Reversible Reduction Peaks Research Articles

Synthesis and Characterization of Cross-linkable Viologen Derivatives

In this study, crosslinkable allyl functional viologen derivative (ALV-Br) was synthesized with 4-4'biridyl in the presence of allyl bromide in acetonitrile and the precipitated product was separated by filtration. Chemical characterization of the obtained structure was carried out as a result of FT-IR and 1H-NMR spectra. In the cyclic voltammetry (CV) measurements performed for electrochemical characterization, a two-step reversible reduction peak attributed to viologen salts was clearly observed in the 0-0.8 V range. According to the UV-Vis absorption spectra, it is seen that they only absorb in the UV region below 400 nm in both solution and thin film. Thin films of ALV-Br salt were then spray coated in the presence of a tetrathiol-based crosslinker (pentaerythritol tetrakis(3-mercapto-propionate).In the final step, the surface morphology of the crosslinked thin film was examined by Atomic force microscopy (AFM) and compared with the results of the non-crosslinked one. Finally, the patterned film of ALV-Br could be obtained by this technique.

Regenerable sensor based on tris(4,7′-diphenyl-1,10-phenanthroline)ruthenium (II) for anodic and cathodic electrochemiluminescence applications

Tris(4,7′-diphenyl-1,10-phenanthroline) ruthenium (II) dichloride [Ru(dpp)32+] was used for the first time to construct a regenerable electrochemiluminescence (ECL) sensor. The Ru(dpp)32+-modified carbon paste electrode (CPE) showed several unique features in comparison with commonly studied Ru(bpy)32+-modified electrodes. On the one hand, a quite reversible reduction peak was observed at −0.96 V where no obvious hydrogen evolution occured, enabling the sensitive detection of S2O82−. Moreover, our proposed S2O82− sensor showed a good linear range from 3 × 10−9 to 3 × 10−4 M with a detection limit of 2 nM, indicating higher sensitivity for the same analyte than previously reported ECL methods by about two orders of magnitude. On the other hand, the Ru(dpp)32+-modified electrode showed an irreversible oxidation peak because electrogenerated Ru(dpp)33+ is very reactive in aqueous solutions, while Ru(bpy)32+-modified electrode showed a reversible oxidation peak. Moreover, the present sensor showed a good linear range from 10−7 M to 10−3 M for oxalate with a detection limit of 60 nM. It detected oxalate in urine samples with nice recoveries. The regenerable ECL sensor presented good characteristics, such as low cost, simple fabrication procedure and fast response time. The Ru(dpp)32+ based regenerable sensor is an attractive alternative to Ru(bpy)32+-based regenerable sensor, as it can be used for both anodic and cathodic ECL analysis with high sensitivity in aqueous media.

Physical properties and electrochemical performance of Zn-substituted [formula omitted] nanostructures as cathode in Na-ion batteries

We report the synthesis, physical properties and electrochemical performance of Zn substituted Na0.44Mn1−xZnxO2 (x= 0 – 0.02) nanostructures as cathode in Na-ion batteries for energy storage applications. These samples stabilize in the orthorhombic structure and the morphology is found to be slab like with 100 – 200 nm width and few micrometer of length. The resistivity measurements show highly insulating nature for all the samples, where the activation energy decreases with increasing Zn concentration indicating more defect levels in the band gap. The cyclic voltammogram (CV) shows reversible oxidation and reduction peaks, which clearly shift towards higher/lower potentials with increasing Zn concentration up to 2%. We observed the specific capacity of about 100 mAh/g at current density of 4 mA/g and improved cycle life for Zn substituted x=0.005 sample. However, with further increasing the Zn concentration (x=0.02), the specific capacity decreases, which can be a manifestation of the decreased number of reduction peaks in the CV data.

