Effect of ethyl cellulose microencapsulated ammonium polyphosphate on flame retardancy,mechanical and thermal properties of flame retardant poly(butylene succinate) composites

Ethyl cellulose, a widely used bio-degradable shell material, microencapsulated ammonium polyphosphate (MAPP) was added to the bio-degradable poly(butylene succinate) (PBS) to improve its flame retardancy, compatibility, and thermal stability. The MAPP was well characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), water contact angle, and thermogravimetric (TG) analysis. The SEM results indicate the improved dispersion of MAPP into PBS matrix and the formation of the strong interfacial adhesion between MAPP and PBS than APP. With the incorporation of MAPP and char-forming agent into PBS, the limiting oxygen index of the composite was increased to 35.5 %, and the sample can pass the UL-94 V-0 rating, while the un-microencapsulated counterpart cannot reach the rating. The cone calorimeter test showed that the peak heat release rate was decreased by 46.7 % and the burning time was also prolonged compared to the pure PBS. The increased melt flow index and rheology test indicated the increase of viscosity and the improvement of anti-dripping properties. Moreover, the mechanical properties and thermal stability of MAPP composite were also obviously enhanced after the microencapsulation by mechanical, dynamical mechanical thermal analysis, and TG analysis.     

Electrochemical myoglobin biosensor based on carbon ionic liquid electrode modified with Fe3O4@SiO2 microsphere

In this paper, a Fe₃O₄@SiO₂ core-shell structure microsphere was synthesized and used to investigate the direct electron transfer of myoglobin (Mb) with a 1-butylpyridinium hexafluorophosphate based carbon ionic liquid electrode (CILE) as the substrate electrode. The mixture of Mb and Fe₃O₄@SiO₂ microsphere could form an organic–inorganic composite, which was immobilized on the surface of CILE with a chitosan (CS) film. Cyclic voltammetric experiments indicated that a pair of well-defined quasi-reversible redox peaks appeared on CS/Mb-Fe₃O₄@SiO₂/CILE with the formal peak potential (E ^0′) located at ?0.31 V (vs. saturated calomel electrode), which was corresponded to the electroactive center of Mb heme Fe(III)/Fe(II) redox couples. Direct electrochemical behaviors of Mb in CS-Fe₃O₄@SiO₂ composite film were carefully investigated with the electrochemical parameters calculated. The CS/Mb-Fe₃O₄@SiO₂/CILE showed good electrocatalytic behaviors to the reduction of trichloroacetic acid in the concentration range from 0.2 to 11.0 mmol L^?1 with the detection limit of 0.18 mmol L^?1 (3σ). Based on CS/Mb-Fe₃O₄@SiO₂/CILE, a new third-generation reagentless electrochemical biosensor was constructed with higher sensitivity and reproducibility.     

Biosynthesis of Streptolidine Involved Two Unexpected Intermediates Produced by a Dihydroxylase and a Cyclase through Unusual Mechanisms

Streptothricin‐F (STT‐F), one of the early‐discovered antibiotics, consists of three components, a β‐lysine homopolymer, an aminosugar D ‐gulosamine, and an unusual bicyclic streptolidine. The biosynthesis of streptolidine is a long‐lasting but unresolved puzzle. Herein, a combination of genetic/biochemical/structural approaches was used to unravel this problem. The STT gene cluster was first sequenced from a Streptomyces variant BCRC 12163, wherein two gene products OrfP and OrfR were characterized in vitro to be a dihydroxylase and a cyclase, respectively. Thirteen high‐resolution crystal structures for both enzymes in different reaction intermediate states were snapshotted to help elucidate their catalytic mechanisms. OrfP catalyzes an Fe^II‐dependent double hydroxylation reaction converting L ‐Arg into (3R,4R)‐(OH)₂‐L ‐Arg via (3S)‐OH‐L ‐Arg, while OrfR catalyzes an unusual PLP‐dependent elimination/addition reaction cyclizing (3R,4R)‐(OH)₂‐L ‐Arg to the six‐membered (4R)‐OH‐capreomycidine. The biosynthetic mystery finally comes to light as the latter product was incorporation into STT‐F by a feeding experiment.     

A Chiral Gold Nanocluster Au20 Protected by Tetradentate Phosphine Ligands

The chirality of a gold nanocluster can be generated from either an intrinsically chiral inorganic core or an achiral inorganic core in a chiral environment. The first structural determination of a gold nanocluster containing an intrinsic chiral inorganic core is reported. The chiral gold nanocluster [Au₂₀(PP₃)₄]Cl₄ (PP₃=tris(2‐(diphenylphosphino)ethyl)phosphine) has been prepared by the reduction of a gold(I)–tetraphosphine precursor in dichloromethane solution. Single‐crystal structural determination reveals that the cluster molecular structure has C₃ symmetry. It consists of a Au₂₀ core consolidated by four peripheral tetraphosphines. The Au₂₀ core can be viewed as the combination of an icosahedral Au₁₃ and a helical Y‐shaped Au₇ motif. The identity of this Au₂₀ cluster is confirmed by ESI‐MS. The chelation of multidentate phosphines enhances the stability of this Au₂₀ cluster.     

