Synthesis of Anomerically Pure,Furanose‐Free α‐Benzyl‐2‐amino‐2‐deoxy‐d‐altro‐ and d‐manno‐pyranosides and Some of Their Derivatives

The anomerically pure benzyl α‐d‐glycoside of 2‐amino‐2‐deoxy‐mannopyranoside was synthesized from d‐glucopyranose via 2‐amino‐2‐deoxy‐d‐altrose intermediates. Unlike the direct synthesis from mannosamine in the literature, our method provides furanose‐free products. A new method for the preparation of cis‐2,3‐oxazolidinones of 2‐amino‐2‐deoxy‐sugars was developed. A selective removal of the glycosidic benzyl group in the presence of 4,6‐O‐benzylidene protection was developed, which may provide new routes for the synthesis of oligosaccharides. Furanose‐free derivatives of α‐benzyl‐2‐amino‐2‐deoxy‐mannopyranuronic acids synthesized here offered possibilities for direct comparisons to prior literature preparations.     

Using “Threading Followed by Shrinking” to Synthesize Highly Stable Dialkylammonium‐Ion‐Based Rotaxanes

Herein, we report a “threading followed by shrinking” approach for the synthesis of rotaxanes by using an “oxygen‐deficient” macrocycle that contained two arylmethyl sulfone units and the dumbbell‐shaped salt bis(3,5‐dimethylbenzyl)ammonium tetrakis(3,5‐trifluoromethylphenyl)borate as the host and guest components, respectively. The extrusion of SO₂ from both of the arylmethyl sulfone units of the macrocyclic component in the corresponding [2]pseudorotaxane resulted in a [2]rotaxane that was sufficiently stable to maintain its molecular integrity in CD₃SOCD₃ at 393 K for at least 5 h.     

Interference of Transformer oil Matrices to the Internal Standards on PCB Quantification

Abstract

Polychlorinated biphenyls (PCBs) are toxic, perssstent, global environmental contaminants which were formulated as complex mixtures of congeners. Many methods have been developed in the past to analyze PCB in transformer oil samples for regulatory purposes. The most important consideration in the cleanup procedure is the ability to remove the oil from the sample matrix, since trace amount of oil will interfere with the subsequent GC-MS analysis. Electron capture detection (ECD) has been the most common method for gas chromatographic analysis of PCBs because of its high sensitivity toward halogenated compounds. ECD can also respond to some non-PCB compound resulting in biased concentrations of PCB. In this work, a two-stage cleanup method, using DMSO liquid/liquid extraction and HPLC column chromatography. has been applied to two types of transformer oil. Five internal standards have been selected to show their performance in the presence of different oil matrices. The comparison of the PCB quantification at different conditions for GC-MS and GC-ECD will be demonstrated.     

New nanotube synthesis strategy--application of sodium nanotubes formed inside anodic aluminium oxide as a reactive template

Formation of Na nanotubes inside the channels of anodic aluminium oxide (AAO) membranes has been achieved by decomposing NaH thermally on AAO. The as-produced material, Na@AAO, is applied as a reactive template to prepare other tubular materials. Reacting Na@AAO with gaseous C6Cl6 generates carbon nanotubes (ca. 250 nm, wall thickness of 20 nm, tube length of 60 microm) inside the AAO channels. Highly aligned bundles of nearly amorphous carbon nanotubes are isolated after AAO is removed.     

Kinetics study of imidazole-cured epoxy-phenol resins

The reaction kinetics of diglycidyl ether of bisphenol A (DGEBA) cured with different concentrations of imidazole and bisphenol A (BPA) were investigated by using differential scanning calorimetry. Both dynamic and isothermal DSC were studied. Two initiation mechanisms were found to play roles in the curing reactions. One was based on adduct formation of epoxy groups with pyridine-type nitrogen and the other was based on ionic complexes of imidazole and BPA. The subsequent propagation was composed of three main reactions, viz. the epoxide/phenol reaction, the acid/base reaction, and the epoxide/R-O⁻ reaction. A generalized kinetics model was developed and used to predict the conversion of epoxide groups using a wide range of imidazole and BPA concentrations, and cure temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3233–3242, 1999     

Production of hydrogen by oxidative steam reforming of methanol over Cu/SiO2 catalysts

