N-heterocyclic carbene-silver complexes: Potential conductive materials for silver pastes in electronic applications

New organosilver complexes, silver(I) tetraalkylbis(benzimidazolidene) halide [1a-3a] and silver(I) dimethyl-N,N′-hexyl(imidazolyl) bromide [4a], were synthesized and incorporated into electroconductive silver pastes. Complex 3a had a 15-fold higher conductivity than conventional silver salt pastes, specifically silver(I) hexanoate, and exhibited a smooth, homogeneous surface after reductive heat-treatment of the silver paste. While the conductivity of silver(I) hexanoate can be increased by up to 33% by the addition of a supporting silver source, such as Ag₂O, the conductivity of 3a was markedly decreased by Ag₂O treatment. Thus, 3a can be used in silver pastes with moderate conductivity and can reduce the amount of conventional silver supporting materials without loss of electroconductivity.     

延胡索酸泰妙菌素在碳糊电极上的电化学性质及电分析方法

运用循环伏安法(CV)、计时电流法(CA)和计时电量法(CC)研究了延胡索酸泰妙菌素(Tiamulin fumarate,TF)在碳糊电极(Carbon Paste Electrode,CPE)上的电化学及其电化学动力学性质。结果表明,TF在CPE上的电化学过程是一不可逆的氧化过程,氧化峰电位Ep为0.772 V。在扫描速度10～1 000 mV.s-1范围内,其氧化峰电流Ip与扫描速度v呈良好的线性关系,表明TF在CPE上的伏安行为是一受吸附控制的过程。方波伏安(SWV)法结果表明TF氧化峰电流与其浓度在5.0×10-7～1.0×10-5mol.L-1及1.0×10-5～1.0×10-4mol.L-1范围内均呈良好的线性关系,相关系数r分别为0.9980及0.9966,检出限(S/N=3)为5.8×10-8mol.L-1,相对标准偏差(RSD)为0.8%～2.8%,加样回收率为97.6%～102.0%。据此建立了TF含量的电化学测定方法。该方法简便快捷,测定结果令人满意。     

Studies on the Synthesis and Characterization of Pd?TiO2?SiO2 Nanocomposite for Electroanalytical Applications

A nanocomposite of Pd? TiO₂? SiO₂ is developed through a sol‐gel process from the reaction products of titanium isopropoxide followed by mixing the same with palladium linked 3‐glycidoxypropyltrimethoxysilane. The reaction product is sonicated and calcinated to obtain the nanocomposite of Pd? TiO₂? SiO₂. The calcination at 600 °C yielded an amorphous structure whereas at 900 °C it resulted into a nanocrystalline structure. The nanocomposite of palladium was further characterized by TEM, XRD, IR and EDS. The material acts as an efficient electrocatalyst. Electrocatalysis of ascorbic acid is observed at 0.1 V vs. Ag/AgCl, shows linearity between 1 µM and 1 mM in 0.1 M phosphate buffer (pH 7.0).     

A novel palygorskite-modified carbon paste amperometric sensor for catechol determination

A palygorskite-modified carbon paste electrode (CPE) was constructed using graphite powder mixed with palygorskite particles. Compared with the unmodified CPE, the resulting palygorskite-modified CPE remarkably increases the peak currents of catechol, and greatly lowers the peak potential separation. Therefore, the palygorskite exhibits catalytic activity to catechol and significantly improves the determining sensitivity. The electrocatalytic activity of palygorskite is attributed to its high adsorption capability and the –OH groups on its surface, which plays an important role in the electron transfer between the modified CPE and the catechol in the solution. The sensor shows a linear response range between 5 and 100 μM catechol with a correlation coefficient of 0.998. The detection limit was calculated as 0.57 μM (s/n = 3).     

奥美拉唑在碳糊电极上的吸附伏安测定法研究

研究了奥美拉唑在碳糊电极上的电化学行为及检测方法 ;在1.2mol·L -1H2SO4 底液中 ,通过富集用碳糊电极吸附伏安法测定奥美拉唑 ;阴极峰电位为0.403V(vsSCE) ,峰电流与奥美拉唑的浓度在7.8×10-8～3.7×10-5 mol·L-1 范围内呈良好的线性关系 ;该法的检出限为1.43×10-8 mol·L-1;用标准加入法测得回收率范围为94 %～102 % ;对奥美拉唑胶囊用该法进行了测定 ,获得了满意的结果 ;该法的优点是成本低 ,操作方便 ,重复性好及检出限较低 ;对电极响应机理进行了探讨 ,奥美拉唑的电极过程是一个两电子两质子的准可逆过程     

