Sharif Digital Repository

The electrochemical behavior of catechol in the presence of propylthiouracil (PTU) and methylthiouracil (MTU) at a glassy carbon electrode is thoroughly investigated. The cyclic voltammetric studies of the systems are performed in different pHs and sweep rates. The results of the voltammetric foundations show an electrocatalytic oxidation of catechol in the presence of PTU and MTU, leading to a remarkable increase in the anodic peak current of catechol together with the contemporaneous disappearance of the corresponding cathodic wave. The presented mechanism shows the nucleophilic addition/reduction of the electro-generated o-quinone by the PTU or MTU, which produced chemically reduced... 

The mechanism of electrochemical behavior of catechol in the presence of thiaproline is investigated by cyclic voltammetry, controlled-potential coulometry and spectrophotometric tracing of the reaction coordinate. The results indicate that thiaproline participate in with an ECEC mechanism in a nucleophilic (Michael) addition to o-quinone. Effect of pH of buffer solution on reaction pathway is studied and showed that addition of thiaproline to the o-quinone is performed only in solutions with pHs higher than 5. These results indicate that the addition of thiaproline is occurred first from amine functional group. In the second step, the addition of carboxylate group of thiaproline to C-5 of... 

A novel electrochemical sensor based on nanocellulose-carbon nanoparticles (NC-CNPs) nanocomposite film modified glassy carbon electrode (GCE) is developed for the analysis of metoclopramide (MCP). Atomic force microscopy, scanning electron microscopy and electrochemical impedance spectroscopy were used to characterize the roughness, surface morphology and performance of the deposited modifier film on GCE. SEM image demonstrated that modifier nanoparticles are uniformly deposited on GCE, with an average size of less than 50nm. The electrochemical behavior of MCP and its oxidation product is studied using linear sweep and cyclic voltammetry over a wide pH range on NC-CNPs modified glassy... 

Nowadays cobalt is mostly produced through the electrowinning process of sulfate solutions. Regarding to the competition between the precipitation of cobalt ions and evolution of hydrogen gas on the cathode surface during the reduction process in a sulfate bath, investigation on the mechanism of metal precipitation is of great importance. In the present work, study on the kinetics of cobalt electrowinning and the mechanism of the involved reactions have been carried out. The obtained results, confirm the mechanism of cobalt precipitation by depletion of hydroxides. The effects of temperature and scan rate parameters were studied on electrowinning of cobalt by cyclic voltammetry technique.... 

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 pKa 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  

A multi-walled carbon nanotube paste electrode (MWCPE) is prepared as an electrochemical sensor with high sensitivity and selectivity in responding to isoniazid. The electrochemical oxidation of isoniazid is investigated in buffered solution by cyclic and differential pulse voltammetry. The electrode is shown to be very effective for the detection of isoniazid in the presence of other biological reductant compounds. The electrochemical oxidation of cysteine, due to the high overvoltage, is completely stopped at the surface of MWCPE. The electrode exhibits a very good resolution between the voltammetric peak of isoniazid and the peaks of ascorbic acid (AA) and dopamine (DA). A resolution of... 

A carbon-paste electrode chemically modified with a Schiff-base complex of cobalt (cobalt(II)-4-chlorosalophen, CoClSal) is utilized to investigate the voltammetric response of propylthiouracil (PTU). The mechanism of electrocatalytic oxidation of the compound is investigated by means of cyclic voltammetric studies applying various pHs to the buffered solutions. The modified electrode exhibits effective catalytic properties that lower the anodic overpotential and enhance the rate of electron transfer for the electrochemical oxidation of PTU. The results of the cyclic voltammetric (CV) and differential pulse voltammetric (DPV) techniques showed that the modified electrode exhibits good... 

