Volume 52, Nº 4 (2016)

The possibility of assessing the selectivity of composite perfluorated membranes MF-4SK modified with polyaniline (PANI), based on the concentration dependence of their specific conductivity in terms of the extended three-wire model of conduction of ion-exchange materials is investigated. To check the reliability of results obtained, the transport numbers of ions are calculated based on the electrodiffusion coefficients of counter ions and coions determined from concentration dependences of conductivity and diffusion permeability of ion-exchange membranes. The transport numbers of hydrogen ions found by these two methods are shown to coincide with high accuracy throughout the whole range of concentrations of HCl solutions for the original MF-4SK membrane and membranes with the fixed thickness of the modified polyaniline layer on their one side. For the MF-4SK sample the with gradient distribution of polyaniline, which exhibits asymmetrical transport characteristics, the deviation between the transport numbers of ions calculated with the use of electrodiffusion coefficients of counter ions and coions and those determined in terms of the extended three-wire model of conduction is shown to increase with the increase in solution concentration but not exceed 4%.

New solid electrolytes with a high rubidium-cation conductivity, which are based on Rb₃PO₄ with partial substitution of three-charged yttrium, lanthanum, and neodymium cations for Rb⁺ cations, are synthesized and studied. Introduction of M³⁺ cations leads to an abrupt increase in the conductivity of rubidium orthophosphate due to the formation of cationic vacancies and stabilization of high-temperature cubic β-modification of Rb₃PO₄. In all systems, the highest conductivity is observed in the single-phase region of β-phase existence: it is ~10^–1 S cm^–1 at 700°C and above 10^–2 S cm^–1 at 400°C. The factors, which have an effect on the transport properties of studied electrolytes, are considered.

In the present study, the electrochemical behavior of 6-Thioguanine (6-TG) and its interaction with double-strand DNA (ds-DNA) were investigated at the surface of hanging mercury drop electrode (HMDE) in neutral media. The interaction of 6-TG with ds-DNA in neutral buffer was clearly demonstrated by the elimination of 6-TG signal and the advent of a new reduction peak. To investigate the interaction, various parameters including accumulation time and potential as well as ds-DNA concentration were optimized using a combination of adsorptive stripping voltammetry (AdSV) and square wave voltammetry (SWV) techniques. As a consequence a low detection limit of 1.1 μM was obtained in a dynamic range of 16.0 to 360.0 μM. To better understand the interaction mechanism between 6-TG anti-cancer drug and ds-DNA, cyclic voltammetry and UV-Vis spectroscopy measurements were carried out and the intercalation of 6-TG into ds-DNA was proposed as the plausible mechanism. The application of this screening assay in real sample analysis was investigated by using the procedure for determination of 6-TG in 6-Thioguanine tablets and also in spiked 6-TG blood serum. Overall, the results were indicative of a DNA sensor which could be applied effectively in the analysis of 6-TG in vitro.

Experimental information on the electrochemical behavior of guanine synthetic derivatives (acyclovir, valacyclovir, ganciclovir, and famciclovir) with the strong antiviral activity on presynthesized activated carbosital electrode (CSE) in aqueous solutions of different acidity is obtained. The mechanism of irreversible oxidation of substances containing guanidine group (–NH–C(NH–)=N–) is discussed and the dependences of current and potential of experimental anodic peaks on the potential scan rate, the nature and acidity of supporting electrolyte solution, and also on the concentration of depolarizer and the time of its accumulation on the electrode surface are found. It is shown that all other factors being equal (0.1 М phosphate buffer, рН 6), the position of the observed anodic peak depends substantially on the nature of acyclic substituent at N(9) of imidazole ring in the aminopurine molecule: the susceptibility to oxidation decreases in the series Gua (E_pa = 0.84 V), ACV (E_pa = 1.00 V), VACV (E_pa = 1.04 V), GCV (E_pa = 1.07 V), FCV (E_pa = 1.20 V). It is shown that the electrocatalytic activity and the high absorbability of the activated CSE with respect to substances tested make it possible to reach their lower detection limits (20–40 nM) in multicomponent solutions.

Three-dimensional (3D) porous Au nanocoral network (GNN) structure was fabricated on glassy carbon (GC) electrode by one-step, template-free electrodeposition and decorated with ultrathin Pt film by combining the underpotential deposition (UPD) of copper adatoms and the galvanic displacement (GD) between PtCl₆^2- and Cu. The thickness of Pt atomic layers can be controlled precisely by repeating the UPD–GD process. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) were employed to characterize the morphology of GNN and Pt_n/GNN (n, the cycles of repeating the UPD–GD process). Cyclic voltammometric and chronoamperometric tests indicate that all Pt_n/GNN samples effectively support the direct oxidation of formic acid and show higher electrocatalytic performance than the commercial Pt/C catalyst (Pt, 20 wt %, Johnson Matthey Co.), where Pt₁/GNN completely eliminates the indirect oxidation of formic acid, exhibiting the best electrocatalytic activity and stability among all Pt_n/GNN samples due to the optimal coverage and distribution of Pt atoms on GNN.

Heterovalent substitution solid solutions of tetragonal modification isostructural with β-PbSnF₄ and having fluoride anions localized in three structurally nonequivalent positions are formed in the (1–x)PbF₂–xYF₃–SnF₂ system in the concentration range 0 < x ≤ 0.17. The conductivity of the synthesized samples is provided by the interstitial fluoride anions and is independent of the concentration of the heterovalent substituent at temperatures below 300 K. The contribution of the surface conductivity of the crystallites of the synthesized samples to the total bulk conductivity was not found. The temperature dependences of electric conductivity of each of the synthesized samples show an inflection at 435–475 K, which is due to the increased mobility of fluoride anions at elevated temperatures. The transport numbers of the fluoride anions are close to unity over the whole range of concentrations of the synthesized samples and are almost independent of the YF₃ concentration. The electronic conductivity of the samples was two orders of magnitude lower than the ionic conductivity.

The phase composition of alloys in the Ag–Bi–S–I system (in the region AgI–Bi–Bi2S3–BiSI) for Т ≤ 550 K was studied by physicochemical analysis methods. Equations of overall potential-forming reactions involving the BiSI and Bi₁₉S₂₇I₃ phases were composed. The reactions were performed in the C|Ag|glass Ag₃GeS₃I|D|C electrochemical cells (C are inert (graphite) electrodes; Ag, D are the cell electrodes; D are the four-phase alloys of the system; and glass Ag₃GeS₃I is a membrane with pure Ag⁺ ion conductivity). The linear dependences of EMF of the cells in the range 485–525 K were used for calculating the standard thermodynamic properties of saturated solid solutions of the compounds BiSI and Bi₁₉S₂₇I₃ in the AgI–Bi–Bi₂S₃–BiSI system.