The kinetics of electroreduction of peroxodisulfate anions on a mechanically renewed silver electrode is studied by voltammetric and impedance methods. Impedance diagrams obtained in the region of ...negatively charged metal surface are successfully modeled by the equivalent circuit formed by the solution resistance and also the reaction resistance connected in parallel with the constant-phase element substituted for the double layer capacitance. The analysis of experimental data carried out in terms of this circuit and their comparison with the literature data makes it possible to assume that the reduction kinetics of S2O 8 2− anions on this electrode can be adequately described in the framework of the phenomenological theory of slow discharge. The reasons for deviation of the literature data on the kinetics of this reaction on polycrystalline Ag electrode from the relationships following from the slow discharge theory are put forward and substantiated.
A series of neutral mononuclear complexes M{κ2S,S-S2C-piperazine-C2H4N=C(R)}n {R = Ph; M = Co(III) 1, Ni(II) 2, Cu(II) 3, Zn(II) 4; R = Naph; M = Co(III) 5, Ni(II) 6, Cu(II) 7, Zn(II) 8; n = 2 for ...2-4, 6-8 and n = 3 for 1, 5} bearing pendant Schiff base moieties were synthesized through self-assembly involving N-phenylmethylidene-2-piperazin-1-ylethanamine (L1) or N-naphthylmethylidene-2-piperazin-1-ylethanamine (L2) with two equivalents each of CS2 and corresponding metal acetates. The complexes 1-8 were characterized by microanalysis, ESI-MS, IR, 1H, 13C NMR, DEPT 135, UV-visible absorption, and emission spectroscopy. Complexes 1, 3, and 8 exhibit fluorescence emissions at 342, 344, and 348 nm upon excitation at 273 (for 1 and 3) and 263 (for 8) with concomitant Stokes shifts of 69, 71, and 85 nm. The spectral and magnetic moment data support octahedral geometry around Co(III) and square planar/tetrahedral geometry around other metal centers. Thermal stabilities of 1-8 have been investigated by thermogravimteric analysis. The cyclic voltammograms clearly suggest that the complexes exhibit electroreduction principally associated with pendant imine moieties except Cu(II) complex 7 which displays quasi-reversible reduction corresponds to the Cu(II)/Cu(I) redox couples, in addition to reversible electroreduction of pendant imine groups associated with the coordinated ligands.
This thesis describes investigations into the development of new electrochemical methodologies applicable to organic synthesis. Initial investigations were focused on the development of new ...strategies for the generation and utilisation of alkoxy radicals under electrochemical conditions. To this end, a new procedure for an electrochemical manganese-catalysed deconstructive chlorination of cycloalkanols was developed. In this study, tertiary cyclopropanols and cyclobutanols were conveniently converted into synthetically useful distally chlorinated ketones via alkoxy radical intermediates. This methodology utilises an inexpensive manganese (II) pre-catalyst to facilitate the synthesis of a diverse range of β- and γ-chloroketones (40 examples, 30-90% yield). Facile scale-up was also performed by employing a recirculating flow-electrochemistry system and mechanistic investigations, including the use of cyclic voltammetry, allowed the proposal of alkoxy radical intermediates. Further work on the electrochemical generation of alkoxy radicals was then performed to overcome the limitations associated with the manganese-catalysed method. This work centred around the use of cerium (III) or (IV) salts to generate alkoxy radicals under electrochemical conditions. Following these unsuccessful investigations, the development of a photoelectrochemical system for the cerium-mediated generation of alkoxy radicals was subsequently explored. Chapter 4 of this thesis then describes investigations into an electrochemical alkene hetero-difunctionalisation procedure that proceeds via a 1,4-nitrile migration. In this study, cyanohydrin substrates bearing a distal alkene were converted into synthetically useful 1,2-azidonitriles using a manganese (II) salt as an azide transfer reagent (28 examples, 27-75% yield). This methodology was then extended to perform electrochemical alkene sulfonylcyanation and trifluoromethylcyanation, as well as to access a trifunctionalised hexanenitrile from a functionalised malononitrile starting material. The utility of the products formed was demonstrated through orthogonal derivatisation, and mechanistic investigations, including cyclic voltammetry studies and a radical clock experiment, allowed the proposal of radical intermediates within the reaction mechanism.
