Study on surface acid-base property of carboxylic acid-terminated self-assembled monolayers by cyclic voltammetry and electrochemical impedance spectroscopy

Cyclic voltammetry and electrochemical impedance spec-troscopy were used to study the surface acid-base property of carboxylic acid-terminated self-assembled monolayers(SAMs).A carboxylic acid-terminated thiol,such as thioctic acid(1,2-dithiolane-3-pentanoic acid),was self-assembled on gold electrodes.Electron transfer between the bulk solution and the SAM modified electrode was studied at different pH using Fe(CN)63-as a probe.The surface pka of thioctic acid was determined by cyclic voltammetry and electrochemical impedance spectroscopy to be 5.6 ±0.1 and 5.8±0.1,respectively.The method is compared with other methods of monolayer pKa measurement.     

阶梯扫描催化伏安法及其卷积和导数的研究

本文系统研究了静态电极下阶梯扫描平行催化伏安法及其各阶导数卷积和导数的理论。推导了这一伏安法的催化电流及其各阶导数卷的导数的理论方程, 在此基础上建立了一组简便测定化学反应速率常数的新方法。并以Ti(IV)-KClO3,Ti(IV)-NH2OH, Yb(III)-KNO3和YB(III)-NaNO2四个平行催化体系从实验上验证了理论的正确性, 同时用本文提出的新方法测定了这四个体系的化学反应速率常数,结果良好.     

Determination of linuron in water and vegetable samples using stripping voltammetry with a carbon paste electrode

A carbon paste electrode was used for the electrochemical determination of linuron concentrations in water and vegetable extracts. Optimal conditions were established with respect to electrode activation (electrochemical pretreatment), time accumulation, potential accumulation, scan rate, and pH. The limit of detection achieved with a pre-concentration step was 23.0 μg L⁻¹. Recovery measurements in vegetable extract and natural water samples were in the range of 98-103%, indicating that the proposed electrochemical method can be employed to analyze linuron in these matrices. The determination results were in good agreement with HPLC results.     

Electrochemical synthesis for new thiosemicarbazide complexes,spectroscopy, cyclic voltammetry,structural properties,and in silico study

A new thiosemicarbazide derivative ligand (HDCTS) was prepared from the reaction between 2,4‐dinitrophenylhydrazine and 4‐chlorophenyl isothiocyanate. Co(II) and Cu(II) complexes were synthesized from HDCTS derivative by electrochemical method to reach preferable yield in a safe environment. The new complexes as well as the original ligand were fully characterized to establish their chemical formulae. The spectral (infrared, Raman, mass, and ultraviolet–visible), analytical (elemental, thermogravimetric analysis [TGA], and cyclic voltammetry), and conformational techniques were implemented for characterization. According to spectral data and magnetic moments, the octahedral arrangement was proposed around metals through mono‐negative bidentate mode of bonding. TGA discriminates and quantitatively evaluates the presence of water molecules within two complexes. Electrochemical study was interested for all new compounds and suggests the electrode couples to be close for quasi‐reversible behavior. Elaborated conformational study was displayed to extract significant characteristics, which assert firstly on the mode of bonding inside the complexes. The perfect distribution of NH and CS groups inside the optimized structures facilitates their coordination as spectrally proposed. Crystal explorer program was used to investigate the degree of contact between molecules inside crystal packing systems. Effective contribution in surface contact feature was noticed from O and Cl atoms. A certified in silico study concerning the docking feature of new compounds against effective proteins in allergy and inflammation diseases was done. According to data exported, a promising anti‐allergic or anti‐inflammatory efficiency is expected strongly from Cu(II)–DCTS complex.     

