Cyclic Voltammetric Studies Research Articles

Voltammetric Determination of Ophthalmic Drug Dexamethasone Using Poly-glycine Multi Walled Carbon Nanotubes Modified Paste Electrode

Background: Dexamethasone has been used in ophthalmology for the treatment of different eye diseases and it is a powerful synthetic member of the glucocorticoid class of steroid medicament having anti-inflammatory and immunosuppressant characteristics. The aim of this study is to develop a rapid, sensitive and selective voltammetric method for its determination using polygylcine-multi walled carbon nanotubes (polyglycine-MWCNTs) modified paste electrode. Methods: The electro-activity and the voltammetric behavior of dexamethasone on the polyglycine- MWCNTs electrode were deduced by cyclic voltammetry (CV), square wave stripping voltammetry (SWSV), differential pulse voltammetry (DPV) and linear sweep voltammetry (LSV). The method permits accurate and sensitive detection of the ophthalmic drug dexamethasone in the presence of ascorbic acid, dopamine and uric acid from the generated anodic peaks at +950 mV, +740 mV and +700 mV, respectively. Results: The cyclic voltammetric study indicates that dexamethasone created a single anodic peak at about +1100 mV in pH 3 B-R solution and none of the cathodic peak appeared in the subsequent reverse scan. The detection and quantification limits measured for LSV were 0.087 mg/L and 0.29 mg/L, respectively. The extent of recoveries in the presence of equal amounts (1:1 mass ratio) of ascorbic acid, dopamine and uric acid were calculated as 98.28 ± 0.45, 94.46 ± 1.77 and 98.57 ± 0.60%, respectively. The voltammetric procedure was also applied to dexamethasone spiked urine samples(5.0 mg/L) and the percent recovery was determined as 95.2% with the relative standard deviations of 3.29%. Conclusion: Sensitive and selective voltammetric method was proposed for the direct determination of dexamethasone. The modified polyglycine-MWCNTs paste electrode enabled the direct determination of dexamethasone in the presence of biological molecules such as ascorbic acid, dopamine and uric acid. Keywords: Dexamethasone, ophthalmic drug, modified electrode, voltammetry, determination, carbon nanotubes.

Square Wave Voltammetric Determination of Ibuprofen at Poly(L-Aspartic Acid) Modified Glassy Carbon Electrode

A simple and fast modification of bare glassy carbon electrode (GCE) by electropolymerization of L-aspartic acid (L-Asp) using cyclic voltammetry was reported for the detection of ibuprofen (IBP). The poly(L-Asp)/GCE was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and electroactive surface area measurements. The cyclic voltammetric and square wave voltammetric study of IBP in 0.25-M acetate buffer solution at pH 4 showed an obvious electrocatalytic effect toward IBP oxidation, which resulted in a higher current response and a negative shift in the peak potential, at the polymer film modified electrode compared with the bare GCE. Under the optimized conditions, a calibration curve was obtained by the square wave voltammetry at the poly(L-Asp)/GCE. The square wave voltammetric peak current linearly varied with IBP concentrations in the range of $1.0 \times 10^{-6}$ M to $1.5 \times 10^{-4}$ M with the limit of detection (3S b /m) and the limit of quantification (10S b /m) of $2.2 \times 10^{-7}$ and $7.4 \times 10^{-7}$ M, respectively. The method was successfully applied for the determination of IBP in pharmaceutical formulations and biological samples with satisfactory recovery values, 90%–108%. The proposed sensor also demonstrated good selectivity, repeatability, and reproducibility with appreciable long term stability.

