Synthesis, characterization and self-assemble behavior of chitosan-O-poly(ε-caprolactone)

A facile strategy was proposed for synthesizing chitosan-O-poly(ε-caprolactone) (CS-O-PCL). Stoichiometric sodium dodecyl sulfate-chitosan complex (SCC) which was soluble in common organic solvents was adopted as an intermediate. Regioselective conjugation of PCL onto SCC could be achieved through condensation reaction between isocyanate-terminated PCL and hydroxyl groups of chitosan. The grafting level of PCL could be modulated by varying PCL/SCC weight ratio. SDS was removed from SCC-O-PCL using trihydroxymethylamine (Tris) as a decomplexation agent. The self-assemble behavior of the amphiphilic copolymers was studied by fluorometry, TEM and laser light scattering. The morphology of the CS-O-PCL nanoparticles was found to be dependent on PCL grafting level. Both spherical micelles and vesicle could be formed by dialysis method.     

Surfactant-free fabrication of Cu2O nanosheets from Cu colloids and their tunable optical properties

Novel sheetlike Cu₂O two-dimensional (2D) nanoarchitectures were successfully synthesized via a copper nanoparticle-mediated process for the first time. Uniform and nearly monodisperse Cu nanocolloids were firstly synthesized by disproportionating reaction of Cu⁺ at the surfactant-free ambient conditions, and Cu₂O nanosheets were subsequently synthesized by choosing ethanol solvent agent to limit the oxidized processes of Cu nanocolloids. The synthesized products were systematically studied by X-ray powder diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis absorption spectra. It was demonstrated that the solvent agent of ethanol played key roles in the formation of the as-synthesized nanosheets. By choosing the different solvent agents to limit the oxidized processes, Cu₂O nanospheres and nanocubes can be selectively synthesized accordingly.     

Adsorption of xylene isomers on ordered hexagonal mesoporous FDU-15 polymer and carbon materials

The oil industry has been facing the challenges of separation of xylene isomers, o-xylene, m-xylene and p-xylene or removing them from the environment. In our present work, we investigated the adsorption of the three isomers on two mesoporous materials, FDU-15-350 polymer and FDU-15-900 carbon materials. The isomer adsorption capacities are well correlated with their physical pore properties. It is found that the micropores are very crucial for the adsorption of these three isomers. The more micropore volume the adsorbent has, the better the adsorption capacity is. Henry’s constants were also calculated for the three isomers on the two adsorbents. Both on FDU-15-350 polymer and FDU-15-900, the Henry’s constants for the three isomers show the same trend o>m>p xylene which is coincidently in accordance with their polarity trend, indicating more polar adsorbate is preferred for adsorption on the two adsorbents. The isosteric heats of adsorption are correlated with the microporosity and the size of the adsorbate molecule. More microporosity and smaller molecules give higher heats of adsorption. Extracted information on pore properties of adsorbents by using the three isomers has very similar results as that resolved from nitrogen adsorption, indicating the feasibility of using the three isomers as adsorbates to extract pore information. This work is devoted to commemorating the 60th birthday of Professor Mieczyslaw (Mietek) Jaroniec.     

Investigations of flow field designs in direct methanol fuel cell

An experimental and simulation research had been performed to investigate the performance as well as the flow distribution in the cathode flow field in the case of direct methanol fuel cells (DMFCs). The gas was well distributed in serpentine flow field, whereas stagnation of the gas was observed in parallel flow field. These would contribute to the cell performance greatly due to mass transfer effect when the cells start operating. In addition, the durability test of DMFC was drastically affected in parallel flow field due to poor ability to drain flooded water produced electrochemically at cathode and crossover from anode. In addition, pressure drops of different flow fields were also investigated to evaluate their contribution and feasibility as an economic application for DMFC. DMFC with serpentine flow field featuring higher pressure difference resulted in a larger parasitic energy demand. However, the optimal flow field designs are needed to balance the performance and pressure loss to achieve a uniform fluid distribution and simultaneously minimize energy demand for mass transport. Consequently, flow field with grid pattern appears to be the optimal design for the DMFC cathode.     

