Voltammetry Studies Research Articles

Diarylamines with switchable intramolecular H-bonding: a new approach to molecular logic gates

New ortho-substituted diarylamines prone to different types of the intramolecular H-bonding (IMHB) were obtained. In-depth NMR, IR and voltammetry study allowed selecting the amine that demonstrates stable reversible switching of the IMHB bond under the external stimuli, which can be used for the logic gate construction.

Effects of N-functional groups on the electron transfer kinetics of VO2+/VO2+ at carbon: Decoupling morphology from chemical effects using model systems

Carbons and nanocarbons are important electrode materials for vanadium redox flow battery applications, however, the kinetics of vanadium species are often sluggish at these surfaces, thus prompting interest in functionalization strategies to improve performance. Herein, we investigate the effect of N-functionalities on the VO2+/VO2+ redox process at carbon electrodes. We fabricate thin film carbon disk electrodes that are metal-free, possess well-defined geometry and display smooth topography, while featuring different N-site distribution, thus enabling a mechanistic investigation of the intrinsic surface activity towards VO2+/VO2+. Voltammetry and electrochemical impedance spectroscopy show that N-functionalities improve performance, with pyridinic/pyrrolic-N imparting the most significant improvements in charge transfer rates and reversibility, compared to graphitic-N. This was further supported by voltammetry studies on nitrogen-free electrodes modified via aryldiazonium chemistry with molecular pyridyl adlayers. Computational modeling using an electrochemical-chemical mechanism indicates that introduction of surface pyridinic/pyrrolic-N can increase the heterogeneous rate constants by approximately two orders of magnitude relative to those observed at nitrogen-free carbon (k0 = 1.29 × 10−4 vs 9.34 × 10−7 cm/s). Simulations also suggest that these N-functionalities play a role in affecting reaction rates in the chemical step. Our results indicate that nitrogen incorporation via basic functional groups offers an interesting route to the design of advanced carbon electrodes for VRFB devices.

Dysprosium particles decorated Ambroxol imprinted polymer sensor to detect carbide-treated mango

In this study, an important mucolytic agent Ambroxol (AMB) has been identified as an artificial ripening marker (ARM) of Himsagar mango. A rare earth dysprosium oxide decorated polyacrylamide cross-linked AMB-imprinted sensor (Dy2O3 @AMB-IP) has been developed. The AMB-IP has been characterized using Fourier transform infrared (FTIR) spectroscopy, and Field emission scanning electron microscopy (FESEM). Carried out to study its analytical performance (buffer variation, scan rate variation). Also, the sensing characteristics (repeatability, reproducibility, stability, selectivity) of the sensor have been studied using differential pulse voltammetry. Novel biomimetic recognition by imprinted polymer has been tailor-made to selectively detect AMB using a voltammetry study. The sensor is repeatable and reproducible with a relative standard deviation of 1.16%, and 0.71%, respectively. Also, it beholds a wide linear detection range (10 μM – 500 μM) with a limit of detection of 6.48 μM/L. Finally, the response of the sensor was correlated to high-resolution liquid chromatography/ mass spectrometry results of Himsagar mango and showed satisfactory results with a correlation factor of 0.99.

Preparation and Properties of Three Plasticiser-Free Novel Di-benzo-18-Crown-6 Aldimine-Derived Lead(II) Ion-Selective Electrodes

Three novel dibenzo-18-crown-6 aldimines were successfully synthesised and structurally characterised via various spectroscopic methods (1H,13H NMR, FT-IR) and their solution phase lead binding behaviours probed via absorption spectroscopy, the results are supported by Density Functional Theoretical (DFT) modelling. These methods revealed that the asymmetric nature of these compounds is such that at equilibrium the ether cavity adopts an open configuration where the constituent oxygen atoms exhibit a highly negative electrostatic potential; hence, they spontaneously (ΔG~−58 kJ mol−1) interact/bind aqueous lead ions to form stable 2:1 metal–ligand complexes. As indicated by cyclic and square voltammetry studies, all compounds are redox active and polymerise relatively easily onto a platinum surface to form a multi-layered lead Ion-selective Membrane (ISM), the structure of which is confirmed by Scanning Electron Microscopy (SEM) and Electrochemical Impedance Spectroscopy (EIS). These novel Ion-selective Electrodes (ISEs), as characterised by Differential Pulse Anodic Stripping Voltammetry (D PASV), allow selective electrochemical detection and quantification of lead at concentrations as low as 10 ppm, over a range of 15–60 ppm, with only minimal interference from mercury(II) and aluminium(III) ions at a 1:1 analyte-interferent ratio.