Electrochemical Behavior of Aromatic Compounds on Nanoporous Gold Electrode

This study aimed at investigating the electrochemical behavior of benzene and its substituted derivatives on nanoporous gold and assessing the possibility of utilizing this electrode as a platform for simultaneous detection of different aromatic compounds. Cyclic voltammetric studies were performed with benzene, hydroquinone, catechol, phenol, 2-aminophenol, 2-chlorophenol as well as their mixtures on the nanoporous gold prepared from dealloying of AuxSi1-x films. The nanoporous structure was found to provide enhanced electro-oxidation of hydroquinone, catechol, phenol, 2-aminophenol and 2-chlorophenol and remarkable fouling resistance in the electro-oxidation of phenol and 2-aminophenol compared to the compact and flat gold electrode. Interestingly, oxidation potentials of these aromatics appear to be affected significantly by the attachment of functional groups to the benzene ring. Based on the onset oxidation potentials, the easiness of oxidation at nanoporous gold was found to follow the order: hydroquinone > catechol > 2-aminophenol > 2-chlorophenol, phenol > benzene. Moreover, nanoporous gold was found to be advantageous over nanoporous platinum for potential application in simultaneous analysis employing voltammetric techniques as it could offer discernable peak potential separation in the electro-oxidation of the different aromatics.

Enhanced and Synergistic Catalysis of Green Synthesized Pd-Ag Alloy Nanoparticles for Anodic Oxidation of Propan-2-ol in Alkali

Bimetallic PdxAgy alloy along with monometallic Pd, Ag nanoparticle were synthesized in a single pot using a green synthetic protocol in absence of any capping agent. X-ray diffraction and microscopic studies of synthesized material demonstrate the formation of nanoballs with radius of ca 25 nm of face centred cubic metals and alloys. The electrochemical studies of as-synthesized materials loaded on carbon support reveal that the Pd4Ag nanoparticles exhibit the best and synergistic electro-catalytic activity in reference to oxidation of propan-2-ol in alkali. The most active Pd4Ag nanoparticles show higher peak current (124.54mAmg-1) in comparison to that (92.54mAmg-1) of Pd in cyclic voltammetric study (CV). The electrode shows the highest exchange current density (0.284mAmg-1of Pd) for propan-2-ol oxidation reaction. CV studies of reaction product reveal that Ag accelerates the formation of acetone rather than carbonate elucidating the plausible mechanism of the reaction. These findings have important implications for further fine-tuning of the Pd nano alloys toward highly active and selective catalysts for alcohol fuel cells.

Synthesis, Spectroscopic, Structural Characterization, Conductivity and Electrochemical Studies of a Schiff Base Ligand and Its Copper Complexes

Schiff base ligand (L) derived from glyoxal and 4-aminoantipyrine was synthesized. The ligand (L) has been characterized by IR, NMR, electronic spectral studies and electrochemical studies. Cu(II) complexes of a Schiff base ligand (L) from 4-aminoantpyrine and glyoxal having the composition [CuL1]X2 where X = Cl¯ or NO3¯ have been prepared and characterized by elemental analysis, electrical conductivity in non-aqueous solvent, infrared and electronic, as well as cyclic voltammetric studies. L acts as a neutral tetradentate ligand coordinating through both the carbonyl oxygen and azomethine nitrogen. On both the complexes both the anions are not coordinated. A square planar geometry is assigned for complexes. The electrochemical studies of ligand show a typical cyclic voltammogram for an irreversible process. While copper(II) complexes show the typical cyclic voltammograms for quasi reversible process.

Microwave hydrothermal synthesis of α-MnMoO4 nanorods for high electrochemical performance supercapacitors.