Fast Fourier transformation with continuous cyclic voltammetry at an Au microelectrode for the determination of morphine in a flow injection system

For the fast morphine monitoring in flow injection systems a highly sensitive method is being introduced in this work. The fast Fourier transformation with continuous cyclic voltammetry (FFTCV) in a flowing solution as a detection system was applied for the prompt morphine monitoring. Here it should be stressed that this technique is simple, precise, accurate, time saving and economical. This research includes the observation of the effects of various parameters on the sensitivity of the detection system. Eventually, it was concluded that the best condition was obtained within the pH value of 2, scan rate value of 40 V s⁻¹, accumulation potential of 400 mV and accumulation time of 0.6 s.In detail, the noteworthy advantages which this method illustrates in comparison with other reported methods are the following; no necessity for the oxygen removal from the test solution, a sub-nano molar detection limit and the fast determination of any such compound in a wide variety of chromatographic methods.The method proved to be linear over the concentration range of 285-305,300 pg mL⁻¹ (r = 0.999) with a detection limit and a quantitation limit of 95.5 and 285 pg mL⁻¹, respectively. Consequently, the method illustrates the requisite accuracy, sensitivity, precision and selectivity to assay morphine in its tablets and biological fluids.     

Differentiation between o- and p-quinol/quinone functionality with a simple test using cyclic voltammetry

Complexation with boric acid combined with cyclic voltammetry serves to prove theo-quinol/quinone functionality in emmotin H (1) and I (2). Supported by similar investigation of four reference compounds the method is suggested as a quick and reliable test ofo-quinol/quinone functionality and for differentiation fromp-quinol/quinone functionality. Voluminous groups such as 2-isopropanolyl ino-position do not interfere with the complex formation. The test requires quantities of materials in the order of 10 to 100g.     

Co(II) and Fe(II) phthalocyanines: synthesis,investigation of their catalytic activity towards phenolic compounds and electrochemical behaviour

4‐[(1‐Benzylpiperidin‐4‐yl)oxy]‐substituted cobalt(II) and iron(II) phthalocyanine complexes were synthesized and their catalytic activity towards various phenolic compounds was investigated. Converting from environmentally harmful phenolic compounds into less harmful oxidation products using phthalocyanines makes this study attractive. This catalysis is feasible and time‐saving in terms of procedure and the best oxidation conditions determined. Electrochemical studies were also carried out using cyclic voltammetry and square wave voltammetry techniques. Voltammetric analyses of the synthesized phthalocyanine complexes supported their proposed structures. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation,spectral characterization,electrochemistry, EXAFS,antibacterial and catalytic activity of new ruthenium (III) complexes containing ONS donor ligands with triphenylphosphine/arsine

New hexa‐coordinated ruthenium (III) complexes of the type [RuX(EPh₃)₂(L)] (X = Cl or Br; L = dibasic tridentate Schiff base ligand; E = P or As) have been synthesized by the reactions of [RuCl₃(PPh₃)₃], [RuCl₃(AsPh₃)₃] or [RuBr₃(AsPh₃)₃] with the appropriate Schiff base ligands derived by the condensation of salicylaldehyde and 2‐hydroxy‐1‐naphthaldehyde with N(4) substituted thiosemicarbazones. All the new complexes were characterized using various physico‐chemical methods such as elemental analyses, infrared, electron paramagnetic resonance (EPR) spectroscopy, magnetic moment and cyclic voltammetry. Based on the extended X‐ray absorption fine structure (EXAFS) analysis, an octahedral structure has been confirmed for the complexes. The new complexes have been subjected to the catalytic activity and antibacterial studies. Copyright © 2005 John Wiley & Sons, Ltd.     

Study of electrochemical oxidation of nickel catecholate complexes with bis(diphenylphosphino)ethane by cyclic voltammetry and ESR

One-and two-electron electrochemical oxidation of the (dppe)Ni(Cat) complexes (dppe is bis(diphenylphosphino)ethane, Cat is the sterically hindered catechol dianion) was studied. The transfer of the first electron proceeds reversibly to give paramagnetic species; parameters of their EPR spectra attest to a square planar geometry of one-electron oxidation products. The transfer of the second electron is irreversible because of co-proportionation of radical cations involving the initial complexes and the generated dications. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 99–102, January, 2007.     

