Selective transfer of Ag+ at the water|1,2-dichloroethane interface facilitated by complex formation with a calixarene derivative

The facilitated transfer of silver, Ag⁺, has been studied at the Interface between Two Immiscible Electrolyte Solutions (ITIES). The transfer was achieved with the assistance of a calixarene-based silver ionophore. An investigation of the mechanistic details of the transfer was conducted using cyclic voltammetry at both micro and macro liquid|liquid interfaces. The mechanism was found to follow a Transfer by Interfacial Complexation (TIC)/Transfer by Organic phase Complexation (TOC) mechanism. The complex stoichiometry was found to shift from 1:1 to 1:2, metal:ligand, with increasing ionophore concentration. The logarithms of the complex association constants, $\log {\beta }_1^{\mathrm{o}}\mathrm{and}\log {\beta }_2^{\mathrm{o}}$, were estimated at 12.4 and 14.5, respectively. The charge transfer current was also found to be limited by diffusion of the transferring species and was unchanged by the presence of a range of interferents. The system thus shows promise for selective analytical applications.     

Ion transfer voltammetry of tryptamine,serotonin, and tryptophan at the nitrobenzene/water interface

The transfer of the cationic forms of tryptamine and serotonin across the nitrobenzene (NB)/water (W) interface was studied by cyclic voltammetry. Well-defined voltammetric waves were observed within the potential window. The standard potentials of the transfer were determined from the midpoint potentials of the voltammograms. The transfer of the cationic form of tryptophan across the NB/W interface was also observed using an acidic aqueous solution.     

An improved algorithm for the numerical simulation of cyclic voltammetric curves affected by the ohmic potential drops and its application to the kinetics of bis(biphenyl)chromium(I) electroreduction

Previously published algorithms for the modeling of cyclic voltammetric curves affected by ohmic potential drops, in terms of the classical explicit finite differences method, are discussed briefly. A fast and efficient numerical procedure suitable for such simulations is described. This approach exhibits high numerical stability for both high scan rates and large uncompensated ohmic resistances. The procedure is based on the calculation of the faradaic current as a root of the non-linear equation, with a simultaneous calculation of the capacitive current. Comparison of the cyclic voltammograms obtained using this method with those calculated using alternative published procedures proves its validity. For comparison with the experimental data, the cyclic voltammetric response for the reduction of bis(biphenyl)chromium(I) tetraphenylborate in N,N-dimethylformamide is shown and the kinetic parameters of this process are fitted. Compared to earlier modelings, they show better concordance with the results of studies at microelectrodes. In conjunction with earlier successful applications of the analogous numerical procedure to the realistic modeling of electrochemical oscillations and multistability at a constant external voltage, the algorithm presented appears to be one of the most applicable methods of calculation of the electrochemical responses affected by the ohmic potential drops.     

Kinetic and mechanistic study of methanol oxidation on a Pt(100) surface in alkaline media1

A comparative study of methanol oxidation on a Pt(100) surface was carried out in bicarbonate, carbonate and different pH values of sodium hydroxide solutions. It was shown that Pt(100) adsorbs OH and `poisoning species'. The surface activity was directly correlated to the OH<sub>ad</sub> species coverage. The `poisoning species', produced in methanol oxidation, participate in the reaction at higher potentials, but block the surface partially at lower potentials. A dual path reaction mechanism, common to all the alkaline solutions used, was proposed based on the assumptions that HCO is a reactive intermediate and that a formate is a reaction product in the main path, while CO₂ is a product of `poisoning species' oxidation in a parallel reaction path.     

EIS study of the redox reaction of Fe(CN)63−/4− at poly(3,4-ethylenedioxythiophene) electrodes: influence of dc potential and cOx:cRed ratio