Pristine α-MnMoO4 nanorods were facilely prepared via co-precipitation (Cp) and microwave hydrothermal (MH) methods. X-ray diffraction (XRD) patterns showed pure monoclinic crystalline phase α-MnMoO4 for the heat treated powder at 500 °C. Fourier Transform Infrared (FTIR) spectra showed that the chemical bond structure of α-MnMoO4 corresponds to the strong vibrational modes of Mo–O–Mo, Mo–O and Mo Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O. Raman spectra showed the structural bonding and crystalline nature of α-MnMoO4. Field Emission Scanning Electron Microscope (FE-SEM) images exposed the nanorod shape of the α-MnMoO4 powder, with diameters of ∼200 nm and lengths of ∼1.6 μm. Electrochemical studies of the Cp- and MH-MnMoO4 nanorods with 2 M NaOH as the electrolyte showed specific capacitances of 143 F g−1 and 551 F g−1, respectively, at a 1 A g−1 constant discharge current density. Cyclic voltammetric (CV) studies of the MH-MnMoO4 nanorods at various scan rates revealed the presence of redox pairs, suggesting a pseudocapacitive nature. The structural stability at different current densities demonstrated the high rate performances and good reversible capacity retention of the calcined MH-MnMoO4 nanorods. A cycling life stability study of MH-MnMoO4 demonstrated a good capacity retention of 89% of the initial specific capacitance at 5 A g−1 after 1000 cycles.

Voltammetric study of multiwalled carbon nanotube modified screen printed carbon electrode for the determination of a phytoconstituent wedelolactone

Multiwalled carbon nanotube based screen printed sensor was fabricated and utilized for the cyclic voltammetric (CV) study of a phytoconstituent wedelolactone (WDL). The analyte system was studied with Britton Robinson buffer as the supporting electrolyte. Square wave voltammetry (SWV) technique was performed for the optimization of the pH, where the pH (2.5) of the system was optimized for further investigation of the analyte system. Multiwalled carbon nanotube modified screen printed electrode (M-SPE) offered high sensitivity towards WDL as compared to the bare screen printed electrode (SPE). Voltammetric studies with M-SPE revealed the oxidation of WDL with two oxidation peaks (a1and a2) with Ea1 = 0.08V and Ea2 =0.5 V with scan rate varying from 10-120 mV/s and exhibits diffusion-controlled process.

Cyclic Voltammetric Studies of Benzilic Acids and their Derivatives

Cyclic Voltammetric Studies of Benzilic Acids and their Derivatives

Cyclic voltammetric study of the influence of porosity on electrochemical response of nickel-alumina modified glassy carbon electrode

Pure and nickel-modified alumina powders with different porosity were synthesized and applied on the glassy carbon electrode by means of Nafion polymer. The data obtained from the nitrogen adsorption-desorption isotherm confirmed that the pore structures in these materials are complex and tend to be made up of interconnected networks of pores of different size and shape. The addition of Ni2+ ions caused the changes in the textural properties of the samples. The influence of porosity on the electrochemical behavior of modified electrodes in quasi-reversible process was tested by cyclic voltammetry. Numerical correlations between electrochemical responses of GCE modified with alumina samples and textural properties have been established.

Electrochemical oxidation pathway of the anti-cancer agent dasatinib using disposable pencil graphite electrode and its adsorptive stripping voltammetric determination in biological samples

The present study describes the use of pencil graphite electrode (PGE) for the investigation of electro-oxidation mechanism and voltammetric stripping determination of dasatinib (DST) in Britton-Robinson buffer solution (BR). Relating to cyclic voltammetric studies, an irreversible oxidation signal was obtained at about 1.0 V. The oxidation electrode process is adsorption-controlled and pH-dependent. For quantitative determination of DST, square wave adsorptive stripping voltammetry (AdsSWV) was employed in BR of pH 3.0. The oxidation peak current varies linearly with the DST concentration in the range of 0.0092 – 1.0 µM. Dedection (LOD) and quantification (LOQ) values are founded as 0.0028 µM and 0.0092 µM, respectively. The developed AdsSWV method based on disposible and cheap PGE was applied successfuly to the real urine samples and the recovery results are given in the range of 97.94% to 100.82%.

