Irreversible Cathodic Peak Research Articles

Novel bioinspired dinuclear Cu(II) ‘paddle wheel’ acetate complex: Catalytic and in vitro biological activity studies

A versatile bioinspired metallocatalyst [Cu2L2(OAc)4] (L = 2-(3-(dimethylamino)propyl)isoindoline-1,3-dione) has been synthesized and found distorted octahedral complex on the basis of various spectroscopic characterization. XRD date shows that it is monoclinic system with space group C 2/c. Non classical intramolecular H-bond stabilise it's dimeric nature. The additional signal appeared at g ca 2.10 in EPR and shifting of irreversible cathodic peak from −0.292 V to −0.910 V in CV confirm it is phenoxazinone synthase activity while base peak at m/z 221.15 obtained from ESI Mass and irreversible cathodic peak shifting from −0.292 to −0.211 V ratify it's catechol oxidase activity. Besides, Michaelis-Menten analysis shows prominent catalytic activity towards 3,5-DTBC and 2-AP (Kcat 12.0726×103 h-1 and 6.6654×103 h-1). In vitro study supported by molecular docking study exposes substantial dose dependent anti-leukemic activity against Hep-G2 cell line (GI50 ˂ 10 µg/mL). Moreover, promising anti-bacterial property was also detected on multi-drug resistant E. coli and B. cereus bacteria (B. cereus OD 0.21 ± 0.016; E. coli OD 0.172 ± 0.013) at 100mM concentration of complex.

Oxo transfer reaction: Dioxido and monooxidovanadium(V) complexes

A dioxidovanadium(V) complex of type [(LONOH−)(VO2)] (1) was isolated where LONOH2 is a tridentate ONO donor benzhydrazide ligand. 1 undergoes an oxo transfer reaction with triphenylphosphine in presence of 8-hydroxyquinoline (HQ) and affords a monooxidovanadium(V) complex of type [(LONO2−)(VO)(Q−)] (2). 1 and 2 were substantiated by elemental analyses, ESI-mass, IR, 1H NMR, 51V NMR and UV–vis spectra. The molecular geometries of 1 and 2 were authenticated by single crystal X−ray crystallography. UV–vis absorption spectra of 1 and 2 display bands respectively at 325 and 320 nm due to oxido → vanadium(V) charge transfer transitions. 1 exhibit an irreversible cathodic peak at −0.44 V whereas 2 displays a reversible cathodic wave at −0.60 V in cyclic voltammogram due to the VO3+/VO2+ redox couple.

Coordination Complex of Cu(II) with Ligand Containing Carboxylic Acid Group: Synthesis, Characterization and Catecholase Activity

Present work reports the synthesis, characterization and catecholase like activity of a diaqua Cu(II) complex of type [(L2–)Cu(H2O)2] (1) with a tridentate ligand (E)-2-(3- hydroxy-3-phenyltriaz-1-en-1- yl)benzoic acid (LH2). Complex 1 is characterized by FT-IR, mass, EPR and UV-Vis spectroscopy. The isotropic hyperfine four line EPR spectrum of complex 1 in solution confirms the Cu(II) state in complex 1. The complex exhibits catalytic activity towards the oxidation of 3,5-di-tert. butyl catechol (3,5-DTBC) to 3,5-di-tert. butyl benzoquinone (3,5-DTBQ) with turnover number (Kcat) = 132.8 h-1 via formation of radical intermediate. The oxidation of 3,5-DTBC in presence of complex 1 is confirmed by the UV-Vis spectroscoy, mass spectra and EPR spectra. Complex 1 is EPR active in solution but the solution containing complex 1 and 3,5-di-tert. butyl catechol is EPR silent authenticating the formation of an organic radical in the catalytic oxidation process. In cyclic voltametry of complex 1, an irreversible cathodic peak appear at -0.19 V may be due to the Cu2+/Cu+ couple and an irreversible anodic wave appear at +1.35 V may be due to the oxidation of N3 – to N3 •–. Cyclic voltammetry of complex 1 with 3,5-DTBC gives a new anodic peak at +0.11 V, which is assigned as cat/sq•– redox couple [cat= 3,5-DTBC, sq•– = benzosemiquinonate anion radical].