The Importance of Electrode Material in Bioelectronic Electrophoretic Ion Pumps

AbstractBioelectronic ion pumps deliver ions and biomolecules from a source to a target biological system with high spatiotemporal control for bioengineering and regenerative medicine applications. A voltage between a working electrode and a reference/counter electrode delivers the charged ions and biomolecules from a source to the desired target. The source and the target are separated by an ion exchange membrane so that only the charged molecules of interest are delivered. Future wearable and implantable applications require high efficiency of delivery to minimize power consumption. The majority of recent efforts on improving ion pump efficiency have focused on optimizing the ion exchange membrane. However, the contribution of the working electrode material to the ion pump efficiency has been mostly overlooked. This work identifies how changing the working electrode material greatly affects the efficiency of delivery in ion pumps. With an electrical circuit model analysis, voltammetry studies on silver, platinum, and palladium hydride working electrodes, and implementation of the Butler–Volmer equation, results show that the material‐dependent equilibrium potential at the working electrode surface has a large impact on ion pump efficiency. With this knowledge, a simple predictive model to optimize the working electrode material for delivering each specific ion or molecule of interest is designed.

Mathematical Modeling of ROS Production and Diode-like Behavior in the SDHA/SDHB Subcomplex of Succinate Dehydrogenases in Reverse Quinol-Fumarate Reductase Direction

Succinate dehydrogenase (SDH) plays an important role in reverse electron transfer during hypoxia/anoxia, in particular, in ischemia, when blood supply to an organ is disrupted, and oxygen is not available. It was detected in the voltammetry studies about three decades ago that the SDHA/SDHB subcomplex of SDH can have such a strong nonlinear property as a "tunnel-diode" behavior in reverse quinol-fumarate reductase direction. The molecular and kinetic mechanisms of this phenomenon, that is, a strong drop in the rate of fumarate reduction as the driving force is increased, are still unclear. In order to account for this property of SDH, we developed and analyzed a mechanistic computational model of reverse electron transfer in the SDHA/SDHB subcomplex of SDH. It was shown that a decrease in the rate of succinate release from the active center during fumarate reduction quantitatively explains the experimentally observed tunnel-diode behavior in SDH and threshold values of the electrode potential of about -80 mV. Computational analysis of ROS production in the SDHA/SDHB subcomplex of SDH during reverse electron transfer predicts that the rate of ROS production decreases when the tunnel-diode behavior appears. These results predict a low rate of ROS production by the SDHA/SDHB subcomplex of SDH during ischemia.

Size-dependent electrochemical kinetics of nano-granular WO3 thin films

Electrochromic devices are mainly investigated for energy harvesting and saving applications. Electrochromic supercapacitors (ECSC) attract smart electronics device applications by integrating electrochromic materials into energy storage devices. WO3 has been predominantly investigated materials for this application. Amorphous, transparent WO3 thin films owing to diffusive charge storage kinetics with improved active sites promote the better intercalation of Li+ ions in the porous surface area, which yields electrochromic supercapacitive performance. In the present study, WO3 thin films were prepared by electrodeposition and studied for their physicochemical, electrochemical, and electrochromic properties. Electronic properties of WO3 thin films were measured by using electrochemical impedance spectroscopy (EIS) in terms of density of states [D(Ef)] at the Fermi level. Charge storage kinetics of WO3 thin films studied by EIS corroborated with the voltammetry studies. The WO3 electrode exhibits wide optical modulation (∼90%) with the highest coloration efficiency (η) of 132.89 cm2/C, including higher areal capacitance of 39.81 mF/cm2 and volumetric capacitance of 180.91 mF/cm3 at 20 mV/s scan rate with the capacitance retention up to 83% after 1000 CV cycles.