Electrochemical characterization of a Porphyridium cruentum-modified carbon paste electrode by cyclic voltammetry

ABSTRACTA carbon paste electrode was modified with red algal specie of Porphyridium cruentum and then characterization of its electrocatalytic activity was demonstrated with cyclic voltammetric studies of potassium ferricyanide (K3[Fe(CN)6]) system. Stable and fast response of modified electrode to redox couple of [Fe(CN)6]3−/[Fe(CN)6]4− was highlighted by performing experiments in comparison to bare carbon paste electrode. Fourier transform infrared spectra revealed the functional moieties of bare and modified electrode. Electrochemical surface area and surface coverage capacity were calculated for both electrodes. The effect of scan rate helped evaluate the nature of electrode process, electron transfer mechanism, and kinetic parameters (rate constant, charge transfer coefficient).

Hydrazinylpyridine based highly selective optical sensor for aqueous source of carbonate ions: Electrochemical and DFT studies

A series of new receptors PDZ1–3 based on 2-(arylidenehydrazinyl)pyridines have been designed and synthesized for the detection of biologically and environmentally important ions. The colorimetric detection of CO32− using neutral organic receptor PDZ-1 has been achieved with characteristic visual colour change from yellow to green accompanied by a large redshift of 215nm in absorption maxima. UV–Vis spectroscopic and cyclic voltammetric studies reveal the stoichiometry of binding and electrochemistry of host-guest complex formation. The binding constant was found to be 0.77×104M−2. In addition, electrochemical studies provide an insight into the stability of the complex. DFT studies performed on the PDZ-1 and PDZ-1−CO32− complex reveal the binding mechanism involved in the anion detection process. PDZ-1 is highly selective for carbonate and does not show any colorimetric response towards any other anions or cations, while PDZ-2 and PDZ-3 remain inactive in the ion detection process. The limit of detection (LOD) and limit of quantification (LOQ) of PDZ-1 for carbonate was found to be 0.11mM and 0.36mM respectively. Considerable binding constant and limit of detection make PDZ-1 to be used as a real time sensor for the detection of carbonate in environmental and biological samples.

Fabrication of an electrochemical biosensor with ZnO nanoflakes interface for methylglyoxal quantification in food samples.

Increased consumption of fried foods such as grilled chicken contains elevated levels of methylglyoxal (MG), which is associated with diabetes mellitus. Hence, in this work, glyoxalase 1(GLO 1) based, zinc oxide (ZnO) flakes interfaced mediator free electrochemical biosensor was developed to detect MG in grilled chicken. ZnO flakes were synthesized by direct precipitation method. X-ray diffractometer and field emission scanning electron microscope were used to study the structural and morphological characteristics of ZnO flakes. The immobilization of GLO 1 on Pt/ZnO flakes modified electrode was confirmed by Fourier transform infrared spectroscopy. Cyclic voltammetric and amperometric studies were carried out using Pt/ZnO flakes/GLO 1 working electrode. The developed biosensor exhibited linear range of 0.6-2.0µM, sensitivity of 0.281µAµM-1, LOD of 9nM with a response time of <4s and shelf life of 18days (89%).

Analytical Fukui and cyclic voltammetric studies on ferrocene modified carbon electrodes and effect of Triton X-100 by immobilization method

In the present work, we have used the analytical Fukui and cyclic voltammetry (CV) to understand the electron transfer (ET) nature of ferrocene (FC) on the FC modified carbon paste electrode (FMCPE). We have also studied the effect of TX-100 on the reactivity of FC molecule at the FMCPE interface. Frontier orbital energies (HOMO) and anodic peak potential of TX-100 associated FC results confirm that after the TX-100 association it is difficult to remove an electron from the FC. As a part of work, we have also sensed the partially aggregated ferrocene based on the reduction peak currents of ferrocenium (FC+) and FC+ formed by TX-100 associated FC. Throughout the work, theoretical and electrochemical results are in good agreement with each other.

