolism of β-valine via a CoA-dependent ammonia lyase pathway.

Pseudomonas species strain SBV1 can rapidly grow on medium containing β-valine as a sole nitrogen source. The tertiary amine feature of β-valine prevents direct deamination reactions catalyzed by aminotransferases, amino acid dehydrogenases, and amino acid oxidases. However, lyase- or aminomutase-mediated conversions would be possible.

Cofactor Specificity Engineering of Streptococcus mutans NADH Oxidase 2 for NAD(P)(+) Regeneration in Biocatalytic Oxidations.

Soluble water-forming NAD(P)H oxidases constitute a promising NAD(P)(+) regeneration method as they only need oxygen as cosubstrate and produce water as sole byproduct. Moreover, the thermodynamic equilibrium of O2 reduction is a valuable driving force for mostly energetically unfavorable biocatalytic oxidations. Here, we present the generation of an NAD(P)H oxidase with high activity for both cofactors, NADH and NADPH.

Biochemical properties and crystal structure of a β-phenylalanine aminotransferase from Variovorax paradoxus.

By selective enrichment, we isolated a bacterium that can use β-phenylalanine as a sole nitrogen source. It was identified by 16S rRNA gene sequencing as a strain of Variovorax paradoxus. Enzyme assays revealed an aminotransferase activity.

Engineering methylaspartate ammonia lyase for the asymmetric synthesis of unnatural amino acids.

The redesign of enzymes to produce catalysts for a predefined transformation remains a major challenge in protein engineering. Here, we describe the structure-based engineering of methylaspartate ammonia lyase (which in nature catalyses the conversion of 3-methylaspartate to ammonia and 2-methylfumarate) to accept a variety of substituted amines and fumarates and catalyse the asymmetric synthesis of aspartic acid derivatives. We obtained two single-active-site mutants, one exhibiting a wide nucleophile scope including structurally diverse linear and cyclic alkylamines and one with broad electrophile scope including fumarate derivatives with alkyl, aryl, alkoxy, aryloxy, alkylthio and arylthio substituents at the C2 position.

Mechanism-inspired engineering of phenylalanine aminomutase for enhanced β-regioselective asymmetric amination of cinnamates.

Turn to switch: A mutant of phenylalanine aminomutase was engineered that can catalyze the regioselective amination of cinnamate derivatives (see scheme, red) to, for example, β-amino acids. This regioselectivity, along with the X-ray crystal structures, suggests two distinct carboxylate binding modes differentiated by C(β)-C(ipso) bond rotation, which determines if β- (see scheme) or α-addition takes place.

Engineering of an enantioselective tyrosine aminomutase by mutation of a single active site residue in phenylalanine aminomutase.

By replacing a single active-site residue Cys107 with Ser in phenylalanine aminomutase (PAM), the enzyme gained tyrosine aminomutase (TAM) activity while retaining PAM activity and high enantioselectivity. This engineered enantioselective TAM also catalyzed formation of β-tyrosine from p-coumaric acid and may prove to be useful for the synthesis of enantiopure β-tyrosine and its derivatives.

Phenylalanine aminomutase-catalyzed addition of ammonia to substituted cinnamic acids: a route to enantiopure alpha- and beta-amino acids.

An approach is described for the synthesis of aromatic alpha- and beta-amino acids that uses phenylalanine aminomutase to catalyze a highly enantioselective addition of ammonia to substituted cinnamic acids. The reaction has a broad scope and yields substituted alpha- and beta-phenylalanines with excellent enantiomeric excess. The regioselectivity of the conversion is determined by substituents present at the aromatic ring.

Enzymatic synthesis of enantiopure alpha- and beta-amino acids by phenylalanine aminomutase-catalysed amination of cinnamic acid derivatives.

The phenylalanine aminomutase (PAM) from Taxus chinensis catalyses the conversion of alpha-phenylalanine to beta-phenylalanine, an important step in the biosynthesis of the N-benzoyl phenylisoserinoyl side-chain of the anticancer drug taxol. Mechanistic studies on PAM have suggested that (E)-cinnamic acid is an intermediate in the mutase reaction and that it can be released from the enzyme's active site. Here we describe a novel synthetic strategy that is based on the finding that ring-substituted (E)-cinnamic acids can serve as a substrate in PAM-catalysed ammonia addition reactions for the biocatalytic production of several important beta-amino acids.

An exceptionally DMSO-tolerant alcohol dehydrogenase for the stereoselective reduction of ketones.

A novel short-chain alcohol dehydrogenase from Paracoccus pantotrophus DSM 11072, which is applicable for hydrogen transfer, has been identified, cloned, and overexpressed in E. coli. The enzyme stereoselectively reduces several ketones in a sustainable substrate-coupled approach using 2-propanol (5% v/v) as hydrogen donor.

Stereoselective bioreduction of bulky-bulky ketones by a novel ADH from Ralstonia sp.

Ketones with two bulky substituents, named bulky-bulky ketones, as well as less sterically demanding ketones were successfully reduced to the corresponding optically highly enriched alcohols using a novel identified recombinant short-chain alcohol dehydrogenase RasADH from Ralstonia sp. DSM 6428 overexpressed in E. coli.

One-way biohydrogen transfer for oxidation of sec-alcohols.

Quasi-irreversible oxidation of sec-alcohols was achieved via biocatalytic hydrogen transfer reactions using alcohol dehydrogenases employing selected ketones as hydrogen acceptors, which can only be reduced but not oxidized. Thus, only 1 equiv of oxidant was required instead of a large excess. For the oxidation of both isomers of methylcarbinols a single nonstereoselective short-chain dehydrogenase/reductase from Sphingobium yanoikuyae was identified and overexpressed in E.

Enantioselective gas chromatographic analysis of aqueous samples by on-line derivatisation. Application to enzymatic reactions.

A new gas chromatography (GC) method is presented for analysing both the conversion and the enantiomeric excess (e.e.) of samples from alcohol dehydrogenase reactions.