Incorporation Of Monomers Research Articles

Production of D-lactic acid containing polyhydroxyalkanoate polymers in yeast Saccharomyces cerevisiae.

Polyhydroxyalkanoates (PHAs) provide biodegradable and bio-based alternatives to conventional plastics. Incorporation of 2-hydroxy acid monomers into polymer, in addition to 3-hydroxy acids, offers possibility to tailor the polymer properties. In this study, poly(D-lactic acid) (PDLA) and copolymer P(LA-3HB) were produced and characterized for the first time in the yeast Saccharomyces cerevisiae. Expression of engineered PHA synthase PhaC1437Ps6–19, propionyl-CoA transferase Pct540Cp, acetyl-CoA acetyltransferase PhaA, and acetoacetyl-CoA reductase PhaB1 resulted in accumulation of 3.6% P(LA-3HB) and expression of engineered enzymes PhaC1Pre and PctMe resulted in accumulation of 0.73% PDLA of the cell dry weight (CDW). According to NMR, P(LA-3HB) contained D-lactic acid repeating sequences. For reference, expression of PhaA, PhaB1, and PHA synthase PhaC1 resulted in accumulation 11% poly(hydroxybutyrate) (PHB) of the CDW. Weight average molecular weights of these polymers were comparable to similar polymers produced by bacterial strains, 24.6, 6.3, and 1 130 kDa for P(LA-3HB), PDLA, and PHB, respectively. The results suggest that yeast, as a robust and acid tolerant industrial production organism, could be suitable for production of 2-hydroxy acid containing PHAs from sugars or from 2-hydroxy acid containing raw materials. Moreover, the wide substrate specificity of PHA synthase enzymes employed increases the possibilities for modifying copolymer properties in yeast in the future.

Efficient Copolymerization of Acrylate and Ethylene with Neutral P, O-Chelated Nickel Catalysts: Mechanistic Investigations of Monomer Insertion and Chelate Formation

The efficient copolymerization of acrylates with ethylene using Ni catalysts remains a challenge. Herein, we report two neutral Ni(II) catalysts (POP-Ni-py (1) and PONap-Ni-py (2)) that exhibit high thermal stability and significantly higher incorporation of polar monomer (for 1) or improved resistance to tert-butylacrylate (tBA)-induced chain transfer (for 2), in comparison to previously reported catalysts. Nickel alkyl complexes generated after tBA insertion, POP-Ni-CCO(py) (3) and PONap-Ni-CCO(py) (4), were isolated and, for the first time, characterized by crystallography. Weakened lutidine vs pyridine coordination in 2-lut facilitated the isolation of a N-donor-free adduct after acrylate insertion PONap-Ni-CCO (5) which represents a novel example of a four-membered chelate relevant to acrylate polymerization catalysis. Experimental kinetic studies of six cases of monomer insertion with aforementioned nickel complexes indicate that pyridine dissociation and monomer coordination are fast relative to monomer migratory insertion and that monomer enchainment after tBA insertion is the rate limiting step of copolymerization. Further evaluation of monomer insertion using density functional theory studies identified a cis-trans isomerization via Berry-pseudorotation involving one of the pendant ether groups as the rate-limiting step for propagation, in the absence of a polar group at the chain end. The energy profiles for ethylene and tBA enchainments are in qualitative agreement with experimental measurements.

Styrene intermolecular associating incorporated-polyacrylamide flooding of crude oil in carbonate coated micromodel system at high temperature, high salinity condition: Rheology, wettability alteration, recovery mechanisms