Nickel(I) salen-catalyzed reduction of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113): CO2-mediated carbon–fluorine bond cleavage

Cyclic voltammetry, controlled-potential (bulk) electrolysis, gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), and high-performance liquid chromatography–electrospray ionization–mass spectrometry (HPLC–ESI–MS) have been used to investigate the direct and nickel(I) salen-catalyzed reduction of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) in both Ar- and CO2-saturated dimethylformamide (DMF) containing 0.10 M tetra-n-butylammonium tetrafluoroborate (TBABF4). Cyclic voltammograms show one irreversible cathodic peak for direct reduction of CFC-113 in CO2-saturated DMF to afford 1-chloro-1,2,2-trifluoroethene (CFC-1113), whereas cyclic voltammograms in Ar-saturated DMF exhibit two irreversible cathodic peaks. Bulk electrolyses of CFC-113 in CO2-saturated DMF at a potential 400 mV more negative than the resolved cathodic peak cause partial reduction of CFC-1113 to yield di-, tri-, and tetrafluoro species. Cyclic voltammograms for reduction of nickel(II) salen in the presence of CFC-113 in CO2-saturated DMF show two cathodic peaks attributable to formation of CFC-1113 and HFC-1123; cyclic voltammograms in Ar-saturated DMF exhibit similar behavior. Bulk electrolyses involving electrogenerated nickel(I) salen in CO2-saturated DMF yield mixtures of HFC-1123, isomers of difluoroethene, and traces of other species. No electrocarboxylation of CFC-113 or its derivatives was seen in the presence of CO2; however, excess CO2 increases the extent of dechlorination of CFC-113 during bulk electrolyses when compared with analogous electrolyses in an Ar-saturated medium. Structural modification of nickel(II) salen during catalytic reduction of CFC-113 in the presence of CO2 was determined with the aid of HPLC–ESI–MS.

Direct Electrochemical Reduction of Acetochlor at Carbon and Silver Cathodes in Dimethylformamide

Cyclic voltammetry and controlled-potential (bulk) electrolysis have been employed to investigate the direct electrochemical reduction of acetochlor (1) at carbon and silver cathodes in dimethylformamide. Voltammograms of 1 exhibit a single irreversible cathodic peak at both cathode materials. Catalytic properties of silver towards carbon–halogen bond cleavage are evidenced by a positive shift in the reduction of acetochlor as compared to the more inert glassy carbon electrode. Voltammograms in the presence of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), and comparisons of calculated relative interaction energies between acetochlor, possible intermediates, and deschloroacetochlor in the presence of different proton donors, suggest strong hydrogen-bonding interactions between HFIP and a carbanion intermediate. Addition of HFIP to electrolysis conditions promotes complete reduction at both cathode materials, with formation of deschloroacetochlor in high yields. In deuterium labelling studies, the use of DMF-d7 led to no evidence for deuterium atom incorporation. However, when HFIP-OD or D2O were employed as a proton source, substantial amounts of deuterated deschloroacetochlor were observed. A mechanism for the reduction of acetochlor is proposed, in which radical intermediates do not play a significant role in reduction, rather a carbanion intermediate pathway is followed.

