Tuning the Chiral Structures from Self-Assembled Carbohydrate Derivatives.

Carbohydrates have been regarded as one of the most ideally suited candidates for chirality study via self-assembly owning to their unique chemical structures, abundance, and sustainability. Much efforts have been devoted to design and synthesize diverse carbohydrate derivatives and self-assemble them into various supermolecular morphologies. Nevertheless, still inadequate attention is paid to deeply and comprehensively understand how the carbohydrate structures and self-assembly approaches affect the final morphologies and properties for future demands. Herein, to fulfill the need, a range of recently published studies relating to the chirality of carbohydrates is reviewed and discussed. Furthermore, to tune the chirality of carbohydrate-based structures on both molecular and superstructural levels via chirality transfer and chirality expression, the designing of the molecules and choosing of the proper approaches for self-assembly are elucidated.

Additive Manufacturing of α-Amino Acid Based Poly(ester amide)s for Biomedical Applications.

α-Amino acid based polyester amides (PEAs) are promising candidates for additive manufacturing (AM), as they unite the flexibility and degradability of polyesters and good thermomechanical properties of polyamides in one structure. Introducing α-amino acids in the PEA structure brings additional advantages such as (i) good cytocompatibility and biodegradability, (ii) providing strong amide bonds, enhancing the hydrogen-bonding network, (iii) the introduction of pendant reactive functional groups, and (iv) providing good cell-polymer interactions. However, the application of α-amino acid based PEAs for AM via fused deposition modeling (FDM), an important manufacturing technique with unique processing characteristics and requirements, is still lacking. With the aim to exploit the combination of these advantages in the creation, design, and function of additively manufactured scaffolds using FDM, we report the structure-function relationship of a series of α-amino acid based PEAs. The PEAs with three different molecular weights were synthesized via the active solution polycondensation, and their performance for AM applications was studied in comparison with a commercial biomedical grade copolymer of l-lactide and glycolide (PLGA). The PEAs, in addition to good thermal stability, showed semicrystalline behavior with proper mechanical properties, which were different depending on their molecular weight and crystallinity. They showed more ductility due to their lower glass transition temperature (Tg; 18-20 °C) compared with PLGA (57 °C). The rheology studies revealed that the end-capping of PEAs is of high importance for preventing cross-linking and further polymerization during the melt extrusion and for the steadiness and reproducibility of FDM. Furthermore, our data regarding the steady 3D printing performance, good polymer-cell interactions, and low cytotoxicity suggest that α-amino acid based PEAs can be introduced as favorable polymers for future AM applications in tissue engineering. In addition, their ability for formation of bonelike apatite in the simulated body fluid (SBF) indicates their potential for bone tissue engineering applications.

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. The radical degradation can be offset by the addition of a radical inhibitor. The radical is probably formed on the methylene unit between the oxygen atoms and subsequently undergoes a rearrangement.

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. Subsequently, the conditions towards pyrazine formation using δ-amino-levulinic acid were optimized, and these were employed to synthesize a relevant set of five functional dimethylpyrazines in high purity. These pyrazines can be considered a versatile toolbox of aromatic building blocks for a wide range of applications, such as in the synthesis of polymers or metal-organic frameworks.

Quantification of biases in predictions of protein stability changes upon mutations.

Motivation: Bioinformatics tools that predict protein stability changes upon point mutations have made a lot of progress in the last decades and have become accurate and fast enough to make computational mutagenesis experiments feasible, even on a proteome scale. Despite these achievements, they still suffer from important issues that must be solved to allow further improving their performances and utilizing them to deepen our insights into protein folding and stability mechanisms. One of these problems is their bias toward the learning datasets which, being dominated by destabilizing mutations, causes predictions to be better for destabilizing than for stabilizing mutations. Results: We thoroughly analyzed the biases in the prediction of folding free energy changes upon point mutations (ΔΔG0) and proposed some unbiased solutions. We started by constructing a dataset Ssym of experimentally measured ΔΔG0s with an equal number of stabilizing and destabilizing mutations, by collecting mutations for which the structure of both the wild-type and mutant protein is available. On this balanced dataset, we assessed the performances of 15 widely used ΔΔG0 predictors. After the astonishing observation that almost all these methods are strongly biased toward destabilizing mutations, especially those that use black-box machine learning, we proposed an elegant way to solve the bias issue by imposing physical symmetries under inverse mutations on the model structure, which we implemented in PoPMuSiCsym. This new predictor constitutes an efficient trade-off between accuracy and absence of biases. Some final considerations and suggestions for further improvement of the predictors are discussed. Supplementary information: Supplementary data are available at Bioinformatics online. Note: The article 10.1093/bioinformatics/bty340/, published alongside this paper, also addresses the problem of biases in protein stability change predictions.

