I. V. Aristov

Kinetics and dynamics of redox sorption

ABSTRACT The paper reviews the current state-of-the-art of the kinetics and dynamics of redox soiption. The comparison of existing and proposed theoretical models in description of experimental results obtained by studying different redox processes on redoxites, i.e. sorbents with functional redox centers, is presented and discussed. The practical application of the results obtained is demonstrated.

Transfer of amino acids through a membrane/solution interface in the presence of heterogeneous chemical protonation reaction

A physicochemical model for the transfer of amino acids through the interface between a cation-exchange membrane and an amino acid aqueous solution is proposed. The model allows for a heterogeneous reaction of protonation of the amino acid zwitterion. The model calculations are compared with experimentally determined migration transport numbers for glycine cations in an electromembrane system with an MK-40 membrane. The comparison shows that, owing to the protonation reaction, the glycine flux can increase by ca. 30%.

Electrotransport mechanisms in the ion-exchange membrane-amino acid solution systems

Electroconductivities of heterogeneous ion-exchange membranes MK-40 and MA-41I are studied experimentally by a band method in solutions of amino acids with various isoelectric points. Based on the data obtained, three possible mechanisms of electrotransport in a system membrane-amino acid solution are considered: the charge transfer by hydrogen (hydroxyl) ions, amino acid ions, and simultaneously by inorganic and amino acid ions (mixed mechanism).

Mobilities of glycine and alanine ions in aqueous hydrochloric solutions at 25°C

By means of a multidimensional regression analysis of experimental data on the electroconductivities of aqueous hydrochloric solutions of glycine and alanine, mobilities of cations of the studied amino acids are obtained at 25°C. Conclusions are made as to various mechanisms of ionic transport in the HCl-Gly and HCl-Ala systems.

Transport of glycine in systems with cation-exchange membranes in hydrochloric acid solutions: Effect of a heterogeneous protonation reaction

The electrical mass transfer of cations in electromembrane systems (EMS) with an MK-40 cation-exchange membrane and glycine in aqueous solutions of hydrochloric acid is studied using the method of a rotating membrane disk. Limiting current densities and limiting steps of the transport of cations in such systems are determined. Shown is the possibility of an increase in the electrical mass transfer of glycine as a consequence of the occurrence of a heterogeneous reaction of protonation of its zwitterions. The effect of the membrane surface state on the kinetic regularities of transport of cations in EMS with glycine in solutions of hydrochloric acid is exposed.

Limiting Current Densities in a System with Cation-Exchange Membrane MK-100 Rotating in a Glycine–HCl Solution

Limiting diffusion current densities in an electromembrane system (EMS) comprising cation-exchange membrane MK-100 and a glycine solution containing hydrochloric acid are studied on a rotating membrane disk. The dependence of the limiting current density at a given rotation rate of the disk on the equilibrium volume concentrations of glycine cations and protons in solution is described by a regression model. The diffusion fluxes of these cations in the EMS are shown to be independent.

Interfacially driven ionic transport in the electromembrane systems under influence of small excess of hydrostatic pressure

Abstract We continue a series of experiments especially designed to demonstrate the action of hydrostatic pressure on the selectivity of the cation-exchange membranes. The experimental results are explained qualitatively by the change of the interfacial transport of the ions owing to local water flows under the hydrostatic pressure action. The values of the hydrostatic pressure differences exclude the possibility of the through water flows across the membrane. We estimated the decrease in energy of activation of co-ion transition in the membrane from the side of concentration cell due to an excess of pressure in this cell.

Glycine and L-Lysine Ionization in a Mixed Aqueous Solution

In mixed aqueous solution of glycine and L-lysine the ionization of both amino acids increases due to the proton transfer from glycine zwitterion to lysine zwitterion. This is manifested by a considerable nonlinear (pairwise interaction of amino acids) increase in the mixed solution electroconductivity at high amino acid concentrations. The solution pH varies negligibly, as the amino acids in aqueous solutions demonstrate buffering. The refraction coefficient additively depends on glycine and L-lysine concentrations.

Limiting current densities in electromembrane systems with carboxyl-containing polyamidoimide membranes

Voltammetric characteristics of electromembrane systems with carboxyl-containing polyamidoimide membranes in 0.01 M solutions of sodium and hydrogen chlorides are studied using a rotating membrane disc. The limiting current density increases with the decrease in the exchange capacity and an increase in the generation temperature and imidization degree of membranes, due to variations in their structures. The difference in the structure of membranes with various exchange capacities is proved by the standard porosimetry method. The distinguishing feature of the limiting state in the HC1 solutions is that the generation of the hydrogen and hydroxyl ions in the near-surface layer occurs long before its concentration exhaustion.