Polymer flooding is one of the most well-known research interests in the enhanced oil recovery (EOR) due to the excess oil production and limited petroleum reserve. Commercial polymers such as polyacrylamide (PAM) and its hydrolyzed form (HPAM) can be easily degraded at high temperature, high salinity, and high shear rate in attempt to the EOR purposes for the harsh reservoir conditions. In this work, a hydrophobically modified copolymer consisting of acrylamide and styrene (HSPAM) was produced via inverse emulsion polymerization as a wettability modifier and viscosifying agent, applicable under harsh reservoir conditions to direct insights into the synergic oil recovery pore scale mechanisms and overcoming the aforementioned challenges through the EOR process. In the first part of this study, a set of analytical techniques including FTIR, NMR, TGA, and molecular weight measurement was carried out, confirming successfully incorporation of styrene monomer in water-soluble skeleton and higher thermal resistivity of HSPAM compared with HPAM. By analyzing the rheological behavior of HSPAM under harsh reservoir conditions, it was found that the viscosity of HSPAM aqueous solution was increasingly influenced by the total dissolved solids, even up to 40,572 mg/L. In the second part, stability tests, contact angle (CA), interfacial tension (IFT), and carbonate coated glass micromodel flooding experiments were conducted by deionized water (DIW), seawater (SW) and formation brine (FB) in the absence and presence of HSPAM and HPAM. HSPAM illustrated a great stability in seawater and formation brine in comparison with HPAM after 120 days at 80 °C. The presence of HSPAM in seawater resulted in a more water-wet state up to 42° compared to HPAM by contact angle of 31° after 72 h. Findings provided synergic oil recovery mechanisms approved by emulsification and coalition phenomena to show a better wettability alteration and IFT reduction for HSPAM in spite of HPAM alongside drastically improving the brine-based flooding performance, yielding an ultimate recovery of about 82% original oil in place (OOIP).

Imprinted Particles for Direct Fluorescence Detection of Sialic Acid in Polar Media and on Cancer Cells with Enhanced Control of Nonspecific Binding

Glycoproteins are abundant on the cell surface of mammals, providing structural support, modulating cell membrane properties, and acting as signaling agents. Variation of glycosylation patterns has been found to indicate various disease states, including cell malignancy. Sialic acid (SA) is present as a terminating group on cell-surface glycans, and its overexpression has been linked to several types of cancer. Detection of SA on the cell surface is therefore critical for detection of cancer in its early stages. In this work, a fluorescent molecularly imprinted polymer layer targeting SA was synthesized on the surface of silica-coated polystyrene (PS) particles. Compared to previous works, a PS core supplies a lighter, lower-density support for improved suspension stability and scattering properties. Moreover, their smaller size provides a higher surface-area-to-volume ratio for binding. The incorporation of a fluorescent monomer in the MIP shell allowed for simple and rapid determination of binding specificity in polar media due to a deprotonation–reprotonation interaction mechanism between the fluorescent monomer and SA, which led to spectral changes. Upon titration of the MIP particles with SA in suspension, an increase in fluorescence emission of the particles was observed, with the MIP particles binding SA more selectively compared to the nonimprinted polymer (NIP) control particles. In cell staining experiments performed by flow cytometry, the binding behavior of the MIP particles compared favorably with that of SA-binding lectins. NIPs prepared with a “dummy” template served as a better negative control in cell binding assays due to the favorable inward orientation of template-binding functional groups in the polymer shell, which reduced nonspecific binding. The results show that fluorescent MIPs targeting SA are a promising tool for in vitro fluorescence staining of cancerous cells and for future diagnosis of cancer at early stages.

PH/Thermo-Responsive Grafted Alginate-Based SiO2 Hybrid Nanocarrier/Hydrogel Drug Delivery Systems.

