CeO2-ZrO2包覆石墨粉增强铝基复合材料的制备与耐蚀性能

采用非均匀成核法,在机械搅拌条件下通过硝酸亚铈和氧氯化锆水解生成无定形氧化铈、氧化锆对石墨进行表面包覆,利用扫描电镜、 X射线衍射和XPS对所得样品进行了表征,通过搅拌铸造法制备了氧化铈/锆包覆石墨颗粒增强铝基复合材料,并对复合材料耐蚀性能进行了初步研究. SEM和XPS表明,氧化铈/锆在石墨表面形成了均匀、致密的纳米级包覆层,氧化铈/锆通过与铝液的反应性润湿提高了石墨颗粒与铝液的润湿性,阻止了石墨与铝发生化学反应. 测试结果表明,氧化物的包覆基本抵消了由于石墨的添加而降低复合材料的腐蚀电位,也降低了腐蚀电流(两个数量级).     

Investigations into the synthesis and fluorescence properties of Eu(III), Tb(III), Sm(III) and Gd(III) complexes of a novel bis-beta-diketone-type ligand

A novel bis-beta-diketon ligand, 1,1'-(2,6-bispyridyl)bis-3-phenyl-1,3-propane-dione (L), was designed and synthesized and its complexes with Eu(III), Tb(III), Sm(III) and Gd(III) ions were successfully prepared. The ligand and the corresponding metal complexes were characterized by elemental analysis, and infrared, mass and proton nuclear magnetic resonance spectroscopy. Analysis of the IR spectra suggested that each of the lanthanide metal ions coordinated to the ligand via the carbonyl oxygen atoms and the nitrogen atom of the pyridine ring. The fluorescence properties of these complexes in solid state were investigated and it was discovered that all of the lanthanide ions could be sensitized by the ligand (L) to some extent. In particular, the Tb(III) complex was an excellent green-emitter and would be a potential candidate material for applications in organic light-emitting devices (OLEDs) and medical diagnosis.     

Optical spectra of protected diamine 10-bond-bridged intervalence radical cations related to N,N,N'N'-tetraalkylbenzidine

The optical absorption spectra of the delocalized intervalence radical cations of seven o,o'-linked benzidine derivatives that have the nitrogens protected as 9-(9-aza-bicyclo[3.3.1]nonan-3-one) derivatives are discussed and compared with that of the p-phenylene radical cation. The linking units are CH2, CH2CH2, NMe, S, SO2, and C=O, and we also studied H,H (the unlinked benzidine). The lowest-energy absorption band is assigned as the transition from the antibonding combination of symmetrical N and aromatic orbitals to the antibonding combination of the antisymmetric N and aromatic orbitals using TD-DFT calculations, and a good correlation between the observed transition energies and those calculated using the simple Koopmans theorem-based "neutral in-cation geometry" calculations on the UB3LYP/6-31G* structures is found. The use of the two-state model that equates the electronic interaction through the bridge between the amino groups with half of the lowest transition energy is seriously incorrect for these and other delocalized intervalence compounds. The problem of extracting the electronic interactions that actually are involved from calculated transition energies is discussed.     

Two new monodesmosidic triterpene saponins from Gypsophila oldhamiana

Two new monodesmosidic triterpene saponins were isolated from the roots of Gypsophila oldhamiana (Caryophyllaceae). Their structures were elucidated on the basis of spectral data to be quillaic acid, alpha-L-arabinopyranosyl-(1-->4)-alpha-L-arabinopyranosyl-(1-->3)-beta-D-xylopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-fucopyranosyl ester (1), and vaccaric acid, beta-D-glucopyranosyl-(1-->3)-[beta-D-xylopyranosyl-(1-->4)]-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-fucopyranosyl ester (2). Compound 1 showed a significant enhancement of granulocyte phagocytosis in vitro.     

Propane fuel cells using phosphoric-acid-doped polybenzimidazole membranes

Propane fuel cells using H(3)PO(4)-doped polybenzimidazole polymer membranes produce low and unsustainable current densities at temperatures up to 250 degrees C under anhydrous conditions. Stable intermediate species blocked the surface of noble metal anode catalysts, and the intermediate species could not react further into desorbable final products. In contrast, when water was introduced by light humidification (S(r) 0.08%) of the propane stream, sustainable and higher current densities were achieved. Water participated in the reaction sequence to form surface-bound hydrocarbon and then oxygen-containing intermediates and thereby generated CO and CO(2) as the only carbon-containing products.     

Synthesis and Properties of Poly(N-isopropylacrylamide-co-acrylamide) Hydrogels

Poly (N-isopropylacrylamide-co-acrylamide) [Poly(NIPAAm-co-AAm)] with different feed ratios were obtained by radiation polymerization using Co⁶⁰γ-rays. Swelling equilibrium data in various media: deionized water, aqueous NaCl solutions and different pH buffer solutions, were determined. It appeared that the lower critical transition temperature (LCST) of the hydrogels increased with an increasing acrylamide content and decreased with increasing ionic strength. Moreover, LCST was affected by pH.     

Loop formation and stability of self-avoiding polymer chains

Using 3-dimensional Langevin dynamics simulations, we investigated the dynamics of loop formation of chains with excluded volume interactions, and the stability of the formed loop. The mean looping time τ _l scales with chain length N and corresponding scaling exponent α increases linearly with the capture radius scaled by the Kuhn length a/l due to the effect of finite chain length. We also showed that the probability density function of the looping time is well fitted by a single exponential. Finally, we found that the mean unlooping time τ _u hardly depends on chain length N for a given a/l and that the stability of a formed loop is enhanced with increasing a/l.     

A Novel endo-1,4-β-Mannanase from <Emphasis Type="Italic">Bispora antennata</Emphasis> with Good Adaptation and Stability over a Broad pH Range

An endo-β-1,4-mannanase encoding gene, man5, was cloned from Bispora antennata CBS 126.38, which was isolated from a beech stump. The cDNA of man5 consists of 1,299 base pairs and encodes a 432-amino-acid protein with a theoretical molecular mass of 46.6 kDa. Deduced MAN5 exhibited the highest amino acid sequence identity of 58% to a β-mannanase of glycoside hydrolase family 5 from Aspergillus aculeatus. Recombinant MAN5 was expressed in Pichia pastoris and purified to electrophoretic homogeneity. The specific activity of the final preparation towards locust bean gum was 289 U mg⁻¹. MAN5 showed optimal activity at pH 6.0 and 70 °C and had good adaptation and stability over a broad range of pH values. The enzyme showed more than 60% of peak activity at pH 3.0–8.0 and retained more than 80% of activity after incubation at 37 °C for 1 h in both acid and alkaline conditions (pH 4.0–11.0). The K _m and V _max values were 1.33 mg ml⁻¹ and 444 μmol min⁻¹ mg⁻¹ and 1.17 mg ml⁻¹ and 196 μmol min⁻¹ mg⁻¹ for locust bean gum and konjac flour, respectively. Of all tested metal ions and chemical reagents, Co²⁺, Ni²⁺, and β-mercaptoethanol enhanced the enzyme activity at 1 mM, whereas other chemicals had no effect on or partially inhibited the enzyme activity. MAN5 was highly resistant to acidic and neutral proteases (trypsin, α-chymotrypsin, collagenase, subtilisin A, and proteinase K). By virtue of the favorable properties of MAN5, it is possible to apply this enzyme in the paper and food industries.