Modeling of neotame and fructose thermochemistry: Comparison with mono and divalent metal ions by Computational and experimental approach

The metal complexes can demonstrate various interesting biological activities in the human body. However, the role of certain metal ions for specific cell activities is still subject to debate. This study is aimed at comparing the thermochemical properties of neotame (artificial sweetener) and α, β-fructose in gas phase and water medium. The interaction of α and β-fructose, neotame with monovalent and divalent metal ions was studied and comprehended by density functional theory (DFT) using B3LYP functional, 6–311 + G (d, p) and D3 basis set. Metal ion affinities (MIA) values depicted that ionic radius of metal ions played an important role in the interaction of α, β-fructose and neotame. The ∆G parameter was calculated to predict and understand the interaction of metal ions with α and β-fructose, neotame. The results suggested that the presence of hydroxyl groups and oxygen atoms in sugar molecules acted as preferred sites for the binding and interaction of mono and divalent ions. For the first time computational study has been introduced in the present study to review the progress in the application of metal binding with sugar molecules especially with neotame. Moreover, voltammetric behaviour of neotame-Zn2+ was studied using cyclic and differential pulse voltammetry. The obtained results suggest that the peak at −1.13 V is due to the reduction of Zn2+ in 0.1 M phosphate buffer medium at pH 5.5. Whereas, addition of 6-fold higher concentration of neotame to the ZnCl2.2H2O resulted in a new irreversible cathodic peak at −0.83, due to the reduction of neotame-Zn2+ complex. The Fourier transform infrared spectroscopy (FTIR) results indicates that the β-amino group (-NH) and carboxyl carbonyl (-C = O) groups of neotame is participating in the chelation process, which is further supported by DFT studies. The findings of this study identify the efficient chelation factors as major contributors into metal ion affinities, with promising possibilities to determine important biological processes in cell wall and glucose transmembrane transport.

Electrocatalytic Production of Hydrogen Gas by a Cobalt Formamidinate Complex

ABSTRACT. A molecular cobalt complex, Co(DippF)2 (where DippF is the anion of N,N’-bis[2,6-diisopropylphenyl]-formamidine), (1),is able to electrochemically produce hydrogen gas from the reduction of organic acids in homogeneous solutions. Compound 1 has a distorted square planar structure as evidenced through X-ray crystallography studies, and an effective magnetic moment of 4.13, obtained by the Evans method, that corresponds to three unpaired electrons. Compound 1 shows an irreversible cathodic peak at –1.59 V vs Fc/Fc+ which is assigned to the reduction of CoII to CoI. In the presence of organic acids the onset of catalytic current is observed at –1.2 V, –1.45 V and –1.89 V vs. Fc/Fc+ with p-toluenesulfonic acid, benzoic acid and phenol as the proton source, respectively, in MeCN as the solvent. Detection of hydrogen gas was obtained by GC-MS with Faradaic efficiencies ranging from 85% to 100%. Kinetic studies using foot-of-the-wave analysis (FOWA) reveal a linear dependence of the observed rate constant, kobs, against acid concentration in the range of 0.065 to 10.02 s-1.

Electrochemical reduction of 2-halo-N-phenylacetamides at glassy carbon cathodes in dimethylformamide

Cyclic voltammetry and controlled-potential (bulk) electrolysis have been employed to investigate the direct electrochemical reductions of 2-bromo-N-phenylacetamide (1a) and 2-iodo-N-phenylacetamide (1b) at glassy carbon cathodes in dimethylformamide containing tetramethylammonium tetrafluoroborate (TMABF4) as supporting electrolyte. Cyclic voltammograms for reduction of 1a and 1b each exhibit a pair of irreversible cathodic peaks; the first peak arises from a combination of one-electron and two-electron reductive cleavage of the respective carbon–halogen bond and the second peak is due to overall two-electron reductive cleavage of the carbon–halogen bond to produce a free halide ion together with 2-oxo-2-(phenylamino)ethan-1-ide. Controlled-potential (bulk) electrolysis of a 5mM solution of 1a or 1b at a potential corresponding to either the first or second cathodic peak affords only phenylacetamide. However, bulk electrolysis of a 10mM solution of 1a or 1b at a potential corresponding to either cathodic peak leads to a mixture of phenylacetamide and 1,4-diphenylpiperazine-2,5-dione. In the presence of a large excess of 1,1,1,3,3,3-hexafluoro-2-propanol (a proton donor), bulk electrolyses of 1a or 1b at a potential on the first peak give phenylacetamide exclusively. When either 1a or 1b is electrolyzed in the presence of 1M D2O, the resulting phenylacetamide is deuterated to a very significant extent (evidence for a carbanion intermediate), and a small quantity of 2-(dimethylamino)-N-phenylacetamide is seen as a side-product. Mechanisms to account for the behavior of 1a and 1b are proposed.