A three-dimensional g-C3N4/MWNTs/GO hybrid modified electrode was constructed as an electrochemical sensor for the simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). ...Due to the high conductivity of MWCNTs and the strong synergy between g-C3N4 and GO, the combination of the three effectively improved the electrocatalytic activity of the modified electrode for the oxidation of AA, DA, and UA, and solved the problems such as overlapping anodic peaks. The electrochemical performance of the as-constructed sensor was investigated and optimized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The linear response range of AA, DA, and UA in the optimal condition was 0.2–7.5 mM, 2–100 μM, and 4–200 μM, respectively. The detection limits (S/N = 3) of AA, DA, and UA were 96, 0.22, and 1.36 μM, respectively. The recoveries of AA, DA and UA in serum samples from three groups were 92.82–106.50%, and the relative standard deviations were less than 2%. The results show that the as-constructed g-C3N4/MWNTs/GO modified electrode has the advantages of simplicity, high sensitivity and good selectivity, and can simultaneously determine AA, DA, and UA.
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•A three-dimensional g-C3N4/MWNTs/GO hybrid electrode was constructed as an electrochemical sensor.•g-C3N4/MWNTs/GO hybrid sensor can simultaneously determine DA, AA, and UA.•The recoveries of DA, AA and UA in serum samples from three groups were 92.82–106.50%.•g-C3N4/MWNTs/GO hybrid sensor has the advantages of simplicity, high sensitivity and good selectivity.
Detection of indole‐3‐acetic acid (IAA), as a phytohormone, is important for precision farming, plant phenotyping, and crop management. Herein, IAA was detected in bean and wheat plant seeds ...extractions using zinc oxide nanorods/carbon paste electrode (ZnO NRs/CPE). ZnO NRs/CPE showed excellent electrocatalytic activity, high sensitivity, and selectivity toward the oxidation of IAA. The linearity range was from 30.×10−8 to 5.0×10−6 M (r2=0.996, n=10), with a detection limit of 1.7×10−8 M. Moreover, ZnO NRs/CPE exhibited high reproducibility, with a standard deviation of 1.0 % for six successive measurements of IAA.
•Antioxidant capacity is an important property in the development of functional foods.•Electrochemical techniques applied to food and beverages were examined and discussed.•Electrochemical techniques ...exhibit good correlation with conventional methods.•Electrochemical assays are quick, simple, and demand little sample preparation.•Electrochemical techniques can be applied using simply a potentiostat.
The growing interest in functional foods had led to the use of analytical techniques to quantify some properties, among which is the antioxidant capacity (AC). In order to identify and quantify this capacity, some techniques are used, based on synthetic radicals capture; and they are monitored by UV–vis spectrophotometry. Electrochemical techniques are emerging as alternatives, given some of the disadvantages faced by spectrophotometric methods such as the use of expensive reagent not environmentally friendly, undefined reaction time, long sample pretreatment, and low precision and sensitivity. This review focuses on the four most commonly used electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, square wave voltammetry and chronoamperometry). Some of the applications to determine AC in foods and beverages are presented, as well as the correlation between both spectrophotometric and electrochemical techniques that have been reported.
A new windows-based, user friendly program (ProMCC) for (i) the determination of metal complexation parameters (ligand concentration (L) and conditional stability constants (K′)) and for (ii) ...theoretical simulation of metal complexometric titration, assuming discrete ligand model, is developed. Although primarily intended for treatment of experimental data obtained either by anodic stripping voltammetry (ASV) or competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV), it could manage titration-type data of other techniques (e.g. ISE, sorption isotherm). Currently, the program is capable to process (fit and/or simulate) titration data up to three discrete ligand classes. Procedure for adjustment of “true” analytical sensitivity incorporated in ProMCC was found to provide reasonably good estimates of sensitivity either for one-ligand or two-ligand system. The particular feature of ProMCC is that it incorporates two complementary fitting methodologies: (1) a non-linear fitting of conventional linearized transformations (e.g. Ružić/Van Den Berg, Langmuir/Gerringa) and (2) a “complete complexation model” — a matrix based optimization of mass balance equations. Comparison test of different non-linear fitting modes and titration types revealed that a slight underestimation of ligand concentration and overestimation of conditional stability constant may occur if titration is performed in logarithmic mode, mainly due to unfavorable noise distribution. An advantage of implemented “complete complexation model” fitting mode is that it allows simultaneous analysis of titrations obtained at multiple detection windows as unified dataset (multi-detection window approach), providing complexation parameters for up to three ligand classes. A new alternative “RAL-approach” in analyzing complexometric titrations obtained at multiple detection windows for copper–salicylaldoxime (Cu–SA) system is suggested. It assumes that the analytical sensitivity is changing along the titration curve respecting the true speciation of Cu–SA in sample. An adapted empirical equation for calculation of relative intensity (RAL) is proposed. Flexibility in adjusting parameters, immediate graphical feedback and visualizations make ProMCC handy for treatment of large set of experimental data, and a tool for research in refinement of the methods of metal complexing capacity determination which is continuously improving.
