Specific features of electrochemical reduction of α,α,α′,α′-tetrabromo-p-xylene at its low concentrations

In the cyclic voltamograms for electrochemical reduction of α,α,α′,α′-tetrabromo-p-xylene at its concentrations of 5 and 10 mM in dimethylformamide solution of 0.1 M Bu₄NBF₄, taken at glassy-carbon electrode, four current peaks corresponding to consecutive stages of the reduction process are observed for the first time. The many times repeated potential cycling from 0 V (SCE) to the value approaching the 2nd peak potential results in the electrode passivation; a film of the intermediate product of the α,α,α′,α′-tetrabromo-p-xylene reduction is deposited at the electrode, whose composition may be-(BrCH-C₆H₄-CHBr-BrCH-C₆H₄-CHBr)_n-. When the electrode covered with the deposited film is transferred to a solution of the same composition, in which the primary cycling was performed, yet free from α,α,α′,α′-tetrabromo-p-xylene, and underwent to potential cycling up to ?2V, the first cycle demonstrates a current peak that is due to the film reduction. A redox-active poly(p-phenylenevinylene) forms at the electrode.     

Redox capacitance of poly-3,4-ethylenedioxythiophene studied by cyclic voltammetry and faradaic impedance spectroscopy

The paper presents results of studying the electrochemical properties of poly-3,4-ethylenedioxythiophene films using the methods of cyclic voltammetry and faradaic impedance spectroscopy in acetonitrile and propylene carbonate solutions of different electrolytes: LiClO₄, Bu₄NBF₄, Bu₄NPF₆. The effect of the film synthesis conditions, the nature of anion and solvent, and the supporting electrolyte concentration on the film redox capacitance is discussed. Main attention is paid to the comparison of values characterizing the redox capacitance of a poly-3,4-ethylenedioxythiophene film C _lf (determined using the faradaic impedance method) and C _cv (determined using the cyclic voltammetry method) and the studies of their dependence on the varied experimental factors. The experimental C _lf vs. E curves are analyzed using the relationships of a model of a uniform film.     

Tetraaryl-1,3-dioxolane-4,5-dimethanols as catalysts for the addition of trimethylsilyl cyanide to benzaldehyde and the oxirane ring

The synthesis of 1,2-, 1,3-, and 1,4-phenylene-bis[(4R,5R)-4,5-di(hydroxydiphenylmethyl)-1,3-dioxolane]s (ortho-, meta-, and para-bis-(R,R)-TADDOLs) and bis[4-{[(4R, 5R)-4,5-di(hydroxydiphenylmethyl)]-1,3-dioxolan-2-yl}phenyl]methane was carried out. The possibilities of the use of these compounds as catalysts for the C-C bond formation in the addition of Me₃SiCN to benzaldehyde and the oxirane ring opening in cyclohexene oxide by Me₃SiCN were investigated. The catalytic activity of different bis-(R, R)-TADDOLs in this series depends on their structure. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1451–1458, August, 2007.     

Spectroelectrochemical study of poly-3,4-ethylenedioxythiophene films in the presence of different supporting electrolytes

Steady-state absorption spectra of poly-3,4-ethylenedioxythiophene (PEDOT) films at different oxidation degrees and their differential cyclic voltabsorptograms are studied in 0.1 M LiClO₄, Bu₄NBF₄, and Bu₄NPF₆ solutions in acetonitrile. Three major absorption bands are obtained in the film electronic spectra: a complex band with a pronounced maximum at λ = 600 nm that corresponds to π → π* electronic transitions in reduced fragments of a PEDOT film and two absorption bands (at λ_max = 850 nm and λ_max > 1100 nm) corresponding to two oxidized film fragments. It is shown that the position and shape of absorption bands are practically independent of the nature of dopant anions, which points to the absence of pronounced interactions with positively charged polymer fragments. An attempt is made to analyze the obtained spectroelectrochemical data qualitatively to estimate the extinction coefficients and concentrations of absorbing particles and their variation in the course of redox processes.     

Cathodic materials for lithium-ion batteries based on spinels Li x Mn2−y Me y O4: Synthesis, phase composition, and structure of Li x Mn2−y Cr y O4 at x = 1.0−1.2 and y = 0−0.5

Extralithiated chromium-doped finely divided lithium-manganese spinels are synthesized as a result of a two-step solid-phase process with use made of the fusion-saturation method. The spinels are intended for application as cathodic materials in lithium-ion batteries. The phase composition and structural characteristics of samples of cathodic materials of the type Li _x Mn_2?y Cr _y O₄ are studied. The samples with x = 1.0?1.2 and y = 0?0.5 are characterized by phase purity and cubic syngony with parameter a = 0.817?0.823 nm and a disperseness equal to 1–2 nm. The maximum content of chromium and lithium in Li _x Mn_2?y Cr _y O₄ that does not lead to violation of cubic syngony is determined. Lithium excess in the cathodic material that does not exceed 0.2 formula units may be used for compensating the irreversible capacity. Replacing some manganese atoms by chromium may facilitate retention of the structures’s integrity in the course of cycling.     