Phenoxo-bridged dicopper complexes: Syntheses, characterizations, crystal structures and catecholase activity

Two new dinuclear copper(II) complexes are synthesized from two reduced Schiff bases namely 2-(((3-(cyclohexylamino)propyl)amino)methyl)-4-methylphenol (HL1) and 2-(((3-(cyclohexylamino)propyl)amino)methyl)-6-methoxyphenol (HL2): [Cu(L1)(ClO4)]2 (1) and [Cu2(L2)2(μ-ClO4)](ClO4) (2) and characterized by various spectroscopic methods. Structural analyses reveal that in 1, two copper(II) ions are held together by bis(phenoxo) bridges, whereas in 2, the copper centres are connected by bis(phenoxo) and μ1,3-ClO4 bridges. Conductivity measurements in methanol of 1 (180 Ohm−1 cm2 mol−1) and 2 (210 Ohm−1 cm2 mol−1) suggest the formation of dicationic species [Cu2(L1/L2)2]2+ with two perchlorates as counter anions. The cyclic voltammograms show two irreversible cathodic peaks for the one electron reduction process CuIICuII → CuIICuI and CuIICuI → CuICuI. The catecholase activity of complexes 1 and 2 has been investigated in methanol under aerobic condition using 3,5-di-tert-butyl catechol (3,5-DtBC) as a substrate. Both complexes follow the enzymatic Michaelis–Menten kinetics with turnover number (TON) 34.32 h−1 (1) and 26.52 h−1 (2). Both steric and electronic factors favour the higher catalytic activity in 1 compared to 2. The formation of product 3,5-di-tert-butyl-o-benzoquinone (3,5-DtBQ) and catechol–substrate complexes were monitored using ESI-mass spectroscopy. A correlation between observed catalytic activities and electrochemical properties has been attempted.

Determination of ultra-trace amounts of neonicotinoid insecticide imidacloprid by cyclic and square wave voltammetric methods using pretreated glassy carbon electrode

<p>Pesticide production and application have progressively increased worldwide during recent decades. Among these compounds, imidacloprid (IMD) is a widely used insecticide in agriculture, and more particularly to control sucking insects in crops. The aim of this work is to develop rapid, simple and sufficiently sensitive cyclic voltammetry (CV) and square wave voltammetry (SWV) for the detection and quantification of this insecticide in water and agriculture samples. Pretreated glassy carbon electrode (PGC) was employed as working electrode. Aqueous solutions were prepared with Confidor 200-SL commercial formulation of IMD. Each voltammogram was characterized by a well-defined single irreversible cathodic peak at approximately -1.38 V/SCE. The electrode reaction is mainly a diffusion controlled process. The optimization of experimental parameters such as IMD initial concentration, potential scan rate, pH and temperature was carried out by CV, and then a comparative study was conducted by SWV. For the detection and quantification of IMD, the results obtained by SWV showed higher sensibility and accuracy than that by CV. The developed methods were successfully used to determine IMD in real samples, namely plum and peach juice.</p>

Sonoelectrochemical Reduction of Tetrabromobisphenol-a at Silver Cathodes in Dimethylformamide