The use of cyclic voltammetry for wine analysis: Determination of polyphenols and free sulfur dioxide

The use of cyclic voltammetry to characterize wines and wine polyphenols in a pH 3.3 model wine solution has been extended to take into account the effects of sulfur dioxide and polyphenol adsorption processes. A good correlation was obtained between a cyclic voltammetric measure, based upon the response produced before and after acetaldehyde additions, and the concentration of free sulfur dioxide in eight white wines (r² = 0.974). By the addition of acetaldehyde to the white wines, an important new step in the methodology, the area under the anodic scan in the potential range from −100 to 1200 mV (Ag/AgCl) closely matched the spectroscopic measure of total polyphenols (absorbance at 280 nm) for the white wines, when both were measured in terms of caffeic acid equivalents (r² = 0.949). The anodic peak area accounted for about 70% of the 280 nm total phenols measure, in catechin equivalents, for the red wines, and a good linear correlation was also obtained (r² = 0.942). The level of catechol and galloyl-containing polyphenols in the wines was calculated by measuring the size of the first anodic peak at around 450 mV after treatment of the wines with acetaldehyde; the peak current correlated well with the total caffeic acid derivatives in the white wines determined by HPLC (r² = 0.982). The concentration of flavonols was estimated by selective adsorption of these compounds onto the carbon electrode and determining the anodic peak current at 1120 mV, with good correlations obtained when compared to total flavonols as measured by HPLC (r² = 0.984 for the red wines, and r² = 0.987 for the white wines).     

A complete numerical simulation of the techniques of alternating current linear sweep and cyclic voltammetry: analysis of a reversible process by conventional and fast Fourier transform methods

We describe the method of achieving the first completely general simulation of ac linear sweep and cyclic voltammetry making use of the fully implicit Richtmyer modification (FIRM) method. The simulation technique is applied to a reversible process under conditions where a sinusoidal waveform of any amplitude is superimposed onto the dc potential which is swept at a finite scan rate. Results, where possible, are compared with the existing theory derived at constant dc potential to confirm the fidelity of the simulation. In particular, we demonstrate excellent agreement with the results of Engblom et al. [J. Electroanal. Chem. xxx (1999) xxx] for large amplitude ac voltammetry described in the companion paper immediately preceding this article. The use of conventional and Fourier transform methods of data analysis are compared to highlight the advantages of the use of the fast Fourier transform algorithm in ac voltammetry.     

Study of the adsorption of cytochrome c on a gold nanoparticle – modified gold electrode by using cyclic voltammetry, electrochemical impedance spectroscopy and chronopotentiometry

Adsorption of cytochrome c (Cyt c) on a gold nanoparticle – modified gold electrode was studied by using cyclic voltammetry, electrochemical impedance spectroscopy and chronopotentiometry in a phosphate buffer solution. It is shown that the charge transfer resistance is directly proportional to the amount of adsorbed Cyt c. The effects of temperature and time on the course of adsorption were also studied. The trends obtained in ΔG_ADS showed that Cyt c was found to have a smaller affinity for the modified electrode as indicated by their smaller negative ΔG_ADS values.     

Electropolymerization of polypyrrole, modified with germanium, on a passivated titanium electrode in aqueous nitrate solution: new results on catalytic reduction of protons and dissolved oxygen

Conductive polypyrrole (PPy) films and PPy films containing Ge microparticles were synthesized by anodic oxidation of pyrrole in acidic nitrate solutions using a bare passivated titanium electrode. Well-adhering black PPy films were obtained both under galvanostatic and potentiodynamic polarization. After the formation of the PPy film, during the first anodic cycle, an increase of the anodic deposition current with the number of cycles was observed, revealing the increase of conductivity of the growing film. The variations of the electrode surface area were estimated by impedance spectroscopy measurements. The kinetics of the PPy film formation is controlled by diffusion of the Py monomer in the solution. The diffusion coefficient, estimated by two different methods, was ca. 2×10^–6 cm² s^–1. The reduction rate of oxygen and protons at the Ti/PPy/Ge electrodes depends on how the Ge microparticles are incorporated in the PPy film. Optimum conditions for this incorporation are realized with thin PPy films and high Ge loading. Thermogravimetric analysis shows that the PPy film containing Ge microparticles is more thermally stable than the blank PPy film. Electronic Publication     