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. Full regioselectivity towards the normal lactones of jasmatone and menthone was observed, whereas the oxidation of other substrates such as α,ß-thujone and 3,3,5-trimethylcyclohexanone resulted in mixtures of regioisomers. This exploration of the substrate scope of both established and newly discovered BVMOs towards biobased ketones contributes to the development of branched polyesters from renewable resources.

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.g., thermal degradation) encountered upon polymerization of carbohydrate-derived monomers in the melt. The polymers derived from the modified galactaric acid monomers vary in terms of glass transition temperature, thermal stability, hydrophilicity, and functionality.

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. RESULTS: Using reaction engineering, the reaction rate and product formation of the regio-isomeric branched lactones were improved and the use of co-solvents and the initial substrate load were investigated. Substrate inhibition and poor product solubility were overcome using continuous substrate feeding regimes, as well as a biphasic reaction system with toluene as water-immiscible organic solvent. A maximum volumetric productivity, or space-time-yield, of 1.20 g L-1 h-1 was achieved with continuous feeding of substrate using methanol as co-solvent, while a maximum product concentration of 11.6 g L-1 was achieved with toluene acting as a second phase and substrate reservoir. CONCLUSION: These improvements in key process metrics therefore demonstrate progress towards the up-scaled Baeyer-Villiger monooxygenase-biocatalyzed synthesis of the target building blocks for polymer application. © 2018 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Microgels with controlled network topologies by photocrosslinking-assisted continuous precipitation polymerization.

In this study, we present a new synthesis methodology based on photo-crosslinking-assisted continuous precipitation polymerization which allows controlling the distribution of crosslinks in microgels. In our approach we substituted conventional crosslinking agent by a comonomer carrying photo-crosslinkable 4-oxocyclopent-2-en-1-yl group. Microgel size, morphology, distribution of crosslinks and packing density of the polymer chains are studied as a function of retention time (Rt) in the flow reactor. Dynamic and static light scattering (DLS and SLS) as well as small angle X-ray scattering (SAXS) proved an excellent level of control over the distribution of crosslinks in microgels during the polymerization process. These results were confirmed by atomic force microscopy (AFM), indicating a difference in microgel stiffness and arrangement of the polymer network as resulting from increased Rt.

Renewable and Functional Latexes Synthesized by Polymerization-Induced Self-Assembly for UV-Curable Films.

After the development of polymer coatings and films based on renewable resources, there remains a challenge of combining the advantages of water-borne acrylic latexes with the excellent physical properties of cross-linked solvent-borne coatings. After polymerization, the renewable 4-oxocyclopentenyl acrylate (4CPA) is capable of undergoing photocyclodimerization under UV light, yielding a cross-linked polyacrylate. In this work, we investigate the polymerization-induced self-assembly (PISA) of 4CPA with several renewable acrylic monomers in the presence of a macro-RAFT agent. The produced latexes have a small particle size, good colloidal stability, and are free of volatile organic compounds. After film formation and UV curing, flexible to rigid films can be obtained depending on the monomer composition and UV irradiation time. The cross-linked films show promise as oil and water barriers in paper coating applications. This work outlines the development and application of renewable and functional cross-linkable latexes synthesized by PISA.

Biobased Photopolymer Resin for 3D Printing Containing Dynamic Imine Bonds for Fast Reprocessability.