Electrochemical Reduction of CO2 Facilitated By Vitamin-Based Catalysts

The electrochemical conversion of carbon dioxide to valuable fuels is in the focus of academic and industrial research due to increasing demand for greener alternatives. Thus far, pyridine has been shown as the most promising homogenous electrocatalyst in the electrochemical reduction of CO2 to methanol due to the low overpotential required to achieve faradaic yields of ca. 20%. Family of water-soluble vitamins B3 and B2 represent environmentally friendly class of electrocatalysts. Therefore, this study investigated the activity of nicotinic acid, nicotinamide and riboflavin to convert carbon dioxide to methanol (Figure). The optimization experiments revealed improvements in efficiency for methanol formation by varying the working electrode, electrocatalyst concentration, electrolysis duration and temperature. Vitamins B3 exhibit chemically reversible one electron reduction at ca. -0.5 to -0.6 V vs. Ag/AgCl with a Pt working electrode. The respective electrochemical systems are energy efficient with having overpotential less than 100 mV, however the evolution of hydrogen appears to be main competitive reaction on Pt. Riboflavin demonstrated chemically reversible reduction peak at ca. -0.65 V and -0.55 V vs. Ag/AgCl with Pt and GC electrode, respectively. Glassy carbon electrodes are known to have higher capacitance, resistance and relatively large overpotentials to hydrogen. Consequently, most methanol was generated on GC with 20 mM riboflavin and within the first 10 minutes of electrolysis, giving a yield of 19%. The result findings revealed that vitamins can served as the alternative electrocatalysts to a more expensive, toxic and less environmentally friendly pyridine. Recent developments and challenges in mechanism for future efficient and selective CO2 reduction to methanol will be discussed in the frame of attractive and sustainable energy sources. Figure 1

B-phenylated o-carboranes and its chromium derivatives: Synthesis, electrochemical properties, and X-ray structural studies

The electron accepting capability of B-phenylated o-carborane is greatly improved through favorable electronic interactions between the two adjoining phenyl-π* and cage carbon-σ* orbitals. Phenyl substitution at the boron atom in the 3-position directs the two phenyl groups of the cage carbon atoms to a face-to-face position and locks them into a rigid conformation, which gives rise to extensive electronic delocalization and maximum energy stabilization from the lowest unoccupied molecular orbital (LUMO). A reversible reduction peak from the cyclovoltammogram (CV) at −1.72 V and a broad and extended UV absorption (λmax = 277 nm) substantiate such LUMO stabilization, thereby augmenting the electron accepting capability of o-carborane. Due to electron depletion from the adjacent o-carborane, the adjoined phenyl groups act as potential π-acid; indeed, when B-phenylated 1,2-diphenyl-o-carborane was reacted with Cr(CO)6, bi- and trimetallic chromium complexes were selectively formed in an η6-bonding fashion between the chromium atoms and phenyl groups.

Effect of the change of heteroatom on phenyl capped benzazole: Photophysical and electrochemical properties from the structural viewpoint

Donor-acceptor-donor type phenyl capped benzazoles were synthesized and their photophysical properties were studied. By changing the heteroatom (N, O, S and Se) of central acceptor benzazole unit, the emission color was varied from blue to green. Phenyl capped benzotriazole (1) and benzooxadiazole (2) were characterized by single crystal X-ray crystallography. The absolute solid state fluorescence quantum yields of these compounds were obtained in the range of 0.05–0.93 by a calibrated integrating sphere method. High solid state quantum yield can be attributed to the non-planarity and absence of strong intermolecular interactions in the solid state. Except phenyl capped benzotriazole (1), all compounds showed reversible reduction peak in cyclic voltammetry experiments which reflects the considerable n-type nature.

Perylene Diimide as a Precise Graphene-like Superoxide Dismutase Mimetic.

Here we show that the active portion of a graphitic nanoparticle can be mimicked by a perylene diimide (PDI) to explain the otherwise elusive biological and electrocatalytic activity of the nanoparticle construct. Development of molecular analogues that mimic the antioxidant properties of oxidized graphenes, in this case the poly(ethylene glycolated) hydrophilic carbon clusters (PEG–HCCs), will afford important insights into the highly efficient activity of PEG–HCCs and their graphitic analogues. PEGylated perylene diimides (PEGn–PDI) serve as well-defined molecular analogues of PEG–HCCs and oxidized graphenes in general, and their antioxidant and superoxide dismutase-like (SOD-like) properties were studied. PEGn–PDIs have two reversible reduction peaks, which are more positive than the oxidation peak of superoxide (O2•–). This is similar to the reduction peak of the HCCs. Thus, as with PEG–HCCs, PEGn–PDIs are also strong single-electron oxidants of O2•–. Furthermore, reduced PEGn–PDI, PEGn–PDI•–, in the presence of protons, was shown to reduce O2•– to H2O2 to complete the catalytic cycle in this SOD analogue. The kinetics of the conversion of O2•– to O2 and H2O2 by PEG8–PDI was measured using freeze-trap EPR experiments to provide a turnover number of 133 s–1; the similarity in kinetics further supports that PEG8–PDI is a true SOD mimetic. Finally, PDIs can be used as catalysts in the electrochemical oxygen reduction reaction in water, which proceeds by a two-electron process with the production of H2O2, mimicking graphene oxide nanoparticles that are otherwise difficult to study spectroscopically.