Functionalization of Carbon Nanotubes with Water‐Insoluble Porphyrin in Ionic Liquid: Direct Electrochemistry and Highly Sensitive Amperometric Biosensing for Trichloroacetic Acid

A functional composite of single‐walled carbon nanotubes (SWNTs) with hematin, a water‐insoluble porphyrin, was first prepared in 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([BMIM][PF₆]) ionic liquid. The novel composite in ionic liquid was characterized by scanning electron microscopy, ultraviolet absorption spectroscopy, and electrochemical impedance spectroscopy, and showed a pair of direct redox peaks of the Fe^III/Fe^II couple. The composite–[BMIM][PF₆]‐modified glassy carbon electrode showed excellent electrocatalytic activity toward the reduction of trichloroacetic acid (TCA) in neutral media due to the synergic effect among SWNTs, [BMIM][PF₆], and porphyrin, which led to a highly sensitive and stable amperometric biosensor for TCA with a linear range from 9.0×10^?7 to 1.4×10^?4 M . The detection limit was 3.8×10^?7 M at a signal‐to‐noise ratio of 3. The TCA biosensor had good analytical performance, such as rapid response, good reproducibility, and acceptable accuracy, and could be successfully used for the detection of residual TCA in polluted water. The functional composite in ionic liquid provides a facile way to not only obtain the direct electrochemistry of water‐insoluble porphyrin, but also construct novel biosensors for monitoring analytes in real environmental samples.     

Effect of stability of internal standard on quantification of 15 flavonoids in Epimedium using CZE

A CZE method was developed for the simultaneous determination of 15 flavonoids, including epimedin B, epimedin A, hexandraside F, epimedin C, icariin, sagittatoside B, sagittatoside A, hexandraside E, 2′′‐O‐rhamnosyl icariside II, baohuoside VII, baohuoside I, caohuoside C, epimedoside C, baohuoside II, and kaempferol‐3‐O‐rhamnoside, in different species of Epimedium, and the effect of stability of internal standard (IS) on quantification was also investigated. As a result, rutin was not available for use as an IS because of its unstable property in sample solution, which suggested that the stability of IS both in standards and sample solution should be considered for the analysis. Using stable daidzein as IS, the analysis was performed within 35 min by using 50 mM borax buffer containing 20% ACN as a modifier (pH 10.0), while separation voltage was 25 kV and temperature was at 30°C. The method was validated to be accurate, simple, and repeatable, and was successfully applied to the analysis of 36 samples from 17 species of Epimedium.     

Self－assembly of Novel Hetero[3]rotaxane, [2]Rotaxanes and [2]Catenane

One linear template 13 and one cyclophane template 15, both incorporating two electron rich 1,4‐dialkoxybenzene units and one diamide unit, have been synthesized. By utilizing donor‐acceptor interaction and/or intermolecular hydrogen bonding assembling principles, one novel hetero[3]rotazane 22·4Cl, possessing one neutral and one tetracationic ring components, has been synthesized from 13, through neutral [2]rotaxane 21 as intermediate. With 15 as template, tetracationic [2]catenane 23·4PF₆ was assembled by using donor‐acceptor interaction, but no neutral [2]rotaxane could be obtained under the typical conditions of hydrogen bonding assembling principle. The interlocked supramolecular compounds have been characterized and their spectral properties are investigated.     

