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The determination of cholesterol concentration in the blood is an important characteristic of the state of health. Modern methods for the detection of cholesterol involve the use of enzymes or expensive and complicated equipment. In this study, an enzymeless electrochemical method for the quantitative determination of cholesterol using cobalt (II) chloride as an electrocatalyst has been proposed. An analytical signal was peak current of cobalt (II) chloride faradaic oxidation on a platinum disk electrode in acetonitrile media in the presence of cholesterol via linear sweep voltammetry. A possible path of the electrocatalytic oxidation of cholesterol on the electrode surface was proposed. The catalytic constant k cat and the Michaelis constant K m calculated for the electrocatalytic oxidation process of cholesterol on the electrode surface are comparable in magnitude to the natural enzyme cholesterol oxidase, indicating the high efficiency of CoCl 2 as an electrocatalyst for oxidation and, therefore, the determination of cholesterol. The highest value and the best reproducibility of analytical signal are reached at a CoCl 2 concentration of 25 mM and a scan rate of 100 mV·s − 1 . The linear region of the calibration curve “current-cholesterol concentration” obtained using a developed method in a solution of 0.1 M LiClO 4 and 25 mM CoCl 2 in acetonitrile is 25–200 μM (R 2 = 0.971) with a detection limit of 2 μM. [ABSTRACT FROM AUTHOR]

An electrochemical immunosensor for diagnosis of Forest-Spring encephalitis has been proposed. It comprises a screen-printed thick-film graphite electrode serving as the transducer and a layer of the Forest-Spring encephalitis antigen immobilized on the electrode and functioning as the biorecognition substance. The procedure includes formation of an antigen–antibody immune complex, localization of colloidal gold-labeled protein A on the complex, and recording of gold oxidation voltammogram, which provides information about the presence and the concentration of antibodies in blood serum. The response is proportional to the concentration of antibodies over the interval from 10-7 to 10-2 mg mL-1. The detection limit is 10-7 mg mL-1. [ABSTRACT FROM AUTHOR]

Several new derivatives of 2,2′‐bipyridines with a spacer group separated from the 2,2‐bipyridine fragment, namely, an ethynyl fragment, were obtained using the Sonagashira cross‐coupling reaction. The resulting derivatives were physically adsorbed on platinum electrode and were then used as activators of the catalytic activity of a platinum electrode in the reaction of cholesterol electrooxidation in an acetonitrile medium. Sensitivity, limit of detection and detectable concentration range were calculated, and the best results was established as 6.2±0.6 μA/mM, 0.08 mM and 0–0.3 mM, respectively. These results show that the prepared compounds adsorbed on platinum electrode are perspective systems for developing of new enzymeless cholesterol sensor based on them. [ABSTRACT FROM AUTHOR]

AbstractFor the first time, Neutral Red (NR) has been used as a redox probe for comparative evaluation of the electrochemical performance of screen-printed carbon electrodes (SPCEs) modified with bismuth under different potentiostatic pre-plating conditions (Bi/SPCEs). It was shown that protonated NR undergoes quasi-reversible redox transformations at bare-SPCE and Bi/SPCEs in the pH range 5–6 in phosphate buffer solutions (PBS) in the potential range of (−0.2)–(−0.8) V, where bismuth is not electroactive. Bi/SPCEs have been characterized morphologically by scanning electron microscopy (SEM) and electrochemically by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) employing NR as a redox probe. The obtained SEM, CV, and EIS data are in good agreement. The highest charge transfer resistance (Rct) values (3.9 and 3.3 kΩ) were obtained at bare-SPCE and Bi/SPCE having low degree of bismuth coverage. Contrarily, the lowest Rct value (8 Ω) was recorded at Bi/SPCE, with the highest degree of bismuth coverage. CV experiments showed a significant increase in the electrochemical performances of Bi/SPCEs, whose surface is half or more covered with bismuth, in comparison to the bare-SPCE. Nickel (II) ions and formaldehyde (FM), in the form of formaldehyde hydrazone (FAH), were used as model analytes to determine the electroanalytical performance of Bi/SPCEs. A comparison of roughness factor and sensitivity toward both analytes for Bi/SPCEs with two-tailed Pearson’s criterion showed a high degree of correlation between their electrochemical and electroanalytical characteristics. The data acquired indicates that the use of NR as a redox probe may be quite helpful to control modification processes when developing novel bismuth-containing sensors. [ABSTRACT FROM AUTHOR]

