In order to elucidate the mechanism of the flavonoid taxifolin (dihydroquercetin) oxidation under the electrochemical experiment conditions in the aqueous solutions the chronoamperometry and bulk ...electrolysis with following characterization of the oxidation products by means of the HPLC with both UV–vis and MS detection have been coupled. The taxifolin diffusion coefficient has been evaluated in the aqueous solution as 3.63 × 10−6 cm2/s. The experimentally obtained number of electrons per one taxifolin molecule falls between 2 and 3 demonstrating that under electrochemical oxidation conditions only part of initially oxidized taxifolin molecules participates in dimerization and further transformation.
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•The taxifolin electrochemical oxidation leads to the di- and trimer formation in solutions.•The number of transferred electrons increases due to the di- and trimers further electrooxidation.•The diffusion coefficient of taxifolin has been evaluated in the aqueous solution.
Titanium and platinum samples as components of bimetallic implants for the osteoregeneration process have been modified in solutions modeling biological systems and studied by means of cyclic ...voltammetry, electrochemical impedance spectroscopy and scanning probe microscopy. While aspartic and glutamic acids did not adsorb significantly on platinum in the potential region investigated, the presence of the amino acids affects oxide layer growth on the titanium surface under anodic polarization. The two studied amino acids behave differently on the titanium electrode surface due to differences in adsorption modes of these substances. The adsorption of the glutamic acid depends on the polarization potential to a large extent, and most of quantitative adsorption characteristics (EIS data, the surface roughness) undergo drastic change at the polarization potential value of 750 mV (vs. Ag/AgCl) in the presence of this substance. Equivalent circuit modeling of the surface processes has been carried out, and a scheme for aspartic and glutamic acid adsorption onto the titanium surface has proposed.
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•Glutamic acid adsorption is determined by potential applied to the titanium electrode.•Aspartic acid adsorbs on a titanium electrode surface through both carboxylic groups.•Titanium surface characteristics depend on both potential and amino acid presence.•Dicarboxylic amino acids interact strongly with a titanium electrode surface.•Aspartic and glutamic amino acids adsorption on platinum electrode is negligible.
The electrochemical features of the interactions of sulfur- and iron-containing compounds (ferrous sulfate, elemental sulfur, pyrite tailings, cysteine, sodium thiosulfate) with a model acidophilic ...consortium, including the genera
Leptospirillum
,
Sulfobacillus
,
Acidithiobacillus
,
Ferroplasma
, and
Acidiplasma
, were studied. The method of cyclic voltammetry recorded redox processes at the electrode/solution interface in the presence of the studied sulfur- and iron-containing compounds. In general, the modeling consortium led to the intensification of these processes. The characteristics of the diffuse layer near the electrode/solution interface were studied using electrochemical impedance spectroscopy. The introduction of microorganisms and/or substrates into the supporting electrolyte led to a decrease in the slope and can be interpreted as evidence of their effect on the diffusion part of the double layer. Its contribution decreases in favor of ion transport. All this, in general, does not contradict the assumption of cell adsorption on the electrode surface. Confocal laser scanning microscopy confirmed this assumption and showed cell adhesion to the surface. The data obtained confirm the importance of bioelectrochemical processes of the studied group of microorganisms in biotechnological processes associated with the leaching of metals from sulfide ores.
An attempt was made to simulate the electrochemical behavior of the osteocalcin active site simple models on the platinum component of a bimetallic Ti/Pt implant. Dicarboxylic glutamic acid and ...dicarboxylic aspartic acid, and ethylmalonic acid as the third model successfully complementing the model range. The surface coverage of the platinum electrode during adsorption of model dicarboxylic acids was estimated using cyclic voltammetry and electrochemical impedance spectroscopy. All three compounds demonstrate similar trends in the surface coverage dependencies on the adsorption potential, acids' adsorption onto platinum surface is weak, and in none of cases studied amino group participates in adsorption on the platinum electrode surface. Using quantum chemical calculations, the most stable conformations of model compounds and the values of voids between adsorbed dicarboxylic acid molecules were obtained. Since all three models have a relatively low surface coverage and are participants in the outer sphere process of nonspecific adsorption on platinum, the residues of γ-carboxyglutamic acid present in osteocalcin will not be specifically adsorbed on the platinum component of the bimetallic implant, and the absence of interactions between it and the platinum electrode should have a positive effect on the dynamics of osteoregeneration.
Reducing fuel cells electrical losses is achieved by the use of a catalyst. Being inexpensive and renewable, biocathodes have an advantage over synthetic and chemical ones. Here the microbial fuel ...cell (MFC)-utilizing biocathode based on the acidophilic chemolythotrophic microorganisms (ACM) mixed culture has been studied. The Leptospirillum sp., Acidithiobacillus sp., Ferroplasma sp. consortium has been used as a cathode biocatalyst. Pyrite enrichment tails of a mining and processing enterprise served as the catholyte substrates. It is experimentally demonstrated that ACM mixed culture Leptospirillum sp., Acidithiobacillus sp., Ferroplasma sp. introduced into the catholyte leads to MFC electrical characteristics increase by approximately two times. With the selected external load (30 Ω) Cathodic bioagents increased the MFC electric power four-fold (from 137 to 579 µW). Catholyte redox potential increased from 431 to 581 mV during 11 d in the presence of acidophilic iron-oxidizing microorganisms. At 33 d, this value increased up to 695 mV. This is an indirect evidence for active processes of iron oxidation. The analysis results for the Fe
3+
content in the medium also support this assumption. Thus, in a course of a 33-d experiment Fe
3+
concentration increased from 0 to 1.5 g/l. The redox processes intensification in the studied systems also confirmed by the cyclic voltammetry (CV). Under pyrite utilization conditions in the presence of ACM mixed culture cyclic voltammograms show an increase in the reduction current at the cathodic potentials region. The results obtained herein suggest that the studied biochemical system is a perspective catholyte for MFC capable to reduce a cathodic overpotential.