Unraveling the Atomic Redox Process in Quantum Conductance and Synaptic Events for Neuromorphic Computing

AbstractManipulation of atomic point contact (APC) in memristive devices is considered as an essential approach in emulating biological synaptic functions and paves the way for developing neuromorphic computing systems. In this article, the conductance modulation in a polyvinylimidazole (PVI)‐based memristor that mimics the synaptic functions underlying the sensory memory, short‐term memory, long‐term memory, and forgetting events of the human brain, is demonstrated. A detailed analysis of resistive switching, quantum conductance, and synaptic behaviors in the silver (Ag) included PVI memristor is investigated by means of DC sweep and pulse current–voltage (I–V) measurements. Based on the synaptic plasticity of the Ag‐PVI memristor, the biological synaptic functions such as learning and forgetting two images are mimicked using 5 × 5 synaptic memristor arrays. To explain the relationship between the atomic redox process and synaptic events in the memristor, the I–V/cyclic voltammetry study is introduced. As a consequence, the concentration of charges in the APC region increases as the conductance state increases. This study is essential in order to explore the progressive growth of APC under confined redox reaction in the electrochemical metallization‐based memristors for developing both synaptic devices and high‐density multilevel memories.

Quantitative Analysis of Pb(II) Based on Differential Pulse Anodic Stripping Voltammetry and IIP-Carbon Paste Electrodes

It is well known that Pb(II) is considered a highly toxic metal. The slight difference between toxic and permissible levels in drinking water is a matter of concern; therefore, highly sensitive and selective techniques have been proposed for quantification, such as the electrochemical ones. In this work, an easy, simple, low-cost, and high selective sensor based on carbon paste electrodes (CPE) and ion-imprinted polymers (IIP) is proposed for Pb(II) analysis in real water samples. Recognition cavities, selective to Pb(II), were synthesized based on a cross-linked polymer using vinyl pyridine. A modified CPE was constructed by a mixture of graphite powder, IIP, and paraffin oil. By voltammetry studies, a notable difference was observed in the electrochemical response of the electrodes modified with IIP and those with non-imprinted polymer (NIP), confirming the existence of the recognition cavities in the IIP. The construction and analysis parameters related to the analytical response of Pb(II) (anodic current intensity of stripping voltammetry), were optimized; the selectivity was also studied considering potential interference ions. A linear concentration range from 3.3 mg l−1 to 33 mg l−1 and a limit of detection of 0.99 mg l−1 were achieved. Pb(II) was successfully quantified in real complex samples without previous treatment.

Diffusion behavior of oxygen in the electro-deoxidation of uranium oxide in LiCl-rich melt

The role of oxygen in the electrolytic reduction of uranium oxide in molten salt has received increased attention in recent years. In contrast to solubility, few studies were reported on the kinetic property of oxygen in LiCl. In this work, diffusion behaviors of oxygen anion in the bulk salt and oxide cathode were both studied. A gold working electrode was used to conduct corresponding voltammetry studies in LiCl-rich melt at 923 K. The obtained diffusion coefficient increased when another salt (KCl or LiF) was introduced to LiCl. A model based on ohmic, concentration and electrochemical polarizations was derived and used to describe the electro-deoxidation of uranium oxide in molten salt. By analyzing experimental current-time curves obtained from potentiostatic electrolysis, parameters such as exchange current density, conductivity of porous uranium filled with electrolyte and diffusion coefficient of oxygen anion in porous uranium were calculated. Taken together, the behavior of oxygen in the electro-deoxidation of uranium oxide in LiCl-rich melt can be better understood.

Electrochemistry as a Complementary Technique for Revealing the Influence of Reducing Agent Concentration on AgNPs.

