A LABEL-FREE VOLTAMPEROMETRIC SENSOR BASED ON ELECTRIC CONDUCTIVE POLYMER COATINGS OF 3,4-ETHYLENEDIOXYTHIOPHENE / 3-ETHYNYLTHIOPHENE FOR DETERMINATION OF E.COLI AND S.AUREUS

This work was supported by a grant from the President of the Russian Federation for young scientists - candidates of sciences MK-567.2020.3

Biomolecular Release from Alginate-modified Electrode Triggered by Chemical Inputs Processed through a Biocatalytic Cascade – Integration of Biomolecular Computing and Actuation

Biocatalytic cascades involving more than one or two enzyme-catalyzed step are inefficient inside alginate hydrogel prepared on an electrode surface. The problem originates from slow diffusion of intermediate products through the hydrogel from one enzyme to another. However, enzyme activity can be improved by surface immobilization. We demonstrate that a complex cascade of four consecutive biocatalytic reactions can be designed, with the enzymes immobilized in an LBL-assembled polymeric layer at the alginate-modified electrode surface. The product, hydrogen peroxide, then induces dissolution of iron-cross-linked alginate, which results in release process of entrapped biomolecular species, here fluorescently marked oligonucleotides, denoted F-DNA. The enzymatic cascade can be viewed as a biocomputing network of concatenated AND gates, activated by combinations of four chemical input signals, which trigger the release of F-DNA. The reactions, and diffusion/release processes were investigated by means of theoretical modeling. A bottleneck reaction step associated with one of the enzymes was observed. The developed system provides a model for biochemical actuation triggered by a biocomputing network of reactions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, WeinheimNational Science Foundation, NSF: CBET-1403208Russian Science Foundation, RSF: 17-13-01096This work was supported by National Science Foundation, USA, (award CBET-1403208) and by Russian Science Foundation (project no. 17-13-01096)

Electrochemical behavior of chloramphenicol on carbon electrodes in a microelectrochemical cell

Express determination of antibiotics is an extremely important task today. Portable electrochemical microdevices are a viable alternative to traditional methods of analysis. The development of such devices requires the study of redox processes in detail. This article is devoted to the comparative study of the electrochemical behavior of chloramphenicol in water solvents in standard laboratory and portable microelectrochemical cells. It was found that the electrochemical reduction of chloramphenicol proceeds via a 3-electron mechanism to the formation of a dimer. In the transition from the macrocell to the microcell, a decrease in the electrochemical reduction current and a shift of the peak potential to the cathode region are observed, which is apparently associated mainly with the type of the electrode material. The best characteristics of the direct electrochemical response were obtained in the differential pulse voltammetry mode. Under the selected operating parameters, the peak current of the electrochemical reduction of chloramphenicol is linearly dependent on the concentration of the antibiotic in the range of 2∙10–3–1∙10–5 M with a detection limit of 3∙10–5 M. Obtained characteristics are sufficient for the quality control of pharmaceuticals and can be improved through the use of organic and hybrid modifiers of the working electrode surface

The electrochemical behavior’s character of a potential antiviral drug 3-nitro-4-hydroxy-7-methylthio-4H-[1,2,4]triazolo[5,1-c][1,2,4]triazinide monohydrate

The results of this study of the electrochemical transformation of 3-R-4-hydroxy-1,4-dihydro-7-X-1,2,4-triazolo[5,1-c][1,2,4] obtained by voltammetry are presented. It was found that 3-R-4-hydroxy-1,4-dihydro-7-X-1,2,4-triazolo[5,1-c][1,2,4] derivatives are capable of electrochemical reduction in the potential range of –0.28 to –0.33 V (relative to Ag/AgCl) in Britton–Robinson buffer at pH = 2. The electrochemical behavior of the sodium salt of 3-nitro-4-hydroxy-7-methylthio-4H-[1,2,4]triazolo[5,1-c][1,2,4]triazinide monohydrate (compound 1), which in silico modeling predicted possible biological activity against various tick-borne encephalitis and Coxsackie B3 viruses. At the potentials of the first stage of electroreduction at pH = 2, the main transformation process is the three-electron reduction scheme of the nitro group of compound 1. It was established that compound 1 in an aprotic medium is reduced in ionic form, most likely in the form of an ion pair with the Na+ cation, and in an aqueous medium in the form of a protonated particle. Based on this, a scheme was proposed for the probable electrochemical transformation of the studied compound

Evaluation of Electrochemical Performance of Antimony Modified Screen-Printed Carbon Electrodes

