Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The activity of Zn²⁺ ions bound to carboxyl groups of pectin of esterification degree E 0 to 90% and to oligomeric potassium galacturonates of polymerization degree 1 to 7 was estimated by the metallochromic indicator (tetramethylmurexide) method. The zinc ions are stoichiometrically bound to pectin, one Zn²⁺ cation to two free carboxyl groups. The stability constant K of zinc pectinates strongly decreases with the increasing esterification degree in a relationship close to a linear logarithmic function, log K = f(E) similarly, as with the binding of Ca²⁺ ions to pectin. Pectin reveals a little higher selectivity to Zn²⁺ ions when considering this couple of cations. The zinc ions are bound to the monomeric D-galacturonic acid to a very low extent in contrast to some toxic cations as e.g. Pb²⁺, Cu²⁺, and Cd²⁺. A continuous increase of the degree of association of Zn²⁺ ions with carboxyl groups of oligomers takes place with the increasing polymerization degree. The validity of the increment additivity of terminal and inner uronic acid units to the final activity of zinc counterions bound to these oligomers was proved. The results are discussed from the standpoint of application of pectin as an active component of prophylactic diets against poisoning with cations of toxic metals with respect to the excretion of Zn²⁺ ions from the human body. Findings concerning the interaction of Zn²⁺ ions with pectin in dependence on its esterification degree (E) constitute a theoretical basis for a potential application of pectin as a useful ligand of Zn²⁺ ions in medical treatment of zinc deficiency in the human body.