Sorption of picolinic acid by Cu(II)-containing sulfocationite KU-2-8
Authors: Altshuler H. N. , Nekrasov V. N. , Lyrshchikov S. Yu. , Altshuler O. H. 
Published: March 2024

Objectives. To study the equilibrium distribution of components between KU-2-8 sulfocationite and an aqueous solution containing picolinic acid and Cu(II); to show the possibility of immobilization of cations of picolinic acid and Cu2+ in sulfonic cation exchanger KU-2-8; to calculate the component compositions of the equilibrium solution, in order to obtain the required ionic composition of the KU-2-8 sulfonic cation exchanger according to the selectivity coefficients of binary ion exchange, and the constants of formation of such complexes in water.

Methods. The concentrations of the individual components in multicomponent solutions were calculated using the HySS 2009 program (Hyperquad Simulaton and Speciation). The calculation of the equilibrium ionic compositions of KU-2-8 sulfocationite was performed using the selectivity coefficients of binary ion exchanges and the formation constants of complexes of picolinic acid with Cu2+ and H+ cations. Experimental study of the equilibrium distribution of components between aqueous solutions of picolinic acid, copper nitrate, and KU-2-8 sulfocationite was carried out by means of the dynamic method at a temperature of 298 K. Fourier-transform infrared spectroscopy and electron paramagnetic resonance spectroscopy were used, in order to determine the ionic forms of the components contained in the sulfocationite.

Results. It was shown that the equilibrium solution contains H+ protons, Cu2+ cations, LH picolinic acid molecules, protonated picolinic acid cations [H2L]+, deprotonated picolinic acid anions L-, Cu2+ complexes with the deprotonated picolinic acid anion [CuL]+, and Cu2+ complexes with two anions of deprotonated picolinic acid [CuL2]. The concentration of H+, Cu2+, and [H2L]+ cations in the solution significantly exceeds the concentration of other components at pH values from 0 to 0.5. The content of [CuL]+ cations and neutral complexes [CuL2] increases significantly in the solution, while the [H2L]+ cations disappear at pH greater than 1. It was experimentally established that the concentrations of picolinic acid and copper in the polymer phase are many times higher than the concentrations of these components in an aqueous solution. The partition coefficients are about 24 and 210 for picolinic acid and Cu(II), respectively. The calculated dependencies of the concentrations of Cu2+, [H2L]+, H+, [CuL]+ cations in the polymer vs pH of an equilibrium solution containing picolinic acid were obtained. The experimental data on the concentrations of all cations in the ion exchanger is in the intervals of the calculated compositions within the limits of measurement errors.

Conclusions. KU-2-8 sulfocationite is proposed as a container for obtaining drugs based on picolinic acid and Cu2+ cations. It was shown that the selectivity coefficients of binary ion exchanges and the formation constants of [H2L]+, [CuL]+ complexes can be used to precalculate the ionic compositions of the equilibrium solution, in order to obtain the required compositions of the sulfocationite.