The relevance of studying the regulation of protein-ligand interactions is due to the emergence of new views on the role of metabolites and their key importance in vital processes. To study the protein-ligand interaction, the AB0 antigen-antibody blood system and the enzyme-substrate system of dehydrogenases were used as a test system, and ethanol was used as an influencing factor. In experiments performed with A and B blood erythrocyte antigens, natural AB0 system antibodies and monoclonal antibodies under the influence of ethanol performed change of the degree of agglutination and the time to onset of erythrocyte agglutination. It was found that ethanol can regulate the enzyme-substrate interactions of dehydrogenases: lactate dehydrogenase (EC 220.127.116.11), glyceraldehyde phosphate dehydrogenase (EC 18.104.22.168), and α-glycerol phosphate dehydrogenase (EC 22.214.171.124). The increase in the activity of studied enzymes under the influence of ethanol in the whole blood hemolysate was 2.5 - 3 times higher than in the isolated medium (with pure enzyme preparations).
Solid-state reaction of CaHPO4 with CaCO3 in >2:1 ratio at 1350 °C resulted in α-tricalcium phosphate (α-TCP) formation, following sintering at 850 °C produced a homogeneous β-TCP phase which does not contain crystalline impurities.
The review addresses and highlights the main results of research on the physicohemical properties of single-phase and composite materials based on transition metal oxides in relation to their practical application as electrode materials for symmetrical solid oxide fuel cells. The electronic structures and thermodynamic stability of transition metal oxides with the perovskite structure are discussed. A detailed consideration is given to the thermal behaviour, chemical stability, electrical conductivity and electrochemical properties of a broad range of electrode materials based on iron-, chromium- and manganese-containing perovskite-like oxides and oxides that crystallize in other structure types. The analysis revealed the most promising compositions of electrode materials for symmetrical solid oxide fuel cells and effective approaches to the improvement of their functional characteristics.
Using the path integral approach, we obtain the characteristic functions of the gyration radius distributions for Gaussian star and Gaussian rosette macromolecules. We derive the analytical expressions for cumulants of both distributions. Applying the steepest descent method, we estimate the probability distribution functions (PDFs) of the gyration radius in the limit of a large number of star and rosette arms in two limiting regimes: for strongly expanded and strongly collapsed macromolecules. We show that in both cases, in the regime of a large gyration radius relative to its mean-square value, the PDFs can be described by the Gaussian functions. In the shrunk macromolecule regime, both distribution functions tend to zero faster than any power of the gyration radius. Based on the asymptotic behavior of the distribution functions and the behavior of statistical dispersions, we demonstrate that the PDF for the rosette is more densely localized near its maximum than that for the star polymer. We construct the interpolation formula for the gyration radius distribution of the Gaussian star macromolecule which can help to take into account the conformational entropy of the flexible star macromolecules within the Flory-type mean-field theories.
Perfluorinated sulfonic acid (PFSA) polymer membranes are widely used as ion-conducting electrolytes in energy-conversion devices. The development of novel hybrid materials containing inorganic dopants offers the route towards optimization of the performance of the PFSA membranes. In this work, the effect of ultrasonic (US) treatment of the PFSA solutions in the presence of SiO2 nanoparticles on the characteristics of the cast hybrid Nafion+SiO2 membranes was studied for the first time. Upon ultrasonication of polymer solutions, the length of macromolecules is reduced, and the number of sulfo groups decreases. When polymer solutions are ultrasonicated in the presence of SiO2, they experience additional crosslinking due to the interaction of SiO2 with sulfo groups of the PFSA polymer. As a result, up to 20% of -SO3H groups appears to be excluded from the ion-exchange process, and the temperature corresponding to destabilization of ionic clusters is reduced. When a hydrophilic dopant is incorporated within pores, the overall water uptake of the hybrid membranes increases, and their proton conductivity is improved. Maximum conductivity (78.6 mS/cm) at 40°С in the contact with water is observed for the Nafion+1 wt% SiO2 membrane cast from polymer solutions upon the ultrasonication for 10 min. The membranes preserve their high conductivity at low relative humidity (4.1 mS/cm at 30°С, 30% RH), and this value is 1.7 times higher than that of the pristine Nafion membrane. Hydrogen permeability of the hybrid Nafion+SiO2 membranes appears to be lower than that of the Nafion membranes by 15%. Hence, US-assisted dispersion of dopant nanoparticles in the PFSA solutions allows preparation of hybrid membranes with improved transport characteristics.
The computational modeling within a density functional theory was applied for simulations of electronic spectra and calculations of structural and energy characteristics of the cubic double perovskite oxides Sr2Mg1−xNixMoO6–δ, where x = 0, 0.5, and 1. The oxygen stoichiometric molybdates are antiferromagnetic semiconductors with an energy gap near 2 eV. The energy-based arguments show that anti-site cation disorder may contribute to the structural stability of the molybdates. It is found that nickel doping is favorable for mitigated chemical expansion. The replacement of magnesium by nickel is accompanied by the contribution of Ni3d states to the valence band while leaving hybrid Mo4d-O2p states in the conduction band virtually unchanged. It is shown that the compounds under study are thermodynamically unstable in heavily reducing conditions which is confirmed by experimental results. The appearance of oxygen deficiency in Sr2Mg1−xNixMoO6–δ results in the formation of oxygen vacancy associated donor states near the bottom of the conduction band and the transition from the intrinsic to degenerate semiconductor. It is suggested that the influence of nickel dopants on the energy and density of the donor states may help to explain variations of the conducting properties with doping level.