Sensitive Determination of Toxic Clenbuterol in Pig Meat and Pig Liver Based on a Carbon Nanopolymer Composite

The acidified single-walled carbon nanotubes (SWCNTs) were self-assembled on graphene oxide (GO) and then ultrasonically dispersed in a copolymer, Nafion solution, to form a GO/SWCNTs-Nafion polymer nanocomposite, which was employed to modify glassy carbon electrode (GCE). The surface morphological characteristics of different modified electrodes including bare GCE, GO-Nafion/GCE, and GO/SWCNTs-Nafion/GCE were imaged by scanning electron microscopy. For comparison, the differential pulse voltammetry and cyclic voltammetry behaviors were investigated, showing that the GO/SWCNTs-Nafion polymer composite has strong enhancement effect towards oxidation of clenbuterol (CLB). And the corresponding mechanism has been well discussed. During the reaction process, the anilino group of CLB molecule (1) was firstly oxidized to form a radical cation (2), exhibiting a characteristic oxidation peak (I) at 0.95 V, then two radical cations reacting via head-to-head coupling to form a diphenylamine intermediate (3), which was transformed into a CLB dimmer (4) through an azo bond by intramolecular electrons transferring under low potential, exhibiting a pair of reversible oxidation peak (II) and reduction peak (III). Under the optimum conditions, the composite modified electrode showed linear response to CLB in a concentration range of 1.0 × 10−8~6.0 × 10−6 mol/L with a detection limit of 6.0 × 10−9 mol/L. The modified electrode possessed good selectivity, reproducibility, and stability. In comparison with two routine analytical methods like ELISA kit and high-performance liquid chromatography (HPLC), the electrode can be successfully applied to determination of content of CLB in pig meat and pig liver samples with a recovery rate of 96.4~104.2%, suggesting a promising application in food security field.

Heptagons in Aromatics: From Monocyclic to Polycyclic.

Heptagons in Aromatics: From Monocyclic to Polycyclic.

Fluorescence quenching of (dimethylamino)naphthalene dyes Badan and Prodan by tryptophan in cytochromes P450 and micelles.

Fluorescence of 2-(N,N-dimethylamino)-6-propionylnaphthalene dyes Badan and Prodan is quenched by tryptophan in Brij 58 micelles as well as in two cytochrome P450 proteins (CYP102, CYP119) with Badan covalently attached to a cysteine residue. Formation of nonemissive complexes between a dye molecule and tryptophan accounts for about 76% of the fluorescence intensity quenching in micelles, the rest is due to diffusive encounters. In the absence of tryptophan, fluorescence of Badan-labeled cytochromes decays with triexponential kinetics characterized by lifetimes of about 100 ps, 700–800 ps, and 3 ns. Site mutation of a histidine residue in the vicinity of the Badan label by tryptophan results in shortening of all three decay lifetimes. The relative amplitude of the fastest component increases at the expense of the two slower ones. The average quenching rate constants are 4.5 × 108 s–1 (CYP102) and 3.7 × 108 s–1 (CYP119), at 288 K. Cyclic voltammetry of Prodan in MeCN shows a reversible reduction peak at −1.85 V vs NHE that becomes chemically irreversible and shifts positively upon addition of water. A quasireversible reduction at −0.88 V was observed in an aqueous buffer (pH 7.3). The excited-state reduction potential of Prodan (and Badan) is estimated to vary from about +0.6 V (vs NHE) in polar aprotic media (MeCN) to approximately +1.6 V in water. Tryptophan quenching of Badan/Prodan fluorescence in CYPs and Brij 58 micelles is exergonic by ≤0.5 V and involves tryptophan oxidation by excited Badan/Prodan, coupled with a fast reaction between the reduced dye and water. Photoreduction is a new quenching mechanism for 2-(N,N-dimethylamino)-6-propionylnaphthalene dyes that are often used as solvatochromic polarity probes, FRET donors and acceptors, as well as reporters of solvation dynamics.