Determination of Cr (in small quantities) by adsorptive stripping voltammetry: a comparative study of square wave versus differential pulse

The usefulness of an analytical method must be measured according to its practical application possibilities. A comparative study has been carried out here between the SW (working in an open atmosphere) and DP (working with de-aerated solutions) variants of catalytic-stripping adsorptive voltammetry applied to the determination of chromium traces in triethylenetetraminehexaacetic acid (TTHA) medium. In order to optimise the analytical signal, accumulation potential, nitrate ion concentration, pH, and TTHA concentration parameters were evaluated. Four linearity ranges were established within the interval 0.5–2000 nmol L^–1 chromium concentration in the cell, each with the recommended accumulation time. Quality parameters such as repeatability, linear regression, validity limits, precision, and sensitivity were evaluated. The SW variant is significantly advantageous when the chromium concentration in cell is less than 10 nmol L^–1 and even more if analysis time, cost, and being able to work in an open atmosphere are considered. The results are comparable to those obtained using GTAAS. Employing a CRM (tomato leaves), the accuracy is 1–4%. The proposed procedure, using tree leaves as samples, has been successfully tested for the possible monitoring of chromium contamination of the atmosphere.     

Thiolate chemistry: a powerful and versatile synthetic tool for immobilization/functionalization of oligothiophenes on a gold surface

The synthesis and characterization of a series of quaterthiophenes (4Ts) with thiolate groups protected with 2-cyanoethyl (CNE), 2-trimethylsilylethyl (TMSE), and acetyl (Ac) groups are described. Sequential cleavage of these different protecting groups allows for the preparation of 4Ts derivatized with ferrocene and/or alkanethiol chains. The electrochemical behavior of these compounds has been analyzed in solution by cyclic voltammetry (CV). A ferrocene-derivatized dithiol 4T 14 and a dithiol 4T 15 with two TMSE-protected thiolate groups have been immobilized on a gold surface as monolayers that have been characterized by CV, ellipsometry, contact-angle measurement, and X-ray photoelectron spectroscopy (XPS). The results show that molecules 14 and 15 are doubly grafted with a horizontal orientation of the conjugated system relative to the surface. Furthermore, application of the deprotection/alkylation sequence of the remaining protected thiolate groups on a monolayer of 15 allows for efficient post-functionalization.     

Cyclic voltammetry modeling, geometries, and electronic properties for metallofullerene complexes with mu3-eta2:eta2:eta2-C60 bonding mode

Reduction potential (E(red)) values have been calculated and compared with available cyclic voltammetry (CV) data for 10 metallofullerene complexes with the mu(3)-eta(2):eta(2):eta(2)-C(60) (M(3)-C(6)[C(60)]) bonding mode. Consideration of bulk solvent effects is essential for the calculation of the E(red) values. Scaling factors for the electrostatic terms of the solvation energies have been introduced to fully describe the experimental cyclic voltammograms with a small mean deviation of 0.07 V. Multiple electron reductions induce movement of the metal cluster moieties on the C(60) surface, which is accompanied with the changes in some M-C[C(60)] bonds from pi-type to sigma-type mode. However, the changes in M(3)-C(60) distances, as well as the geometric changes of M(3) and C(60), are small for the reductions, which is in harmony with the high chemical and electrochemical stability of the metallofullerenes. Our population analyses reveal that the added electrons are not localized at the C(60) moieties, and electron population in the metal clusters is significant, more than 20% (av. 37%), for all the reductions. Furthermore, we demonstrated that the two close one-electron redox waves in CV diagrams are strongly correlated with significant electron delocalization, about 40-80%, to the metal-cluster moieties in these metallofullerene complexes.     

