Open‐circuit Electrochemical Polymerization for the Sensitive Detection of Phenols

We report on a novel electrochemical method for electro‐polymerizing phenols under open‐circuit conditions. The method developed here is simple, sensitive, rapid, and overcomes the well‐documented surface fouling of carbon electrodes by phenols. A pre‐charged disposable graphite pencil electrode (pCGPE) was found to be useful for both phenol sampling and sensing. The pCGPE was prepared by charging the surface of a graphite pencil electrode by applying a cyclic voltammetry electrochemical treatment in a NaOH solution. Phenol sampling was accomplished by immersing the pCGPE into a phenol solution. This method permitted phenol detection with a detection limit of 4.17 nM (0.39 ppt).     

Electrochemical Method to Quantify Antioxidants Employing Cupric Reducing Antioxidant Capacity,CUPRAC

CUPRAC is a method used to determine antioxidants quantifying the chromophore [Cu(Nc)₂]⁺, generated upon increases of added antioxidants to a Cu(II) containing solution. In this work, an electrochemical alternative to quantify this complex is presented using cyclic voltammetry and chronoamperometry, compared with the classical spectroscopic determinations by UV-Vis. The final results show that the analysis performed by electrochemical methodologies is statistically similar, affording an efficient determination the total antioxidant capacity.     

Electrochemical Cyclization of Adrenaline,the Simplest Derivatization for its Selective Determination

Electrochemical techniques are the most reliable techniques for determination of neurotransmitters and selective determination is their most challenging issue. Herein we have optimized the condition for oxidation of adrenaline and noradrenaline, as the most similar neurotransmitters, to find a simple and fast technique for their selective determination. Under mild acidic condition, oxidation of adrenaline is followed by a cyclization reaction and oxidation of the product (ECE mechanism) whereas noradrenaline undergoes just oxidation (E mechanism). The redox potential of the product of ECE mechanism has 350 mV difference with the product of E mechanism. This different in reactivity and redox potential yields two baseline separated reduction peaks for the oxidation products of adrenaline and noradrenaline, which used for their selective determination.     

Electrochemical Redox Behaviour of Temozolomide Using a Glassy Carbon Electrode

The electrochemical behaviour of temozolomide on a glassy carbon electrode has been investigated. The reduction of temozolomide is an irreversible process, pH dependent, and the mechanism involves the addition of one electron and one proton to C5 to form an anion radical, causing the irreversible breakdown of the tetrazinone ring. The oxidation mechanism of temozolomide is an irreversible, adsorption‐controlled process, pH dependent up to value close to the pK_a and occurs in two consecutive charge transfer reactions, with the formation of the hydroxylated product. The electroanalytical determination of TMZ led to a detection limit of 1.1 µM.     

Electrochemical Analysis of Liposome-encapsulated Colistimethate Sodium

In this study, the neutral and cationic liposomal formulations of Colistimethate sodium (CMS), an antibiotic for multi-drug resistant gram-negative bacteria, were prepared and electrochemical quantification of CMS from these liposomes were achieved. This is the first study of the electrochemical detection of CMS released from liposomes. First, the electrochemical properties of CMS were analysed, then the encapsulation efficiency, and the release kinetic of CMS from liposomes were determined with Differential Pulse Voltammetry (DPV) measurements. In addition, Cyclic Voltammetry were applied to determine oxidation signal of CMS. A higher encapsulation efficiency was found in the cationic liposome compared to the neutral liposome. Moreover, CMS was controlled released from liposomes with zero-order drug release kinetics.     

Electrochemical Kinetic Characterization of Redox Mediated Glucose Oxidase Reactions: A Simplified Approach

One of the main drawbacks affecting first‐generation electrochemical biosensors in the analysis of real matrices is the interference of electroactive species present in the sample under investigation. Several approaches have been attempted to overcome this problem in the past ten years but the best results were achieved by using mediated based electrochemical biosensors. Despite this, the kinetic of the redox mediators‐enzymatic proteins interaction has not been studied deeply enough. In this work we have developed a theoretical‐methodological approach for the characterization of the kinetic of interaction between redox enzymes and substrates and/or redox mediators. Particularly, the interaction of glucose oxidase (GOx) with several commercially available redox mediators has been studied by means of amperometry and cyclic voltammetry. The main kinetic parameters for different mediators were exploited and discussed with the aim of finding the best mediator for a glucose biosensor to be used on real samples.     