Mechanistic Insights into the Interface‐Directed Transformation of Thiols into Disulfides and Molecular Hydrogen by Visible‐Light Irradiation of Quantum Dots

Quantum dots (QDs) offer new and versatile ways to harvest light energy. However, there are few examples involving the utilization of QDs in organic synthesis. Visible‐light irradiation of CdSe QDs was found to result in virtually quantitative coupling of a variety of thiols to give disulfides and H₂ without the need for sacrificial reagents or external oxidants. The addition of small amounts of nickel(II) salts dramatically improved the efficiency and conversion through facilitating the formation of hydrogen atoms, thereby leading to faster regeneration of the ground‐state QDs. Mechanistic studies reveal that the coupling reaction occurs on the QD surfaces rather than in solution and offer a blueprint for how these QDs may be used in other photocatalytic applications. Because no sacrificial agent or oxidant is necessary and the catalyst is reusable, this method may be useful for the formation of disulfide bonds in proteins as well as in other systems sensitive to the presence of oxidants.     

Balancing the Rate of Cluster Growth and Etching for Gram‐Scale Synthesis of Thiolate‐Protected Au25 Nanoclusters with Atomic Precision

We report a NaOH‐mediated NaBH₄ reduction method for the synthesis of mono‐, bi‐, and tri‐thiolate‐protected Au₂₅ nanoclusters (NCs) with precise control of both the Au core and thiolate ligand surface. The key strategy is to use NaOH to tune the formation kinetics of Au NCs, i.e., reduce the reduction ability of NaBH₄ and accelerate the etching ability of free thiolate ligands, leading to a well‐balanced reversible reaction for rapid formation of thermodynamically favorable Au₂₅ NCs. This protocol is facile, rapid (≤3 h), versatile (applicable for various thiolate ligands), and highly scalable (>1 g Au NCs). In addition, bi‐ and tri‐thiolate‐protected Au₂₅ NCs with adjustable ratios of hetero‐thiolate ligands were easily obtained. Such ligand precision in molecular ratios, spatial distribution and uniformity resulted in richly diverse surface landscapes on the Au NCs consisting of multiple functional groups such as carboxyl, amine, and hydroxy. Analysis based on NMR spectroscopy revealed that the hetero‐ligands on the NCs are well distributed with no ligand segregation. The unprecedented synthesis of multi‐thiolate‐protected Au₂₅ NCs may further promote the practical applications of functional metal NCs.     

Self‐Assembly of Pyridinium‐Functionalized Anthracenes: Molecular‐Skeleton‐Directed Formation of Microsheets and Microtubes

Two amphiphilic regioisomers, 9‐AP (1‐[11‐(9‐anthracenylmethoxy)‐11‐oxoundecyl]pyridinium bromide), and 2‐AP (1‐[11‐(2‐anthracenyl methoxy)‐11‐oxoundecyl]pyridinium bromide), were synthesized and their assembly behaviors were studied. Due to the anisotropic features of the anthracene structure, different substituted positions on the anthracene ring lead 9‐AP and 2‐AP to adapt “shaver” and “spatula”‐like molecular shapes, respectively, which consequently dictate the structure of their final assemblies. While “shaver”‐shaped 9‐AP assembled into microsheets, driven by π–π interactions, “spatula”‐shaped 2‐AP assembled into microtubular structures, promoted primarily by charge‐transfer interactions.     

Direct Resolution of Enantiomers of DL-Amino Acids by Thin-Layer Chromatography with Vancomycin as Impregnating Agent

JPC – Journal of Planar Chromatography – Modern TLC -     

Enzymatic Desymmetrising Redox Reactions for the Asymmetric Synthesis of Biaryl Atropisomers

Atropisomeric biaryls carrying ortho‐hydroxymethyl and formyl groups were made enantioselectively by desymmetrisation of dialdehyde or diol substrates. The oxidation of the symmetrical diol substrates was achieved using a variant of galactose oxidase (GOase), and the reduction of the dialdehydes using a panel of ketoreductases. Either M or P enantiomers of the products could be formed, with absolute configurations assigned by time‐dependent DFT calculations of circular dichroism spectra. The differing selectivities observed with different biaryl structures offer an insight into the detailed structure of the active site of the GOase enzyme.     

Control of Chiral Nanostructures by Self‐Assembly of Designed Amphiphilic Peptides and Silica Biomineralization

Peptides, the fundamental building units of biological systems, are chiral in molecular scale as well as in spatial conformation. Shells are exquisite examples of well‐defined chiral structures produced by natural biomineralization. However, the fundamental mechanism of chirality expressed in biological organisms remains unclear. Here, we present a system that mimics natural biomineralization and produces enantiopure chiral inorganic materials with controllable helicity. By tuning the hydrophilicity of the amphiphilic peptides, the chiral morphologies and mesostructures can be changed. With decreasing hydrophilicity of the amphiphilic peptides, we observed that the nanostructures changed from twisted nanofibers with a hexagonal mesostructure to twisted nanoribbons with a lamellar mesostructure, and the extent of the helicity decreased. Defining the mechanism of chiral inorganic materials formed from peptides by noncovalent interactions can improve strategies toward the bottom‐up synthesis of nanomaterials as well as in the field of bioengineering.