Theoretical study of nitric oxide adsorption on Au clusters

The adsorption properties of NO molecule on anionic, cationic, and neutral Au(n) clusters (n=1-6) are studied using the density functional theory with the generalized gradient approximation, and with the hybrid functional. For anionic and cationic clusters, the charge transfer between the Au clusters and NO molecule and the corresponding weakening and elongation of the N-O bond are essential factors of the adsorption. The neutral Au clusters have also remarkable adsorption ability to NO molecule. The adsorption energies of NO on the cationic clusters are generally greater than those on the neutral and anionic clusters.     

Assembly of well-aligned multiwalled carbon nanotubes in confined polyacrylonitrile environments: electrospun composite nanofiber sheets

Highly oriented, large area continuous composite nanofiber sheets made from surface-oxidized multiwalled carbon nanotubes (MWNTs) and polyacrylonitrile (PAN) were successfully developed using electrospinning. The preferred orientation of surface-oxidized MWNTs along the fiber axis was determined with transmission electron microscopy and electron diffraction. The surface morphology and height profile of the composite nanofibers were also investigated using an atomic force microscope in tapping mode. For the first time, it was observed that the orientation of the carbon nanotubes within the nanofibers was much higher than that of the PAN polymer crystal matrix as detected by two-dimensional wide-angle X-ray diffraction experiments. This suggests that not only surface tension and jet elongation but also the slow relaxation of the carbon nanotubes in the nanofibers are determining factors in the orientation of carbon nanotubes. The extensive fine absorption structure detected via UV/vis spectroscopy indicated that charge-transfer complexes formed between the surface-oxidized nanotubes and negatively charged (-CN[triple bond]N:) functional groups in PAN during electrospinning, leading to a strong interfacial bonding between the nanotubes and surrounding polymer chains. As a result of the highly anisotropic orientation and the formation of complexes, the composite nanofiber sheets possessed enhanced electrical conductivity, mechanical properties, thermal deformation temperature, thermal stability, and dimensional stability. The electrical conductivity of the PAN/MWNT composite nanofibers containing 20 wt % nanotubes was enhanced to approximately 1 S/cm. The tensile modulus values of the compressed composite nanofiber sheets were improved significantly to 10.9 and 14.5 GPa along the fiber winding direction at the MWNT loading of 10 and 20 wt %, respectively. The thermal deformation temperature increased with increased MWNT loading. The thermal expansion coefficient of the composite nanofiber sheets was also reduced by more than an order of magnitude to 13 x 10(-6)/ degrees C along the axis of aligned nanofibers containing 20 wt % MWNTs.     

CeO2担载Cu纳米粒子电催化CO2还原产乙烯：CeO2不同暴露晶面对催化性能的影响

Fossil fuels are expected to be the major source of energy for the next few decades. However, combustion of nonrenewable resources leads to the release of large quantities of CO₂, the primary greenhouse gas. Notably, the concentration of CO₂ in the atmosphere is increasing annually at an astounding rate. Electrochemical CO₂ reduction (ECR) to value-added fuels and chemicals using electricity from intermittent renewable energy sources is a carbon-neutral method to alleviate anthropogenic CO₂ emissions. Despite the steady progress in the selective generation of C₁ products (CO and formic acid), the production of multi-carbon species still suffers from low selectivity and efficiency. As an ECR product, ethylene (C₂H₄) has a higher energy density than do C₁ species and is an important industrial feedstock in high demand. However, the conversion of CO₂ to C₂H₄ is plagued by low productivity and large overpotential, in addition to the severe competing hydrogen evolution reaction (HER) during the ECR. To address these issues, the design and development of advanced electrocatalysts are critical. Here, we demonstrate fine-tuning of ECR to C₂H₄ by taking advantage of the prominent interaction of Cu with shape-controlled CeO₂ nanocrystals, that is, cubes, rods, and octahedra predominantly covered with (100), (110), and (111) surfaces, respectively. We found that the selectivity and activity of the ECR depended strongly on the exposed crystal facets of CeO₂. The overall ECR Faradaic efficiency (FE) over Cu/CeO₂(110) (FE ≈ 56.7%) surpassed that of both Cu/CeO₂(100) (FE ≈ 51.5%) and Cu/CeO₂(111) (FE ≈ 48.4%) in 0.1 mol·L^-1 KHCO₃ solutions with an H-type cell. This was in stark contrast to the exclusive occurrence of the HER over pure carbon paper, CeO₂(100), CeO₂(110), and CeO₂(111). In particular, the FE toward C₂H₄ formation and the partial current density increased in the sequence Cu/CeO₂(111) < Cu/CeO₂(100) < Cu/CeO₂(110) within applied bias potentials from -1.00 to -1.15 V (vs. the reversible hydrogen electrode), reaching 39.1% over Cu/CeO₂(110) at a mild overpotential (1.13 V). The corresponding values for Cu/CeO₂(100) and Cu/CeO₂(111) were FE_C2H4 ≈ 31.8% and FE_C2H4 ≈ 29.6%, respectively. The C₂H₄ selectivity was comparable to that of many reported Cu-based electrocatalysts at similar overpotentials. Furthermore, the FE for C₂H₄ remained stable even after 6 h of continuous electrolysis. The superior ECR activity of Cu/CeO₂(110) to yield C₂H₄ was attributed to the metastable (110) surface, which not only promoted the effective adsorption of CO₂ but also remarkably stabilized Cu⁺, thereby boosting the ECR to produce C₂H₄. This work offers an alternative strategy to enhance the ECR efficiency by crystal facet engineering.     

