Studies of the Interphase Distribution of Polyuronides in a System Consisting of Two Immiscible Solvents

Abstract

Partition coefficients of polyuronides and their salts (pectin, sodium alginate, calcium alginate) in a water/octan-1-ol system were measured at different temperatures and different pH values. Changes in the thermodynamic functions accompanying interphase partition (enthalpy, entropy, Gibbs free energy) were identified to evaluate the potential for distribution to occur spontaneously.The importance of developing drugs acting as enterosorbents for heavy metals and radionuclides arises from the difficult ecological situation associated with the widespread use of atomic energy, radioactive isotopes, and heavy metals in various areas of industry. Potential antidotes with high efficacy and biological compatibility with the human body include polyuronides (acid polysaccharides), i.e., pectins and alginates [1]. Introduction of these substances into pharmaceutical practice as therapeutic agents with detoxifying properties requires studies of their pharmacokinetic properties, as one of the key points in assessment of biological actions is how substances distribute in biological substrates, as this determines their absorption and the selectivity of their interactions with biological structures. Initial predictions for assessment of pharmacokinetic properties are provided by studies of the interphase partition of study compounds in in vitro experiments, and this defined the present studies.The aim of the present work was to study the partition of polyuronides in a system consisting of two immiscible liquids to predict the accumulation of polyuronides in hydrophilic and hydrophobic biological substrates. EXPERIMENTAL SECTIONPartition coefficients (C p ) were measured as the ratio of the concentrations of polyuronides or their salts in the layers of polar and nonpolar solvents, allowing for the degree of association of the substances (n). [2]. Analysis of the initial (C 0 ) and equilibrium (C 1 ) concentrations of polyuronides in the aqueous medium were measured by acid-base titration [3]; concentrations of polyuronide calcium salts were measured by compleximetric titration [3]. Equilibrium concentrations of polyuronides and their salts in the nonpolar solvent layer (C 2 ) were calculated as the difference between C 0 and C 1 . Calculations [4,5] were made to determine changes in thermodynamic functions: enthalpy (DH°), entropy (DS°), Gibbs free energy (isobaric-isothermic potential DG°), and the entropy component (T. DS°) accompanying the interphase partition of polyuronides.The system consisting of two immiscible solvents was a mixture of water and octan-1-ol, in which water was the model for hydrophilic and octan-1-ol was the model for hydrophobic biological substrates. Octan-1-ol was selected among other nonpolar solvents (butan-1-ol, butan-2-ol, pentan-1-ol, pentan-3-ol, butyl acetate, heptane, xylene) because of the optimum ratio of its hydrophobic and lipophilic properties [2]. The pH values of the prepared aqueous sodium alginate (Na-I) solution (0.02 -0.30 mM), beet pectin (II) (0.02 -0.11 mM), calcium pectinate (Ca...