First reported in the early 1930s, sonoelectrochemistry is an analytical technique that seeks to incorporate ultrasound into electrochemical experiments. Compton and co-workers reviewed the numerous advantages of sonoelectrochemistry over “silent” experiments without ultrasound, including increased mass transport and electrode surface roughening.1 Presently, there is a lack of research employing sonoelectrochemistry to study environmental remediation, a topic of particular interest in our group. As a beginning inquiry into the various factors that optimize sonoelectrochemical reduction, a comparative study into the reduction of the flame retardant 3,3',5,5'-tetrabromobisphenol-A (TBBPA) was undertaken with the aid of cyclic voltammetry, controlled-potential (bulk) electrolysis, and sonoelectrochemistry. Cyclic voltammograms of TBBPA at silver cathodes in dimethylformamide containing 0.10 M tetramethylammonium tetrafluoroborate (TMABF4) show three irreversible cathodic peaks with peak potentials of –0.50 V, –0.70 V, and –1.34 V versus a cadmium-saturated mercury amalgam reference electrode (Cd(Hg)). However, bulk electrolyses of TBBPA at –1.50 V versus Cd(Hg) under the same conditions show minimal debromination as a result of competitive reduction pathways between the carbon–bromine bonds and the phenolic hydrogens within the molecule. To improve debromination, two alternate pathways are explored: the methylation of TBBPA (MeTBBPA) to prevent O–H reduction and the introduction of ultrasound to electrochemical analysis. Cyclic voltammograms of MeTBBPA show two irreversible cathodic peaks (–0.70 V and –0.90 V versus Cd(Hg)) and bulk electrolyses at –1.50 V versus Cd(Hg) show complete debromination in TMABF4–DMF. Similarly, sonoelectrochemical bulk electrolysis experiments at –1.50 V vs. Cd(Hg) show a substantial increase in debromination compared to electrolyses under “silent” conditions. 1 R. G. Compton, J. C. Eklund, F. Marken, Electroanalysis 1997, 9, 509–522.

Highly Sensitive Carbon Based Sensors Using Zinc Oxide Nanoparticles Immobilized Multiwalled Carbon Nanotubes for Simultaneous Determination of Desvenlafaxine Succinate and Clonazepam

Carbon paste electrode modified with zinc oxide nano particles immobilized on multi-walled carbon nano tubes (MWCNTs/ZnO-NPs/CPE) was exploited for the simultaneous determination of Desvenlafaxine succinate (DVS) and Clonazepam (CLZ) in drug substance and combined drug products as well as in spiked human urine. The electrochemical response characteristics of the modified electrode toward DVS and CLZ were investigated by cyclic and differential pulse voltammetry (CV and DPV). The cyclic voltammograms showed well defined, irreversible cathodic peaks (reduction) at potential around −407 and −636 mV in Britton-Robinson (BR) buffer (pH 9.0) for DVS and CLZ, respectively. Different experimental factors affecting the method sensitivity have been investigated and optimized including pH of supporting electrolyte, electrode modifiers, different surfactant and scan rate. A good linear relationship was obtained between the peak current and the concentration within the range of 0.66–8.42 μg/mL and 0.39–7.70 μg/mL for DVS and CLZ, respectively using DPV method. The proposed method was successfully applied for the estimation of DVS and CLZ in its combined dosage form and in spiked human urine. The results obtained were validated according to ICH guideline and were found to be in agreement with those obtained by the reference HPLC methods.

Electrochemical reduction of dihalothiophenes at silver cathodes in dimethylformamide: Evidence for a halogen dance