Anthracene‐containing conjugated polymer showing four optical transitions upon doping: A spectroscopic study

ABSTRACTAn anthracene‐containing poly(arylene‐ethynylene)‐alt‐poly(arylene‐vinylene) (PAE‐PAV) of general constitutional unit (PhCCAnthrCCPhCHCHAnthrCHCH)n bearing two 2‐ethylhexyloxy solubilizing side chains on each phenylene (Ph) unit has been synthesized and characterized. The basic electrochemical characterization was done, showing the existence of two non‐reversible oxidation and one reversible reduction peaks. The optical properties, the real and imaginary part of the dielectric function, were probed using spectroscopic ellipsometry (SE). The vibrational structure of the undoped/doped polymer was investigated using Fourier transformed infrared spectroscopy. A strong change in the polaronic absorption was observed during the doping, which after modeling revealed the existence of two separated transitions. The optical changes upon doping were additionally recorded using the SE technique. Similar to the results from FT‐IR spectroscopy, two new in‐the‐gap absorptions were found. Moreover, the electrical conductivity as well as the mobility of positive carriers were measured. In the undoped state, the conductivity of the polymer was found to be below the detection limit (<μS cm−1), after doping the conductivity increased to 0.69 S cm−1. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 338–346

Electro-optical properties of poly[di(2-thiophenyl)carborane] and its opto-electronic application

Electrochemical and optical properties of a hybrid carborane based polymer called poly(di(2-thiophenyl)carborane) (P1) obtained electrochemically were reported as well as its electrochromic device application. Thiophene donor units and m-carborane acceptor unit were combined under the same umbrella via donor–acceptor–donor approach to obtain di(2-thiophenyl)carborane (1). Contrary to the literature, extreme conditions like highly dried solvent or inert atmosphere were not used for polymerization and characterization. Polymer P1 has an ambipolar character since it exhibited a reversible oxidation peak at a half wave potential (E1/2) of 1.08 V and a quasi reversible reduction peak at E1/2 = −1.82 V vs. Ag/AgCl. The polymer film has an optical band gap of 1.95 eV with a maximum absorption band centered at 488 nm. Also, it exhibited multicolor electrochromic behavior between its reduced and oxidized states changing from dark orange to light blue. Furthermore, the electrochromic device prepared based on P1 film was stable and robust.

Electrochemical synthesis and characterization of poly(3,4-ethylenedioxythiophene) doped with sulfonated calixarenes and sulfonated calixarene–fullerene complexes

Poly(3,4-ethylenedioxythiophene) (PEDOT) films were electrochemically deposited on glassy carbon (GC) disk electrodes using aqueous solutions containing 3,4-ethylenedioxythiophene (EDOT) and sulfonated calixarenes or fullerene-sulfonated calixarene (C60–calixarene) complexes. The EDOT monomer was added to aqueous sulfonated calixarene solutions with and without C60 and from these solutions PEDOT(calixarene) and PEDOT(C60–calixarene) films were electrochemically deposited on GC disk electrodes. The electrochemical properties of GC/PEDOT(C60–calixarene) were compared with those of GC/PEDOT doped with other ions, both in aqueous and organic electrolyte solutions using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV measurements carried out on GC/PEDOT(C60–calixarene) in 0.1M aqueous KCl solution showed a reduction peak at ca. −0.55V vs. Ag/AgCl/3M KCl only during the first potential scan. This was attributed to the irreversible reduction of C60 to C60− inside the PEDOT film. This additional reduction peak was, however, not observed when recording the CVs in organic solution, indicating that C60 was dissolved from the PEDOT film into the organic electrolyte solution, that is a good solvent for C60. When performing CV measurements in an organic electrolyte solution containing C60, all GC/PEDOT electrodes with various doping ions and bare GC electrodes showed a reversible reduction peak characteristic for the C60/C60− redox couple. Interestingly, the peak potential and the shape of the reoxidation peak for the fulleride anion (C60−) on GC/PEDOT in the organic electrolyte solution were found to depend on the PEDOT film thickness. The electrochemical properties of GC/PEDOT(C60–calixarene) were compared further to those of GC/PEDOT(calixarene) by fitting EIS data to equivalent electrical circuits and the morphology was studied by scanning electron microscopy.

