Iron(I)-carbonyl clusters tethered to (trifluoromethyl)thiophenolates

Two diironhexacarbonyl clusters containing (trifluoromethyl)thiophenolates, as models for the active site of [Fe?CFe] hydrogenase enzyme, have been prepared and characterized. The crystal and electronic structures of the complexes have been probed by X-ray crystallography and spectroscopic methods. Cyclic voltammetric studies in the presence of acetic acid show that both compounds catalyze the electrochemical reduction of acetic acid to produce hydrogen with favorable overpotentials.     

Voltammetric Studies of the Interaction of Tris (1,10-phenanthroline) Cobalt (III) with Bovine Serum Albumin

Recently, the studies on the interaction of DNA with small molecules have been attracting much interest1-6. These researches not only gave the important information about thermodynamics and kinetics, but also can prompt the combination between the electrode substances and biomacromolecule with super catalysis and sensor character. It is of great significance in understanding energy conversion and metabolism in live body, biomolecular structure, various physical and chemical characters for e…     

High Sensitive Voltammetric Gentamicin Sensor using Poly (3-thiophenecarboxylic acid-co-3-methylthiophene) Modified Glassy Carbon Electrode

For the determination of gentamicin in biomedical applications, sensitive, fast and low cost voltammetric sensor has been developed. Prepared sensor was successfully used for determination of gentamicine in synthetic urine samples with different voltammetric measurement methods. Firstly, glassy carbon electrode was modified using cyclic voltammetry technique by electropolymerization of 3-thiophenecarboxylic acid and 3-methylthiophene. Then, optimization of the electrochemical parameters was carried out for modified electrode. With this modified electrode, gentamicin determination was performed in the linear range of 0.05–4.00 mM. The correlation coefficient, limit of detection and limit of quantitation were calculated as 0.9999, 0.039 mM and 0.129 mM, respectively.     

A New Type of Microelectrode-Ag-Hg(Film) Ring Electrode

In this paper, a new method for preparing Silver-Mercury(film) Microring Electrodes (SMRE) by chemical plating is presented. The cyclic voltammetric responses of benzoquinone on SMRE have been studied in detail. The results show that the reduction of benzoquinone in Mcllvaine buffer(pH=7.0) is a one-electron reversible reaction. Values of n and D₀ determined agree with those obtained by other electrochemical methods found in literature.     

Voltammetric characteristics of diazinon on carbon paste electrode modified with tris(ethylenediamine) cobalt(II) iodide

In this study, cyclic and differential pulse voltammetric methods were used to investigate the electrochemical behavior of diazinon at carbon paste electrode modified with tris(ethylenediamine) cobalt(II) iodide ([Co(en)₃]I₂). Cobalt complex showed an anodic peak at 620 mV (vs. Ag/AgCl, in KNO₃ 0.1 M as supporting electrolyte) at carbon paste modified electrode. In the presence of diazinon, anodic peak intensity increased with increasing concentration of diazinon that confirmed electrocatalytic activity of cobalt complex for oxidation of diazinon (EC’ mechanism). Under optimized conditions, a linear calibration curve for diazinon was obtained in the range from 0.05 to 27 mg/L with detection limit 0.0075 mg/L (3S _b /m). Applications of the modified electrode to the determination of diazinon in different water samples were also tested. The results showed a very good precision (RSD < 0.04%) and very stable voltammetric response towards diazinon.     

Potentiometric response mechanism of a poly(acrylamide)-phthalocyaninato tin(II) film coated platinum electrode in acetonitrile and N,N-dimethylacetamide.

A new sensor constructed by a platinum electrode coated with a non-plasticized poly(acrylamide) polymer (PAA) film coupled with phthalocyaninato tin(II) ([Sn(II)(pc)]) was developed. The potentiometric response behavior of this PAA-[Sn(II)(pc)] electrode for such anions as CN-, F-, Cl-, and Br- in dimethylacetamide and acetonitrile were investigated. The electrode showed a Nernstian response to CN- and F- and a quite poor response to Cl- and Br-. The mechanism of the peculiar selective response was studied by cyclic voltammetric and spectrophotometric methods. The voltammetric investigation suggested that the charge of the host compound in the sensor membrane had no effect on the potential response of the electrode. It was also found by a spectrophotometric investigation that the complexing of [Sn(II)(pc)] with CN- and F- lead to the selective response of the electrode. The motive force of the complexing was considered to be a ligand exchange of CN- or F- with molecules at the axial site of [Sn(II)(pc)] due to solvent effects to the interest anions.     