We report the preparation of mesoporous silica nanoparticles covered by layer by layer (LbL) oppositely charged weak polyelectrolytes, comprising poly(allylamine hydrochloride) (PAH) and a sodium alginate, highly grafted by N-isopropylacrylamide/N-tert-butylacrylamide random copolymers, NaALG-g-P(NIPAM90-co-NtBAM10) (NaALG-g). Thanks to the pH dependence of the degree of ionization of the polyelectrolytes and the LCST-type thermosensitivity of the grafting chains of the NaALG-g, the as-prepared hybrid nanoparticles (hNP) exhibit pH/thermo-responsive drug delivery capabilities. The release kinetics of rhodamine B (RB, model drug) can be controlled by the number of PAH/NaALG-g bilayers and more importantly by the environmental conditions, namely, pH and temperature. As observed, the increase of pH and/or temperature accelerates the RB release under sink conditions. The same NaALG-g was used as gelator to fabricate a hNP@NaALG-g hydrogel composite. This formulation forms a viscous solution at room temperature, and it is transformed to a self-assembling hydrogel (sol-gel transition) upon heating at physiological temperature provided that its Tgel was regulated at 30.7 °C, by the NtBAM hydrophobic monomer incorporation in the side chains. It exhibits excellent injectability thanks to its combined thermo- and shear-responsiveness. The hNP@NaALG-g hydrogel composite, encapsulating hNP covered with one bilayer, exhibited pH-responsive sustainable drug delivery. The presented highly tunable drug delivery system (DDS) (hNP and/or composite hydrogel) might be useful for biomedical potential applications.

Comparative Analysis of Ethylene/Diene Copolymerization and Ethylene/Propylene/Diene Terpolymerization Using Ansa-Zirconocene Catalyst with Alkylaluminum/Borate Activator: The Effect of Conjugated and Nonconjugated Dienes on Catalytic Behavior and Polymer Microstructure.

The copolymerization of ethylene‒diene conjugates (butadiene (BD), isoprene (IP) and nonconjugates (5-ethylidene-2-norbornene (ENB), vinyl norbornene VNB, 4-vinylcyclohexene (VCH) and 1, 4-hexadiene (HD)), and terpolymerization of ethylene-propylene-diene conjugates (BD, IP) and nonconjugates (ENB, VNB, VCH and HD) using two traditional catalysts of C2-symmetric metallocene—silylene-bridged rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 (complex A) and ethylene-bridged rac-Et(Ind)2ZrCl2 (complex B)—with a [Ph3C][B(C6F5)4] borate/TIBA co-catalyst, were intensively studied. Compared to that in the copolymerization of ethylene diene, the catalytic activity was more significant in E/P/diene terpolymerization. We obtained a maximum yield of both metallocene catalysts with conjugated diene between 3.00 × 106 g/molMt·h and 5.00 × 106 g/molMt·h. ENB had the highest deactivation impact on complex A, and HD had the most substantial deactivation effect on complex B. A 1H NMR study suggests that dienes were incorporated into the co/ter polymers’ backbone through regioselectivity. ENB and VNB, inserted by the edo double bond, left the ethylidene double bond intact, so VCH had an exo double bond. Complex A’s methyl and phenyl groups rendered it structurally stable and exhibited a dihedral angle greater than that of complex B, resulting in 1, 2 isoprene insertion higher than 1, 4 isoprene that is usually incapable of polymerization coordination. High efficiency in terms of co- and ter- monomer incorporation with higher molecular weight was found for complex 1. The rate of incorporation of ethylene and propylene in the terpolymer backbone structure may also be altered by the conjugated and nonconjugated dienes. 13C-NMR, 1H-NMR, and GPC techniques were used to characterize the polymers obtained.

Charge-Based Separation of Acid-Functional Polymers by Non-aqueous Capillary Electrophoresis Employing Deprotonation and Heteroconjugation Approaches.

Water-borne polymers are in ever-increasing demand due to their favorable ecological profile compared to traditional solvent-borne polymer systems. Many water-borne polymer particles are stabilized in aqueous media by the incorporation of acid-functional monomers. Due to the large variety of comonomers applied, these water-borne polymers have various superimposed statistical distributions, which make it challenging to obtain in-depth information regarding incorporation of the acidic monomers. For selective analysis of the incorporated acidic monomers, a charge-based non-aqueous capillary electrophoresis (NACE) separation was developed. Two approaches were developed: (i) deprotonation of the acid functionality with an organically soluble strong base and (ii) heteroconjugation of anions of carboxylic acids with incorporated acid functionality. In both approaches, N-methylpyrrolidone, as a strong solvent for polymers with a favorable relative permittivity for the presence of dissociated ionic species, was used for the separation. It was shown that anions of carboxylic acids specifically associate with the incorporated acid groups in the polymers, resulting in negatively charged complexes that could be separated based on charge-to-size ratio by NACE. Although both approaches give comparable results with respect to acid distribution for acid-functional polymers, the effective mobility of the deprotonated polymers is roughly double that obtained from the heteroconjugation approach. Unlike the heteroconjugation approach, deprotonation conditions were detrimental to the fused-silica capillary, limiting practical use. Polymers with different chemical compositions, molecular weights, and acid contents were subjected to the CE approaches developed. Polymers with varying molecular weight but similar relative acid monomer content were shown to have similar migration times, which confirms that this approach separates polymers based on charge-to-size ratio.