Selective production of hydrogen by oxidative steam reforming of methanol (OSRM) was studied over Cu/SiO₂ catalyst using fixed bed flow reactor. Textural and structural properties of the catalyst were analyzed by various instrumental methods. TPR analysis illustrates that the reduction temperature peak was observed between 510?K and 532?K at various copper loadings and calcination temperatures and the peaks shifted to higher temperature with increasing copper loading and calcination temperature. The XRD and XPS analysis demonstrates that the copper existed in different oxidation states at different conditions: Cu₂O, Cu⁰, CuO and Cu(OH)₂ in uncalcined sample; CuO in calcined sample: Cu₂O and metallic Cu after reduction at 600?K and Cu⁰ and CuO after catalytic test. TEM analysis reveals that at various copper loadings, the copper particle size is in the range between 3.0?nm and 3.8?nm. The Cu particle size after catalytic test increased from 3.6 to 4.8?nm, which is due to the formation of oxides of copper as evidenced from XRD and XPS analysis. The catalytic performance at various Cu loadings shows that with increasing Cu loading from 4.7 to 17.3?wt%, the activity increases and thereafter it decreases. Effect of calcination shows that the sample calcined at 673?K exhibited high activity. The O₂/CH₃OH and H₂O/CH₃OH molar ratios play important role in reaction rate and product distribution. The optimum molar ratios of O₂/CH₃OH and H₂O/CH₃OH are 0.25 and 0.1, respectively. When the reaction temperature varied from 473 to 548?K, the methanol conversion and H₂ production rate are in the range of 21.9–97.5% and 1.2–300.9?mmol?kg^?1?s^?1, respectively. The CO selectivity is negligible at these temperatures. Under the optimum conditions (17.3?wt%, Cu/SiO₂; calcination temperature 673?K; 0.25 O₂/CH₃OH molar ratio, 0.5 H₂O/CH₃OH molar ratio and reaction temperature 548?K), the maximum hydrogen yield obtained was 2.45?mol of hydrogen per mole of methanol. The time on stream stability test showed that the Cu/SiO₂ catalyst is quite stable for 48?h.     

A Self‐Digitization Dielectrophoretic (SD‐DEP) Chip for High‐Efficiency Single‐Cell Capture,On‐Demand Compartmentalization,and Downstream Nucleic Acid Analysis

The design and fabrication of a self‐digitization dielectrophoretic (SD‐DEP) chip with simple components for single‐cell manipulation and downstream nucleic acid analysis is presented. The device employed the traditional DEP and insulator DEP to create the local electric field that is tailored to approximately the size of single cells, enabling highly efficient single‐cell capture. The multistep procedures of cell manipulation, compartmentalization, lysis, and analysis were performed in the integrated microdevice, consuming minimal reagents, minimizing contamination, decreasing lysate dilution, and increasing assay sensitivity. The platform developed here could be a promising and powerful tool in single‐cell research for precise medicine.     

Bis‐benzimidazolium‐palladium system catalyzed Suzuki‐Miyaura coupling reaction of aryl bromides under mild conditions

Bis‐benzimidazolium salts were prepared successfully from commercially available and inexpensive o‐phenylenediamine through a series of simple reactions. The bis‐NHC‐Pd complexes prepared in situ can catalyze Suzuki‐Miyaura cross‐coupling reaction under very mild conditions in aqueous media with excellent yields. The efficiency of this reaction is demonstrated by its compatibility with a range of functional groups. Di‐ortho‐substituted biaryls could be accomplished in 89–99% yields. Moreover, the rigorous exclusion of air or moisture is not required in these transformations.     

Effects of phenolic compounds on gelation behavior of gelatin gels

The effects of phenolic additives on the gelation behavior of gelatin gels were investigated using thermomechanical analysis (TMA) for study of gel‐melting temperature, dynamic mechanical analysis (DMA) for study of gel‐storage modulus and gel‐aging stability, viscometry for study of gelation time, and texture analyzer for study of gel strength and gel melting. Thermodynamically, the addition of 1,3‐benzenediol, 1,4‐benzenediol or 1,3,5‐benzenetriol favored the gelation process of gelatin solutions (increases in T_m and aging stability) due to the introduction of extra physical crosslinks among gelatin chains through hydrogen bonding, while the addition of 1,2‐benzenediol had a negative effect (decreases in T_m and aging stability) possibly due to intra‐hydrogen bonding of the additive molecule itself. All the phenolic compounds had little effect on gel moduli. Kinetically, the introduction of 1,2‐benzenediol or 1,4‐benzenediol slowed the gelation process, while introduction of catechin, a polyphenol, accelerated the first stage of the gelation process. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 224–231, 2001