Electroanalytical determination of d(GCGAAGC) hairpin

Hairpins (or hairpin-like structures) may play a major role in expansion events of triplet repeat expansion diseases (X syndrome, Huntington's disease, Friedreich's ataxia). The d(GCGAAGC) fragment has been found in the replication origins of phage phiX 174 and herpes simplex virus, in a promoter region of an Escherichia coli heat-shock gene, and in rRNA genes. The paper deals with the application of electrochemical methods to the determination of the DNA heptamer-d(GCGAAGC) which forms very stable hairpin structure in aqueous solutions. On mercury electrodes, this hairpin provides voltammetric reduction signals of adenine and cytosine, and oxidation signals of guanine. Both signals have been studied by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and elimination voltammetry with linear scan (EVLS) in dependence on pH, accumulation time, scan rate, and loop sequences. The EVLS in combination with the adsorptive stripping was employed to the determination of the detection limit (LD) of this mini-hairpin (2 nM). Multidimensional voltammetric data were worked up by Fourier Transform (FT) and for the first coefficient a confidence ellipse was calculated in order to drop out some outlier data. The same method was used also for detection limit determinations. The values of LD obtained by two approaches were compared.     

Voltammetric,dynamic light scattering (DLS) and electrophoretic mobility characterization of FeS nanoparticles (NPs) in different electrolyte solutions

Voltammetric response of FeS nanoparticles (NPs) dispersion based on the oxidation exchange voltammetric peak between Hg electrode and FeS NPs at around ?0.45 V was studied in different electrolytes (chloride, acetate, perchlorate). Several experiments were designed to monitor in parallel to voltammetric measurements, physicochemical and surface characteristics of the formed FeS NPs (ζ-potential and size) under same experimental conditions. It was shown that recorded voltammetric peak produced by FeS NPs from bulk solution is changing with electrolyte concentration and composition, as well as observed size and ζ-potential of the studied FeS NPs. Our measurements indicate relationship between measured ζ-potential of FeS NPs dispersions and recorded voltametric peak charge and potential, pointing to a promising potential of voltammetry in characterization of physicochemical and surface chemistry features of metal sulphide NPs in water environment. The best voltammetric response is obtained in presence of small NPs, <100 nm.     

Detection of ferritin in human serum with a MAP-H(2)O(2)-HRP voltammetric enzyme-linked immunoassay system

A voltammetric enzyme-linked immunoassay based on new system of m-aminophenol (MAP)-H(2)O(2)-horseradish peroxidase (HRP) has firstly been developed and used for the detection of HRP, labelled HRP and ferritin in human serum. HRP or labelled HRP catalyzes the oxidation reaction of MAP with H(2)O(2), the product of which produces a sensitive voltammetric peak at potential of -0.46 V (vs. SCE) in Britton-Robinson (BR) buffer solution. By using this voltammetric peak, HRP can be measured with a detection limit of 9.5x10(-1) mU/l and a linear range of 2.5-2.5x10(2) mU/l. The detection limit to ferritin is 0.25 ng/ml and the linear range 0.25-320 ng/ml. The processes of the electro-reduction of the product of the enzyme-catalyzed reaction have been investigated in detail.     

Indirect electrochemical determination of antioxidant capacity with hexacyanoferrate(III) reduction using a gold nanoparticle-coated o-phenylenediamine-aniline copolymer electrode

In spite of the many unstandardized literature methods for the determination of the antioxidant activity/capacity (AOA/AOC) of food extracts, there are a very limited number of documented voltammetric nanosensors, despite the fact that commercial electrochemical devices for rapid AOA estimation are on the rise. The mechanism of the developed sensor is based on the chemical reduction of hexacyanoferrate(III) to hexacyanoferrate(II) by antioxidants, followed by the decrement of the cathodic current intensity of hexacyanoferrate(III) in proportion to antioxidant concentration. During voltammetric measurements, the surface of the glassy carbon electrode was coated with an o-phenylenediamine-aniline copolymer and gold nanoparticles were accumulated on this electrode surface to increase the conductivity. It was shown that the developed electrode gave a reversible voltammogram for the hexacyanoferrate(III)/(II) redox couple, and that the cathodic peaks due to strong antioxidants having a standard redox potential less than that of this couple (E^o < 0.36 V) continuously emerged at very close peak potentials. Single antioxidants as well as binary–ternary mixtures were analyzed with this electrode using square wave voltammetry. The trolox-equivalent antioxidant capacities of selected antioxidants were evaluated with this electrode. The modified voltammetric sensor allowed precise measurement of the total antioxidant capacity of plant tea samples such as green tea, lime, and coral moss, and was not interfered by the food preservative sulfite. The results of the developed voltammetric sensor were statistically compared with those of a reference differential pulse voltammetry-cupric reducing antioxidant capacity electrochemical method established in literature.     