The electron transfer between the ferri/ferrocyanide redox couple and poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes has been investigated by electrochemical impedance spectroscopy (EIS). Different thicknesses of the conducting polymer films were investigated (i) at a constant concentration of ferrocyanide in the solution at different applied dc potentials and (ii) at the open circuit potential with different ratios of Fe(CN)₆^3?:Fe(CN)₆^4? in the solution. PEDOT was prepared by galvanostatic electropolymerization on platinum electrodes from aqueous solutions containing 0.01 M 3,4-ethylenedioxythiophene (EDOT) and 0.1 M poly(sodium 4-styrenesulfonate) (NaPSS) as the supporting electrolyte. All impedance spectra were obtained in aqueous solutions with 0.1 M KCl as the supporting electrolyte at dc potentials, where the polymer is in the oxidized state. The EIS data were fitted to an equivalent electrical circuit resembling the Randles' circuit, where the double layer capacitance is replaced by the bulk redox capacitance and the associated transport impedance of the conducting polymer. The same potential and thickness dependence of the charge transfer resistance (R_ct) were obtained both (i) by varying the concentration ratio of the redox species in the solution and (ii) by applying different potentials at a constant concentration of ferrocyanide. The potential dependence of k₀ calculated from R_ct indicates that the conducting polymer influences the rate of electron transfer for the ferri/ferrocyanide redox couple.     

结节型舍格伦综合征与恶性淋巴瘤关系初探

目的 探讨结节型舍格伦综合征(tumor like Sj(o)gren’s syndrome,TLSS)与非TLSS( non-TLSS,NTLSS)患者临床、实验室特征及淋巴瘤的发生情况,以期为临床预测舍格伦综合征尤其是TLSS患者发生恶性淋巴瘤转化提供依据.方法 收集1998年1月至2010年1月就诊于北京大学口腔医学院·口腔医院并诊断为原发性舍格伦综合征或TLSS的患者199例,回顾性研究199例患者临床及实验室资料,根据有无腺体肿块将患者分为TLSS组(25例)及NTLSS组(174例),分析临床及实验室指标的差异并行统计学分析.结果 25例TLSS患者中23例为腮腺肿块,2例为颌下腺肿块;TLSS患者在腮腺造影阳性率(P =0.018)、γ球蛋白异常水平(P =0.014)、类风湿因子异常水平(P=0.001)、唇腺生发中心样结构形成(P=O.O14)、抗SSA抗体及抗SSB抗体双阳性率(P ＜0.001)方面与NTLSS患者差异均有统计学意义;25例TLSS患者中3例发生淋巴瘤,占入选病例总数的1.5％(3/199),占TLSS患者的12％ (3/25),3例淋巴瘤包括腹股沟区弥漫性大B细胞淋巴瘤1例及黏膜相关淋巴组织淋巴瘤2例;NTLSS患者无淋巴瘤发生.结论 TLSS与NTLSS患者在临床及实验室特征方面存在差异,TLSS患者更易出现淋巴瘤.     

Kinetic and mechanistic study of hydroxyl ion electrosorption at the Pt(111) surface in alkaline media

The adsorption of OH^? ions on the Pt(111) plane has been studied by fast cyclic voltammetry in sodium hydroxide solutions (0.03 to 1 M), under quasi-equilibrium and Tafel approximation conditions. It was shown that the OH^? ion adsorption is an electrosorption process with one electron exchanged between an OH^? ion and the platinum surface. The electrosorption process follows the Frumkin adsorption isotherm with low intensity repulsive interactions of the adsorbed species (f=2–3). The estimated values of the standard electrochemical rate constant (k°=5.6×10^?4 cm s^?1) and the standard exchange current density (j^o_o=5.45×10^?2 A cm^?2) indicate a rather fast electrochemical process.     

Evaluation of the effectiveness of Er: YAG laser and calcium sodium phosphosilicate (Novamine) prophylaxis paste on remineralization of incipient enamel lesions in primary teeth: An in-vitro study

AimThe aim of this study was to evaluate the potential remineralization effect of Novamine and Er:YAG laser on artificial enamel lesions in primary teeth.Materials and methodsIn this in vitro study, 30 sound buccal and lingual surfaces of human primary canines were randomly divided (6 per group) into 5 groups (Novamine, Laser, Novamine+ Laser, Positive control, and a negative control). Remineralization agents were applied for 1 min to teeth using a rubber cup after creating artificially demineralised lesions. EDX analysis was performed to evaluate the Ca/P ratio and take Scanning electron microscope images.ResultsData were analyzed using Kruskal Wallis analysis. Ca/P ratio was higher in all 4 groups than the negative control group, and higher in Novamine+ Laser group than the positive control group with a statistically significant difference between groups. Overall Ca/P ratio was found to be highest in the Novamine group followed by the laser then positive control group. There were no significant differences between groups regard to Ca/P Ratios.ConclusionBased on these result Er:YAG laser combined with Novamine was provided the greatest contribution to remineralization process of primary teeth.