Thermodynamic investigations of interaction of aqueous solutions of 2′,3′-dideoxyinosine and 2′,3′-dideoxyadenosine with glycyl-glycine

2′3′-dideoxyinosine (ddI) and 2′3′-dideoxyadenosine (ddA) are known to exhibit relatively selective activityvs. HIV strains in cell cultures and low toxicityin vivo; ddI has been approved for the treatment of HIV infection in humans. It is therefore interesting to determine the thermodynamic properties of aqueous solutions of these compounds. For this purpose, we determined their apparent molar volumesV _? and heat capacitiesC _P?. The preliminary measurements of interaction of these compounds with peptides were made. The volume and molar heat capacities of transfer of ddI and ddA from aqueous solutions to glycyl-glycine (Gly-Gly) ones were calculated. For both compounds the significant values ofC _P?3,tr which depended on the concentration of Gly-Gly were observed.     

Adsorption phenomena on a mercury electrode in aqueous cryptand[2.2.2] solutions by the background of tetraalkylammonium salts

The electrochemical behavior of cryptand[2.2.2] (Cry) is studied on a mercury electrode in aqueous solutions of tetraalkylammonium tetrafluoroborates (Me₄N⁺, Et₄N⁺, and Bu₄N⁺). Cryptand [2.2.2] is shown to exhibit high surface activity in Me₄ NBF₄ nd Et₄NBF₄ solutions. Based on the model of two parallel capacitors supplemented by the Frumkin adsorption isotherm, the adsorption parameters of Cry by the background of Me₄BNF₄ were calculated using the regression analysis methods. The calculated dependences of the differential capacitance on the potential adequately agree with experimental curves. The adsorption characteristics of Cry in the studied solutions are compared with those in MgSO₄ solutions. By the background of Bu₄NBF₄, Cry molecules and Bu₄N⁺ cations exhibit very close surface activity and form a mixed adsorption layer.     

Anodic Doping of Electropolymerized Copper 2,9,16,23-Tetraaminophthalocyanine

Anodic polymerization of 2,9,16,23-tetraamino substituted copper phthalocyanine is studied in 0.1 M Bu₄NBF₄and Bu₄NClO₄in dimethylformamide (DMF). The electropolymerization rate in DMF is two to three times that in dimethyl sulfoxide, due to a lesser donor ability of DMF and a weaker blocking of radical cations formed during the oxidation of initial copper phthalocyanine. According to a study of the electrochemical behavior of polymerized copper phthalocyanine in neutral aqueous solutions, the anodic doping of the polymer is accompanied by one redox transition. The two redox transitions, observed in an aqueous solution of acid, are explained by two successive steps of oxidation of an aniline-like structure or by the involvement of two protonated systems in the doping process, specifically, a stacked system (phthalocyanine ligands collected in parallel stacks) and a polyaniline system.     

Electrochemical behavior of fullerene C60 and substituted fullerenes immobilized on an electrode surface

The effect of substituents with different donor capabilities, which are inserted into a molecule of fullerene C₆₀, on the kinetics and thermodynamics of redox conversions of fullerenes that are immobilized on an electrode, is studied for the first time. To this end, redox conversions that occur with rubbed-on films of fullerene and fulleropyrrolidines are studied using cyclic voltammetry in 0.5 M KCl/H₂O and a 0.1 M (C₄H₉)₄NBF₄/AN solution in acetonitrile. A hypothesis that the kinetics of redox conversions occurring with films of individual fullerenes is defined largely by changes in the structure of initial films in the process of their cathodic doping is used. The effect of the substituents is explained in the framework of this hypothesis by a transition from a dense crystalline structure of nonsubstituted fullerene C₆₀ to an amorphous structure of substituted fullerenes. It is demonstrated that the formal potentials corresponding to redox conversions of fullerenes in a solid cationic lipid matrix are defined by the energy of interaction of anions, which are products of reduction of fullerenes, with cations of the matrix. As a result of this interaction, the formal potentials of the process of cathodic doping shift to less negative values. It is established that the insertion of a donor substituent and increase in its donor capability amplify the energy of interaction of the fullerene anions with the lipid cations.     