Electrocatalytic Oxidation of Carbohydrates Mediated by Nitroxyl Radical‐modified Electrodes in Aqueous Solution

AbstractThe electrocatalytic activity of a 2,2,6,6‐tetramethylpipridine‐N‐oxyl (TEMPO)‐modified electrode toward the oxidation of carbohydrates in phosphate buffer solution was investigated under neutral aqueous solution conditions at 25 °C. The modified electrode was prepared on the surface of a glassy carbon electrode by the electrochemical polymerization of a TEMPO precursor containing a pyrrole side chain. Cyclic voltammetric studies showed that the anodic peak current increased with the concentration of carbohydrates in a dose‐dependent manner.

Independent Photochemical Generation and Reactivity of Nitrogen-Centered Purine Nucleoside Radicals from Hydrazines.

Photochemical precursors that produce dA• and dG(N2-H)• are needed to investigate their reactivity. The synthesis of two 1,1-diphenylhydrazines (1, 2) and their use as photochemical sources of dA• and dG(N2-H)• is presented. Trapping studies indicate production of these radicals with good fidelity, and 1 was incorporated into an oligonucleotide via solid-phase synthesis. Cyclic voltammetric studies show that reduction potentials of 1 and 2 are lower than those of widely used "hole sinks", e.g., 8-oxodGuo and 7-deazadGuo, to investigate DNA-hole transfer processes. These molecules could be useful (a) as sources of dA• and dG(N2-H)• at specific sites in oligonucleotides and (b) as "hole sinks" for the study of DNA-hole transfer processes.

Sensitive voltammetric determination of hydroxyzine and its main metabolite cetirizine and identification of oxidation products by nuclear magnetic resonance spectroscopy

The electrochemical detection and electrooxidation path of the first-generation antihistamine receptor hydroxyzine (HDZ) and its main metabolite cetirizine (CTZ) are addressed in this research. A carbon black-modified electrode to explore the electrochemical responsivity and electroanalytical detection of HDZ and CTZ was designed. Compared to the bare electrode, the irreversible anodic responses observed for HDZ and CTZ were considerably improved on the proposed carbon black-modified electrode, including twenty times enhancement of the anodic peak currents and the shifting of anodic peak potentials to less positive potentials. In order to identify the electrooxidation products resulting from the previously verified irreversible redox processes, cyclic voltammetric studies and potentiostatic electrolysis assays followed by products identification by nuclear magnetic resonance (NMR) spectroscopy were carried out. From the combination of electrochemistry and NMR spectroscopy data it was possible to propose electrooxidation reaction mechanisms for HDZ and CTZ molecules. By applying square-wave adsorptive anodic stripping voltammetry (SWAdASV) under optimized experimental conditions, the obtained analytical curves for HDZ and CTZ were linear from 2.99×10−7 to 9.81×10−6molL−1 and from 4.97×10−7 to 1.08×10−5molL−1, with limits of detection of 1.00×10−7molL−1and 4.00×10−7molL−1, respectively. Finally, spiked synthetic human biological fluids were analysed by the proposed SWAdASV procedures, with recovery percentages close to 100%.

Pd nanoparticles-embedded carbon nanotube interface for electrocatalytic oxidation of methanol toward DMFC applications

Pd nanoparticles-embedded multiwalled carbon nanotubes (Pd–MWCNTs) were synthesized via in situ chemical reduction method, which provided promising results for preparing finely divided and uniform sized Pd nanoparticles supported on MWCNTs. The Pd–MWCNT catalysts were synthesized in three different weight (wt) ratios of Pd and MWCNT (1:5, 2:5 and 3:5). Morphology and crystallinity of the catalysts were studied by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Electrocatalytic activity of these catalysts toward methanol oxidation was analyzed with two different dispersing agents, such as chitosan (CS, 0.1% w/v) and Nafion (Nf, 0.05% w/v), for the preparation of catalytic inks. Dramatic increases in the electrocatalytic activity of Pd–MWCNT–CS catalysts compared to Pd–MWCNT–Nf catalysts toward methanol oxidation were revealed from cyclic voltammetric, chronoamperometric and CO stripping analysis studies. The anodic peak current densities of the Pd–MWCNT (2:5 wt ratio) interface prepared with chitosan and Nafion inks in alkaline 1 M CH3OH were 2541 and $$1 0 4 1\,\,{\text{A}}\,\,\mathop {{\text{g}}^{ - 1} }\nolimits_{\text{Pd}}$$ , respectively. High CO tolerance of the Pd–MWCNT catalysts was ascertained from the ratio of peak currents and coulombic charges of forward and reverse scans (I f/I b and Q f/Q b) of CV studies and from the less positive potentials for CO stripping, as low as − 0.2 V versus Ag|AgCl. The steady-state current density for methanol oxidation at Pd–MWCNT–CS electrode is nearly five times higher than that of Pd–MWCNT–Nf electrode.