Received: 07.03.2024. Revised: 25.03.2024. Accepted: 28.03.2024. Available online: 09.04.2024.Neutral red was used as redox probe for comparative evaluation of the electrochemical performance of SPCEs modified with antimony.CV experiments showed an increase in the electroactive surface area of Sb/SPCEs compared to the bare-SPCE, depending on surface morphology.The obtained SEM, cyclic voltammetry and EIS data are in good agreement.A good correlation between electrochemical and electroanalytical characteristics of Sb/SPCEs was observed.NR as a redox probe can help controlling modification processes during the development of innovative antimonycontaining sensors.This study compares the electrochemical performance of screen-printed carbon electrodes (SPCEs) modified with antimony (Sb/SPCEs) under different potentiostatic pre-plating conditions. Neutral Red (NR) was employed as a novel redox probe to evaluate the electrochemical performance of Sb/SPCEs. It was demonstrated that NR in the protonated form performs quasi-reversible redox transformations at bare SPCE and Sb/SPCEs in phosphate buffer solutions (pH 5.5±0.5) in the potential range of (−0.30)–(−0.75) V, where the antimony is not electroactive. Sb/SPCEs were studied electrochemically by cyclic voltammetry (CV) / electrochemical impedance spectroscopy (EIS), and morphologically by scanning electron microscopy (SEM). Cyclic voltammetry investigations revealed the dependence of the electrochemical performance of Sb/SPCEs on the degree of coverage of the substrate with the metal. The obtained CV, EIS, and SEM data are consistent. The lowest charge transfer resistance (Rct) value (6 Ω) was obtained at Sb/SPCE with the highest degree of antimony coverage. To investigate the electroanalytical performance of Sb/SPCEs, nickel (II) ions were utilized as a model analyte. A study of roughness factors and sensitivity towards nickel (II) ions for Sb/SPCEs using twotailed Pearson's criterion revealed a high degree of correlation between their electrochemical and electroanalytical properties. The results show that using NR as a redox probe can help controlling modification processes during the development of innovative antimony-containing sensors.This work was supported by the Ministry of Science and Higher Education of the Russian Federation (Ural Federal University Program of Development within the Priority-2030 Program)

SMALL ORGANIC MOLECULES FOR SELECTIVE ELECTROCHEMICAL DETERMINATION OF NITROAROMATIC COMPOUNDS

The work was carried out with the financial support of the Russian Science Foundation grant No. 20-13-00142

Determination of E. Coli in Water Using the Enzyme Free Electrochemical Impedimetric Immunosensors

In this article, we have shown the results of E. coli bacteria determination in water using the enzyme free electrochemical immunosensor with covalent via click chemistry immobilized receptor layer in comparison with dropwise immobilized antibodies. Covalent immobilization was realized by creating precursors on the surface of the working electrode with the reaction of azide-alkyne copper-catalysed cycloaddition approach. The detection limit of the immunosensor with covalent and dropwise immobilization of antibodies was estimated as 6.6 CFU/ml and 11.2 CFU/ml, respectively, a linear range was 103-106 CFU/ml. Moreover, the sensor with "click"immobilized antibodies showed good stability for 30 days when stored in a phosphate buffer, while the sensor with dropwise immobilized receptor layer was stable for 3 days. © Published under licence by IOP Publishing Ltd.This work was supported by the Presidential Grants Fund of the Russian Federation (grant MK-567.2020.3)

Redox Conversions of 5-Methyl-6-nitro-7-oxo-4,7-dihydro-1,2,4triazolo[1,5-a]pyrimidinide l-Arginine Monohydrate as a Promising Antiviral Drug

This article presents the results of a study of electrochemical transformations in aqueous and aprotic media of 5-methyl-6-nitro-7-oxo-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidinide l-arginine monohydrate (1a, Triazid) obtained by electrochemical methods and ESR spectroscopy. The effect of pH on the current and the reduction potential of 1a in an aqueous Britton–Robinson buffer solution was studied. It was found that 1a is irreversibly reduced in aqueous acidic media on a glassy carbon electrode in one stage with the participation of six electrons and the formation of 5-methyl-6-amino-7-oxo-1,2,4-triazolo[1,5-a]pyrimidin. The electroreduction of 1a in DMF on a background of tetrabutylammonium salts proceeds in two stages, controlled by the kinetics of second-order reactions. In the first stage, the reduction of 1a is accompanied by protonation by the initial compound of the basic intermediate products formed in the electrode reaction (self-protonation mechanism). The second quasi-reversible stage of the electroreduction 1a corresponds to the formation of a dianion radical upon the reduction of the heterocyclic anion 5-methyl-6-nitro-7-oxo-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidin, which is formed upon the potentials of the first peak. The ESR spectrum of the radical dianion was recorded upon electroreduction of Triazid in the presence of Bu4NOH. The effect of the formation of ion pairs on the reversibility of the second peak of the 1a transformation is shown. A change in the rate and regioselectivity of the protonation of the dianion radical in the presence of Na+ and Li+ ions is assumed. The results of studying the electroreduction of 1a by ESR spectroscopy with a TEMPO trap make it possible to assume the simultaneous formation of both a nitroxyl radical and a radical with the spin density localized on the nitrogen at the 4 position of the six-membered ring. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This work was supported by the Russian Foundation for Basic Research (RFBR, project No. 19-29-08015 mk)

Electrochemical creatinine determination with metal-organic framework catalyst based on copper and acetylenedicarboxylic acid

Fast and accurate determination of creatinine is critical in kidney function diagnostics. This paper discusses the usage of the metal-organic framework based on copper(II) and acetylenedicarboxylic acid (CuADCA) as a catalyst of electrochemical oxidation of creatinine, glucose and urea. CuADCA was synthesized by deprotonation with triethylamine for the first time. Successful synthesis was confirmed by FTIR and EDS. The material was characterized by SEM, EIS, and CV. CuADCA forms laminated-like flakes with diameter from 1 µm to 20 µm, which is consistent with the polymer-like structure. CV and EIS analyses showed that CuADCA immobilized on GCE acts as a catalyst in electrooxidation reaction of glucose, urea, and creatinine. The sensitivity of creatinine detection, 1057±99 µA/mM, was higher than the detection sensitivity of glucose and urea by more than 100 times with the limit of detection of 2 µM, so CuADCA is a promising material for further development of enzymeless sensors for creatinine