Characterization of the Reduction of Oxygen at Anthraquinone-Modified Glassy Carbon and Highly Oriented Pyrolytic Graphite Electrodes

1-(N-Boc-aminomethyl)-4-(aminomethyl)benzene, bearing a protected amine group, was electrochemically grafted to glassy carbon and edge plane and basal plane highly oriented pyrolytic graphite electrodes by the oxidation of the corresponding linker. Following the removal of tert-butyloxycarbonyl protecting group, anthraquinone-2-carboxylic acid was coupled to the amine-terminated linker using solid-phase synthesis. The surface coverage of the immobilized anthraquinone redox centers was investigated by cyclic voltammetry and found to be the highest at edge plane and the lowest at the basal plane electrodes. The electrocatalytic activity of the anthraquinone-modified electrodes toward oxygen reduction was explored by cyclic voltammetry, chronoamperometry, and chronocoulometry at the unmodified and modified graphite electrodes. The immobilized anthraquinone was shown to catalyze the reduction of oxygen to hydrogen peroxide and the number of electrons transferred was two for all modified electrodes.     

An N-protection free ligation of the peptide thioester and the peptide with an N-alkoxy- or N-aryloxyamino group at its N-terminus

Peptides with an N-alkoxy or N-aryloxy amino acid at their N-terminus were synthesized and successfully ligated with a peptide thioester by silver ion activation under a slightly acidic condition without requiring protection of the side chain amino groups. The N-methoxy group was easily cleaved by the SmI₂ reduction in CH₃OH aq. to obtain the desired peptide with a native peptide bond. This method was successfully applied to the synthesis of the human atrial natriuretic peptide showing the efficiency of the novel ligation.     

Reduction-responsive vesicles composed of dimethylaminopropyl octadecanamide and dithiodipropionic acid

Reduction-responsive vesicle was prepared by salt-bridging N-[3-(dimethylamino)propyl]-octadecanamide (DMAPODA, a cationic amphiphile) using 3,3′-dithiodipropionic acid (DTPA, a disulfide diacid compound). According to the transmission electron micrograph and the fluorescence quenching degree (53.2%), it could be said that vesicles were formed when the DMAPODA to DTPA molar ratio was 2:2. The DMAPODA/DTPA associate was considered to be a building block for vesicle formation because DTPA could electrostatically associate with DMAPODA and help the cationic amphiphile assemble into the vesicle. On a differential scanning calorimetric thermogram, the DMAPODA/DTPA vesicle showed two endothermic peaks at 50.6°C and 63.2°C. The peak found at the lower temperature was possibly due to the solid gel-to-liquid crystal phase transition of the vesicular membrane and the peak found at the higher temperature was considered to be due to the melting of DMAPODA, indicating that unassociated DMAPODA coexisted with DMAPODA/DTPA vesicles. The release of calcein enveloped in the vesicle was promoted by DL-dithiothreitol, possibly because DTPA can be broken by the reducing agent to form mercaptopropionic acids and the vesicle could be disintegrated and/or the vesicular membrane would become defective.     

Mg/Al物质的量比对Ce-La/MgAl2O4-x催化剂催化CO还原NO性能的影响

采用初始浸渍法制备了不同Mg/Al物质的量比的Ce-La/MgAl₂O₄-x催化剂,并通过低温N₂-吸附脱附、XRD、H₂-TPR和CO-TPR等手段对其进行了表征。结果表明,在Mg/Al物质的量比为0.5时,催化剂催化CO还原NO的性能最好。这主要是因为适量Mg的添加促进了CeO₂的分散和Ce-O-La固溶体的形成,从而使得表面Ce³⁺和氧空穴增加。两者的协同作用使得Ce-La/MgAl₂O₄-0.5表现出最佳的催化性能。另外,适量Mg的引入可以抑制Ce（SO₄）₂和Ce₂（SO₄）₃的形成,从而提高了Ce-La/MgAl₂O₄-0.5催化剂抗硫中毒能力。     

湿法脱硫浆液中Hg2+的还原机制研究

针对燃煤电厂湿法脱硫浆液中Hg²⁺易被还原的特性,研究Hg²⁺在模拟湿法脱硫系统中的迁移机制,考察了浆液温度、pH值以及SO₃^2-、Cl^-、Ca²⁺、Mg²⁺浓度等因素对Hg²⁺还原性能的影响。结果表明,Hg²⁺还原率随着浆液中SO₃^2-浓度的增大而降低;pH值对Hg²⁺的还原呈先增加后降低的趋势,在pH值为5.5时还原率最高;温度的升高不利于浆液中稳定的二价汞盐络合物存在,导致Hg²⁺还原率增加;Ca²⁺、Mg²⁺以及Cl^-浓度的增加有利于形成稳定化合物,从而抑制Hg²⁺的还原。     

石墨化氮化碳负载Cu纳米颗粒用作高效氧还原电催化剂

高活性低成本氧还原反应(ORR)电催化剂是燃料电池和金属/空气电池等可再生能源技术的关键组成部分.在离子液体[(C16mim)2CuCl4]和质子化的石墨化氮化碳(g-CN)的存在下,采用简易的水热反应制备了Cu/g-CN电催化剂用于ORR.与纯的g-CN相比,所制Cu/g-CN表现出高的ORR催化活性:起始电势正移99 mV,为2倍动力学电流密度.另外,Cu/g-CN还表现出比商用Pt/C(HiSPECTM 3000,20%)催化剂更好的稳定性和甲醇容忍性.因此,该催化剂作为廉价的高效ORR电催化剂有望应用于燃料电池中.     