The synthesis process of AgNPs has been attracting a lot of attention in the fields of biosensors/sensors, diagnostics, and therapeutic applications. An attempt to understand the effect of different concentrations of reducing agents on the synthetic design process has been made. In this paper, we gather information on voltammetry studies and relate it with UV–vis and scanning electron microscopy (SEM) analyses. Given the kinetics, localized surface plasmon absorption (LSPR) band, and narrow size distribution of these methods, it was possible to compare the obtained measurements and clearly distinguish sizes and aggregation. AgNPs measured by SEM showed a statistically significant reduction of the nanoparticle sizes from 65 to 37.5 nm as the reducing agent increased. Well-matched d-spacing data calculated from selected area electron diffraction (SAED) patterns and X-ray diffraction (XRD) were obtained for all of the samples. The UV–vis studies showed that the SPR bands shift toward the blue region as the reducing agent concentration is increased, indicating a decrease in particle sizes. It is worth emphasizing that cyclic voltammetry (CV) and differential pulse voltammetry (DPV) coincide well with SEM on the aggregation of AgNPs at higher concentrations. A 10 mM reducing agent concentration resulted in uniform outcomes for producing AgNPs with the smallest size in terms of full width at half-maximum (FWHM) in all of the methods used in this study, while UV–vis band gaps increase with increasing reducing agent concentration. In agreement with all of the methods investigated, the results suggested that the best concentration of the reducing agents is 10 mM for a target application. These findings suggest the usefulness of voltammetry as a complementary method that can be used as a qualitative guide to identify the size and aggregation of NPs.

Cobalt (II), Nickel (II) and Copper (II) complexes of Tetradentate Schiff bases ligands derived from 4-Nitro-O-phenylenediamine: Synthesis, Characterization, cyclic voltammetry and biological studies

Cobalt (II), Nickel (II) and Copper (II) complexes of Tetradentate Schiff bases ligands derived from 4-Nitro-O-phenylenediamine: Synthesis, Characterization, cyclic voltammetry and biological studies

Synthesis and antioxidant activity of six novel N-ferrocenylmethyl-N-(nitrophenyl)- and -N-(cyanophenyl)-acetamides: Cyclic voltammetry and molecular docking studies

Cyclic voltammetry (CV) assays were performed to measure superoxide anion radical (O–2-) scavenging activities of six novel N-ferrocenylmethyl-N-(nitrophenyl)-acetamides and N-fer­rocenylmethyl-N-(cyanophenyl)acetamides (FMA1-FMA6), followed by molecular docking simulations and in silico toxicity prediction. The obtained values of IC50 from CV assays indicated that all studied compounds showed promising scavenging activity against O.2- radicals, with the compounds FMA1, FMA3, and FMA4 possessing the most significant potency. A molecular docking study revealed that all compounds interact with amino acid residues of glutathione reductase via hydrogen bonding and hydrophobic interactions. The compound FMA4 was the most inactive compound against the glutathione reductase enzyme having the highest inhibitory concentration of 2.61 µM and the lowest docking score of -31.85 kJ/mol. Toxicity studies demonstrated that among six studied compounds, FMA4, FMA5, and FMA6 are predicted to be nontoxic.

Diazepam attenuates the effects of cocaine on locomotion, 50-kHz ultrasonic vocalizations and phasic dopamine in the nucleus accumbens of rats.

Currently, there is no effective drug to treat cocaine-use disorder, which affects millions of people worldwide. Benzodiazepines are potential therapeutic candidates, as microdialysis and voltammetry studies have shown that they can decrease dopamine concentrations in the nucleus accumbens of rodents and block the increase in dopamine levels and appetitive 50-kHz ultrasonic vocalizations (USVs) induced by amphetamine in rats. Here, we tested whether administration of 2.5-mg·kg-1 diazepam (i.p.) in adult male rats could block the effects of 20-mg·kg-1 cocaine (i.p.) on electrically evoked phasic dopamine signals in the nucleus accumbens measured by fast-scan cyclic voltammetry, as well as 50-kHz USV and locomotor activity. Cocaine injection increased evoked dopamine signals up to threefold within 5 min, and the increase was significantly higher than baseline for at least 75 min. The injection of diazepam, 5 min after cocaine, attenuated the cocaine effect by nearly 50%, and this attenuation was maintained for at least 40 min. Behaviourally, cocaine increased the number of appetitive 50-kHz calls by about 12-fold. Diazepam significantly blocked this effect for the entire duration of the session. Also, cocaine-treated rats were more active than controls and diazepam significantly attenuated cocaine-induced locomotion, by up to 50%. These results suggest that the neurochemical and psychostimulant effects of cocaine can be mitigated by diazepam. This article is part of a themed issue on Building Bridges in Neuropharmacology. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.8/issuetoc.