Nitrofurazone and its Nitroheterocyclic Analogues: a Study of the Electrochemical Behavior in Aqueous Medium

The biological action of drugs with potential antichagasic activities can be better understood by knowing their reduction mechanism. For this proposal, the electrochemical reduction of nitrofurazone (NF) and its analogues, nitrofurfurilidene thiosemicarbazone (NFS), nitrothiophene semicarbazone (NT), nitrothiophene thiosemicarbazone (NTS), was studied by differential pulse and cyclic voltammetries and chronoamperometry in aqueous medium by using a glassy carbon electrode. Those three synthetic analogues have oxygen and sulfur atoms arranged between the nitroheterocyclic ring (furan and thiophene, respectively) and the carbonyl group (semicarbazone and thiosemicarbazone, respectively). The respective hydroxylamine derivatives are the main products formed in acidic medium, being its formation linearly pH dependent. Although chronoamperometric data show that this reduction involves 4 electrons, its corresponding reduction voltammetric wave, in alkaline medium, is unfolded and a reversible reduction peak at a more positive potential appears. This peak is characterized as a nitro anion radical formation, whose decay is caused by a disproportionation reaction. Its kinetic stability was studied by the current ratio values of the R - NO2/R - NO2• - redox couple and the second-order constant (k2) was determined, being NTS the analogue that registered the highest stability.

Arylamine‐Modified Thiazoles as Donor–Acceptor Dyes: Quantum Chemical Evaluation of the Charge‐Transfer Process and Testing as Ligands in Ruthenium(II) Complexes

AbstractA series of new 4‐hydroxy‐1,3‐thiazole‐based chromophores bearing different arylamine components (triarylamines, carbazole, and phenothiazine) as electron donors and azaheterocycle components (pyridine, pyrazine and pyrimidine) as electron‐acceptor moieties have been synthesized. Elaborate quantum chemical calculations were carried out with two selected compounds to identify the natures of the HOMO/LUMO transition and of the intramolecular charge‐transfer state. The electrochemical properties were investigated: the dyes show reversible first oxidation and reduction peaks, with the former strongly dominated by the type of arylamine. The donor moieties were synthesized under Buchwald–Hartwig conditions. Several of the presented X‐ray structures provide deeper insight into the geometries of the ligands. The bidentate nature of the chromophores makes them suitable as ligands in transition metal complexes. The corresponding ruthenium(II) polypyridine complexes – Ru(dmbpy)2(L)(PF6)2 (dmbpy = 4,4′‐dimethyl‐2,2′‐bipyridine) – were successfully synthesized for seven of the ligands. The MLCT bands in these complexes are significantly broadened, resulting in improved light‐harvesting efficiencies.

Synthesis and Battery Studies of Sodium Cobalt Oxides, NaCoO<sub>2</sub> Cathodes

Sodium based batteries presented a new and promising battery system. This work attempted to develop NaCoO2 material using a new sol-gel method. The characterization of this sodium based material was done by using Thermogravimetric Analysis (TGA), X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). Cyclic voltammetry showed that the material exhibit reversible oxidation and reduction peaks which meant that a sodium based battery was possible for this material. Electrochemical charge-discharge profile was performed to study the voltage plateaus exhibited by the material. It showed discharge plateaus of between 3.2 to 2.3 V and another plateau at 0.6 V.