Acrylic photopolymer resins are widely used in stereolithographic 3D printing. However, the growing demand for such thermosetting resins is weighing on global issues such as waste management and fossil fuel consumption. Therefore, there is an increasing demand for reactive components that are biobased and enable recyclability of the resulting thermoset products. In this work, the synthesis of a photo-cross-linkable molecule containing dynamic imine bonds based on biobased vanillin and dimer fatty diamine is described. Using the biobased building blocks, formulations containing reactive diluent and a photoinitiator were prepared. The mixtures could be rapidly cross-linked under UV light, yielding vitrimers. Using digital light processing, 3D-printed parts were prepared, which were rigid, thermally stable, and reprocessed within 5 min at elevated temperature and pressure. The addition of a building block containing a higher concentration of imine bonds accelerated the stress relaxation and improved the mechanical rigidity of the vitrimers. This work will contribute to the development of biobased and recyclable 3D-printed resins to facilitate the transition to a circular economy.

Amphiphilic Crosslinked Four-Armed Poly(lactic-co-glycolide) Electrospun Membranes for Enhancing Cell Adhesion.

Common poly(lactide-co-glycolide) (i-PLGA) has emerged as a biodegradable and biocompatible material in tissue engineering. However, the poor hydrophilicity and elasticity of i-PLGA lead to its limited application in tissue engineering. To this end, an amphiphilic crosslinked four-armed poly(lactic-co-glycolide) was prepared. First, four-armed PLGA (4A-PLGA) was synthesized by polymerizing l-lactide (LA) and glycolide (GA) with pentaerythritol as the initiator. Then, the hydrophilic polymer poly(glutamate propylene ester) (PGPE) was prepared through the esterification of glutamic acid and 1,2-propanediol. The hydrophilic 4A-PLGA-PGPE was finally synthesized through the condensation reaction of 4A-PLGA and PGPE with the aid of triphosgene. 4A-PLGA-PGPE was then used to prepare amphiphilic membranes by electrospinning. It was demonstrated that the mechanical properties and biocompatibility of 4A-PLGA were improved after the introduction of PGPE. Furthermore, the introduction of glutamate improved the hydrophilicity of 4A-PLGA, thus effectively promoting cell entry and adhesion, which makes the electrospun 4A-PLGA-PGPE membranes promising for tissue engineering.

Additive Manufacturing Using Melt Extruded Thermoplastics for Tissue Engineering.

Melt extrusion of thermoplastic materials is an important technique for fabricating tissue engineering scaffolds by additive manufacturing methods. Scaffold manufacturing is commonly achieved by one of the following extrusion-based techniques: fused deposition modelling (FDM), 3D-fiber deposition (3DF), and bioextrusion. FDM needs the input material to be strictly in the form of a filament, whereas 3DF and bioextrusion can be used to process input material in several forms, such as pellets or powder. This chapter outlines a common workflow for all these methods, going from the material to a scaffold, while highlighting the special requirements of particular methods. A few ways of characterizing the scaffolds are also briefly described.

Development of Lignin-Based Mesoporous Carbons for the Adsorption of Humic Acid.

There is an increasing urge to make the transition toward biobased materials. Lignin, originating from lignocellulosic biomass, can be potentially valorized as humic acid (HA) adsorbents via lignin-based mesoporous carbon (MC). In this work, these materials were synthesized for the first time starting from modified lignin as the carbon precursor, using the soft-template methodology. The use of a novel synthetic approach, Claisen rearrangement of propargylated lignin, and a variety of surfactant templates (Pluronic, Kraton, and Solsperse) have been demonstrated to tune the properties of the resulting MCs. The obtained materials showed tunable properties (BET surface area: 95-367 m2/g, pore size: 3.3-36.6 nm, V BJH pore volume: 0.05-0.33 m3/g, and carbon and oxygen content: 55.5-91.1 and 3.0-12.2%, respectively) and good performance in terms of one of the highest HA adsorption capacities reported for carbon adsorbents (up to 175 mg/g).