Voltammetric Determination of Leucoindigo Adsorbed on Pretreated Carbon Paste Electrodes: Its Application in a Flow System

The determination of leucoindigo adsorbed on the surface of pretreated carbon paste electrodes has been performed by cyclic (CV) and alternating current voltammetry (ACV). The water‐soluble compound called leucoindigo is obtained through the reduction of water insoluble indigo in an alkaline media and in presence of a dithionite salt (Na₂S₂O₄) as a reducing agent. Cyclic voltammograms of leucoindigo show two reversible electrodic processes, in the aqueous 0.1 M Tris‐HCl pH 7.2, at the formal potential of ?0.4 V and +0.3 V (vs. Ag/AgCl/sat. KCl). In a batch protocol, leucoindigo was quantified by CV with a change of medium between accumulation and detection steps. Reversible voltammetric processes of leucoindigo were greatly enhanced by other voltammetric technique like alternating current voltammetry. Limit of detection in the nanomolar range was achieved for a 2 min accumulation time by ACV in a batch procedure. A flow system was also employed, with adsorptive voltammetric detection of leucoindigo, since this automates the methodology and decreases analysis time. Parameters related to the electrochemical technique are optimized and calibration plots obtained are reported. These data provide useful information about the suitability of using leucoindigo in the detection system of alkaline phosphatase (AP) and horseradish peroxidase (HRP) based affinity devices, in which indigo is generated by the enzymatic hydrolysis of the 3‐indoxyl phosphate substrate.     

聚吡咯碳糊电极的研制及应用

研制了聚吡咯电极，探讨了该电极的性能和实用性，实验结果表明，该电极可用于伏安法快速测定Ｌ－抗坏血酸，在０．１ｍｏｌ／ＬＫＮＯ３底液中，线性范围为１．０×１０＾－１１～９．０×１０＾－９ｍｏｌ／Ｌ检测限为５．０×１０＾－１２ｍｏｌ／Ｌ，电极具有具有良好的重现性和高选择性，响应迅速，使用寿命３个月以上。     

Calorimetric determination of enthalpies of lysozyme folding at a liquid-solid interface

Summary Two hydrated and aged cement pastes from India (NCB), w/c=0.4, of a similar chemical composition but of a different specific surface and different strength (OPC, C-33 and C-43), hydrated at w/c=0.4 for 1 month, were studied by XRD after 1 year and 5-6 year ageing on contact with air. They were tested by static heating (SH) in fresh state, and by DTA/DTG/TG, IR and mass spectrometry (MS), after ageing, presented elsewhere. The main XRD peaks of (i) portlandite were decreasing with T and disappearing about 450°C, (ii) calcite peak at room T was small and broad, it increased gradually, especially after portlandite disappearance; above 600°C it was lowered and it was lost above 700°C. Important variation in the d(001) of portlandite with ageing was observed, exceeding the standard value of d(001)=4.895 Å (72-0156). It was higher in the paste C-33 (4.925-4.936 Å), containing more carbonates, than in the paste C-43 (4.916-4.927 Å). Small variations only were found in the value of d(101), i.e. 2.627-2.635 Å (nominally 2.622 Å), whereas the d(104) of calcite could be used as internal standard and other calcium carbonates (vaterite and aragonite) showed a small variation only. The increase ind(hkl) with temperature was straight linear (in portlandite d(001)=0.095 Å, at 30-400°C) and the thermal expansion coefficient estimated thereform was high (4.75-4.95·10^-5 K^-1). Close to the T of decomposition the d/T became steeper. The thermal variation of d(104)=3.035 Å of calcite (d=0.015 Å at 30-400°C) was smaller than that ofd(101) of portlandite (d=0.025 Å at 30-400°C) and was similar in C-33 and C-43. The thermal expansion coefficient was 1.54 10^-5 K^-1, thus higher than the reported _a=0.65·10^-5 K^-1.     

Surface energy and mechanical behaviour of hardened cement paste

The Bangham equation indicates a direct proportionality between the length change of a porous body and a change of surface energy. In our experiments surface energy of hardened cement paste has been modified by desorbing or adsorbing water molecules. The internal pressure created by surface energy could be directly determined with the help of Mössbauer experiments. Based on these results it is possible to determine to what extent shrinkage or swelling is caused by a change of surface energy. Using Griffith's criterion our findings can explain quantitatively the decrease of stength as a function of increasing water content. Results are in good agreement with other methods of studying surface energy such as experiments to determine van der Waals forces.