Preparation and electrochemistry of azobenzene self-assembled monolayers on gold--long range tunneling and end-group hydrogen bonding effect

A series of thiol-functionalied azobenzene derivatives (RAzoCnSH: R=H for n=3-6, abbreviated as AzoCnSH; R=CH(3)CONH for n=4, abbreviated as aaAzoC4SH) on gold electrodes were prepared and their self-assembly and electrochemical properties were studied by cyclic voltammetry. They all formed uniform and reproducible self-assembled monolayers (SAMs) on gold and showed well-behaved voltammetric responses in aqueous solution. Both the length of the alkyl chain spacer and the H-bonding of the end acetamino group had effects on the stability and the electrochemical kinetics of the SAMs, and the effect of the H-bonding was dominant. The surface coverage of the SAMs (AzoCnSH) is gradually increased with an increase of the alkyl chain spacer length, whereas the presence of the terminal acetamino group leads to a greater increase of the surface coverage. At a low scan rate, voltammetric responses corresponding to an irreversible two-electron, two-proton reduction/oxidation of the trans-azobenzene redox center were obtained in the range of +300 mV and -800 mV, which exhibited very large peak-to-peak splitting. At a high scan rate of 500 mV/s, two steps of reversible one-electron, one-proton reduction/oxidation corresponding to the cis-isomer in azobenzene-thiol SAMs (n is odd) was clearly observed between +300 and -200 mV. The apparent electron-transfer rate is decreased with increasing distance between the azobenzene redox center and the gold electrode. The existence of the end acetamino group which restricted the conformational change during the redox process also led to a decrease of the standard rate constant, and this restriction effect is more predominant than the distance effect.     

含二氧杂环异黄酮的合成

本文报道含有3', 4'-亚甲二氧基, 3', 4'-亚乙二氧基, 3, 4'-三亚甲二氧基的异黄酮类化合物的合成, 所得25个新化合物的结构经元素分析、^1H NMR谱确证; 紫外光谱表明有异黄酮特征吸收。文中并对反应机理进行了探讨。     

碱性介质中高择优取向（220）镍电极上丙醇的电氧化

对１．０ｍｏｌ／ＬＮｉＳＯ４和０．５ｍｏｌ／Ｌ Ｈ３ＢＯ３体系，控制电位为一１．２５Ｖ，沉积６０ｍｉｎ，制得高择优取向镍电极。该镍电极经Ｘ射线衍射测定其织构度ＴＣ２２０为９２％。采用循环伏安法研究了１ｍｏｌ／Ｌ ＮａＯＨ溶液中高择翁取向镍电极上丙醇的电催化氧化机理有活性，结果表明：高择优取向镍电极对正丙醇的电催化活性高，对异丙醇的电催化活性小；推导出正丙醇的电氧化动力学方程，运用稳态极经曲线测定了     

高效毛细管电泳法手性分离伪麻黄碱

以三甲基-β-环糊精(TM-β-CD)为手性选择剂,用毛细管区带电泳法对手性药物伪麻黄碱进行了分离.系统地考察了不同的手性选择剂及其浓度、缓冲溶液的浓度和pH、分离电压等对分离的影响.结果发现,在Tris-H3PO4(10 mmo1.L-1 Tris,5 mmo1.L-1 H3PO4,PH 2.74)缓冲溶液中,TM-β-CD为15 mmo1.L-1,分离电压18 kV条件下,伪麻黄碱对映体在6 min内获得快速基线分离.由此建立了可靠、快速的分析方法.     

LiCoO_2 electrode/electrolyte interface of Li-ion batteries investigated by electrochemical impedance spectroscopy

The storage behavior and the first delithiation of LiCoO2 electrode in 1 mol/L LiPF6-EC:DMC:DEC elec- trolyte were investigated by electrochemical impedance spectroscopy (EIS). It has found that, along with the increase of storage time, the thickness of SEI film increases, and some organic carbonate lithium compounds are formed due to spontaneous reactions occurring between the LiCoO2 electrode and the electrolyte. When electrode potential is changed from 3.8 to 3.95 V, the reversible breakdown of the resistive SEI film occurs, which is attributed to the reversible dissolution of the SEI film component. With the increase of electrode potential, the thickness of SEI film increases rapidly above 4.2 V, due to overcharge reactions. The inductive loop observed in impedance spectra of the LiCoO2 electrode in Li/LiCoO2 cells is attributed to the formation of a Li1-xCoO2/LiCoO2 concentration cell. Moreover, it has been demonstrated that the lithium-ion insertion-deinsertion in LiCoO2 hosts can be well described by both Langmuir and Frumkin insertion isotherms, and the symmetry factor of charge transfer has been evaluated at 0.5.     

高效液相色谱法测定食品中安赛蜜、苯甲酸、山梨酸、糖精钠、脱氢乙酸

近年来，由于消费者对食品的安全性日益关注，食品中常用添加剂，特别是人工合成甜味剂[主要是糖精钠（SA）、乙酰磺胺酸钾（安赛蜜，AK）]和防腐剂[苯甲酸（BA）、山梨酸（SOR）、脱氢乙酸（DHA）]的使用情况越来越受到人们的重视，而GB2760《食品添加剂使用卫生标准》对其最高限量作了规定。目前，大多数分析方法只能测定上述物质中的二种或少数几种，能够同时测定上述五种食品添加剂的方法未见报道。     

一缩二甘醇酸体系荧光分析法同时测定钆和铽

本文研究了Ｇｄ＾３＾＋，Ｔｂ＾３＾＋与一缩二甘醇酸形成络合物的荧光性能及发光机理，探讨了Ｇｄ＾３＾＋，Ｔｂ＾３＾＋同时测定的最佳条件和共存离子的影响。Ｇｄ＾３＾＋，Ｔｂ＾３＾＋的检测限分别为１６０和３ｎｇ／ｍｌ。并将该法成功地应用于稀土氧化物中Ｇｄ＾３＾＋，Ｔｂ＾３＾＋的测定。     

Characterization of mesoporous nanocrystalline TiO2 photocatalysts synthesized via a sol-solvothermal process at a low temperature

Nanocrystalline TiO₂ samples with mesoporous structure were prepared via a solvothermal treatment of surfactant-stabilized TiO₂ sols. The samples were obtained from media of different acidities including nitric acid, deionized water, and ammonia (denoted as HT-1, HT-2 and HT-3, respectively). These samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂-sorption (BET surface area), micro-Raman spectroscopy, infrared absorption spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of the samples were tested by the self-photosensitized degradation of an azo dye, Mordant Yellow 10 (MY), in aqueous solution under visible light irradiation. The results reveal that all three samples have high surface area and are pure anatase phase. The sample prepared in nitric acid medium possesses the most ideal mesoporous structure and also exhibits a blue shift in the Raman spectrum. All three samples show much higher photocatalytic activity than the commercial P-25. The activity order of the three samples is HT-1>HT-2>HT-3.     

NITROXIDE-MEDIATED FREE RADICAL SYNTHESIS OF MESOGEN-JACKETED LIQUID CRYSTAL POLYMERS*

The first TEMPO-mediated "living" free radical polymerization of liquid crystallinemonomer, 2, 5-bis[(4-methoxyphenyl)oxycarbonyl]styrene(MPCS), was carried out at 130℃ withBPO as an initiator. The molecular weight of the polymer can be varied from rather low values to highvalues while maintaining narrow polydispersity. It was observed that the polymerization of MPCSproceeded much faster than that of styrene. A tentative explanation for this fast polymerization wassuggested.