Advances in the Synthesis of Polyolefin Elastomers with “Chain-walking” Catalysts and Electron Spin Resonance Research of Related Catalytic Systems

In recent years, polyolefin elastomers play an increasingly important role in industry. The late transition metal complex catalysts, especially α-diimine Ni(II) and α-diimine Pd(II) complex catalysts, are popular “chain-walking” catalysts. They can prepare polyolefin with various structures, ranging from linear configuration to highly branched configuration. Combining the “chain-walking” characteristic with different polymerization strategies, polyolefins with good elasticity can be obtained. Among them, olefin copolymer is a common way to produce polyolefin elastomers. For instance, strictly defined diblock or triblock copolymers with excellent elastic properties were synthesized by adding ethylene and α-olefin in sequence. As well as the incorporation of polar monomers may lead to some unexpected improvement. Chain shuttling polymerization can generate multiblock copolymers in one pot due to the interaction of the catalysts with chain shuttling agent. Furthermore, when regarding ethylene as the sole feedstock, owing to the “oscillation” of the ligands of the asymmetric catalysts, polymers with stereo-block structures can be generated. Generally, the elasticity of these polyolefins mainly comes from the alternately crystallineamorphous block structures, which is closely related to the characteristic of the catalytic system. To improve performance of the catalysts and develop excellent polyolefin elastomers, research on the catalytic mechanism is of great significance. Electron spin resonance (ESR), as a precise method to detect unpaired electron, can be applied to study transition metal active center. Therefore, the progress on the exploration of the valence and the proposed configuration of catalyst active center in the catalytic process by ESR is also reviewed.

Molecular engineering of carbon nitride towards photocatalytic H2 evolution and dye degradation

The development of superior heterogeneous catalyst for hydrogen (H2) evolution is a significant feature and challenging for determining the energy and environmental crises. However, the dumping of numerous lethal colorants (dye) as of textile manufacturing has fascinated widespread devotion-aimed water pollution anticipation and treatment. In this regard, a photocatalytic H2 evolution by visible light using low-dimensional semiconducting materials having pollutant degradable capacity for Rhodamine B dyes (RhB) has been anticipated as a route towards environmental aspect. Here we fabricated the incorporation of organic electron-rich heterocyclic monomer 2,6-dimethylmorpholine (MP), inside electron-poor graphitic carbon nitride (g-CN) semiconductor by solid-state co-polymerization.The supremacy of copolymerization process was successfully examined via absorbent, calculated band gap, and migration of electrons on the photocatalytic performance of as-constructed CN-MP copolymer. The density functional theory (DFT) calculation provides extra support as evident for the successful integration of MP into the g-CN framework by this means-reduced band gap upon co-polymerization. The hydrogen evolution rate (HER) for g-CN was found as 115.2 μmol/h, whereas for CN-PM0.1was estimated at 641.2 μmol/h (six times higher). In particular, the pseudo-order kinetic constant of CN-MP0.1 for photodegradation of RhB was two times higher than that ofg-CN. Results show an important step toward tailor-designed and explain the vital role of the D-A system for the rational motifs of productive photocatalysts with effective pollutant degradable capability for future demand.