Cyclic voltammetry and controlled-potential (bulk) electrolysis have been used, along with gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS), to investigate the electrochemical reductions of 2-bromo-5-chlorothiophene (1), 3-bromo-2-chlorothiophene (2), and 2,5-dibromothiophene (3) at silver cathodes in dimethylformamide (DMF) containing 0.050M tetramethylammonium perchlorate (TMAP) as the supporting electrolyte. Cyclic voltammograms for each compound exhibit two irreversible cathodic peaks that correspond to successive cleavage of the relevant carbon–halogen bonds. Controlled-potential electrolyses of 2-bromo-5-chlorothiophene revealed a two-electron cleavage of the carbon–bromine bond to afford 2-chlorothiophene as the major product along with traces of 3-bromo-2-chlorothiophene and 4-bromo-2-chlorothiophene, each arising from occurrence of a halogen dance. Bulk electrolysis of 3-bromo-2-chlorothiophene produces only 2-chlorothiophene in a two-electron process. Controlled-potential electrolysis of 2,5-dibromothiophene yields only 2-bromothiophene, via a process that involves a carbanion intermediate. A mechanistic scheme for the two-electron reduction of 2-bromo-5-chlorothiophene (1) is proposed that accounts for the formation of 2-chlorothiophene as well as two minor products that arise via a halogen dance.

Proposed binding mechanism of galbanic acid extracted from Ferula assa–foetida to DNA

Recently, galbanic acid (GA), a sesquiterpenoid coumarin, has been introduced as an apoptotic and geno/cytotoxicity agent. In the present study, GA has been extracted from Ferula assa-foetida, a native medicinal plant in Iran, and characterized by 1H NMR, mass spectroscopy. Additionally, spectroscopic studies have been performed in order to investigate its DNA-interaction mode. The electrochemical behavior of GA has been studied by cyclic voltammetry (CV) in various scan rates. In neutral media (pH=7.3) one irreversible cathodic peak was obtained at −1.46 V, while in higher scan rates an irreversible one was determined at −1.67 V. According to the voltametric data GA can be easily reduced by 2e−/2H+ mechanism at hanging mercury drop electrode (HMDE). The interaction of GA with ct-DNA was evaluated by CV, differential pulse voltammetry (DPV), enhancement fluorescence, UV–Vis, FT-IR spectroscopy and molecular docking. The molecular docking study shows that the GA interacts to DNA on partial intercalation mode via DNA groove binding and forms a complex by van der Waals and electroastatic interactions. In addition, the thermodynamic parameters of GA-DNA complex were investigated with ΔH°, ΔS° and ΔG° values of 15.81KJmol−1, 133.95Jmol−1 and −23.10KJmol−1, respectively. All data revealed that the GA is binding to DNA by van der Waals and electrostatic interactions through the partial intercalations from the DNA's grooves.

Direct Reduction of 1-Bromo-6-chlorohexane and 1-Chloro-6-iodohexane at Silver Cathodes in Dimethylformamide

Cyclic voltammetry and controlled-potential (bulk) electrolyses have been employed to probe the electrochemical reductions of 1-bromo-6-chlorohexane and 1‐chloro-6-iodohexane at silver cathodes in dimethylformamide (DMF) containing 0.050M tetra-n-butylammonium tetrafluoroborate (TBABF4). A cyclic voltammogram for reduction of 1-bromo-6-chlorohexane shows a single major irreversible cathodic peak, whereas reduction of 1-chloro-6-iodohexane gives rise to a pair of irreversible cathodic peaks. Controlled-potential (bulk) electrolyses of 1-bromo-6-chlorohexane at a silver gauze cathode reveal that the process involves a two-electron cleavage of the carbon–bromine bond to afford 1-chlorohexane as the major product, along with 6-chloro-1-hexene, n‐hexane, 1‐hexene, and 1,5-hexadiene as minor species. In contrast, bulk electrolyses of 1-chloro-6-iodohexane indicate that the first voltammetric peak corresponds to a one-electron process, leading to production of a dimer (1,12-dichlorododecane) together with 1-chlorohexane and 6-chloro-1-hexene as well as 1‐hexene and 1,5-hexadiene in trace amounts. At potentials corresponding to the second cathodic peak, reduction of 1-chloro-6-iodohexane is a mixture of one- and two-electron steps that yields the same set of products, but in different proportions. Mechanistic schemes are proposed to explain the electrochemical behavior of both 1‐bromo-6-chlorohexane and 1-chloro-6-iodohexane.