Electrochemical oxidation of acetaminophen (N–acetyl–p–aminophenol) (1) has been studied in the presence of dimethylamine (2) as a nucleophile in aqueous solution, by means of cyclic voltammetry and controlled-potential coulometry. The results indicate the participation of electrochemically generated N-acetyl-p-quinoneimine (1a) in Michael reaction with dimethylamine (2). Based on ECE mechanism, the observed homogeneous rate constant (kobs) of the above mentioned reaction is estimated by comparing the experimental cyclic voltammograms with the digital simulated results. Further more; kinetics and mechanism of the reaction were studied with ab initio calculation, Monte Carlo and QM/MM... 

A glassy carbon electrode (GCE) was modified with a thin layer of multiwalled carbon nanotubes (MWCNTs) and subsequently, electrochemically deposited poly-pyrrole. The electrochemical behavior of mesalazine was studied on the surface of the modified electrode by applying linear sweep voltammetry (LSV). The electropolymerization process and the electrochemical response toward mesalazine were investigated in the presence of different aromatic anion dopants including, benzenesulfonic acid (BSA), 1,3-benzenedisulfonic acid (1,3-BDSA), 1,5-naphthalenedisulfonic acid (1,5-NDSA) and new coccine (NC). By using 1,5-NDSA as dopant, a significant increase (~418 times) in the peak current of mesalazine... 

Nanodiamond-graphite (NDG) decorated with Ag nanoparticles (AgNPs-NDG) was prepared and used to construct a novel sensitive sensor for the voltammetric determination of thioridazine (TR). The results indicate a remarkable increase in the oxidation peak currents together with a negative shift in the oxidation peak potentials, in comparison to the bare pyrolytic graphite electrode. Remarkable enhancement in microscopic area of the electrode along with strong adsorption of TR on the surface of the modified electrode resulted in a considerable increase in the peak current of TR. The surface morphology and the nature of the composite film deposited on PGE were characterized by scanning electron... 

We have prepared a pyrolytic graphite electrode (PGE) whose surface is covered with a thin film of a nano-mixture of graphite/diamond (NGD). The electrode is shown to be capable of electrochemically sensing of tryptophan (TRP) and 5-hydroxytryptophan (HTRP). The presence of the NGD film resulted in a remarkable increase in the peak currents and sharpness of the waves so that submicromolar concentrations of TRP and HTRP become detectable. Potential scan rates, the pH of the solution, the accumulation conditions and the amount of the modifier were optimized via cyclic voltammetry. Linear sweep voltammetry, under optimized accumulation time and in open circuit operation, was applied to the... 

The electrochemical response of sodium levo-thyroxin (T4) at the surface of an edge plane pyrolytic graphite (EPPG) electrode is investigated using cyclic voltammetric technique in the presence of 0.1M HCl as supporting electrolyte. T4 underwent totally irreversible oxidation at this system and a well-defined peak at 821mV was obtained. Compared to the signals obtained in the optimized conditions at bare glassy carbon and carbon paste electrodes, the oxidation current of T4 at an EPPG electrode was greatly enhanced. The electrochemical process of T4 was explored and the experimental conditions were optimized. The oxidation peak current represented a linear dependence on T4 concentration from... 

This work describes the development of a novel electrochemical sensor based on electrodeposition of copper oxide nanoparticles onto carbon nanoparticle (CNP) film modified electrode for the analysis of the anti-HIV drug, nevirapine (NEV). The electrochemical experiments were performed using linear sweep and cyclic voltammetry. Atomic force microscopy was applied for surface characterization of the deposited modifier film (CuO-CNP) on glassy carbon electrode (GCE). No oxidation peak was observed for NEV on the bare GCE, but both CNP-GCE and CuO-CNP-GCE showed a distinctive anodic response towards NEV with considerable enhancement (276-fold and 350-fold, respectively) compared to CuO-GCE. The... 

The electrochemical behavior of the anti-inflammatory drug piroxicam is studied at the surface of a plain pyrolytic graphite electrode modified with chitosan-doped carbon nanoparticles. An electroactive surface was produced by drop-casting a suspension of the modifier and characterized by atomic force microscopy. A remarkable enhancement is found in studies on the cyclic voltammetric response towards piroxicam. This is described on the basis of the thin-layer mass transport regimes within the porous films, which leads to a considerable increase in the active surface area of the electrode. The electrode shows a linear response to piroxicam in the range of 0.05-50 μM, with a detection limit of... 