Camphoric acid as renewable cyclic building block for bio-based UV-curing polyhexylene itaconate

Polymer resins, such as polyester-, polyurethane- and alkyd resins are frequently applied as binder component in paints, printing inks, coatings or materials for additive manufacturing. Besides aliphatic building blocks with different chain lengths, cyclic monomers are used as starting materials, to increase the hardness of the resulting coatings materials. For this, mostly aromatic compounds derived from petrochemical sources, such as phthalic anhydride, isophthalic acid or terephthalic acid are being used. Monomers from renewable resources with similar chemical structures and chemical properties are scarce. In this study, (1R,3S)-(+)-camphoric acid is used as alternative building block for UV-curing polyester resins derived from itaconic acid and 1,6-hexanediol. The properties of both resins and final materials are compared to similar resins derived from isophthalic acid. In both cases, the incorporation of the cyclic monomer led to an increase in glass transition temperature, as well as viscosity of the resins. Thermal as well as mechanical properties of the cured materials were also improved in comparison to a resin without any cyclic building block incorporated.

The effects of addition of functional monomers and molecular imprinting on dual drug release from intraocular lens material

Although cataract surgery is considered a safe procedure, post-surgery complications such as endophthalmitis and ocular inflammation, may occur. To prevent this, antibiotics and anti-inflammatories are prescribed in the form of eye drops during the post-operatory period, but they lead to a low drug bioavailability in target tissues. The objective of this work is to develop an intraocular lens (IOL) material to deliver simultaneously one antibiotic, moxifloxacin (MXF), and one anti-inflammatory, diclofenac (DFN), in therapeutic concentrations to prevent both complications. The IOL material was modified through the incorporation of functional monomers, as well as molecular imprinting with both drugs using the same functional monomers, namely acrylic acid (AA), methacrylic acid (MAA), 4-vinylpiridine (4-VP) and a combination of MAA + 4-VP. The best results were obtained with MAA. Molecular imprinting did not influence the drug release, except with AA. Application of a mathematical model predicted that the released MXF and DFN concentrations would stay above the pre-determined MIC of S. aureus and S. epidermidis and the minimum values of IC50 of COX-1 and COX-2, for 9 and 14 days, respectively. Antibacterial tests showed that the released antibiotic remained active. The physical properties of the drug-loaded MAA-hydrogel remained adequate. The developed system proved to be non-irritant and non-cytotoxic.

The effects of pH and ionic strength on the volume phase transition temperature of thermo-responsive anionic copolymer gels

Applications of thermo-responsive (TR) gels in biomedicine and biotechnoligy require modulation of their volume phase transition temperature Tc in a rather wide interval. This is conventionally performed by incorporation of hydrophilic or hydrophobic monomers in the feed. The most pronounced growth of Tc occurs when TR monomers are copolymerized with anionic, cationic or ampholyte monomers.The effect of ionic monomers on the volume phase transition temperature of copolymer gels is traditionally analyzed in equilibrium swelling tests in distilled water. To evaluate how pH and ionic strength of aqueous solutions affect Tc, a constitutive model is developed. Adjustable parameters are found by fitting observations on poly(N-isopropylacrylamide-co-acrylic acid) and poly(N-isopropylacrylamide-co-itaconic acid) macro- and microgels below and above their critical temperature. The ability of the model to predict Tc is validated by comparison of experimental data with results of simulation. An analytical formula is derived that describes the influence of molar fraction of comonomers, pH and molar fraction of salt in aqueous solutions on the volume phase transition temperature of TR anionic gels.

Effect of Polymer Species on Maximum Aqueous Phase Supersaturation Revealed by Quantitative Nuclear Magnetic Resonance Spectroscopy.

