Graphene Oxide/Polyacrylamide/Aluminum Ion Cross‐Linked Carboxymethyl Hemicellulose Nanocomposite Hydrogels with Very Tough and Elastic Properties

Development of high‐strength hydrogels has recently attracted ever‐increasing attention. In this work, a new design strategy has been proposed to prepare graphene oxide (GO)/polyacrylamide (PAM)/aluminum ion (Al³⁺)‐cross‐linked carboxymethyl hemicellulose (Al‐CMH) nanocomposite hydrogels with very tough and elastic properties. GO/PAM/Al‐CMH hydrogels were synthesized by introducing graphene oxide (GO) into PAM/CMH hydrogel, followed by ionic cross‐linking of Al³⁺. The nanocomposite hydrogels were characterized by means of FTIR, X‐ray diffraction (XRD), and scanning electron microscopy/energy‐dispersive X‐ray analysis (SEM‐EDX) along with their swelling and mechanical properties. The maximum compressive strength and the Young's modulus of GO_3.5/PAM/Al‐CMH_0.45 hydrogel achieved values of up to 1.12 and 13.27 MPa, increased by approximately 6488 and 18330 % relative to the PAM hydrogel (0.017 and 0.072 MPa). The as‐prepared GO/PAM/Al‐CMH nanocomposite hydrogels possess high strength and great elasticity giving them potential in bioengineering and drug‐delivery system applications.     

Effects of cosolvent on formation and morphology of microspheres in precipitation polymerization of divinylbenzene in supercritical carbon dioxide

Precipitation polymerizations of divinylbenzene(DVB) in pure supercritical carbon dioxide,and parallel runs with presence of a cosolvent were carried out.The results showed that use of acetone as the cosolvent contributed greatly to the formation of the monodisperse microspheres.PDVB microspheres,with obviously higher uniformity than reported up to date,were achieved using 6-7 mL of acetone in a reactor of 50 mL with DVB concentration of 0.4 mol/L under 16 MPa,a much lower pressure than previously reported without use of cosolvent.     

Low-temperature activation of methane over rare earth metals promoted Zn/HZSM-5 zeolite catalysts in the presence of ethylene

At low temperature of 723 K, methane can be easily activated in the presence of ethylene in the feed, and converted to higher hydrocarbons (C2–C4) and aromatics (C6–C10), through its reaction over rare metals modified Zn/HZSM-5 zeolite catalysts without undesirable carbon oxides formation. Methane can get 37.3% conversion over the above catalysts under low temperature, and the catalysts show a longer lifetime than usual metal supported HZSM-5 zeolite catalysts without adding any rare earth metals. The effects of methane activation over various rare earth metal promoted Zn/HZSM-5 catalysts on the products and influences of several reaction conditions such as temperature, catalyst lifetime and molar ratio of CH4/C2H4 have been discussed.     

Spectroscopic Investigation on Sonocatalytic Damage of BSA Molecules by FeIII Complexes with Binary Organic Acid Ligands Under Ultrasonic Irradiation

The interaction between bovine serum albumin (BSA) and Fe^III complexes with three binary organic acid (biorga) ligands, [Fe^III(oxa)(H₂O)₄]⁺ (oxa = oxalic acid), [Fe^III(pra)(H₂O)₄]⁺ (pra = propanedioic acid) and [Fe^III(sua)(H₂O)₄]⁺ (sua = succinic acid), as well as the sonocatalytic damage of BSA in the presence of these three Fe^III–biorga complexes under ultrasonic irradiation, were studied by UV–vis and fluorescence spectra. The experimental results show that the fluorescence quenching process of BSA caused by three Fe^III–biorga complexes are all static quenching and the corresponding quenching rate constants (K _q), equilibrium constants (K _A) and the binding site numbers (n) were calculated. The results reveal that, under ultrasonic irradiation, the BSA molecules were obviously damaged by these Fe^III–biorga complexes. In addition, the effects of several factors on the damage of BSA molecules were examined. The experimental results demonstrate that the damage degree of BSA increased with an increase of ultrasonic irradiation time, Fe^III–biorga complex concentration, and ionic strength. In comparison, [Fe^III(pra)(H₂O)₄]⁺ exhibited higher sonocatalytic activity than [Fe^III(oxa)(H₂O)₄]⁺ and [Fe^III(sua)(H₂O)₄]⁺. Finally, the extent of generation of $ \cdot {\text{O}}_{2}^{ - } $ · O 2 ? and ·OH during sonocatalytic processes was estimated. Perhaps, the results will be significant for promoting sonodynamic treatment (SDT) of tumors at the molecular level.     

1—酰基—4—氯环己烷与取代芳烃的区域与立体选择性反应

从环己烯合成了１－酰基－４－氯环己烷，发现在其在ＡｌＣｌ３催化与苯，氯苯，溴苯等优先生成反式１－芳基－４－酰基环己烷，与联苯反应时选择性较差。     

Stereoselective Glycosidic Coupling Reactions of Fully Benzylated 1,2-Anhydro Sugars with N-Tosyl- or N-Benzyloxycarbonyl-l-serine Methyl Ester

Abstract

The glycosidic coupling reaction of 1,2-anhydro-3,4,6-tri-O-benzyl-β-d-mannopyranose (7), 1,2-anhydro-3,4,6-tri-O-benzyl-α-d-galactopyranose (21), and 1,2-anhydro-3,4-di-O-benzyl-α-d-xylopyranose (18) with N-tosyl- (10) or N-benzyloxycarbonyl- (11) L-serine methyl ester provides a new stereocontrolled synthesis of 1,2-trans linked glycopeptides. The 1,2-anhydro sugars are shown to react smoothyl with 10 or 11 in the presence of Lewis acid (ZnCl₂ or AgOTf) as well as powdered 4A molecular sieves in CH₂Cl₂ at room temperature to afford glycosyl serine derivatives with high stereoselectivity and high yield in less than 30 min. An improved method using 2-O-acetyl-3,4,6-tri-O-benzyl-α-d-mannopyranosyl chloride (6) as the key intermediate for ring closure was applied for the synthesis of 1,2-anhydro-3,4,6-tri-O-benzyl-β-d-mannopyranose.     