粘性减阻技术及其应用

本文综述了几种粘性减阻方法及其减阻的机理，联系了其在水相、油相中节约能源、材料，提高速度和效率等方面的应用     

The influence of flow-induced non-Newtonian fluid properties on turbulent drag reduction

Friction factors and velocity profiles in turbulent drag reduction can be compared to Newtonian fluid turbulence when the shear viscosity at the wall shear rate is used for the Reynolds number and the local shear viscosity is used for the non-dimensional wall distance. On this basis, an apparent maximum drag reduction asymptote is found which is independent of Reynolds number and type of drag reducing additive. However, no shear viscosity is able to account for the difference between the measured Reynolds stress and the Reynolds stress calculated from the mean velocity profile (the Reynolds stress deficit). If the appropriate local viscosity to use with the velocity fluctuation correlations includes an elongational component, the problem can be resolved. Taking the maximum drag reduction asymptote as a non-Newtonian flow, with this effective viscosity, leads to agreement with the concept of an asymptote only when the solvent viscosity is used in the non-dimensional wall distance.     

Photochemical Reduction of Carbon Dioxide Catalyzed by a Ruthenium‐Substituted Polyoxometalate

A polyoxometalate of the Keggin structure substituted with Ru^III, ⁶Q₅[Ru^III(H₂O)SiW₁₁O₃₉] in which ⁶Q=(C₆H₁₃)₄N⁺, catalyzed the photoreduction of CO₂ to CO with tertiary amines, preferentially Et₃N, as reducing agents. A study of the coordination of CO₂ to ⁶Q₅[Ru^III(H₂O)SiW₁₁O₃₉] showed that 1) upon addition of CO₂ the UV/Vis spectrum changed, 2) a rhombic signal was obtained in the EPR spectrum (g_x=2.146, g_y=2.100, and g_z=1.935), and 3) the ¹³C NMR spectrum had a broadened peak of bound CO₂ at 105.78 ppm (Δ_1/2=122 Hz). It was concluded that CO₂ coordinates to the Ru^III active site in both the presence and absence of Et₃N to yield ⁶Q₅[Ru^III(CO₂)SiW₁₁O₃₉]. Electrochemical measurements showed the reduction of Ru^III to Ru^II in ⁶Q₅[Ru^III(CO₂)SiW₁₁O₃₉] at ?0.31 V versus SCE, but no such reduction was observed for ⁶Q₅[Ru^III(H₂O)SiW₁₁O₃₉]. DFT‐calculated geometries optimized at the M06/PC1//PBE/AUG‐PC1//PBE/PC1‐DF level of theory showed that CO₂ is preferably coordinated in a side‐on manner to Ru^III in the polyoxometalate through formation of a Ru? O bond, further stabilized by the interaction of the electrophilic carbon atom of CO₂ to an oxygen atom of the polyoxometalate. The end‐on CO₂ bonding to Ru^III is energetically less favorable but CO₂ is considerably bent, thus favoring nucleophilic attack at the carbon atom and thereby stabilizing the carbon sp² hybridization state. Formation of a O₂C–NMe₃ zwitterion, in turn, causes bending of CO₂ and enhances the carbon sp² hybridization. The synergetic effect of these two interactions stabilizes both Ru–O and C–N interactions and probably determines the promotional effect of an amine on the activation of CO₂ by [Ru^III(H₂O)SiW₁₁O₃₉]^5?. Electronic structure analysis showed that the polyoxometalate takes part in the activation of both CO₂ and Et₃N. A mechanistic pathway for photoreduction of CO₂ is suggested based on the experimental and computed results.     

An effective synthesis of N,N-dimethylamides from carboxylic acids and a new route from N,N-dimethylamides to 1,2-diaryl-1,2-diketones

Carboxylic acids were heated at 150 °C in DMF in the presence of 1.25 equiv of thionyl chloride to give corresponding N,N-dimethylamides in good yields. Tandem chlorination and amidation reactions occurred in the one-pot procedure. Dicarboxylic acids needed prolonged reaction time to produce bisamides in good yields. Some benzamides were efficiently converted into corresponding 1,2-diaryl-1,2-diketones (benzils) under acyloin condensation conditions in the presence of 4,4′-di-tert-butylbiphenyl (DBB) in THF. Ultrasonic irradiation effectively accelerates the reaction, but it is not critical. However, the presence of DBB is fatal to the reaction. Although a few synthetic methods for benzils from benzoic acids have been reported so far, this method is one of the most convenient and highly reproducible procedures.