Functionalized Carbon Nanotubes for Chemical Sensing: Electrochemical Detection of Hydrogen Isotopes

In this study, we propose a palladium-functionalized CNT composite working as a sensitive material to evaluate the deuterium concentration in aqueous samples. The sensitive material was prepared by the deposition of Pd nanoparticles onto MWCNT–OH by the micellization process. A modified electrode was prepared by drop casting 60 μL of Pd-decorated MWCNT suspension on a clean glassy carbon electrode surface. The sensing behavior was investigated in a series of deuterium-enriched solutions ranging from 25 to 10,000 ppm. We performed cyclic voltammetry and impedance spectroscopy studies on the samples. The process is quasi-reversible with the reduction curve more pronounced than the oxidation curve, which indicates a low tendency to desorption for the hydrogen atoms.

Surfactant-free synthesis of carbon-supported silver (Ag/C) nanobars as an efficient electrocatalyst for alcohol tolerance and oxidation of sodium borohydride in alkaline medium

We have synthesized carbon-supported silver (Ag/C) nanobars by a simple surfactant-free hydrothermal method using glucose as the reducing reagent as well as the source of carbon in Ag/C nanobars. Physicochemical characterization of the materials was performed by X-ray Diffraction (XRD), field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The XRD pattern confirmed the presence of a pure metallic silver phase. No carbon phase was detected, which indicates that the carbon exists mainly in the amorphous form. The electrocatalytic activity of Ag/C in different electrolyte solutions such as 0.5 M NaOH, 0.5 M NaOH + 1 M ethanol (EtOH), 0.5 M NaOH + 1 M ethylene glycol (EG), and 0.5 M NaOH + 0.01 M NaBH4 (sodium borohydride) was studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA) study. Alcohol tolerance of the catalysts was also established in the presence of ethanol and ethylene glycol. The forward-to-backward current ratio from cyclic voltammetry (CV) study of Ag/C-20 (20 h) in 0.5 M NaOH + 1 M ethanol solution at 100 mV s−1 scan rate is 4.13 times higher compared to that of Ag/C-5 (5 h). Hence, Ag/C-20 is a better candidate for the tolerance of ethanol. In the presence of ethylene glycol (1 M) in 0.5 M NaOH solution, it is obtained that the forward-to-backward current ratio at the same scan rate for Ag/C-20 is lower than that in the presence of ethanol. The durability of the catalyst was studied by chronoamperometry measurement. We studied the electrochemical kinetics of Ag/C catalysts for borohydride oxidation in an alkaline medium. The basic electrochemical results for borohydride oxidation show that Ag/C has very well strength and activity for direct borohydride oxidation in an alkaline medium. The reaction of borohydride oxidation with the contemporaneous BH4−. hydrolysis was noticed at the oxidized silver surface. Among all the synthesized Ag/C catalysts, Ag/C-20 exhibited the best electrocatalytic performance for borohydride oxidation in an alkaline medium. The activation energy and the number of exchange electrons at Ag/C-20 electrode surface for borohydride electro-oxidation were estimated as 57.2 kJ mol−1 and 2.27, respectively.