A novel electrochemical sensing platform based on Fe3O4-antibody conjugate was developed for the rapid and sensitive determination of Salmonella typhimurium antigen in model suspensions. The conjugates Fe3O4-antibody were synthesized via carbodiimide cross-linking and characterized by infrared spectroscopy and cyclic voltammetry. The electrochemical properties of Fe3O4 magnetic nanoparticles in water were investigated; the possible mechanism of direct electrochemical reduction was proposed and justified as an analytical signal. The design of an electrochemical sensing platform with magnetically controlled flows has been proposed. Under the most appropriate conditions, the developed portable device was provided the linear response as I (µA) = (7.20 ± 0.35) × (–lg CAg) − (23.77 ± 1.95) in the concentration range 1 × 10−7–1 × 10−4 mg/mL. The detection limit was 390 ng/mL and was comparable to other works. [ABSTRACT FROM AUTHOR]

In this work a comparative study of Screen‐Printed Carbon Electrodes (SPCE) – bare and modified by drop casting with carbonaceous nanomaterials (CNMs) as Multi Walled Carbon Nanotubes (MWCNT), Carbon Black and Functionalized Carbon Black for voltammetric determination of 5‐methyl‐6‐nitro‐7‐oxo‐4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidinide l‐arginine monohydrate (Triazid) as a potential drug with a broad spectrum of antiviral activity is reported. Bare SPCE and CNMs modified SPCE (SPCE/CNMs) have been characterized morphologically by SEM and electrochemically by cyclic voltammetry/electrochemical impedance spectroscopy with [Fe(CN)6]4−/3− as redox probe. Significant improvement of electrochemical performances is achieved with SPCE/CNMs compared with the bare SPCE. Among SPCE/CNMs studied SPCE modified with MWCNT (SPCE/CNT) is characterized by the best combination of electrochemical properties and electroanalytical performance towards TD. The linear dynamic range is 25–200 mg L−1 (R2=0.9975) with the limit of detection – 2.8 mg L−1 Triazid using SPCE/CNT and Square‐Wave Voltammetry technique. The developed sensor was successfully used for Triazid determination in the Pharmaceutical Substance "TRIAZID". The results achieved with SPCE/CNMs after chemical binding of dissolved oxygen in 0.04 M Britton‐Robinson buffer+0.04 M Na2SO3 (pH 7.2±0.2) are very useful for further development of cost‐effective and time‐consuming pharmaceutical routine assay. [ABSTRACT FROM AUTHOR]

[Display omitted] A facile synthetic protocol to hard-to-get polycyclic (hetero)-aromatic compounds annulated to [1,2,4]oxadiazolo[3,4- b ]-pyrazine scaffold via the FeCl 3 -mediated intramolecular Scholl cross-coupling has been developed. Based on the electrochemical and photophysical measurements, the synthesized polycyclic systems may be regarded as narrow band-gap (from 1.42 to 1.89 eV) n-type organic semiconductors whose energy levels are comparable to those of the commercially available n-type semiconductors [ABSTRACT FROM AUTHOR]

In this article, an original method is proposed for address and covalent immobilization of anti-E. coli antibodies on a screen-printed electrode (SPE). The method is based on a copper-catalyzed "click" reaction between a polyvinylbenzylazide (PVBA) film electrochemically deposited on the electrode surface and acetylene fragments of propargyl-N-hydroxysuccinimide ester. The products of electrochemical oxidation of copper particles incorporated in the polymer film on the electrode were first used for catalysis of the click reaction. This approach allowed us to reduce the immobilization time from a few hours for conventional methods to just 30 min, and to prevent denaturation of the immunoreceptor. The modified electrodes were characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Based on the results obtained, a label-free impedimetric immunosensor for E. coli detection was developed. The detection limit of the immunosensor was estimated as 6.3 CFU/ml, with a linear range of 103–106 CFU/ml. The immunosensor demonstrated good stability during 30 days of storage in phosphate buffer solution (PBS, pH 7) and selectivity toward excess Staphylococcus aureus bacteria. [ABSTRACT FROM AUTHOR]

Abstract: 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. [ABSTRACT FROM AUTHOR]

Herein, we report a portable electrochemical biosensor based on butyrylcholinesterase (BChE) immobilized on carbon black (CB)-modified screen-printed electrodes (SPEs) for the detection of organophosphorous pesticides in olive oil. The BChE/CB-SPE biosensor was developed to detect paraoxon in standard solutions as well as in olive oil samples previously treated with the QuEChERS method to extract pesticides from the whole fatty matrix. The biosensor shows a linear concentration range of between 20 and 100 ppb for paraoxon both in standard solutions (phosphate buffer 0.05 M) and in olive oil extracts, with a detection limit of 6 ppb in olive oil extract, corresponding to 10% of inhibition. The accuracy of this biosensor in olive oil samples was assessed with olive oil spiked with paraoxon, obtaining satisfactory recovery values. [ABSTRACT FROM AUTHOR]