Synthesis, X-ray structure, spectroscopic, DFT study and catalytic activity of cis-[RuCl2(L)(EPh3)] complexes (E = P, As, Sb; L = NN′N″ tridentate azoimine-quinoline ligands)

Abstract New of complexes of formula cis-[RuCl2(L)(PPh3)] (C1–C5) where L = XC6H4N NC(COCH3) NC9H6N, X = H, L1 (C1); CH3, L2 (C2); Br, L3 (C3); CN, L4 (C4), F, L5 (C5)} and cis-[RuCl2(L1)(EPh3)] where E = As (C6); E = Sb (C7) have been synthesized by refluxing [RuCl2(EPh3)3 ] and L in a mixture of (5:1) chloroform/ethanol solution. The complexes have been characterized by the spectroscopic techniques (IR, NMR and UV–Vis) and geometries have been confirmed by X-ray crystal structures of cis-[RuCl2(L3)(PPh3)] (C3). The electronic structure, redox and absorption properties of the complexes have been explained based on DFT and TDDFT results. Cyclic voltammetric studies show one reversible Ru(III)/Ru(II) oxidation couple and two successive one electron reductions leading to the formation of L(0/−1) and L(−1/−2), respectively. The complexes cis-[RuCl2(L)(EPh3)](C1–C7) catalyze the transfer hydrogenation of acetophenone in 2-propanol at 86 °C and in the presence NaOCH3.

New anthracene based Schiff base ligands appended Cu(II) complexes: Theoretical study, DNA binding and cleavage activities

New anthracene based Schiff base ligands L1 and H(L2), their Cu(II) complexes [Cu(L1)Cl2] (1) and [Cu(L2)Cl] (2), (where L1 = N1,N2‐bis(anthracene‐9‐methylene)benzene‐1,2‐diamine, L2 = (2Z,4E)‐4‐(2‐(anthracen‐9‐ylmethyleneamino)phenylimino)pent‐2‐en‐2‐ol) have been prepared and characterized by elemental analysis, NMR, FAB‐mass, EPR, FT‐IR, UV–Vis and cyclic voltammetry. The electronic structures and geometrical parameters of complexes 1 and 2 were analyzed by the theoretical B3LYP/DFT method. The interaction of these complexes 1 and 2 with CT‐DNA has been explored by using absorption, cyclic voltammetric and CD spectral studies. From the electronic absorption spectral studies, it was found that the DNA binding constants of complexes 1 and 2 are 8.7 × 103 and 7.0 × 104 M−1, respectively. From electrochemical studies, the ratio of DNA binding constants K+/K2+ for 2 has been estimated to be &gt;1. The high binding constant values, K+/K2+ ratios more than unity and positive shift of voltammetric E1/2 value on titration with DNA for complex 2 suggest that they bind more avidly with DNA than complex 1. The inability to affect the conformational changes of DNA in the CD spectrum is the definite evidences of electrostatic binding by the complex 1. It can be assumed that it is the bulky anthracene unit which sterically inhibits these complexes 1 and 2 from intercalation and thereby remains in the groove or electrostatic. The complex 2 hardly cleaves supercoiled pUC18 plasmid DNA in the presence of hydrogen peroxide. The results suggest that complex 2 bind to DNA through minor groove binding.