Kinetic modelling of the solid-liquid extraction process of polyphenolic compounds from apple pomace: influence of solvent composition and temperature.

This study aims to assess kinetic modelling of the solid-liquid extraction process of total polyphenolic compounds (TPC) from apple pomace (AP). In this regard, we investigated the effects of temperature and solvent (i.e. water, ethanol, and acetone) on TPC extraction over various periods. The highest TPC yield of 11.1 ± 0.49 mg gallic acid equivalent (GAE)/g db (dry basis) was achieved with a mixture of 65% acetone-35% water (v/v) at 60 °C. The kinetics of the solvent-based TPC extraction processes were assessed via first-order and second-order kinetic models, with an associated investigation of the kinetic parameters and rate constants, saturation concentrations, and activation energies. The second-order kinetic model was sufficient to describe the extraction mechanism of TPC from AP. This study provides an understanding of the mass transfer mechanism involved in the polyphenolic compound extraction process, thus facilitating future large-scale design, optimization, and process control to valorize pomace waste.

Chitooligosaccharides for wound healing biomaterials engineering.

Chitooligosaccharides (CHOS) are oligomers of ß-(1-4) linked N-acetylglucosamine and D-glucosamine that are produced from chitin or chitosan using different enzymatic or chemical methods. CHOS are water-soluble and non-cytotoxic with diverse bioactivities such as antibacterial, anti-inflammation, anti-obesity, anti-tumor and antioxidant. These biological features make CHOS promising compounds for several medical and food applications. In this review, we critically summarize the biological activities of CHOS in biomaterials engineering with a particular focus on CHOS applications for skin tissue healing and regeneration. We also present an updated overview of CHOS fabrications into wound dressing biomaterials for several in vitro and in vivo studies.

Expansion of Ovarian Cancer Stem-like Cells in Poly(ethylene glycol)-Cross-Linked Poly(methyl vinyl ether-alt-maleic acid) and Alginate Double-Network Hydrogels.

A better understanding of cancer stem cells (CSCs) is essential for research on cancer therapy and drug resistance. Currently, increasingly more investigations are focused on obtaining CSCs to study the mechanism of their enhanced malignancy. In this work, three kinds of double-network hydrogels (PEMM/alginate), consisting of poly(ethylene glycol) (PEG) covalently cross-linked poly(methyl vinyl ether-alt-maleic acid) (P(MVE-alt-MA)) (network 1, denoted as PEMM) and Sr2+ (or Ca2+, Fe3+) ionically cross-linked alginates (network 2, denoted as SrAlg, CaAlg, or FeAlg), were prepared. The stiffness, morphology, and components of the PEMM/alginate hydrogels were systematically investigated to understand their effects on CSC enrichment. Only the PEMM/FeAlg hydrogels could support the long-term growth, proliferation, and spheroid formation of SK-OV-3 cells. The expression of CSC-related markers was evaluated with the levels of protein and gene at different stages. The cell spheroids cultured in the PEMM/FeAlg hydrogels acquired certain CSC-like properties, thus drug resistance was enhanced, especially in the PEMM-1/FeAlg hydrogel. In vivo tumorigenicity experiments also confirmed the presence of more CSCs in the PEMM-1/FeAlg hydrogel. The results suggest that matrix stiffness, morphology, and cations act synergistically on the regulation of the epithelial-mesenchymal transition (EMT), interleukin-6 (IL-6), and Wnt pathways, affecting the invasiveness of ovarian cancer and the conversion of the non-CSCs into CSCs. The PEMM-1/FeAlg hydrogel with lower elastic modulus, a more macroporous morphology, and higher swelling rate can significantly enhance the stemness, malignancy, and tumorigenicity of SK-OV-3 cells.

UV-Curable Biobased Polyacrylates Based on a Multifunctional Monomer Derived from Furfural.