水介质中吡咯的电化学聚合反应

研究了扫描电位上限对循环伏安法制备聚吡咯膜性能的影响，吡咯在水溶液中于玻碳电极表面化学聚合的起始电位为0．58V，在聚吡咯（Ppy）修饰电极表面聚合的起始电位为0．55V，当聚合电位上限在0．80V以上时，Ppy的氧化还原反应可逆性变差，同时，氧化电位过高将导致Ppy膜导电性能下降；研究了聚合介质对循环伏安法制备导电聚吡咯膜的影响，实时观察了吡咯（Py）聚合过程溶液中质子含量的动态变化，发现Py聚合伴随有质掺杂←→释放过程；结合Ppy膜的元素分析、ESR分析和IR光谱分析，总结出了水介质中电化学聚合高导电性聚吡咯膜的条件。     

AQUEOUS POLYMERIZATION OF METHYL METHACRYLATE INITIATED BY TITANIUM(III)—SALICYLALDOXIME REDOX SYSTEM: A KINETIC STUDY

The polymerization of methyl methacrylate initiated by the titanium(III)-salicylaldoxime redox system was studied in an aqueous sulfuric acid-ethanol medium in the temperature range of 20–30°C. The rates of polymerization were investigated at various concentrations of reductant, oxidant, ethanol, sulfuric acid, and monomer. Cyclic voltammetric sensing of salicylaldoxime kinetic conditions demonstrated its reduction behavior. From the results obtained, it was inferred that the polymerization reaction was initiated by an organic free radical arising from the titanium(III)-salicylaldoxime redox system and termination took place predominantly by mutual coupling and small fraction by chain transfer mechanism involving solvent molecules. The effects of some water-miscible organic solvents and surfactants on the rate of polymerization were investigated. The temperature dependence of the rate was studied and the activation parameters were computed using Arrhenius and Eyring plots. A suitable kinetic scheme has been proposed on the basis of experimental observations.     

Characterization of Carbon Film Electrodes for Electroanalysis by Electrochemical Impedance

The interfacial behavior of electrodes fabricated from carbon film resistors of 2 and 20 Ω in supporting electrolyte solutions of varying pH used in electroanalytical experiments has been characterized by electrochemical impedance spectroscopy with complementary cyclic voltammetric experiments. Equivalent circuits are proposed to fit the experimental data and the influence of electrode pretreatment has also been investigated.     

电化学合成金属醇盐的研究

纳米材料在生物、电子、能源、化工等各个领域的应用日益广泛 ,已成为当前研究的热点 [1,2 ] ,纳米材料的制备有多种方法 ,其中溶胶 -凝胶 ( Sol- gel) [3 ] 、醇盐热解、化学气相淀积 ( CVD)等方法所使用的前驱体主要为金属醇盐 .传统化学方法合成金属醇盐是用 MXn[X为 Hal,R,H,NR2 ,N( Si Me3 ) 2等 ]与醇进行交换反应 ,过程复杂 ,且原材料不易得到 ,产率低 ,纯度达不到要求 ,后续分离繁琐 ,所以人们一直努力寻找合成金属醇盐的新方法 .有机电解合成一般在常温常压下进行 ,可通过调节电极电位控制电极反应的方向和速度 .据报道 [4] …     

A Self‐contained Two‐electrode Nanosensor for Electrochemical Analysis in Aqueous Microenvironments

We describe the development, fabrication, and characterization of a novel two‐electrode nanosensor contained within the tip of a needle‐like probe. This sensor consists of two, vertically aligned, carbon structures which function as individual electrodes. One of the carbon structures was modified by silver electrodeposition and chlorination to enable it to function as a pseudo‐reference electrode. Performance of this pseudo‐reference electrode was found to be comparable to that of commercially available Ag/AgCl reference electrodes. The unmodified carbon structure was employed as a working electrode versus the silver‐plated carbon structure to form a two‐electrode sensor capable of characterizing redox‐active analytes. The nanosensor was demonstrated to be capable of electrochemically characterizing the redox behavior of para‐aminophenol (PAP) in both bulk solutions and microenvironments. PAP was also measured in cell lysate to show that the nanosensor can detect small concentrations of analyte in heterogenous environments. As the working and reference electrodes are contained within a single nanoprobe, there was no requirement to position external electrodes within the electrochemical cell enabling analysis within very small domains. Due to the low‐cost manufacturing process, this nanoprobe has the potential to become a unique and widely accessible tool for the electrochemical characterization of microenvironments.     

