Molecular dynamics simulation study of xyloglucan adsorption on cellulose surfaces: effects of surface hydrophobicity and side-chain variation

The effect of surface hydrophobicity and side-chain variation on xyloglucan adsorption onto cellulose microfibrils (CMF) is investigated via molecular dynamics simulations. A molecular model of CMF with (100), (010), (1–10), (110) and (200) crystal faces was built. We considered xylogluco-oligosaccharides (XGO) with three repeating units, namely (XXXG)_3, (XXLG)₃, and (XXFG)₃ (where each (1,4)-β-d-glucosyl residue in the backbone is given a one-letter code according to its substituents: G = β-d-Glc; X = α-d-Xyl-(1,6)-β-d-Glc; L = β-d-Gal-(1,2)-α-d-Xyl-(1,6)-β-d-Glc; F = α-l-Fuc-(1,2)-β-d-Gal-(1,2)-α-d-Xyl-(1,6)-β-d-Glc). Our work shows that (XXXG)₃ binds more favorably to the CMF (100) and (200) hydrophobic surfaces than to the (110), (010) and (1–10) hydrophilic surfaces. The origin of this behavior is attributed to the topography of hydrophobic CMF surface, which stabilizes (XXXG)₃ in flat conformation. In contrast, on the rough hydrophilic CMF surface (XXXG)₃ adopts a less favorable random-coil conformation to facilitate more hydrogen bonds with the surface. Extending the xyloglucan side chains from (XXXG)₃ to (XXLG)₃ hinders their stacking on the CMF hydrophobic surface. For (XXFG)₃, the interaction with the hydrophobic surface is as strong as (XXXG)₃. All three XGOs have similar binding to the hydrophilic surface. Steered molecular dynamics simulation was performed on an adhesive model where (XXXG)₃ was sandwiched between two CMF hydrophobic surfaces. Our analysis suggests that this sandwich structure might help provide mechanical strength for plant cell walls. Our study relates to a recently revised model of primary cell walls in which extensibility is largely determined by xyloglucan located in limited regions of tight contact between CMFs.     

聚丙烯酸双(乙氧羰基)甲酯及其螯合物的合成和磁性能的检测

以溴代丙二酸二乙酯、丙烯酸钠为原料合成了聚丙烯酸双(乙氧羰基)甲酯(PEOCMA),并制备了其相应的与稀土金属Gd3+、Nd3+以及过渡金属Ni2+的高分子螯合物.利用FTIR、1H-NMR、GPC对聚合物和高分子螯合物的结构进行了表征,通过电感耦合等离子质谱仪(ICP)测得了高分子螯合物中的金属含量,借助多功能材料物理特性测试系统(PPMS,physical property measurement system)测定螯合物的磁性能.结果表明这些高分子螯合物具有较高的磁饱和强度,在低温下呈现出一定的铁磁相互作用,且为软磁性材料.     

Reversible Re‐programing of Cell–Cell Interactions

The ability to engineer and re‐program the surfaces of cells would provide an enabling synthetic biological method for the design of cell‐ and tissue‐based therapies. A new cell surface‐engineering strategy is described that uses lipid‐chemically self‐assembled nanorings (lipid‐CSANs) that can be used for the stable and reversible modification of any cell surface with a molecular reporter or targeting ligand. In the presence of a non‐toxic FDA‐approved drug, the nanorings were quickly disassembled and the cell–cell interactions reversed. Similar to T‐cells genetically engineered to express chimeric antigen receptors (CARS), when activated peripheral blood mononuclear cells (PBMCs) were functionalized with the anti‐EpCAM‐lipid‐CSANs, they were shown to selectively kill antigen‐positive cancer cells. Taken together, these results demonstrate that lipid‐CSANs have the potential to be a rapid, stable, and general method for the reversible engineering of cell surfaces and cell–cell interactions.     

Silver‐Catalyzed Decarboxylative Trifluoromethylthiolation of Aliphatic Carboxylic Acids in Aqueous Emulsion

A silver‐catalyzed decarboxylative trifluoromethylthiolation of secondary and tertiary carboxylic acids under mild conditions tolerates a wide range of functional groups. The reaction was dramatically accelerated by its performance in an aqueous emulsion, which was formed by the addition of sodium dodecyl sulfate to water. It was proposed that the radical, which was generated from the silver‐catalyzed decarboxylation in the “oil‐in‐water” droplets, could easily react with the trifluoromethylthiolating reagent to form the product.     

Redox Chemistry of a Hydroxyphenyl‐Substituted Borane

Chemical reduction of a hydroxyphenyl‐substituted borane triggers a sequential electron‐ and intramolecular hydrogen‐atom‐transfer process to afford a hydridoborate phenoxide dianion. On the other hand, hydrogen‐atom abstraction of the borane leads to the isolation of a neutral borylated phenoxyl radical, which can be transformed to the corresponding benzoquinone borataalkene derivative by reduction with cobaltocene.     

Enantioselective Iron‐Catalyzed Intramolecular Cyclopropanation Reactions

An iron‐catalyzed asymmetric intramolecular cyclopropanation was realized in high yields and excellent enantioselectivity (up to 97 % ee) by using the iron complexes of chiral spiro‐bisoxazoline ligands as catalysts. The superiority of iron catalysts exhibited in this reaction demonstrated the potential abilities of this sustainable metal in asymmetric carbenoid transformation reactions.     

Crowning Proteins: Modulating the Protein Surface Properties using Crown Ethers

Crown ethers are small, cyclic polyethers that have found wide‐spread use in phase‐transfer catalysis and, to a certain degree, in protein chemistry. Crown ethers readily bind metallic and organic cations, including positively charged amino acid side chains. We elucidated the crystal structures of several protein‐crown ether co‐crystals grown in the presence of 18‐crown‐6. We then employed biophysical methods and molecular dynamics simulations to compare these complexes with the corresponding apoproteins and with similar complexes with ring‐shaped low‐molecular‐weight polyethylene glycols. Our studies show that crown ethers can modify protein surface behavior dramatically by stabilizing either intra‐ or intermolecular interactions. Consequently, we propose that crown ethers can be used to modulate a wide variety of protein surface behaviors, such as oligomerization, domain–domain interactions, stabilization in organic solvents, and crystallization.     

Transfer of Aryl Halide to Alkyl Halide: Reductive Elimination of Alkylhalide from Alkylpalladium Halides Containing syn‐β‐Hydrogen Atoms

β‐Hydride abstraction is a well‐accepted elementary step for catalytic cycles in organometallic chemistry. It is usually anticipated that alkylpalladium halides containing syn‐β‐hydrogen atoms will undergo β‐hydride abstraction to afford the Heck‐type products. However, this study discloses that the above general knowledge is only conditionally correct. Our experimental results demonstrate that the reductive elimination of alkylhalides from alkylpalladium halides containing syn‐β‐hydrogen atoms may surpass the β‐hydride abstraction or even become exclusive in certain cases.     

Porosity‐Controlled Eggshell Membrane as 3D SERS‐Active Substrate

We report on the fabrication of a surface‐enhanced Raman scattering (SERS) platform, comprised of a three‐dimensional (3D) porous eggshell membrane (ESM) scaffold decorated with Ag nanoparticles (NPs). Both native and treated ESM were used, where the treated ESM pore size and fiber crossing density was controlled by timed exposure to hydrogen peroxide (H₂O₂). Ag NPs were synthesized in situ by reduction of silver nitrate with ascorbic acid. Our results demonstrate that H₂O₂‐treated Ag‐ESM provides a more densely packed 3D network of active material, which leads to consistently higher SERS enhancement than untreated Ag‐ESM substrates.