Electrochemical Reduction of 2,2-Dichlorovinyl Dimethyl Phosphate (Dichlorvos) at Carbon and Silver Cathodes

Despite their negative ecological effects, halogenated organophosphates have been used as pesticides. For example, 2,2-dichlorovinyl dimethyl phosphate (or dichlorvos), found in many household and commercial insecticides, can lead to contamination of runoff and rinse water that is toxic to birds, bees, aquatic organisms, and mammals. Remediation of dichlorvos has focused either on electrochemical oxidation1 or on reductive cleavage of its carbon–chlorine bonds at mercury.2 In this study, we have examined the direct reduction of dichlorvos in dimethylformamide and acetonitrile at both carbon and silver cathodes. Shown in Figure 1 are cyclic voltammograms for reduction of dichlorvos at both carbon and silver electrodes. Whereas reduction of dichlorvos at carbon shows a single irreversible cathodic peak, reduction at a silver electrode results in two overlapping cathodic peaks. Controlled-potential (bulk) electrolyses at potentials corresponding to those of the voltammetric peaks indicate that dichlorvos undergoes carbon–chlorine bond cleavage. Catholytes have been analyzed by means of gas chromatography–mass spectrometry (GC–MS) to separate, identify, and quantitate the electrolysis products.

N‐doped Carbon Nanotubes for the Oxygen Reduction Reaction in Alkaline Medium: Synergistic Relationship between Pyridinic and Quaternary Nitrogen

AbstractN‐doped carbon nanotubes (N‐CNTs) prepared using a sustainable methodology based on a ball milling process were applied as catalysts for Oxygen Reduction Reaction (ORR). From two different N‐doping methodologies using melamine and urea as N‐enriched precursors, resulted in N‐CNTs with surface areas in the range 350–364 m2 g−1, and surface nitrogen contents from 0.2 % to 4.8 %, corresponding to three N‐types: pyridinic, pyrrolic and quarternary. Irreversible cathodic peaks were observed in the cyclic voltammograms of all catalysts in the presence of an O2‐saturated KOH solution, proving their ORR electrocatalytic activity. Onset potentials (Eon) varied from −0.159 to −0.128 V for N‐CNTs, approaching that of Pt/C (−0.124 V). Furthermore, the two best catalysts also exhibited an average number of electrons transferred per O2 of 3.3 and 3.1 e, respectively. These results suggest an O2‐reduction mechanism which is half controlled by the indirect pathway and half determined by the direct pathway. Moreover, the best N‐CNT catalyst exhibited higher durability and methanol tolerance than Pt/C. The correlation between ORR performance data and N‐CNT catalyst composition suggests that the Npyridinic/Nquaternary ratio is more relevant role than the total N content. In fact, the catalysts with the best performance (in terms of Eon and nO2) exhibited the highest Npyridinic/Nquaternary ratio, 5.6 and 3.9 respectively, while their nitrogen contents were 3.1 and 0.8 %.

Electrochemical behavior and analytical detection of Imidacloprid insecticide on a BDD electrode using square-wave voltammetric method

Abstract A sensitive square-wave voltammetric method for the determination of Imidacloprid (IMD) was developed using electrochemically pretreated boron-doped diamond (BDD) electrode. Aqueous solutions were prepared with Confidor 200 SL as the commercial formulation of IMD. Sodium sulfate (Na 2 SO 4 ) was used as supporting electrolyte. The influence of operating parameters, such as the pH of the medium, frequency, pulse amplitude, scan increment and the concentration of IMD was investigated. An irreversible cathodic peak, corresponding to the reduction of IMD is observed at −1.21 V ( vs. SCE) and the electrode reaction was controlled by adsorption. Under optimized conditions, the square-wave reduction peak current was linear over the concentration range of (30–200 μmol L −1 ) with a detection and quantification limits of 8.60 μmol L −1 and 28.67 μmol L −1 , respectively. The results were compared with spectrophotometry and HPLC methods under some conditions and found to be in good agreement. To investigate applicability to real samples, the proposed method was applied to the determination of IMD in plum juice.