Langmuir monolayers of the long-chain alkyl derivatives of a nucleoside analogue and the formation of self-assembled nanoparticles

The long-chain alkyl derivatives of a nucleoside analogue-acyclovir were prepared in the paper. One is stearyl-glycero-succinyl-acyclovir (SGSA) with a single 18-carbon length (C18) alkyl chain. Another is dioctadecyl-aspartate-succinyl-acyclovir (DASA) with double C18 alkyl chains. They were prepared by the esterification of succinyl-acyclovir with the lipids, and sodium salts of them were also prepared. Guanine moieties and alkyl moieties bring the derivatives intermolecular hydrogen bonding and hydrophobic interaction in water separately. The forces are influenced by the number of alkyl chains and the charged state, and determine the solubility and the self-assembly behavior of the derivatives. The double alkyl-chain derivatives (DASA and DASA-Na) formed rigid Langmuir monolayers on air/water surface, while the single alkyl chain derivatives (SGSA and SGSA-Na) did not. However, cholesterol (Chol) could assist SGSA to form rigid monolayers through inserting into the alkyl chains of SGSA to mimic the second alkyl chain. SGSA self-aggregates in water were prepared by the injection method with tetrahydrofuran as solvent. Cuboid-like shape and nanoscale size demonstrated that SGSA self-aggregates were self-assembled nanoparticles. Shape, particle size, zeta potential and phase transition of the nanoparticles were characterized. And they showed an average size of 83.2 nm, a negative surface charge of -31.3-mV zeta potential and a gel-liquid crystalline phase transition of 50.38 degrees C. The formation mechanism of self-assembled nanoparticles was analyzed. Hydrophobic interaction of alkyl chains improves SGSA molecules to form bilayers, and then cuboid-like nanoparticles were obtained by layer-by-layer aggregation based on inter-bilayers hydrogen bonding. However, the charged guanine moieties make SGSA-Na lose the function of hydrogen bonding so that SGSA-Na only forms vesicles in water based on hydrophobic interaction. Strong hydrophobicity and wide-open rigid double alkyl chains of DASA and DASA-Na restrict self-assembly in water media, and no homogeneous suspensions were obtained. Therefore, the molecular self-assembly behavior of the long-chain alkyl derivatives of nucleoside analogues on water surface or in water media is determined by the number of alkyl chains and the charged state.     

Unprecedented isospecific 3,4-polymerization of isoprene by cationic rare earth metal alkyl species resulting from a binuclear precursor

The isospecific 3,4-polymerization of isoprene has been achieved for the first time by use of a combination of a binuclear rare earth metal dialkyl complex, such as [Me2Si(C5Me4)(mu-PCy)YCH2SiMe3]2 (Cy = cyclohexyl), and an equimolar amount of [Ph3C][B(C6F5)4] as a catalyst system. A DFT calculation suggested that a binuclear monocationic monoalkyl species, such as [Me2Si(C5Me4)(mu-PCy)Y(mu-CH2SiMe3)Y(mu-PCy)(C5Me4)SiMe2]+, in which the alkyl group bridges the two metal centers, could be the true catalyst species.     