Review of adsorptive stripping voltammetric methods for cobalt determination in the presence of a zinc matrix

Different polarographic and voltammetric methods for the determination of Co in the presence of a large excess of zinc are reviewed. Adsorptive stripping voltammetry with in-situ matrix exchange and catalytic adsorptive stripping voltammetric methods are recommended for monitoring Co traces in zinc plant electrolyte. The principles of the catalytic adsorptive stripping voltammetric methods for Co determination are presented. The correct selection of the investigated supporting electrolytes, enabling the monitoring of Co traces in a zinc plant electrolyte by means of catalytic adsorptive methods is also discussed. The catalytic adsorptive voltammetric procedures offer the possibility of the determination of Co or Co and Ni traces in metallic zinc and zinc salts.     

Electrochemical studies of potassium ferrate(VI)

The electrochemical reduction of potassium ferrate(VI) in 6N-KOH occurs in three steps, at approximately +0.3, ?0.7, and ?1.4 V vs. Hg/HgO, 6N-KOH. The first reduction appears as a voltammetric wave on a platinum electrode and the second two are observed as polarographic waves with a dropping mercury electrode. Controlled potential coulometric, voltammetric, and chronopotentiometric studies indicate the reduction proceeds stepwise first to iron(III), then to iron(II) and finally to iron(0).     

Investigation into the voltammetric behaviour and detection of selenium(IV) at metal electrodes in diverse electrolyte media

The voltammetric behaviour of selenium(IV) was studied at platinum and gold electrodes in sulphuric acid, perchloric acid and potassium chloride media as a basis for its voltammetric detection. The best voltammetric behaviour was recorded at gold electrodes with perchloric acid as the supporting electrolyte. The concomitant presence of metals, such as copper or lead, and of model biomolecules, such as bovine serum albumin, in the solution resulted in a deterioration of the electrochemical response for selenium(IV). Quantitative detection of selenium(IV) by square wave anodic stripping voltammetry at both a millimetre-sized gold disc electrode and a microband electrode array revealed linear responses to selenium concentration in the ranges 5–15 μM and 0.1–10 μM, respectively, with 60 s preconcentration. The sensitivities were 6.4 μA μM⁻¹ cm⁻² and 100 μA μM⁻¹ cm⁻² at the disc and the microband array, respectively. The detection limit at the microband electrode array was 25 nM, illustrating the potentiality of such microelectrodes for the development of mercury-free analytical methods for the trace detection of selenium(IV).     

Detection of TMV with ODA-H(2)O(2)-HRP voltammetric enzyme-linked immunoassay system

o-Dianisidine (ODA)-H₂O₂-horseradish peroxidase (HRP) voltammetric enzyme-linked immunoassay system has firstly been used for the detection of tobacco mosaic virus (TMV). HRP catalyzes strongly the oxidation reaction of ODA by H₂O₂, the product of which produces a sensitive second order derivative linear sweep voltammetric peak at potential of −0.56 V (versus SCE) in Britton–Robinson (BR) buffer. HRP activity has been measured with this voltammetric peak and TMV detected through immunoreaction. The detection limit for HRP is 9.25×10^-7 mU l⁻¹ and the linear range is 2.5×10⁻⁶–5.0×10⁻⁴ mU l⁻¹. The detection limit for the clarified TMV is 0.25 ng ml⁻¹ and the highest dilution ratio detected for the infected leaf sap is 1:8×10⁵. The sensitivity for TMV detection with this method is higher than that with the enzyme-linked immunosorbent spectrophotometric assay (ELISA) using ODA-H₂O₂-HRP system. The processes of the enzyme-catalyzed reaction and the electro-reduction of the product of the enzyme-catalyzed reaction have been described.     

Modification of Poly‐ and Oligosaccharides with Os(VI)pyridine. Voltammetry of the Os(VI) Adducts Obtained by Ligand Exchange

Polysaccharides and oligosaccharides were modified with Os(VI)pyridine complex followed by ligand exchange with different ligands such as 2,2′‐bipyridine or N,N,N′,N′‐tetramethylethylenediamine. The time of the modification was much shorter (taking about 15 min) then direct modification with the given Os(VI) complex. The resulting saccharide adducts were analyzed by voltammetric methods at carbon and mercury electrodes. The results showed that the proposed technique gives promise for a new approach to analysis of glycoproteins.     