The polymer used in an amorphous solid dispersion (ASD) formulation impacts the maximum achievable drug supersaturation. Herein, the effect of dissolved polymer on drug concentration in the aqueous phase when a drug-rich phase was generated by liquid-liquid phase separation (LLPS) was investigated for different polymers at various concentrations of drug and polymer. Solution nuclear magnetic resonance (NMR) spectroscopy revealed that polyvinylpyrrolidone (PVP), polyvinylpyrrolidone/vinyl acetate (PVP-VA), and hypromellose (HPMC) distributed into the ibuprofen (IBP)-rich phase formed by LLPS when the amorphous solubility of IBP was exceeded. The amount of polymer in the drug-rich phase increased for higher-molecular-weight grades of PVP and HPMC. Moreover, PVP-VA showed a greater extent of distribution into the IBP-rich phase compared to PVP, and this is attributed to its reduced hydrophilicity resulting from the incorporation of vinyl acetate monomers. Direct quantification by NMR measurements indicated that the IBP concentration in the aqueous phase decreased as the amount of polymer in the IBP-rich phase increased. This can be attributed to a reduction of the chemical potential of IBP in the IBP-rich phase. The reduction in dissolved IBP concentration was greater for the IBP/PVP-VA system compared to the IBP/HPMC system, as a result of more extensive drug-polymer interactions in the former system. The present study highlights the impact of polymer selection on the attainable supersaturation of the drug and the factors that need to be considered in the formulation of ASDs to obtain optimized in vivo performance.

Physicomechanical, optical, and antifungal properties of polymethyl methacrylate modified with metal methacrylate monomers

Statement of problemThe high recurrence rates of denture stomatitis may be associated with the resistance of biofilms to therapeutics. Therefore, methods that provide biomaterials with antifungal properties are an attractive solution to improving microbial control. PurposeThe purpose of this in vitro study was to modify conventional polymethyl methacrylate (PMMA) through the incorporation of metal methacrylate monomers and to evaluate the physicomechanical and optical properties and antifungal activity of the modified materials. Material and methodsExperimental denture base acrylic resins were fabricated through the addition of zirconium methacrylate (ZM), tin methacrylate (TM), and di-n-butyldimethacrylate-tin (DNBMT) to the liquid of a commercially available denture base PMMA resin. Unmodified PMMA resin was used as the control. The degree of conversion of the materials was tested through Fourier transform infrared spectroscopy (n=3). A digital spectrophotometer was used to assess the color change of the modified materials (n=8). Differences in Knoop hardness and roughness between experimental groups were also evaluated (n=8). A biofilm accumulation test with Candida albicans (ATCC 62342) (n=4) was performed for 5 days in Sabouraud broth culture supplemented with 10% sucrose. Data were subjected to analysis of variance and the post hoc Tukey honestly significant difference test (α=.05). ResultsThe degree of conversion and color-change values of the experimental materials were statistically similar to those of the control (P=.593). The incorporation of DNBMT significantly increased the hardness of the modified material (P=.014). The ZM, TM, and DNBMT groups had higher antifungal activity against C. albicans (P=.001) and lower roughness than the control group (control 0.65 ±0.05 μm; ZM 0.34 ±0.09 μm, TM 0.34 ±0.11 μm, and DNBMT 0.41 ±0.08 μm). ConclusionsThe metal-containing methacrylate monomers provided antifungal action to the modified materials without affecting the physicomechanical or optical properties of the denture base resin. ZM, TM, and DNBMT are potential reactive agents for the fabrication of PMMA denture base resins with antifungal properties.

Intra-bundle contractions enable extensile properties of active actin networks

The cellular cortex is a dynamic and contractile actomyosin network modulated by actin-binding proteins. We reconstituted a minimal cortex adhered to a model cell membrane mimicking two processes mediated by the motor protein myosin: contractility and high turnover of actin monomers. Myosin reorganized these networks by extensile intra‑bundle contractions leading to an altered growth mechanism. Hereby, stress within tethered bundles induced nicking of filaments followed by repair via incorporation of free monomers. This mechanism was able to break the symmetry of the previously disordered network resulting in the generation of extensile clusters, reminiscent of structures found within cells.