Direct Electron Transfer Reactivity of Hemoglobin in Cationic Gemini Surfactant–Poly (Allylamine) Hydrochloride Composite Film on Glassy Carbon Electrode

A new composite film comprising cationic gemini surfactant butane-α,ω-bis(dimethyl dodeculammonium bromide) (BDDA, C₁₂-C₄-C₁₂) and poly (allylamine) hydrochloride(PAH) have been prepared. The composite film showed good biocompatibility and could promote the direct electron transfer between hemoglobin (Hb) and glassy carbon (GC) electrode. The immobilized Hb exhibited a pair of well-defined, quasi-reversible, and stable redox peaks with a formal potential of ?0.158 V (vs. SCE) in 0.10 M pH 7 phosphate buffer solutions, and showed high affinity to hydrogen peroxide. The cathodic peak current of the electrode was linear with increasing concentration of H₂O₂ in the range of 5.14 to 200 μM.     

Conjugate Elimination of Fluorine Atoms in Halophosphonates

Facile electrochemical elimination of fluorine on a mercury drop electrode in aqueous-ethanol solutions on the background of 0.1 M Bu₄NBF₄ (E _{1 / 2} 2.0 V against saturated calomel electrode) from diethyl chlorofluoromethyl- and diethyl dichlorofluoromethylphosphonates was observed. Under the same conditions, diethyl fluoromethylphosphonate is not reduced.     

Photoelectrochemical Behavior of Poly(3,4-ethylenedioxythiophene) in Acetonitrile Solutions during Cathodic Reduction of Oxygen

The photoelectrochemical behavior of a polymer electrode based on poly(3,4-ethylenedioxythiophene) (PEDT) is studied in acetonitrile solutions during the cathodic reduction of oxygen. The measurements are taken on PEDT films 490 nm thick deposited onto a platinum support in oxygen-saturated 0.1 M Bu₄NBF₄ solutions. The electrode was illuminated with a light of a wavelength 487 nm from a helium–cadmium laser in conditions of modulated illumination, and in doing so, the real and imaginary components of an alternating photocurrent were measured at different modulation frequencies. The peculiarity of the photoelectrochemical behavior of PEDT manifests itself in the emergence of an anodic photocurrent, which increases with a change in potential in the cathodic direction. At low modulation frequencies, the real and imaginary components are of the same sign, whereas at high modulation frequencies the components have opposite signs (photocurrent lags behind a change in the light intensity). The emergence of an anodic photocurrent is connected with the cathodic reduction of oxygen and the formation in a near-electrode layer of radical anion O^– ₂. Such a behavior of PEDT, which makes it different from other polymers of the thiophene series, is explained by different potentials of their anodic oxidation, to which a conductive state of the polymer is related.     

Direct electrochemistry of myoglobin in a layer-by-layer film on an ionic liquid modified electrode containing CeO2 nanoparticles and hyaluronic acid

We describe an ionic liquid modified electrode (CPE-IL) for sensing hydrogen peroxide (HP) that was modified by the layer-by-layer technique with myoglobin (Mb). In addition, the surface of the electrode was modified with CeO₂ nanoparticles (nano-CeO₂) and hyaluronic acid. UV-vis and FTIR spectroscopy confirmed that Mb retains its native structure in the composite film. Scanning electron microscopy showed that the nano-CeO₂ closely interact with Mb to form an inhomogeneously distributed film. Cyclic voltammetry reveals a pair of quasi-reversible redox peaks of Mb, with the cathodic peak at ?0.357?V and the anodic peak at ?0.269?V. The peak separation (??E _p) and the formal potential (E ^0??) are 88?mV and ?0.313?V (vs. Ag/AgCl), respectively. The Mb immobilized in the modified electrode displays an excellent electrocatalytic activity towards HP in the 0.6 to 78.0???M concentration range. The limit of detection is 50?nM (S/N?=?3), and then the Michaelis-Menten constant is 71.8???M. We believe that such a composite film has potential to further investigate other redox proteins and in the fabrication of third-generation biosensors.

Electrochemical systems for galvanic cells in organic aprotic solvents: V. Electrochemical behaviour of gamma-butyrolactone

Gamma-butyrolactone (GBL) was shown to decompose on the clean surface of Li, Na, K, and their amalgams. Polarization curves were obtained on Pt and “Kovar” electrodes at potentials from 4 to ?4 V vs. Li?Hg in 0.5 M LiClO₄ or vs. K?Hg in 0.5 M KPF₆. GBL was found to reduce electrochemically at potentials more positive than 1 V. Various passivation phenomena provoked by the decomposition of the solvent were observed, hindering cathodic deposition of the alkali metals from solutions of their salts in GBL. The presence of a high-molecular surfactant in the electrolyte suppresses the decomposition of GBL and suggests a path to the deposition of Li on the electrode.     