A novel voltammetric biosensor based on nano-TiO2/nafion/carbon nanoparticles modified glassy carbon electrode (TiO2/N/CNP/GCE) was developed for the determination of dobutamine (DBA). Characterization of the surface morphology and property of TiO2/N/CNP layer was carried out by the scanning electron microscopy and atomic force microscopy. The electrochemical performance of the modified electrode was investigated by means of the cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy techniques. Effective experimental variables, such as the scan rate, pH of the supporting electrolyte, drop size of the casted modifier suspension and accumulation... 

A modified glassy carbon electrode with a film of nano diamond-graphite nano mixture decorated with Ag nanoparticles (AgNPs-NDG/GCE) was constructed and used for sensitive voltammetric determination of ceftizoxime (CFX). Morphology of AgNPs-NDG/GCE has been examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Experimental variables such as deposited amount of the modifier suspension, pH of the supporting electrolyte and accumulation potential and time were optimized by monitoring of CV and LSV responses of CFX. The results illustrate that AgNPs-NDG/GCE exhibits an excellent electrocatalytic effect in the electro-oxidation of CFX that leads to a considerable... 

The complexes of zinc tetraphenylporphyrin (ZnTPP) with the azacrown macrocycles bearing pyridine moiety (bp, 1p) as the axial ligand were synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, IR, 1H and 13C NMR, fluorescence, UV–Vis, together with TD DFT calculations. Solution study by employing 1H NMR spectroscopy for ZnTPPbenz and ZnTPPH complexes elucidated that the pyridine moiety was bonded through the fifth-coordination site on the zinc metal atom. The observation of hypsochromic shifts of ca. 15 nm for Q(0,1) (the strongest emission) as well as ca. 15 nm for Q(0,0) (the second) bands testified to significant difference in the fluorescence of ZnTPPbenz... 

This paper reports on a novel low-temperature method for preparing curcumin-reduced graphene oxide (Cur-rGO) from graphene oxide (GO) and investigates their cyclic voltammetry (CV) and photoluminescence (PL) properties. GO sheets were synthesized using modified Hummers’ method and then were chemically reduced using polyphenol curcumin into graphene sheets. Atomic force microscopy, transmission electron microscopy and x-ray photoelectron spectroscopy were used to confirm the formation of Cur-rGO and revealed their functionalization with polyphenol curcumin. The electrochemical and optical properties of the Cur-rGO sheets were investigated using CV and PL spectroscopy. According to the PL and... 

The electrochemical behavior of a tin electrode in citric acid solutions of different concentrations was studied by electrochemical techniques. The E/I curves showed that the anodic behavior of tin exhibits active/passive transition. Passivation is due to the formation of Sn(OH)4 and/or SnO2 film on the electrode surface. Addition of NaCl to citric acid solution, enhances the active dissolution of tin and tends to breakdown the passivity at a certain breakdown potential. Cyclic voltammetry and galvanostatic measurements allow the pitting potential (Epit) and the repassivation potential (Erp) to be determined. Potentiostatic measurements showed that the overall anodic processes can be... 

Ultrathin carbon nanoparticle-poly(diallyldimethylammonium chloride) films (CNP-PDDAC films) are formed on tin-doped indium oxide (ITO) electrodes in a layer-by-layer electrostatic deposition process employing 9-18 nm diameter carbon particles. Transparent and strongly adhering films of high electrical conductivity are formed and characterized in terms of their electrochemical reactivity. When immersed in aqueous 0.1 M phosphate buffer pH 7, each layer of CNP-PDDAC (of ca. 5-6 nm average thickness) is adding an interfacial capacitance of ca. 10 μF cm-2. Absorption into the CNP-PDDAC nanocomposite film is dominated by the sites in the PDDAC cationomer and therefore anionic molecules such as...