Binding of active site directed ligands to phospholipase A2: Implications on the molecular constraints and catalytic mechanism

Molecular constraints for the localization of active site directed ligands (competitive inhibitors and substrates) in the active site of phospholipase A2 (PLA2) are characterized. Structure activity relationships with known inhibitors suggest that the head group interactions dominate the selectivity as well as a substantial part of the affinity. Theab initio fitting of the amide ligands in the active site was carried out to characterize the head group interactions. Based on a systematic coordinate space search, formamide is docked with known experimental constraints such as coordination of the carbonyl group to Ca²⁺ and hydrogen bond between amide nitrogen and ND1 of His48. An optimal position for a bound water molecule is identified and its significance for the catalytic mechanism is postulated. Unlike the traditional “pseudo-triad” mechanism, the “Ca-coordinated-oxyanion” mechanism proposed here invokes activation of the catalytic water to form the oxyanion in the coordination sphere of calcium. As it attacks the carbonyl carbon of the ester, a near-tetrahedral intermediate is formed. As the second proton of the catalytic water is abstracted by the ester oxygen, its reorientation and simultaneous cleavage form hydrogen bond with ND1 of His48. In this mechanism of esterolysis, a catalytic role for the water co-ordinated to Ca²⁺ is recognised.     

Determination of As(III) by anodic stripping voltammetry using a lateral gold electrode: experimental conditions, electron transfer and monitoring of electrode surface

The aim of this work is to evaluate the efficiency of the determination of As(III) by anodic stripping voltammetry (ASV) using a lateral gold electrode and to study the modifications of the electrode surface during use. Potential waveforms (differential pulse and square wave), potential scan parameters, deposition time, deposition potential and surface cleaning procedure were examined for they effect on arsenic peak intensity and shape. The best responses were obtained with differential pulse potential wave form and diluted 0.25 M HCl as supporting electrolyte. The repeatability, linearity, accuracy and detection limit of the procedure and the interferences of cations and anions in solution were evaluated. The applicability of the procedure for As(III) determination in drinking waters was tested. Cyclic voltammetry (CV) was used to study the electrochemical behaviour of As(III) and for the daily monitoring of electrode surface. Also scanning electron microscopy (SEM) analysis was used to control the electron surface. Finally we evaluated the possibility to apply the equations valid for flow systems also to a stirred system, in order to calculate the number of electrons transferred per molecule during the stripping step.     

Theory of two le successive electrochemical surface reactions (Erev Erev or Erev Eirr) associated with surface chemical reactions in polarography and cyclic voltammetry

The theory of a surface electrochemical reaction (strong adsorption) occurring in two le⁻ steps O?R? X, when R can undergo a dimerization R → D and X a first-order reaction X → Z is presented for polarography. It is assumed that adsorption obeys a Langmuir isotherm. The equation of the half-wave potentials as functions of the diverse parameters (rate constants, concentration, surface concentration, drop time) are given; the effects of the two chemical reactions are additive. Kinetic diagrams are constructed. The results can be used to diagnose the type of reaction and to calculate the chemical rate constants.The effects of the dimerization on the half-wave potentials of the two stages do not depend on their separation; in the case of a global 2e⁻ step, they remain hidden until the rate becomes large enough to cause a splitting into two le⁻ waves. These results are generalized to the case where the electrochemical reactions are heterogeneous, and the chemical reactions homogeneous.     

基于苯磺酸和2，2'-联吡啶双配体的锰配合物的结构及其催化Mannich反应性能和机理

由溶剂热法合成了 2 个锰的超分子配合物[Mn₂(2,2''-bipy)₄(H₂O)Cl₃](L₁)·6H₂O (1)和[Mn(2,2''-bipy)₂(H₂O)Cl](L₂)·3H₂O (2)(L₁^-=对甲基苯磺酸根,L₂^-=间硝基苯磺酸根,2,2''-bipy=2,2''-联吡啶),并用单晶X射线衍射、红外光谱、热重分析和氮气吸附-脱附测试对其进行了表征。以Mannich反应为探针,研究了2种配合物的催化性能,并通过对比2种配合物的扫描电镜和粉末X射线衍射表征结果,分析了配合物结构对其催化性能的影响。最后通过密度泛函理论预测了配合物的活性位点,利用X射线光电子能谱证明了活性位点的活化作用,进而阐述了配合物催化Mannich反应的机理。