Theoretical modeling of enzyme catalytic power: analysis of "cratic" and electrostatic factors in catechol O-methyltransferase

A comparative theoretical study of a bimolecular reaction in aqueous solution and catalyzed by the enzyme catechol O-methyltransferase (COMT) has been carried out by a combination of two hybrid QM/MM techniques: statistical simulation methods and internal energy minimizations. In contrast to previous studies by other workers, we have located and characterized transition structures for the reaction in the enzyme active site, in water and in a vacuum, and our potential of mean force calculations are based upon reaction coordinates obtained from features of the potential energy surfaces in the condensed media, not from the gas phase. The AM1/CHARMM calculated free energy of activation for the reaction of S-adenosyl methionine (SAM) with catecholate catalyzed by COMT is 15 kcal mol(-1) lower the AM1/TIP3P free-energy barrier for the reaction of the trimethylsulfonium cation with the catecholate anion in water at 300 K, in agreement with previous estimates. The thermodynamically preferred form of the reactants in the uncatalyzed model reaction in water is a solvent-separated ion pair (SSIP). Conversion of the SSIP into a contact ion pair, with a structure resembling that of the Michaelis complex (MC) for the reaction in the COMT active site, is unfavorable by 7 kcal mol(-1), largely due to reorganization of the solvent. We have considered alternative ways to estimate the so-called "cratic" free energy for bringing the reactant species together in the correct orientation for reaction but conclude that direct evaluation of the free energy of association by means of molecular dynamics simulation with a simple standard-state correction is probably the best approach. The latter correction allows for the fact that the size of the unit cell employed with the periodic boundary simulations does not correspond to the standard state concentration of 1 M. Consideration of MC-like species allows a helpful decomposition of the catalytic effect into preorganization and reorganization phases. In the preorganization phase, the substrates are brought together into the MC-like species, either in water or in the enzyme active site. In the reorganization phase, the roles of the enzymic and aqueous environments may be compared directly because reorganization of the substrate is about the same in both cases. Analysis of the electric field along the reaction coordinate demonstrates that in water the TS is destabilized with respect to the MC-like species because the polarity of the solute diminishes and consequently the reaction field is also decreased. In the enzyme, the electric field is mainly a permanent field and consequently there is only a small reorganization of the environment. Therefore, destabilization of the TS is lower than in solution, and the activation barrier is smaller.     

Zn-Fe-SiO2复合镀层的制备工艺及其耐蚀性研究

在酸性硫酸盐体系中电沉积制备了Zn-Fe-SiO2复合镀层,并研究了工艺因素对镀层SiO2含量的影响.随着电流密度由4.8A/dm2增加到6A/dm2时,镀层中SiO2的含量由0.21%上升到0.47%,但是当电流密度继续增加到7.2A/dm2时,SiO2含量反而下降到了0.18%.当镀液中SiO2浓度由20g/L增加到60g/L时,镀层中SiO2含量由0.40%上升到0.51%.当镀液pH值由2增加到4时,镀层中SiO2含量由0.22%上升到1.17%.采用5%NaCl溶液浸泡试验考察了Zn镀层、Zn-Fe合金镀层与Zn-Fe-SiO2复合镀层的耐蚀性,并研究了镀层中SiO2含量对镀层耐蚀性的影响.结果表明,Zn-Fe-SiO2复合镀层无需钝化处理,其耐蚀性优于Zn镀层及Zn-Fe合金镀层,并且镀层的耐蚀性随着镀层中SiO2含量增大而提高.     

Encapsulation of polyaniline in 3-D interconnected mesopores of silica KIT-6

Composite material PANI/KIT-6, with polyaniline (PANI) chains encapsulated in the 3-D interconnected pore channels of mesoporous silica, KIT-6, has been synthesized via a gas-phase method. The composite formation and the presence of PANI inside the pore channels of KIT-6 were evidenced by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), small-angle X-ray scatter (SAXS), transmission electron microscopy (TEM), and N₂ adsorption–desorption isotherms. The PANI/KIT-6 composite showed good electrical conductivity (2.4 × 10^?3 S/cm) due to the formation of 3-D networks of PANI inside the 3-D interconnected channels of KIT-6. The resistance of PANI/KIT-6 composite at different relative humidities (RH) was investigated. An essentially linear relationship between the relative resistance of the composite and the relative humidity of the environment was found from 11.3% to 97.3% RH.