The utilization of copper(II) phosphate for the anodic stripping voltammetric assay of alendronate sodium, desferrioxamine mesylate and lisinopril

A sensitive differential pulse anodic stripping voltammetric method is described for the determination of alendronate sodium, desferrioxamine mesylate and lisinopril. The procedure is based on the formation of labile drug-copper(II) complex when shaking with copper(II) phosphate suspension. The voltammetric peaks, which correspond to the reduction of the copper(II) moiety of the formed complexes are obtained at −153, −74 and −111 mV, respectively. The different experimental parameters have been carefully studied. The method has been fully validated. The limit of detection was as low as 8.6 ng ml⁻¹. The method has been applied successfully for the determination of the drugs in plasma and in their pharmaceutical preparations. The obtained results were compared statistically with those obtained from a published method, in case of AS, or the official USP methods, for the other two drugs.     

Voltammetry of Os(VI)‐Modified Polysaccharides

Polysaccharides (PSs), such as dextran, yeast mannan, starch and amylose, were modified with complexes of six‐valent osmium with nitrogen ligands [Os(VI)L] and voltammetric behavior of PS‐Os(VI)L adducts was studied at mercury and carbon electrodes. Using Os(VI)temed as a modification agent and adsorptive transfer stripping (ex situ) method it was possible to determine PSs at submicromolar concentrations directly in the reaction mixture in an excess of monomeric glucose or sucrose both at Hg and carbon electrodes. Conventional (in situ) PS determination in the reaction mixture was possible only with mercury electrodes. The above methods have great potentiality in biological research.     

Reduction of NO adlayers on Pt(110) and Pt(111) in acidic media: evidence for adsorption site-specific reduction

We present a combined in situ Fourier transform infrared reflection-absorption spectroscopy and voltammetric study of the reduction of saturated and subsaturated NO adlayers on Pt(111) and Pt(110) single-crystal surfaces in acidic media. The stripping voltammetry experiments and the associated evolution of infrared spectra indicate that different features (peaks) observed in the voltammetric profile for the electrochemical reduction of NO adlayers on the surfaces considered are related to the reduction of NO(ads) at different adsorption sites and not to different (consecutive) processes. More specifically, reduction of high- and intermediate-coverage (ca. 0.5-1 monolayers (ML)) NO adlayers on Pt(110) is accompanied by site switching from atop to bridge position, in agreement with the ultra-high-vacuum data. On Pt(111) linearly bonded (atop) NO and face-centered cubic 3-fold-hollow NO species coexist at high coverages (0.25-0.5 ML) and can be reduced consecutively and independently. On Pt(111) and Pt(110) electrodes, linearly bonded NO species are more reactive than multifold-bonded NO species. Both spectroscopic and voltammetric data indicate that ammonia is the main product of NO(ads) reduction on the two surfaces examined.     

A magnetostructural study of linear NiII MnIII NiII, NiII CrIII NiII and triangular Ni(II)3 species containing (pyridine-2-aldoximato)nickel(II) unit as a building block

Three trinuclear complexes, NiII MnIII NiII, NiII CrIII NiII and Ni(II)3 based on (pyridine-2-aldoximato)nickel(II) units are described. Two of them, and , contain metal-centers in linear arrangement, as is revealed by X-ray diffraction. Complex is a homonuclear complex in which the three nickel(II) centers are disposed in a triangular fashion. The compounds were characterized by various physical methods including cyclic voltammetric and variable-temperature (2-290 K) susceptibility measurements. Complexes and display antiferromagnetic exchange coupling of the neighbouring metal centers, while weak ferromagnetic spin exchange between the adjacent Ni II and Cr III ions in is observed. The experimental magnetic data were simulated by using appropriate models.     

Voltammetric behavior of vitamin B(2) on the gold electrode modified with a self-assembled monolayer of l-cysteine and its application for the determination of vitamin B(2) using linear sweep stripping voltammetry

The voltammetric behavior of Vitamin B(2) (VB(2)) has been studied at the gold electrode modified with a self-assembled monolayer of l-cysteine. The voltammetric responses are evaluated with respect experimental conditions, such as composition and pH of the supporting electrolyte, concentration of VB(2), accumulation potential and accumulation time. On basis of the voltammetric behavior a highly sensitive method is present for the determination of VB(2) by using linear sweep stripping volammetry. The method is suitable for the determination of VB(2) concentrations between 5.0x10(-11) and 5.0x10(-6) mol l(-1). And the detection limit can be reached to 2.5x10(-11) mol l(-1). The method is applied to determine the concentration of VB(2) in the tablets with satisfactory results.