A series of novel D–A–A push-pull systems based on a 2-cyanopyrazine acceptor core bearing various electron-donating fragments are synthesized and investigated. The effect of the cyano group on the spectral-luminescent properties of molecules in solvents of different polarities and films obtained by thermal vacuum deposition has been investigated. Fast and delayed luminescence was studied at room temperature and 77K. The energy gap between the S 1 and T 1 states is estimated. The reasons for the weak thermally activated delayed fluorescence are discussed. It has been found that increasing the efficiency of light-emitting organic diodes up to 20 times took place when a cyano group introduces into fluorophores. [Display omitted] • 2-Cyanopyrazine-based D–A–A emitters were designed and investigated. • Non-doped OLEDs achieved maximum current efficiency up to 0.8 cd/A at 10V. • Blue and green OLEDs demonstrating maximum brightness up to 3 × 103 cd/m2. • Cyano group leads to an increase in the efficiency up to 20 times and in the brightness up to 75 times. [ABSTRACT FROM AUTHOR]

• A new system for the enzymeless electrocatalytic detection of cholesterol has been proposed. • CuCl 2 in acetonitrile served as an effective low potential electrocatalyst for cholesterol oxidation. • Magnetic molecularly imprinted polymer nanoparticles were synthesized and applied for selective cholesterol isolation. • The developed enzymeless electrocatalytic system was validated by using of model mixtures imitating the blood serum. • Microfluidic flow cell was fabricated by 3D printing to perform cholesterol determination. The cholesterol level in blood is an important biomarker for the early diagnosis of atherosclerosis and cardiovascular disease. This paper reports on a new enzymeless electrocatalytic system for the determination of cholesterol. Copper (II) chloride was first used for the enzymeless electrochemical oxidation of cholesterol at a low electrode potential in acetonitrile, and the mechanism for the oxidation process was proposed. Magnetic molecularly imprinted polymer nanoparticles were then synthesized and applied in a 3D printed microfluidic flow cell for selective cholesterol isolation and subsequent analysis. The proposed enzymeless electrocatalytic system allowed for the detection of cholesterol in model solutions with a detection limit of 4 µM and a degree of extraction of more than 90 %. The sensitivity, stability, and duration of the analysis were not inferior to analogs. [ABSTRACT FROM AUTHOR]

A convenient synthetic route to novel 7-substituted benzo[ f]thieno[3,2- h]quinazoline and 8-substituted benzo[ g, h]dithieno[2,3- e:3′,2′- j]perimidine systems, bearing the fused pyrimidine ring, has been advanced. A commercially available 5-bromopyrimidine was used as the starting material to obtain various polycyclic systems through the sequence of nucleophilic aromatic substitution of hydrogen (the SNH reaction), Suzuki cross-coupling and oxidative photocyclization. Evidence for the structure of benzo[ g, h]dithieno[2,3- e:3′,2′- j]perimidines has been obtained by X-ray crystallographic analysis. Molecular orbital calculations (DFT), as well as redox and optical measurements for all new compounds have been performed. The data show that the reported polycyclic systems have potential for use in organic electronic applications. [ABSTRACT FROM AUTHOR]

A novel N,N ’ ,N ” ,O-tetradentate Schiff base ligand was obtained by the condensation of salicylaldehyde and 5-(1-hydrazono-ethyl)-3-(trifluoromethyl)pyrazole. Five-coordinated dinuclear copper(ii) complex with this ligand was characterized by XRD analysis, magnetometry and voltammetry. [ABSTRACT FROM AUTHOR]