Layered γ-zirconium phosphate as novel semiconductor for dye sensitized solar cells: Improvement of photovoltaic efficiency by intercalation of a ruthenium complex-viologen dyad

The performance of photovoltaic cells using as semiconductor a film of layered γ-zirconium phosphate (γ-ZrP) containing Ru(bpy)3 and bipyridinium ions (viologens) as electron relays has been studied. The materials are easily prepared by intercalation of Ru complexes and the bipyridinium ions into preformed γ-ZrP nano sheets as colloidal solutions in the appropriate solvent and concentration. High loading of these two guests has been obtained as determined by elemental analysis. Inclusion of Ru(bpy)3 complex and bipyridinium in the intergallery spaces of γ-ZrP can be assessed by powder XRD monitoring of the d100 peak. A dyad was also synthesized where the Ru(bpy)3 and the 4,4′-bipyridinium were covalently connected by a four-methylene tether. The semiconducting behavior of layered γ-ZrP was supported by cyclic voltammetry (reversible reduction peak at −0.6 V), observation of photocurrent and Mott-Schottky measurements (flat band potential ∼−1.3 V vs.NHE) of thin films of this material supported on FTO electrode. Photovoltaic cells based on γ-ZrP containing Ru(bpy)3, exhibited similar VOC (∼0.5 V) and fill-factor values (0.3–0.4), differing in the current density and therefore in their efficiency. The maximum efficiency was obtained for the material containing high loading of the dyad (JSC = 0.383 mA/cm2, efficiency 0.1%). The photo response spectrum shows that the main limitation of these materials is still the inefficient photo sensitization of the semiconductor by the dye, probably due to the high negative flat band potential of γ-ZrP.

ChemInform Abstract: Synthesis and Electrochemical Properties of the N-Isocyanurate Derivative of Azahomo[60]fullerene.

The cyclic voltammogram of the title compound exhibits three reversible reduction peaks which are less negative than that of [60]fullerene.

<b>Synthesis, characterization and electrochemistry of heterobimetallic complexes containing molybdenum(II) nitrosyl and manganese(II)-schiff base centers</b>

New complexes derived from the reaction of Mo(NO)Tp*Cl2; Tp*= tris(3,5-dimethylpyrazolyl) borate with a series of manganese(II) Schiff bases have been synthesized. Characterization by UV, IR, MS and elemental analysis support their formulations. Cyclic and differential pulse voltammograms of manganese(II) Schiff base monometallic complexes exhibit one reduction peak which may be associated with the reduction of the manganese(II) center. In CH3CN solutions, the molybdenum(II)-manganese(II) bimetallic complexes showed two reversible reduction peaks which are associated with the reduction of the molybdenum and manganese centers. In CH2Cl2, only the reduction of molybdenum(II) center exhibited reversibility while the reduction of manganese(II) center was irreversible. These observations demonstrate that reduction potentials for bimetallic complexes are solvent dependent.KEY WORDS: Tetradentate N,N’,O,O, Schiff base ligands, Monometallic manganese(II) Schiff base complexes, Bimetallic, Mn(II)-Mo(NO)Tp*Cl2 [Tp* = tris(3,5-dimethylpyrazolyl) borate] complexes Bull. Chem. Soc. Ethiop. 2010, 24(1), 47-58.

Electrochemical Reduction Using Glassy Carbon Electrode in Aqueous Medium of a Potential Anti-Chagas Drug: NFOH

Nitrofurazone (NF) presents activity against Chagas’ disease, yet it has a high toxicity. Its analog, hydroxymethylnitrofurazone (NFOH), is more potent against Trypanosoma cruzi and much less toxic than the parent drug, NF. The electrochemical reduction of NFOH in an aqueous medium using a glassy carbon electrode (GCE) is presented. By cyclic voltammetry in anacidic medium, one irreversible reduction peak related to hydroxylamine derivative formation was registered, being linearly pH dependent. However, from , a reversible reduction peak at a more positive potential appears and corresponds to the formation of a nitro radical anion. The radical-anion kinetic stability was evaluated by the current ratio of the redox couple. The nitro radical anion decays with a second-order rate constant of 6.07, 2.06, and corresponding to pH 8.29, 9.29, and 10.2, respectively, with a corresponding half-time life of 0.33, 0.97, and 1.4 s for each pH value. By polishing the GCE surface with diamond powder and comparing with the GCE surface polished with alumina, it is shown that the presence of alumina affects the lifetime of the nitro radical anion.