Electrochemical behavior of 7-deazaguanine- and 7-deazaadenine-modified DNA at the hanging mercury drop electrode

DNA modification with synthetic analogs of natural nucleotides and/or their conjugates with external redox active groups is applied in the development of electrochemical DNA sensors or assay for DNA hybridization, SNP typing, DNA damage and so forth. 7-Deazapurines (Pu*) are analogs of natural purine bases in which N7 atom is replaced by CH group. The Pu* bases retain Watson–Crick base pairing of their parent purines (and the ability to form duplex DNA) but are incapable of Hoogsteen pairing (and thus cannot be involved in triplex or quadruples DNA structures). Previously, we studied electrochemical oxidation of Pu* residues in DNA fragments (prepared by PCR in the presence of Pu* deoxynucleoside triphosphates) at a carbon electrode and reported on significantly lower potentials of oxidation of both 7-deazaguanine (G*) and 7-deazaadenine (A*), compared to natural guanine (G) and adenine (A), respectively. In this work, we studied faradaic and tensammetric responses of G*- or A*-modified DNA on the hanging mercury drop electrode (HMDE). While A* was reduced at the HMDE, giving rise to a similar irreversible cathodic peak as the natural A, G* did not yield any peak analogous to the peak G due to guanine, in agreement with a loss of corresponding redox site in G*. Responses of DNA modified with A* were relatively similar to those of unmodified DNA (albeit we observed certain differences in tensammetric peak currents). Effects of G substitution by G* were more pronounced, being reflected in diminution of peak due to guanine, decrease of the peak CA (due to cytosine and adenine reduction) and in significantly changed shape of tensammetric DNA signals, indicating altered adsorption/desorption processes. While substitution of A by A* resulted in certain destabilization of the DNA duplex at the negatively charged HMDE surface (in qualitative agreement with significantly decreased melting temperature of the same DNA duplexes in solution), G*-modified duplex DNA displayed apparently lower susceptibility to surface denaturation.

Direct Reduction of 1,2- and 1,6-Dibromohexane at Silver Cathodes in Dimethylformamide

Electrochemical reduction of 1,2-dibromohexane (1) and 1,6-dibromohexane (2) at silver cathodes in dimethylformamide (DMF) containing tetramethylammonium perchlorate (TMAP) has been investigated with the aid of cyclic voltammetry and controlled-potential electrolysis. Cyclic voltammograms for reduction of 1 and 2 both exhibit a single irreversible cathodic peak associated with reduction of carbon–bromine bonds; however, the cathodic peak potential (−0.33V) for 1 is significantly less negative than that (−1.00V) for 2, and the peak current for 1 is approximately half of that for 2. Cyclic voltammograms for 0.5–20.0mM solutions of 1 and 2, separately, show that the parameter Ipc/C* increases as the concentration (C*) decreases; this trend is likely due to a combination of adsorption phenomena and a potential-dependent transfer coefficient (α). Coulometric n values and product distributions arising from bulk electrolyses of 5.0mM solutions of 1 and 2 depend on the positions of the bromine atoms: (a) for 1, n was 2.13 and 1-hexene was the only product; (b) for 2, n was 2.12 and a mixture of products was obtained [1-hexene (21%), n-hexane (37%), 1,5-hexadiene (22%), 5-hexen-1-ol (9%), and a trace of n-dodecane]. When 2 was electrolyzed in the presence of a proton or deuteron donor (2,2,2-trifluoroethanol or D2O), the n value and the amount of n-hexane increased, whereas 1-hexene and 1,5-hexadiene decreased in yield. We conclude that reduction of 1 follows a concerted mechanism, but that reduction of 2 proceeds via carbanionic intermediates.