Oxidation of Flavonols in an Electrochemical Flow Cell Coupled Online with ESI‐MS

Flavonols, a class of flavonoids, are jointly responsible for antioxidant activities as free radical acceptors in flowers, fruits and vegetables. Due to their electroactive behaviour, the oxidation of chrysin, flavonol, kaempferol, morin, quercetin and myricetin in methanol was performed in an electrochemical flow cell with glassy carbon as the working electrode. This flow cell was coupled online with electrospray ionisation mass spectrometry to identify the possible oxidation products. Based on these experiments, it was concluded that when certain structural requirement are present, the initial electrode reaction of flavonols involves an electron delivery electrochemical step followed by a chemical step via methanol addition. The redox activity of the selected species explains the number of observed multiple methoxylation. Moreover, we identified a second two‐electron, two‐proton oxidation of the formed oxidation products of quercetin and myricetin for the first time.     

Electrochemical and Spectroscopic Studies of Co(CREATININE)2Cl2

The electrochemical behavior of Co(creatinine)₂Cl₂ was investigated by cyclic voltammetry in organic solvents (DMSO and DMF) and in aqueous solution. Analysis of the results indicates that the electroactive species depend on the nature of the solvent. In DMF a single reduction process Co(II)/Co(I) is observed. In DMSO the redox behavior of the complex changes with the scan rate and a two-electron transfer process can be eventually observed. In aqueous solution the complex immediately decomposes giving rise to the aquo-cation. The characteristic peak of the redox couple Cl₂/Cl^? is observed as a consequence of the chloride released from the coordination sphere. Analysis of the electronic spectra gave additional support to the proposed mechanisms. The Co-Cl and Co-N stretching bands were clearly identified in the low frequency region of the IR spectrum.     

Study of the Electrochemical Behavior of Biodiesel Microemulsion

Microemulsions have become a widely employed technique for the control of biodiesel quality but are still poorly understood as regard to their electrochemical behavior. In this work, we report the fundamental importance associated with the knowledge of electrochemical behavior of microemulsions composed of water in the presence of a supporting electrolyte, soybean biodiesel and propan‐1‐ol as consolute, along with the ferrocyanide–ferricyanide redox system applied as probe. The voltammetric results showed that for different compositions of microemulsions, variation in peak currents and change in system reversibility as well as in the electron transfer process were clearly noted. Furthermore, through the study of the diffusion coefficient, three different types of microemulsions including Oil/Water, Bicontinuous, and Water/Oil were successfully identified. Electrochemical impedance spectroscopy studies were also carried out aiming at obtaining more information regarding the electrode/solution interface. All the studies performed demonstrated that different types of microemulsions were formed upon exerting a direct influence on the electrochemical behavior of the redox probe. These results, in essence, point to the possibility of choosing a more suitable and advantageous microemulsion type for the development of an analytical method, as in the case, for example, of the microemulsions ME‐2 and ME‐3 which presented high voltammetric response in redox probe oxidation.     

Electrochemical Characteristics of a Triphenylamine Derivative by Microelectrode Voltammetry

With the objective of understanding the kinetic redox properties of triphenylamine derivatives in association with chemical reactions, for their future application in functional organic semiconductor devices, the electrochemical characteristics of 4‐(2,2‐diphenylethenyl)‐N,N‐bis(4‐methylphenyl)‐benzenamine (TPA) were evaluated. Based on cyclic voltammograms of TPA on Pt disk electrodes with diameters of 300 μm and 10 μm at slow and fast scan rates in an acetonitrile solution, the TPA^.+ is stable, while the TPA²⁺ is unstable. Importantly, the unstable TPA²⁺ appears to break down by a subsequent chemical reaction. A Cottrell plot analysis from chronoamperometry of a solution containing TPA reveals that both the first and second oxidations are one‐electron reactions. Concerning the stabilization mechanism of the first oxidation state of TPA, the results of molecular orbital calculations indicate that the electrons of the HOMO level are distributed in the triphenylamine group, which induces a resonance‐stabilized TPA^.+. Based on these results, TPA/TPA^.+ is suggested to have a sufficient stability for further application in organic semiconductor devices.     