Nafion-117/PEDOT composite membranes were synthesized by in situ chemical polymerization of 3,4-ethylenedioxythiophene (EDOT) using ammonium persulfate as an oxidant. The polymerization of EDOT in Nafion membranes for various EDOT/oxidant treatment sequences was studied for the first time. PEDOT introduction leads to a slight decrease in both the ion-exchange capacity and water uptake of the composite membranes, as well as to an increase in cationic transport. Membranes initially treated with an oxidant exhibit better conductivity and lower hydrogen permeability. The effect of both modification of Nafion-117 membranes by PEDOT and hot-pressing of hydrogen-oxygen membrane-electrode assemblies (MEAs) on the performance of proton-exchange membrane fuel cells was studied. The maximum power density of the fabricated MEAs increases 1.5-fold: from 510 (for a pristine Nafion-117 membrane) to 810 mW cm(-2) (for a membrane modified by PEDOT). The current density at a voltage of 0.4 V reaches 1248 and 2246 mA cm(-2), respectively
Inorganic-organic composites based on the foil and standard RALEX (R) cation-exchange heterogeneous membranes (Mega a.s., Czech Republic) were prepared by in situ modification with sulfated zirconia (S-ZrO2). The composite membranes were characterized by SEM, TGA, X-ray diffraction, and FTIR spectroscopy. The effect of S-ZrO2 doping on membrane transport properties was studied using measurements of water uptake, ion-exchange capacity, conductivity, cation diffusion, hydrogen permeability, current-voltage characteristics, and membrane specific permselectivity (Ca2+/Na+). The S-ZrO2 incorporation leads to an increase in conductivity and permselectivity of the composite membranes. The proton conductivity of the S-ZrO2-doped foil membrane (0.0316 S/cm at 30 degrees C) is 4 times higher than that of the pristine membrane. The Ca2+/Na+ permselectivity of the standard RALEX (R) CM membrane doped by S-ZrO2 reaches 3.8 at low current densities. Moreover, the composite membranes retain their selectivity during the long-term tests (> 50 h continuous electrodialysis). The sulfated zirconia doping of heterogeneous membranes demonstrated an excellent separation efficiency that can be used in wastewater treatment, desalination, and related electromembrane separation processes as well as to reduce scaling of electrodialysis modules.
Despite the modern level of development of computational chemistry methods and technological progress, fast and accurate determination of solvation free energy remains a huge problem for physical chemists. In this paper, we describe two computational schemes that can potentially solve this problem. We consider systems of poorly soluble drug compounds in supercritical carbon dioxide. Considering that the biggest contribution among all intermolecular interactions is made by van der Waals interactions, we model solute and solvent particles as coarse-grained ones interacting via the effective Lennard-Jones potential. The first proposed approach is based on the classical density functional theory and the second one relies on molecular dynamics simulation of the Lennard-Jones fluid. Sacrificing the precision of the molecular structure description while capturing the phase behavior of the fluid with sufficient accuracy, we propose computationally advantageous paths to obtaining the solvation free energy values with the accuracy satisfactory for engineering applications. The agreement reached between the results of such coarse-graining models and the experimental data indicates that the use of the all-atom molecular dynamic simulations for the studied systems seems to be excessive.
Abstract Herein, we present a novel electrode platform for H2O2 detection based on the immobilization of recombinant Tobacco Peroxidase (r-TOP) onto graphite electrodes (G) modified with p-phenylenediamine (p-PD) diazonium cation grafted multi-walled carbon nanotubes (MWCNTs). The employment of both p-phenylenediamine moieties and covalent cross-linking by using glutaraldehyde allowed to enhance the sensitivity, stability and selectivity toward H2O2 detection, as well as preventing the enzyme inactivation due to the electro-Fenton reaction. This reaction continuously produces hydroxyl radicals, whose high and unselective reactivity is likely to reduce drastically the operating life of the biosensor. The protection against the electro-Fenton reaction is through cross-linking the enzyme in combination with interaction between the uncoupled -NH2 groups (mainly uncharged at pH 7, considering a pKa of 4.6) available on the electrode surface and the enzyme. In particular, the electrode based on the r-TOP/p-PD/MWCNTs/G platform showed a lower limit of detection of 1.8 µM H2O2, an extended linear range between 6 and 900 µM H2O2, as well as a significant increase in sensitivity (63.1 ± 0.1 µA mM-1 cm-2) compared with previous work based on TOP. Finally, the r-TOP/p-PD/MWCNTs/G electrode was tested in several H2O2 spiked food samples as a screening analytical method for the detection of H2O2.