•A new user-friendly tool for analysis of complexometric titration data is developed.•Non-linear and “complete complexation model” fitting modes were incorporated.•An efficient method for correction of true sensitivity was validated.•Simultaneous analysis of multiple analytical windows (CLE-AdCSV) as unified dataset.•An alternative “RAL-approach” for Cu–SA system is proposed.
•An electrochemical Hg(II) sensor based on T–Hg(II)–T sensing motif was fabricated.•A methylene blue-modified DNA probe was used to fabricate the sensor.•Sensor performance was evaluated using ACV, ...CV, SWV, and DPV.•The sensor behaves as a “signal-off” sensor in ACV and CV.•The sensor behaves as either a “signal-on” or “signal-off” sensor in SWV and DPV.
Here we report the characterization of an electrochemical mercury (Hg2+) sensor constructed with a methylene blue (MB)-modified and thymine-containing linear DNA probe. Similar to the linear probe electrochemical DNA sensor, the resultant sensor behaved as a “signal-off” sensor in alternating current voltammetry and cyclic voltammetry. However, depending on the applied frequency or pulse width, the sensor can behave as either a “signal-off” or “signal-on” sensor in square wave voltammetry (SWV) and differential pulse voltammetry (DPV). In SWV, the sensor showed “signal-on” behavior at low frequencies and “signal-off” behavior at high frequencies. In DPV, the sensor showed “signal-off” behavior at short pulse widths and “signal-on” behavior at long pulse widths. Independent of the sensor interrogation technique, the limit of detection was found to be 10nM, with a linear dynamic range between 10nM and 500nM. In addition, the sensor responded to Hg2+ rather rapidly; majority of the signal change occurred in <20min. Overall, the sensor retains all the characteristics of this class of sensors; it is reagentless, reusable, sensitive, specific and selective. This study also highlights the feasibility of using a MB-modified probe for real-time sensing of Hg2+, which has not been previously reported. More importantly, the observed “switching” behavior in SWV and DPV is potentially generalizable and should be applicable to most sensors in this class of dynamics-based electrochemical biosensors.
A La
3+
doped Co
3
O
4
nanocube modified graphite screen-printed electrode (La
3+
-doped Co
3
O
4
nanocube/SPE) was prepared and utilized for the sensitive voltammetric determination of bisphenol A. ...In comparison with an unmodified electrode, the presence of the La
3+
doped Co
3
O
4
nanocubes caused a significant enhancement in the peak current. Differential pulse voltammetry (DPV), cyclic voltammetry (CV), and chronoamperometry approaches were utilized as diagnostic methods. The modified SPE was used to determine bisphenol A concentrations in the range from 0.5 to 900.0 μM with a limit of detection equal to 6.1 × 10
−8
M. Real samples were effectively analyzed with the modified electrode.
Present investigation deals with electrochemical determination of copper(II), lead(II) and mercury(II) ions, using ethylenediaminetetraacetic acid (EDTA) chelating ligand modified polyaniline (PANI) ...and singe walled carbon nanotubes (SWCNTs) based nanocomposite (PANI/SWNCTs). Stainless steel (SS) electrode was modified with PANI and SWCNTs based nanocomposite. PANI/SWCNTs nanocomposite was electrochemically synthesized using potential cycling technique. Further it was modified with EDTA in the presence of 1-ethyl-3(3-(dimethylamin propyl)carbodiimide (EDC) as activating agent, using dip coating technique at room temperature. The EDTA_PANI/SWCNTs/SS electrode was characterized by cyclic voltammetry in 0.5 M H2SO4, which was complemented with electrochemical impedance spectroscopy (EIS). AFM and SEM analysis was applied for the morphological studies of EDTA_PANI/SWCNTs nanocomposite structure. FTIR analysis was applied for the structural and compositional analysis of EDTA_PANI/SWCNTs nanocomposite. All the characterizations were performed before and after the modification of PANI/SWCNTs nanocomposite structure with chelating ligand. Differential pulse voltammetry (DPV) was used for the determination of Cu(II), Pb(II) and Hg(II) ion concentrations. Analytical characteristic such as selectivity and sensitivity of here above-mentioned metal ions was studied. The limit of detection the EDTA_PANI/SWCNTs/SS toward Cu(II), Pb(II) and Hg(II) was determined as 0.08 μM, 1.65 μM and 0.68 μM respectively.
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![[M{[kappa]2S,S-S2C-piperazi...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0095-8972/small "[M{[kappa]2S,S-S2C-piperazine-C2H4N=C(R)}n] {Co(III), Ni(II), Cu(II) or Zn(II)} complexes bearing pendant Schiff base moieties: spectral characterization, fluorescence, cyclic voltammetric and TGA/DTA study")
