Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The binding of Ca²⁺, Pb²⁺, and Cu²⁺ ions to galactaric and 2,5-furandicarboxylic acids and of Pb²⁺ and Cu²⁺ ions to D-galacturonic acid, its α-methylglycoside, and (methyl-4-deoxy-α-D-galactopyranosid)uronic acid was evaluated in terms of the activity coefficients of the counter-ions and the degrees of their association with the carboxylate groups of the acids. The activity of Ca²⁺ ions was determined by the metallochromic indicator method with tetramethylmurexide, that of Pb²⁺ and Cu²⁺ ions, with ion specific electrodes. Galactaric acid bids 89.5% Ca²⁺ ions, practically all (99.9%) Pb²⁺ ions and nearly all (98.6% Cu²⁺ ions, mostly with the formation of insoluble salts. As little as 7.6% Ca²⁺, 34.0% Pb²⁺, and 23.9% Cu²⁺ were bound to 2,5-furandicarboxylic acid in the form of soluble complexes, and slightly more, 4.1% Ca²⁺, 43.9% Pb²⁺, and 38.0% Cu²⁺, to D-galacturonic acid. The difference in the degrees of binding to galactaric acid and 2,5-furandicarboxylic acid is due to the different flexibility of their molecular skeletons. The activities of Pb²⁺ and Cu²⁺ ions in solutions of salts of D-galacturonic acid and its derivatives indicate that the OH group at C₍₄₎ of D-galacturonic acid takes part in the complexation. For the Pb²⁺ complex, the OH group at C₍₁₎ of the unsubstituted acid in the β-anomeric form also seems to participate in the complexation; this is not the case with the similar Cu complex.