The DNA- and protein-binding properties and cytotoxicity of a new copper(II) hydrazone Schiff base complex

A new monomeric copper(II) benzhydrazone complex, [Cu(L)(H2O)(NO3)] (1), has been synthesized using Schiff base derived from quinoline-2-carboxaldehyde and benzhydrazide. Complex 1 was characterized by elemental analysis, FT-IR, UV-Vis spectroscopy along with electrochemical study and single-crystal X-ray crystallography. Single-crystal diffraction study of 1 indicates that the copper(II) ion adopts a distorted square pyramidal (SQP) geometry. The calf-thymus (CT) DNA-binding property of 1 has been evaluated by employing UV-vis and fluorescence spectroscopy, cyclic voltammetry and viscosity studies. The protein-binding ability of 1 was investigated by UV-vis and fluorescence spectroscopy titration using BSA and HSA. The significant interaction of 1 with CT-DNA was further supported by molecular docking approach. Finally, in vitro cytotoxicity of 1 was investigated by MTT assay on the Human Skin Carcinoma cell line A431. All these facts indicate that 1 exhibits a promising anticancer activity.

Current efficiency and mass transfer effects in electrochemical oxidation of C1 and C2 carboxylic acids on boron doped diamond electrodes

The oxidation of acetic, glycolic, glyoxylic, oxalic and formic acid has been studied on boron doped diamond electrodes. Our voltammetry study on rotating disk electrodes highlights clear differences between the carboxylic acids (formic, oxalic, glyoxylic and glycolic acid) that can be oxidized via a direct electron transfer (DET) and acetic acid which can presumably solely be oxidized by •OH radicals formed in the region where water oxidation takes place. In glycolic and glyoxylic oxidation oxalic acid is the main intermediate formed. Surprisingly, glyoxylic acid could not be detected as an intermediate in the glycolic acid oxidation. Chronoamperometric experiments confirm that all compounds except acetic acid react further to CO2, which could be deduced from the electron balances. It was shown that formic, oxalic, glyoxylic and glycolic acid can be selectively oxidized at 2.3 V vs. Ag/AgCl with high current efficiencies, below or close to mass transfer limiting rates. At higher potentials (2.4 V and 2.5 V) simultaneous water electrolysis results in lower current efficiencies. At these potentials the conversion rates can exceed the limiting rates, which might be attributed to effects related to water oxidation (i.e. O2 evolution and •OH radical formation).

Microwave Assisted Chemical Modification of Graphite Oxide for Supercapacitor Application

In present work, graphite oxide was chemically modified with boron, nitrogen and sulfur co-doping in a simple, single step green method by microwave treatment. Borax, urea and thiourea were used as precursors for doping. Mixtures of graphite oxide with precursors were microwave treated using domestic microwave oven at 800 W for 5 min. The products obtained were characterized for its morphology, structure, composition and electrical properties. The results showed that simultaneous reduction of graphite oxide and doping of boron, nitrogen and sulfur were occurred. The elemental doping distorts the structure without much affecting the crystalline nature. The boron, nitrogen and sulfur elements were doped in graphite oxide to the extent of 9.97 at%, 2.67 at% and 0.84 at%, respectively. The cyclic voltammetry and electrochemical impedance spectroscopy studies showed that boron, nitrogen and sulfur co-doped graphite oxide could be a suitable material for supercapacitor application.

Electricity from lignocellulosic substrates by thermophilic Geobacillus species

Given our vast lignocellulosic biomass reserves and the difficulty in bioprocessing them without expensive pretreatment and fuel separation steps, the conversion of lignocellulosic biomass directly into electricity would be beneficial. Here we report the previously unexplored capabilities of thermophilic Geobacillus sp. strain WSUCF1 to generate electricity directly from such complex substrates in microbial fuel cells. This process obviates the need for exogenous enzymes and redox mediator supplements. Cyclic voltammetry and chromatography studies revealed the electrochemical signatures of riboflavin molecules that reflect mediated electron transfer capabilities of strain WSUCF1. Proteomics and genomics analysis corroborated that WSUCF1 biofilms uses type-II NADH dehydrogenase and demethylmenaquinone methyltransferase to transfer the electrons to conducting anode via the redox active pheromone lipoproteins localized at the cell membrane.