A series of novel push-pull fluorophores based on 2 H -imidazole scaffold bearing perfluorophenyl substituent and extended electron-donating conjugating π-system were synthesized. In particular, the Pd-catalyzed Suzuki-Miyaura coupling reactions were exploited as a main synthetic strategy to modify 4-(4-bromophenyl)-2,2-dimethyl-5-(pentafluorophenyl)-2 H -imidazole with various electron-donating functionalities. The comprehensive photophysical studies were carried out for the synthesized fluorophores, including the analysis of absorbance and emission spectra and determination of absolute quantum yields. The designed compounds were found to have a strong emission in the range of 470–610 nm depending on both the nature of solvent used and the structure of electron-donating group attached to the aryl moiety. The pH effect of the aqueous-organic mixture buffer solution on the fluorescent characteristics of the synthesized compounds was established and the deprotonation-induced "turn-on" pH sensing mechanism supported by DFT calculations was proposed for the first time. Particularly, the sequence of deprotonation was confirmed, and free energies for all N-protonated and N-proton-free forms were calculated. No toxic effect on the human embryonic kidney cells (HEK-293) at concentration of ≤512 μM was observed in vitro experiments. In addition, new opportunities for the practical application of these molecular ensembles were demonstrated in case of fluorometric determination of the pH both in model solutions and real saliva probes, with 3-(4-(2,2-dimethyl-5-(pentafluorophenyl)-2 H -imidazole-4-yl)phenyl)-9-phenyl-9 H -carbazole being used. [Display omitted] • Push-pull fluorophores with a strong emission in the range of 470–610 and quantum yields up to 96%. • No toxic effects at concentration of ≤512 μM from in vitro experiments. • Advanced "turn-on" fluorescent probes for determining the pH in saliva. [ABSTRACT FROM AUTHOR]

[Display omitted] • A 1,3/1,4-diazine's modified SPE for NB determination in honey was prepared. • Cathodic currents of NB reduction enhanced the diazine-modified SPEs. • The best NB response was obtained by using co-polymerization of the receptor layer. • The low detection limit 0.107 μM allows NB in honey samples to be detected. • The analysis of spiked probes showed the high precision of the sensor with HPLC. In this work, a screen-printed electrode (SPE) modified by 1,3/1,4-diazines was prepared for the rapid and sensitive determination of nitrobenzene (NB). The obtained results indicated enhanced cathodic currents of direct NB reduction into hydroxylaminophenol on the diazine-modified SPEs. The enhanced effect was most likely due to the combination of complexation and collisional processes of diazines towards nitroaromatic compounds and also the diazine-modified electrodes' increased electroconductivity. The best electrochemical responses were obtained in square wave voltammetry mode by using the carbazolyl substituted diazines as a component of the sensitive layer, which was assembled by co-electropolymerization with the unsubstituted carbazole on the electrode during 5 cycles. The low detection limit estimated as 0.107 μM and wide linear range (1–1000 µM) enables NB in water and food samples to be determined. The developed modified electrode was applied in the analysis of commercial honey samples. [ABSTRACT FROM AUTHOR]

Aqueous suspensions of 10 nm, 50 nm, or 1 μm Fe3O4 particles were injected intraperitoneally (ip) to rats at a dose of 500 mg/kg in 4 mL of sterile deionized water 3 times a week for 5 weeks. Following exposure, functional and biochemical indices and histopathological examinations of spleen and liver tissues of exposed rats were evaluated for signs of toxicity. The iron content of the blood was measured photometrically, and that of the liver and the spleen by atomic adsorption spectroscopy (AAS) and electron paramagnetic resonance (EPR) methods. It was found that, given equal mass doses, Fe 3O4 nanoparticles possess considerably higher systemic toxicity than microparticles, but within the nanometric range the relationship between particle size and resorptive toxicity is intricate and nonunique. The latter fact may be attributed to differences in different nanoparticles’ toxicokinetics, which are controlled by both more or less substantial direct penetration of nanoparticles through biological barriers and their unequal solubility. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

A series of novel D–A and D–π–A push-pull systems based on a pyrazine and quinoxaline acceptor, bearing various electron-donating triphenylamine and carbazole moieties, are compared. A significant difference in electrochemical and photophysical properties was found depending on molecular structure. The compounds have strong solvatochromic properties. Quinoxaline-containing systems exhibit delayed fluorescence (DF) in thermal vacuum deposition films. Despite the low quantum yield of fluorescence in the solid state (less than 10%), organic light-emitting diodes with sufficiently high efficiency (4.2 cd/A) have been fabricated on the basis of this push-pull systems. The best results were obtained for compounds exhibiting DF. The possible channel for increasing the efficiency of OLED can be associated with the "hot excitons" mechanism. Image 1 • 1,4-Diazine-based D–(π)–A emitters were synthesized and investigated. • Non-doped OLEDs achieved maximum current efficiency up to 4.2 cd/A. • Yellow OLEDs demonstrating maximum brightness up to 3.2 × 104 cd/m2. [ABSTRACT FROM AUTHOR]