The developed designs and modifications of biofuel elements (BFC) are presented. The approbation of their work using strains and consortia of microorganisms is given. The proposed designs made it ...possible to solve a number of problems that arise when working with BFC: 1) gain access to the contents of the anode BFC space without disturbing its sterility and anaerobic environment; 2) take samples from the anode space for chemical and microbiological analysis without interrupting the BFC operation; 3) conduct continuous monitoring of electrochemical processes directly in the anode space (Ox-Red media, electrode charge, concentration of hydrogen and other ions by means of potentiometry).
A novel water soluble antioxidant, dihydroquercetin monosuccinate electrochemical transformations have been studied on the graphite electrode in a wide range of pH. In contrast to acidic solutions, ...in basic media dihydroquercetin monosuccinate redox transformations have a weak diffusion control, and occur in the close to electrode surface layer. The number of protons transferred per one electron for different conditions has been elucidated.
•Novel water soluble antioxidant•Unusual voltammetry: diffusion vs. kinetics•How many protons transferred per one electron at different pH
On the basis of the model of a flow-type magnetic filter with a transversely magnetized ordered system of long ferromagnetic rods of rectangular cross section, the process of high-gradient magnetic ...separation of microscopic diamagnetic particles (potato starch granules of sizes 8–30 μm) from a liquid suspension has been investigated. The registered laws of change in the concentration and size distribution of particles at the suspension outlet from the filter agree with the theoretical conclusions obtained from the analysis of the magnetic field structure and thecharacter of the particle motion in the filter volume.
The ability of acidophilic microorganisms to oxidize sulfide minerals is increasingly used in biohydrometallurgical technologies to produce non-ferrous and precious metals from sulfide ores. Strains ...of Acidithiobacillus ferrooxidans and Sulfobacillus thermotolerans often dominate heap bioleaching processes. Due to their high ability to catalyze redox processes, it has been suggested that they can be used in the technology of microbial fuel cells (MFCs). MFC allows using organic and inorganic waste as a substrate for microorganisms, rendering them harmless with parallel generation of electric current. The aim of this work was to study the electrochemical processes that occur in the cathode and anode spaces of MFCs under the action of acidophilic chemolithotrophic microorganisms on sulfur-containing and iron-containing mining wastes. As objects of study, strains of acidophilic chemolithotrophic microorganisms were used: 1) A. ferrooxidans 61, obtained from Dr. Sc. N. Vardanyan, Head of the Laboratory of Geomicrobiology of the Scientific and Production Center ?Armbiotechnology? of the National Academy of Sciences of Armenia; the strain was isolated in Tanzut (gold-polymetallic deposit), from acid drainage at ore deposits in the Lori region of Armenia; 2) S. thermotolerans Kr1 isolated from pulp of a gold-bearing sulfide concentrate treated at 40 ? C in a gold mining factory (Siberia). The substrates for microorganisms were molecular sulfur, iron (II) sulfate, and pyrite tailings from one of the mining and processing plants in Russia. Voltammograms were recorded using a potentiostat and ?IPC Pro? software. The concentration of ferrous and oxide iron was determined by complexometric titration with trilon B. Using the method of cyclic voltammetry, data were obtained that testify to the intensification of redox processes using these systems. So, when utilizing elemental sulfur by A. ferrooxidans 61 strain, redox signals in the cathode and anode regions were recorded on the polarization curves. During utilization of iron sulfate in the voltammogram, significant peaks were noted in the reduction area. The voltammogram in the presence of the S. thermotolerans Kr1 strain in media with all tested substrates also showed significant redox signals in the field of oxidation and reduction. The intensification of the MFC operation was shown when using S. thermotolerans Kr1 and A. ferrooxidans 61 strains as cathode bioagents in them. The obtained materials suggest the possibility of using this biochemical system as catholyte in biofuel elements to reduce overvoltage at the cathode.
Cyclic voltammetric methods have been applied to study the electrochemical behavior of the sulfide minerals in phosphate-buffered alkaline solution. The redox process of electrodes of sulfide ores ...was investigated using silicone-impregnated graphite electrode. The cathodic and anodic reaction products in alkaline solution were determined within the potential range of -2V to +2V (vs. Ag/AgCl). The several successive measurement cycles’ voltammograms leads to the appearance of a new anodic peak at E = 450mV, which is absent in the first cycle and curves, as well as other features that appear in cycling, can probably be explained by secondary electrochemical transformations of the products formed by the oxidation of the original pyrite at the interface between the electrode material.DOI: http://doi.dx.org/10.5564/mjc.v15i0.318 Mongolian Journal of Chemistry 15 (41), 2014, p33-35
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