Rearrangement oftrans-stilbene into diphenylacetaldehyde acetals induced by direct anodic oxidation

Direct anodic oxidation oftrans-stilbene in lower alcohols and in some other solvents in the presence of KF or Bu₄NBF₄ is accompanied by its electrooxidatve rearrangement into diphenylacetaldehyde acetals; a competing reaction yields 1,2-dialkoxy-1,2-diphenylethanes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2202–2205, December, 1997.     

Electrochemical synthesis of poly(<Emphasis Type="Italic">O</Emphasis>-tolidine): Electrochemical and spectroscopic characterization

Polymerization of (O-tolidine), as ring substituted derivative of benzidine was achieved electro-chemically in organic solution containing Bu₄NBF₄ (0.2 M) in dichloromethane as supporting electrolyte. The film was obtained by electropolymerization in solution containing monomer in various ratio ((5 × 10⁻⁴)–(5 × 10⁻²) M). This polymer was characterized by cycling voltammetry, impedance measurement, UV-visible and FT-IR spectroscopy.     

Electrochemical behavior of complex based on ruthenium(II) phthalocyaninate

The electrochemical reactions of ruthenium(II) bis(triethylenediamine)tetra-tret-butyl-phthalocyaninate in dimethylformamide are studied. Two reversible redox reactions on the platinum amalgam electrode are revealed at the potentials of ?0.73 and ?1.16 V (Ag/AgCl). Similarly to several other phthalocyanines, these redox reactions correspond to the successive transfer of two electrons to phthalocyanine ring. A new phenomenon, which has not been reported in the literature for phthalocyanines, namely, the cathodic polymerization, is discovered. Thus formed polymer is redox-active, and only one cathodic reaction at the potentials from ?0.78 to ?0.84 V (a shift in the cathodic direction takes place as the film thickness increases) is observed in the polymer. In addition, the polymer exhibits also considerable electron conductivity that enables one to perform various electrochemical reactions in a wide potential range on the electrode modified with the polymer.     

The Synthesis and Characterization of Ru<Subscript>2</Subscript>(DMBA-X)<Subscript>4</Subscript>Cl<Subscript>2</Subscript> with X as Br and I

New N,N′-dimethylbenzamidine ligands bearing para-Br (HDMBA-Br) and para-I (HDMBA-I) substituents were prepared and crystallographically characterized. The ligand exchange reaction between Ru₂(OAc)₄Cl and HDMBA-X (X = Br and I) afforded the new Ru₂(III) compounds, namely Ru₂(DMBA-X)₄Cl₂, in excellent yields. These new compounds were also characterized with cyclic voltammetric and single crystal X-ray diffraction techniques. Dedicated to the memory of Professor F. A. Cotton.     

Mediated electrochemical synthesis of copper nanoparticles in solution

Environmentally friendly mediated electrochemical synthesis of copper nanoparticles in the solution using a copper anode as a source of copper ions has been realized for the first time. It is shown that at the potential of the redox pair MV²⁺/MV?⁺ methylviologen MV²⁺ is able to mediate a reduction of Cu²⁺ ions in 60% aqueous DMF/0.1 M Bu₄NBF₄. Copper nanoparticles build large aggregates (200—250 nm) in the absence of a stabilizer. The use of polyvinylpyrrolidone as a stabilizer makes it possible to obtain smaller copper nanoparticles (20—50 nm) of spherical and oval shape and to characterize them by physicochemical methods.     

Transport behavior in isomeric alcohols. I. The conductance of tetraalkylammonium salts in isobutyl and isopentyl alcohols at 25°C

Conductance measurements at 25°C have been carried out on Pr₄NBr, Bu₄NBr,n-Pe₄NPr, Pr₄NI, Bu₄NI,n-Pe₄NI, Bu₄NClO₄, Bu₄NBF₄, and Bu₄PClO₄ in isobutyl alcohol and on Bu₄NBr and Bu₄NClO₄ in isopentyl alcohol. The main purpose of the measurements was to investigate the effect of increased branching in the alkyl portion of the alcohol on both ionic mobilities and ionic association. Comparison is made with the two isodielectric solvents butanone andn-butyl alcohol. Branching appears to produce little change in ionic mobilities and approximately a 10% increase in association.