The controlled polymerization of a new biobased monomer, 4-oxocyclopent-2-en-1-yl acrylate (4CPA), was established via reversible addition-fragmentation chain transfer (RAFT) (co)polymerization to yield polymers bearing pendent cyclopentenone units. 4CPA contains two reactive functionalities, namely, a vinyl group and an internal double bond, and is an unsymmetrical monomer. Therefore, competition between the internal double bond and the vinyl group eventually leads to gel formation. With RAFT polymerization, when aiming for a degree of polymerization (DP) of 100, maximum 4CPA conversions of the vinyl group between 19.0 and 45.2% were obtained without gel formation or extensive broadening of the dispersity. When the same conditions were applied in the copolymerization of 4CPA with lauryl acrylate (LA), methyl acrylate (MA), and isobornyl acrylate, 4CPA conversions of the vinyl group between 63 and 95% were reached. The additional functionality of 4CPA in copolymers was demonstrated by model studies with 4-oxocyclopent-2-en-1-yl acetate (1), which readily dimerized under UV light via [2 + 2] photocyclodimerization. First-principles quantum mechanical simulations supported the experimental observations made in NMR. Based on the calculated energetics and chemical shifts, a mixture of head-to-head and head-to-tail dimers of (1) were identified. Using the dimerization mechanism, solvent-cast LA and MA copolymers containing 30 mol % 4CPA were cross-linked under UV light to obtain thin films. The cross-linked films were characterized by dynamic scanning calorimetry, dynamic mechanical analysis, IR, and swelling experiments. This is the first case where 4CPA is described as a monomer for functional biobased polymers that can undergo additional UV curing via photodimerization.

Formation of cyclic structures in the cationic ring-opening polymerization of 1,3-dioxolane.

The cationic ring-opening polymerization of acetals is prone to cyclization of the polymer chains. This is also the case for the polymerization of 1,3-dioxolane. Literature states that this cyclization can be reduced by applying the Active Monomer mechanism, at least if no competition with the Active Chain End mechanism occurs. In this work, a detailed characterization of the different distributions resulting from the cationic ring-opening polymerization of 1,3-dioxolane via the Active Monomer mechanism is made by a combination of gel permeation chromatography, 1H NMR, and for the first time by matrix assisted laser desorption/ionization time of flight mass spectrometry. The influence of monomer addition speed, catalyst to initiator ratio and solvent were studied on both kinetics and composition of the product. Furthermore, it was found that increasing the conversion and monomer to initiator ratios leads to an increased amount of cyclic structures and to broader distributions, in correspondence with the Jacobson-Stockmayer theory. Furthermore, ion trapping experiments using 31P NMR provide insights into the actual reaction mechanism. Finally, purification of the products after the reactions led to a reduction of the cyclic fraction.

Self-Assembled Supramolecular Hybrid Hydrogels Based on Host-Guest Interaction: Formation and Application in 3D Cell Culture.

In recent decades, in vitro three-dimensional (3D) cell culture has been rapidly developed and widely used in many biomedical fields. Based on this background, a kind of self-assembled supramolecular hybrid hydrogel materials based on host-guest interaction of ß-cyclodextrin (ßCD) and adamantane (Ad) is designed for 3D cell culture. First, ßCD is grafted to poly(methyl vinyl ether-alt-maleic acid) (PMM) to obtain the host polymers of ßCD-grafted-PMM (PMM-ßCD). Second, the guest polymers of poly(acrylamide-co-N-adamantyl acrylamide) (PAAm-Ad) are synthesized through free-radical copolymerization of acrylamide and N-adamantyl acrylamide. Finally, the self-assembled supramolecular hybrid hydrogels of PMM-ßCD/PAAm-Ad are formed by simply mixing the aqueous solution of host and guest polymers with a total concentration of 3.3% (w/v) and a ßCD/Ad molar ratio of 1:1. The main cross-linking interactions come from the host-guest interaction of ßCD/Ad as well as hydrogen-bonding interaction of carboxyl/amide groups. The prepared hydrogels with good cytocompatibility have been successfully used as 3D cell culture scaffold for SKOV3, HUVEC, and L929 cells culture. Thus, this work provides a way and biomaterial for the preparation of a functionalized 3D cell culture scaffold, which lays an experimental and theoretical basis for cell follow-up research.