Electrochemical behavior of glassy carbon electrodes modified by electrochemical oxidation

Glassy carbon electrodes were modified electrochemically by pretreatment in sulfate, phosphate or carbonate solutions by means of cycling the potential well into the positive limit of the solvent. Electrodes treated in this manner were then used to incorporate and concentrate a variety of redox species that were either cations or aromatic containing compounds, including Ru(bpy)²⁺₃, Ru(NH₃)³⁺₆, Cu(NH₃)²⁺₄, ferrocene, methylviologen, 1,4-benzoquinone, anthraquinone-2-sulfonate, riboflavin, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Surface-equivalent concentrations ranged from 5 × 10^?9 to 1 × 10^?7 mol cm^?2 for electrodes pretreated for 10 min in sulfuric acid. An E_1/2 vs. pH study of 1,4-benzoquinone, riboflavin, FMN and FAD in modified electrodes shows that the pK_a values shift toward higher pH (nearly 2 pH units). Results concerning the incorporation of redox compounds detected only by mediation with other electroactive complexes and the study of the modified electrodes in electrocatalysis are also discussed.     

Challenge Approach of an Inexpensive Electrochemical Sensor for Rapid Selective Determination of two Non‐classical β‐Lactams in Presence of Different Degradants and Interference Substances

An inexpensive stability−indicating anodic voltammetric method for rapid determination of two non‐classical β ‐lactam antibiotics; Meropenem (MP) and Ertapenem (EP) has been developed and validated. The method was based on the enhancement of voltammetric response at a disposable graphite pencil electrode (GPE). Differential pulse voltammetric (DPV) method was developed for quantification of both drugs in B−R buffer solution (pH 2.0) at GPE. The GPE displayed very good voltammetric behavior with significant enhancement of the peak current compared to glassy carbon electrode (GCE). Stress stability studies were performed using 0.5 M of either HCl or NaOH and H₂O₂. Mass and infrared spectroscopy were used for identification of degradants and their pathways were illustrated. Under optimal conditions, the peak currents showed a linear dependence with drug concentrations. The achieved limits of detection (LOD) were 1.23, 2.07 and 1.50 μM for MP and two waves of EP, respectively. The developed voltammetric method was successfully applied for direct determination of MP and EP in drug substances, pharmaceutical vials and in presence of either their corresponding hydrolytic, oxidative‐degradants or interfering substances with no potential interferences. The differential pulse voltammograms were highly advantageous and applicable in QC laboratories for rapid, selective micro‐determination of MP and EP.     

Fabrication of Au‐Nanoparticle/TiO2‐Nanotubes Electrodes Using Electrochemical Methods and Their Application for Electrocatalytic Oxidation of Hydroquinone

Gold nanoparticle (Au‐NPs)‐Titanium oxide nanotube (TiO₂‐NTs) electrodes are prepared by using galvanic deposition of gold nanoparticles on TiO₂‐NTs electrodes as support. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy results indicate that nanotubular TiO₂ layers consist of individual tubes of about 60–90 nm diameters and gold nanoparticles are well‐dispersed on the surface of TiO₂‐NTs support. The electrooxidation of hydroquinone of Au‐NPs/TiO₂‐NTs electrodes is investigated by different electrochemical methods. Au‐NPs/TiO₂‐NTs electrode can be used repeatedly and exhibits stable electrocatalytic activity for the hydroquinone oxidation. Also, determination of hydroquinone in skin cream using this electrode was evaluated. Results were found to be satisfactory and no matrix effects are observed during the determination of hydroquinone content of the “skin cream” samples.     

Syntheses,Spectral, Thermal and Electrochemical Studies of 3-Carboxylacetonehydroxamic Acid and its Iron(Ii), Cobalt(Ii), Nickel(Ii), Copper(Ii) and Zinc(Ii) Complexes

3-Carboxylacetonehydroxamic acid (CAHA) and its iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes were synthesized and characterized by elemental analysis, UV-Vis and IR spectra and magnetic susceptibility. The pK _a1 and pK _a2 values of the ligand in aqueous solution were found to be 6.5 ± 0.1 and 8.6 ± 0.1, which correspond to dissociation of carboxyl and hydroxamic protons, respectively. The dianion CAH acts as a tetradentate ligand through the hydroxamate and carboxylate groups and coordinates to the divalent metal ions, forming coordination polymers with a metal-to-ligand ratio of 1 : 1 in the solid state. FTIR spectra and thermal decomposition of the ligand and its metal complexes were recorded and briefly discussed. The electrochemical behavior of the complexes was investigated by square wave voltammetry and cyclic voltammetry at neutral pH. In contrast to the solid state, the iron(II) and copper(II) cations form stable complex species with a metal-to-ligand ratio of 1 : 2 in solution. The iron(II), cobalt(II) and nickel(II) complexes show two-electron irreversible reduction behavior, while the copper(II) and zinc(II) complexes undergo quasi-reversible and reversible electrode reactions, respectively. The stability constants of the complexes were determined by square wave voltammetry.