Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The activity of Pb²⁺ ions in solutions of lead oligogalacturonates of polymerization degree DP 1 to 5 (starting concentration of the investigated solutions 3.00 mmol (COOPb_0.5) l^-1, the ionic strenght of the solution I = 0.01 mol l^-1, electrolyte KNO₃, was determined by lead specific ion electrodes. The activity a_Pb²⁺ is independent on the kind of anion in very diluted solutions of lead perchlorate and nitrate. Ions of lead become bound quite firmly even to the monomeric D-galacturonic acid (association degree of Pb²⁺ ions to carboxyl groups of uronic acid β = 0.43). The increase of polymerization degree is associated with a strong decrease of the lead oligogalacturonate solubilities on one hand, and increase of the bond strenght of the Pb²⁺ ions to these oligomers on the other. The association degree of Pb²⁺ ions to carboxyl groups of the pentamer (β = 0.96) almost reaches the value found for the polymeric chain of pectate molecule (D-galacturonan); here, the stoichiometric binding of Pb²⁺ to two carboxyl groups takes place with a great deal of probability. Lead has been found to bind highly preferentially to oligogalacturonates even in the presence of calcium ions. Results presented in this paper help to clear the mechanism of elimination of lead from the human body through pectin and its oligomeric fragments.