Том 55, № 4 (2019)

The effect of addition of mactoheterocyclic compounds of the ABAB and A′BBB types, in which A (1,3-phenylene or 2,6-pyridine)moiety, A′ (1,3-phenylene)moiety, and A′ (1,3-isoindoline)moiety are interlinked by aza-bridges, and also of their complexes with copper(II) and cobalt(II) on the temperature-frequency characteristics of small-scale aluminum oxide capacitors with the vertical chip design is studied in the temperature range from −60°C to +100°C and the frequency range from 50 Hz to 200 kHz. It is shown that under conditions studied, the addition of macroheterocycles and their complexes decreases the resistance and the leakage currents of capacitor.

The data on carbonization and surface activation of raw hogweed (Heracleum) are presented. The structural and electrochemical properties of thus synthesized carbon materials which can be used as the electrode materials in supercapacitors are studied. The hogweed samples are preliminarily carbonized at 400°C and then activated with potassium hydroxide (KOH) at temperatures of 700, 800, and 900°C in argon atmosphere. According to isotherms of nitrogen adsorption and the BET equation, the specific surface area of samples activated at 700, 800, and 900°C is 913 ± 22, 1215 ± 70, and 1929 ± 99 m²/g, respectively. As the activation temperature increases, the specific surface area and the mesopore volume of samples also increases, whereas the micropore fraction decreases. 1,1-Dimethylpyrrolidinium tetrafluoroborate in acetonitrile was used as an electrolyte. The specific capacitance of samples activated at 700, 800, and 900°C at the current density of 1 A/g is 51 ± 4, 114 ± 2, and 108 ± 3 F/g, respectively. The 40% increase in the specific surface area and the 35% increase in the volume of mesopores results in the increase in the specific capacitance. The further increase in the specific surface area and the volume of mesopores up to 70% does not increase the specific capacitance.

In this study, a new biosensor for amisulpride (ASP) determination is defined. The interaction between ASP and fish sperm double-stranded DNA (FSdsDNA) was examined by differential pulse voltammetry (DPV) method utilizing FSdsDNA modified pencil graphite electrode (PGE). Sensitive and reliable ASP determination and detection was performed in pH 4.80 acetate buffer (20% ethanol) before and after the interaction of ASP and FSdsDNA, acting by the change in guanine oxidation signals from the electro-active bases of FSdsDNA. In addition, analytical method validity tests were examined in this study. This modified electrode have used in 1–10 μg/mL determination interval for the quantitative determination of ASP in pharmaceutical forms and the limit of detection (LOD) has been found as 0.46 μg/mL. Also, the binding constants (K_b) of the ASP with FSdsDNA has also been calculated both UV-Vis and DPV techniques.

Two novel, economic, rapid, simple, sensitive and selective square wave voltammetric (SWV) methods have been developed for the determination of cefuroxime axetil (CEFA) in pharmaceutical preparations. Electrochemical reduction and oxidation of the substance on hanging mercury drop electrode and graphene oxide modified glassy carbon electrode were investigated by square wave voltammetric methods which employ scan rates up to 1000 mV/s or faster, allowing much faster determinations. For hanging mercury drop electrode, well-defined peak was obtained at –1.06 V vs. Ag/AgCl/4.6 M KCl in 0.1 M phosphateborate buffer pH 7.0, limit of detection (LOD), limit of quantification (LOQ) and linearity range were found 0.09, 0.26, and 0.26–15 μg mL^–1, respectively. For modified glassy carbon electrode, well-defined peak was obtained at 1.30 V vs. Ag/AgCl/4.6 M KCl in Britton–Robinson buffer pH 2.0, LOD, LOQ and linearity range were found 2.70, 8.20, and 8.20–45 μg mL^–1, respectively. According to validation studies, the developed SWV methods were found as accurate, precise, specific, sensitive, repeatable, rugged and robust. The developed and validated SWV methods were applied to the determination of CEFA in pharmaceutical formulations. The results were compared with those obtained by a published ultraviolet spectroscopic method and no difference was found statistically.

Studies of zinc electrode oxidation under the conditions of limited volume of alkaline electrolyte are carried out. It is shown, that at anodic polarization below 7–8 mV the zinc surface is covered by phase layer of zinc oxides and hydroxides. The last ones hinder diffusion of ions participating in electrochemical reactions. Then, formation of zincate complex [\(\rm{Zn}(OH)\begin{array}{c}2-\\ 4\end{array}\)] starts, with the slow diffusion stage of hydroxide ions to the anode surface. At polarization from 0.08 to 0.12 V formation of supersaturated zincate electrolyte occurs, and its decomposition with formation of the loose zinc oxide layer. At polarization above 0.12 V, nonporous oxide film is formed on zinc surface; zinc oxidation process proceeds by solid-phase mechanism.

The influence of the electrode potential on the electric conductivity of polymer complexes of nickel with salen-type ligands (where salen is N,N′-ethylene-bis(salicylideneimine)) differing by substituents in ligand′s benzene ring is studied in the course of measuring cyclic voltammograms. The highest electron conductivity is observed for the film of poly[N,N′-ethylene-bis(3-methoxysalicylideneiminato) nickel(II)] (poly[Ni(CH₃OSalen)]) in 1 M LiPF₆ solution in the ethylene carbonate-diethylcarbonate mixture (EC: DEC = 1: 1). Poly[N,N′-ethylene-bis(3-methyl-salicyleneiminato) nickel(II)] (or poly[Ni(CH₃Salen)]) was found to have the widest potential range of electronic conductivity. Conditions are selected for synthesizing films from solutions of the corresponding monomers in 1 M LiPF₆ EC: DEC electrolyte. The electrode potential intervals suitable for the use of poly[Ni(CH₃Salen)] as the buffer interlayer between the aluminum substrate and the cathode mass in lithium-ion batteries for protecting the latter against overcharge are found.

The Pt/C, Rh/C, and Pt-Rh/C catalytic systems with uniform distribution of metal phase over the surface of carbon support and an average size of Pt and Rh nanoparticles of 7.3 and 6.5 nm, respectively, are fabricated by the method of electrochemical dispersion of metals in the aqueous electrolytes containing Na⁺. It is shown that the double-layer potential E = 300 mV (RHE) is the optimal potential of CO adsorption for determining the electrochemically active surface area of Pt/C, Rh/C, and Pt-Rh/C catalysts by the method of oxidative desorption of CO. The introduction of Rh into the Pt/C catalyst enables us to increase the specific activity and reduce the potential of the onset of methanol oxidation.