Modeling η5‐C5Me4SiMe3 with η3‐C3H5 for DFT study of a tetranuclear yttrium polyhydrido complex [(η5‐C5Me4SiMe3)YH2]4

π‐Allyl (η³‐C₃H₅), a four‐electron donor, was used as a ligand model to replace η⁵‐C₅Me₄SiMe₃ in DFT calculations on the tetranuclear yttrium polyhydrido complex (η⁵‐C₅Me₄SiMe₃)₄Y₄H₈ containing a Y₄H₈ tetrahedral core structure, which may separate the four π‐allyl groups and hence suppress the allyl ligand coupling during the computation. In terms of the calculated core geometry, isomerization energy barrier, charge population, and frontier orbital features of the complex, the η³‐C₃H₅ ligand model is comparable to η⁵‐C₅H₅. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Recent Advances in Fullerene‐free Polymer Solar Cells: Materials and Devices

What is the most favorite and original chemistry developed in your research group? We focus on developing new organic photovoltaic materials and exploring their applications in photovoltaic devices. Based on the new materials, we can figure out the correlations among chemical strictures, optoelectronic properties, and photovoltaic behaviors. Our group originally demonstrated quite a few build blocks for making conjugated polymers for photovoltaic applications, some of them have been broadly used by the researchers in the field. How do you get into this specific field? Could you please share some experiences with our readers? I got into this field when I was a graduate student in 2002, just because my supervisor gave me a research topic for synthesis of new conjugated polymers. At that moment, as a fresh graduate student, I had no chance to say yes or no, but to do it. The field of organic solar cells is oriented by the new organic photovoltaic materials. In the past decades, the materials have been updated for a few generations, which promoted the device performance to be higher and closer to practical applications. We have to concentrate on the fundamental problems but also need to follow the pace of the filed. How do you supervise your students? In my opinion, the students need more specific projects to get into the field so as to be well trained at the beginning. In the later stage, I prefer to encourage them to find and creatively figure out the real fundamental problems. I used to give them a few questions: Why do you need to do this project? How to make a clear definition for the problem? Can you suggest a new and better approach to solve it? What is the most important personality for scientific research? Passion, perseverance and sense of innovation. What is your favorite journal(s)? The journals publishing the latest and/or systematic research works in chemistry and material science.     

Purification of urokinase by combined cation exchanger and affinity chromatographic cartridges

Crude urokinase from human urine processed through foam flotation and ammonium sulfate precipitation containing 720 National Health Institute Committee on Thrombolytic Agents U/mg activity was purified by an SP cation exchanger followed by a zinc-chelated affinity chromatographic cartridge. The cartridges were of a radial-flow type formed by using acrylic and cellulose composite matrices. The high rigidity of the matrix structure permits fast flow of protein solutions (liters per minute) and thus allows processing of a large volume of crude urokinase under low operating pressures. A greater than six-fold increase in specific enzyme activity of urokinase was achieved by adsorbing and eluting 1 l of a 3 mg/ml crude urokinase solution on an SP cartridge. The eluent was further purified by passing through a zinc-chelated affinity cartridge to achieve greater than a eighteen-fold increase in urokinase specific activity. This report demonstrates the combined use of a cation exchanger with zinc-chelated chromatographic cartridges in purifying urokinase on a relatively large scale. The relationship between the amount of zinc chelated in the matrix to its effect on urokinase purification is also discussed.     

α－甲基丙烯酸烯丙酯的合成及其自由基、阴离子聚合的研究

合成了α－甲基丙烯酸烯丙酯（ＡＭＡ），并对其自由基、阴离子聚合进行了探讨。结果发现，该单体难以进行选择性自由基聚合，但可用作多种单体自由基聚合的交联剂。用１，１′－二苯基己基锂在ＴＨＦ中引发ＡＭＡ，可顺利地进行α位双键的选择性阴离子聚合，分子量实测值与计算值基本一致。在较低温度下（≤－６０℃），可得窄分布ＰＡＭＡ（Ｍｗ／Ｍｎ＝１．１２～１．１５）。随聚合温度升高，间同和无规聚合物含量分别呈下降和上升趋势。ＧＰＣ、１ＨＮＭＲ及ＦＴＩＲ鉴定表明，用阴离子聚合法可得到溶于多种溶剂、每个重复单元上均定量带有烯丙基双键的窄分布官能性ＰＡＭＡ。     

去溶温度对微波诱导等离子体原子吸收光谱法分析性能影响的研究

本文研究了超声雾化微波诱导等离子体原子吸收光谱法(UN-MIP-AAS)中,去溶温度对选择载气流量、微波前向功率等因素的影响,并定量考察了去溶效果。通过改善去溶条件,提高了UN-MIP-AAS的分析性能。