The known unknowns in lignin biosynthesis and its engineering to improve lignocellulosic saccharification efficiency

Biofuels produced from lignocellulosic biomass provide energy security and reduce greenhouse gas emissions with positive impacts on sustainability. Lignocellulose byproducts are expected to impact the production of cellulosic ethanol. However, lignin is a major factor imposing biomass recalcitrance to saccharification. Although structural phenolics can be removed from lignocellulosic biomass, physical and chemical pretreatments are expensive. In turn, the structure and composition of lignin is very flexible. Up- and downregulation of genes and, thereby, enzymes involved in core and non-core lignin biosynthesis can reduce lignin content and improve biomass saccharification. Alternatively, insertion of heterologous genes to the phenylpropanoid pathway may lead to the incorporation of alternative monomers into lignin, creating desirable properties and preserving the biological roles of lignin with a positive effect on saccharification. Studies reporting the effect of fine regulation on lignin structures are mapping how plants can be transformed to enhance saccharification while preserving productivity. Based on these findings and events, this review updates the state-of-art changes in lignin biosynthesis to improve saccharification efficiency. The main findings reported over the last decade were summarized to permit researchers an overview of this relevant scientific subject.

Asymmetric Co-unit Inclusion in Statistical Copolyesters

The biodegradation of isodimorphic random butanediol-succinate/adipate copolymers (PBSAs) can be affected by a change in the semicrystalline morphology. A crucial point for the final semicrystalline structure is the incorporation of monomers of the minority component into the crystals of the majority component. We use proton time-domain NMR and wide-angle X-ray scattering to characterize the copolymers across their complete composition range and analyze the possible inclusion of minority comonomers in the PBA-rich 20/80 and the PBS-rich 60/40 composition by applying different solid-state 13C NMR experiments. For the PBA-rich copolymers, we find a nearly constant volumetric crystallinity of 50% up to the 50/50 composition combined with an increase of the crystalline lamella thickness. NMR has detected the BS units incorporated into the BA crystalline structure, where on average every tenth monomer is a BS comonomer. In PBS-rich crystals, the crystallinity and crystallite thickness decrease from neat PBS to PBSA 60/40 by 37% and ∼20%, respectively. We also find evidence that the BA units are excluded from the bulk crystal but accumulate at the crystallite surface. The amount of BA units in these pocket-like structures can be estimated to be 7–9% of the BA comonomer content.

Correcting dominant‐negative von Willebrand disease

Correcting dominant‐negative von Willebrand disease

Incorporation of catechyl monomers into lignins: lignification from the non-phenolic endviaDiels–Alder cycloaddition?

Catechyl monomers 1-electron-oxidize and undergo radical coupling to produce benzodioxane units in lignin. Derivedo-quinones undergo Diels–Alder reactions giving oxatricyclo and new benzodioxane products, but does this occur in lignification?.

Effects of Glutamate Arginylation on α-Synuclein: Studying an Unusual Post-Translational Modification through Semisynthesis

A variety of post-translational modifications (PTMs) are believed to regulate the behavior and function of α-synuclein (αS), an intrinsically disordered protein that mediates synaptic vesicle trafficking. Fibrils of αS are implicated in neurodegenerative disorders such as Parkinson's disease. In this study, we used chemical synthesis and biophysical techniques to characterize the neuroprotective effects of glutamate arginylation, a hitherto little characterized PTM in αS. We developed semisynthetic routes combining peptide synthesis, unnatural amino acid mutagenesis, and native chemical ligation (NCL) to site-specifically introduce the PTM of interest along with fluorescent probes into αS. We synthesized the arginylated glutamate as a protected amino acid, as well as a novel ligation handle for NCL, in order to generate full-length αS modified at various individual sites or a combination of sites. We assayed the lipid-vesicle binding affinities of arginylated αS using fluorescence correlation spectroscopy (FCS) and found that arginylated αS has the same vesicle affinity compared to control protein, suggesting that this PTM does not alter the native function of αS. On the other hand, we studied the aggregation kinetics of modified αS and found that arginylation at E83, but not E46, slows aggregation and decreases the percentage incorporation of monomer into fibrils in a dose-dependent manner. Arginylation at both sites also resulted in deceleration of fibril formation. Our study represents the first synthetic strategy for incorporating glutamate arginylation into proteins and provides insight into the neuroprotective effect of this unusual PTM.