A Voltammetric Study of the Chemosensor Activity of Aminoanthracene Derivatives

The redox activity of potent chemosensors based on anthryl-containing diamines, thioureas, and ureas in the absence and in the presence of complexing metal cations in solution was studied by cyclic and differential pulse voltammetry. The free energy of intramolecular electron transfer was calculated. The experimental conclusions were confirmed by ab initio RHF/6-31G** calculations. A correlation was found between the electrochemical and photophysical data for the compounds studied.     

Electrochemical transformations of cycloheptatriene derivatives

Redox reactions of a series of substituted cycloheptatrienes are studied on a platinum electrode in acetonitrile using the cyclic voltammetry method. It was found that heptaphenyl-substituted cycloheptatrienes are irreversibly oxidized in two stages in the range of high anodic potentials to form unstable radical cations and dications. As opposed to the unsubstituted and monosubstituted cycloheptatrienes, they are not reduced at the potentials higher than ?2 V (SCE). A new stable radical anion was found in the reduction of N-cycloheptatrienylphthalimide. Its spin density distribution is studied by ESR spectroscopy.     

Use of ultramicroelectrodes for determining lead in natural waters by stripping voltammetry

Anin situ obtained graphite-fiber-based thin-film mercury microelectrode was used for determining lead(II) in natural water by stripping voltammetry without removing oxygen and using no supporting electrolyte. Under the optimum voltammetric conditions (E _el = -1.2 V,t _el = 5 min,c _Hg(II) = 1 x 10^-7 M, ΔE = 40 mV, v= 105 mV/s), the calibration graph was linear in the range of actual lead(II) concentrations in natural waters. At a lead(II) concentration of 0.002 mg/L, the RSD was 11%.     

Frequency dependence of conductivity of ethylene carbonate based electrolyte for Li-ion battery

Specific cell arrangement corresponding to four probe pouch cell with two reversible current and two indifferent potential electrodes is applied to study the existence of frequency dependence on conductivity of a medium between two potential electrodes, i.e., separator impregnated with electrolyte. It is established that frequency dependence of conductivity for carbonate-based electrolyte solution does exist. Series resistance is found to be in a good agreement by specific value with that reported earlier. Low frequency limit of impedance spectra is a few decimal orders higher than that of series resistance. Both low- and high-frequency resistances increase with the interelectrode distance in agreement with Ohm law.     

Electrochemical conversions of pentaphenyl(methoxycarbonyl)cyclopentadiene derivatives

Redox processes of fluctuating pentaphenyl(methoxycarbonyl)cyclopentadiene derivatives on platinum electrode in acetonitrile are studied by cyclic voltammetry. The reduction of derivatives of pentaphenylcyclopentadiene C₅Ph₅M yields a radical anion which decomposes to anion M^- and stable radical C₅Ph ₅ ^• ; the latter reduces to C₅Ph₅. In the first stage of oxidation of these compounds, a stable radical cation forms, with substituent M intact. Reduction of derivatives of pentamethoxycarbonylcyclopentadiene [C₅(CO_2Me)₅]M yields a dianion. Such electrochemical behavior of fluctuating cyclopentadiene compounds reveals additional information on the mechanism of displacement of the element-centered substituents M in them     

Effect of ethylene carbonate concentration on the conductivity of carbonate-based electrolytes with LiPF6 for Li-ion batteries

A four-probe pouch-type cell was used to study the influence of carbonate-based electrolyte composition on the total conductivity of polyolefin separator impregnated with electrolyte through the electrochemical impedance spectroscopy. A frequency dispersion of separator with electrolyte is found to be dependent on the volume ratio of ethylene carbonate and ethyl methyl carbonate in an electrolyte solution. The origin of high- and low-frequency relaxation processes obtained from the impedance spectra is discussed. A correlation between the direct current resistance of separator with electrolyte and dissociation degree of electrolyte salt is found.     

Studies of oxidation of the 9-furylnaphtho[2,3-b]furan derivatives

With the purpose of establishing of mechanism of the furan ring oxidative cleavage in 9-furylnaphtho[2,3-b]furans obtained recently, their cyclic voltammometric study was carried out. Ability of these compounds to undergo three-step oxidation is revealed. Radical cations of the compounds under study formed in the first step of electrooxidation are partially stable. Comparison of the electrochemical characteristics of 9-furylnaphtho[2,3-b]furan with those of the specially prepared unsaturated 1,4-diketones showed that one of the pathways of further transformations of the compounds under investigation is the formation of the corresponding unsaturated 1,4-diketones. The results obtained tell in favor of participation of the 9-furylnaphtho-[2,3-b]furan radical cations in the process of chemical oxidation.     

Thermal reactions of lithiated graphite anode in LiPF6-based electrolyte

The thermal reactions of a lithiated graphite anode with and without 1.3 M lithium hexafluorophosphate (LiPF₆) in a solvent mixture of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) were investigated by means of differential scanning calorimetry (DSC). The products of the thermal decomposition occurring on the lithiated graphite anode were characterized by Fourier transform infrared (FT-IR) analysis. The lithiated graphite anode showed two broad exothermic peaks at 270 and 325 °C, respectively, in the absence of electrolyte. It was demonstrated that the first peak could be assigned to the thermal reactions of PF₅ with various linear alkyl carbonates in the solid electrolyte interphase (SEI) and that the second peak was closely related to the thermal decomposition of the polyvinylidene fluoride (PVdF) binder. In the presence of electrolyte, the lithiated graphite anode showed the onset of an additional exothermic peak at 90 °C associated with the thermal decomposition reactions of the SEI layer with the organic solvents.     

Polarographic Study of the Antioxidant Activity of Amino Acids and Proteins

Classical polarography and cyclic voltammetry were used to study the effect of a series of water-soluble amino acids and serum albumins on oxygen reduction in aqueous solutions. Positive or negative shifts of the reduction potential of oxygen were revealed, depending the nature of the compounds. The feasibility of polarographic methods for studying antioxidant properties of compounds was demonstrated.