Porous composite scaffolds of hydroxyapatite/silk fibroin via two‐step method

A two‐step method was used to fabricate the hydroxyapatite (HAP)/silk fibroin (SF) scaffolds, i.e. the nano‐sized HAP/SF composite powders were prepared by co‐precipitation, which were then blended with SF solution to fabricate the HAP/SF composite scaffolds. The obtained scaffolds showed a 3D porous structure. The porosity was higher than 90% with the average macropore size of 214.2 µm. Moreover, the nano‐sized HAP/SF composite powders were uniformly dispersed in the silk fibroin matrix, which provided the scaffolds enhanced compressive properties. The cell culture assay showed that the scaffolds fabricated by the two‐step method could improve the cell proliferation and osteogenic differentiation when compared with those prepared by the conventional one‐step blending method. The results suggested that the two‐step method could promote the uniform dispersion of HAP in the SF matrix and efficient combination between the HAP and the matrix, which may provide a potential application in the composite scaffold preparation for tissue engineering. Copyright © 2009 John Wiley & Sons, Ltd.     

Unique Thia‐Baeyer–Villiger‐Type Oxidation of Dibenzothiophene Sulfoxides Derivatives

The present research has demonstrated that selective C?S bond cleavages of dibenzothiophene and its derivatives are feasible by thia‐Baeyer–Villiger type oxidation, i. e. the oxygen insertion process within a sulfoxide‐carbon linkage, in the presence of porphyrin iron (III) and by ultraviolet irradiation originating from sunlight, high pressure Hg‐lamp or residentially germicidal ultraviolet lamp under very mild conditions. This reaction with tert‐butylhydroperoxide at 30.0 °C leads to dibenzo[1,2]oxathiin‐6‐oxide ( PBS ) in 83.2 % isolated yield or its hydrated products, 2‐(2‐hydroxyphenyl)‐benzenesulfinic derivatives ( HPBS ) in near 100 % yield based HPLC data. PBS and HPBS are a type of biological products detected on the C?S bond cleavage step through various oxidative biodesulfurization ( OBDS ) pathways, and are useful synthetic intermediates and fine chemicals. These observations may contribute on understanding delicately molecular aspect of OBDS in the photosynthesis system, expanding the C‐S cleavage chemistry of S‐heterocyclic compounds and approaching toward biomemic desulfurization with respect to converting sulfur contaminants to chemically beneficial blocks as needed and performing under the ambient conditions.     

Hyperbranched Poly(ester‐enamine) from Spontaneous Amino‐yne Click Reaction for Stabilization of Gold Nanoparticle Catalysts

Hyperbranched polymers have garnered much attention due to attractive properties and wide applications, such as drug‐controlled release, stimuli‐responsive nano‐objects, photosensitive materials and catalysts. Herein, two types of novel hyperbranched poly(ester‐enamine) (hb‐PEEa) were designed and synthesized via the spontaneous amino‐yne click reaction of A₂ monomer (1, 3‐bis(4‐piperidyl)‐propane (A_2a) or piperazine (A_2b)) and B₃ monomer (trimethylolpropanetripropiolate). According to Flory's hypothesis, gelation is an intrinsic problem in an ideal A₂+B₃ polymerization system. By controlling the polymerization conditions, such as monomer concentration, molar ratio and rate of addition, a non‐ideal A₂+B₃ polymerization system can be established to avoid gelation and to synthesize soluble hb‐PEEa. Due to abundant unreacted alkynyl groups in periphery, the hb‐PEEa can be further functionalized by different amino compounds or their derivates. The as‐prepared amphiphilic PEG‐hb‐PEEa copolymer can readily self‐assemble into micelles in water, which can be used as surfactant to stabilize Au nanoparticles (AuNPs) during reduction of NaBH₄ in aqueous solution. As a demonstration, the as‐prepared PEG‐hb‐PEEa‐supported AuNPs demonstrate good dispersion in water, solvent stability and remarkable catalytic activity for reduction of nitrobenzene compounds.     

Three-dimensionally crossing manifold micro-mixer for fast mixing in a short channel length

In this study, we report a neo-conceptive three-dimensionally (3D) crossing manifold micromixer (CMM) embedded in microchannel. Fabricated by sequential processes of photolithography and two photon absorption stereolithography, this leads to a microfluidic system with a built-in micromixer in a site controlled manner. The effectiveness of CMM is investigated numerically and experimentally. Through the numerical simulation, it is estimated that a high mixing ratio of 90% can be obtained even in a channel length shorter than five times the channel width. This compares well with the conventional passive type of micromixers that have a gradual increase in mixing efficiency with the length of the channel. Furthermore, the mixing performance of the realized CMM built-in microchannel is observed by confocal microscopy.