Binding ability of aldaric acid toward metal(II). X-ray study and solution state investigation on Cu(II)-galactaric acid system and its 2,2′-bypiridine adduct

The interaction of Cu²⁺ with galactaric acid leads to the formation, at acidic pH, of the complex species [CuGala] (Gala=galactaric dianion), while at physiological pH the prevailing species is [Cu(GalaH_-2)]^2- where the carbohydrate acts as chelating agent toward the metal ion through the carboxylic groups and the deprotonated α-hydroxylic oxygens. The crystal structures of galactaric acid (1) and of the ternary complex [CuGala(bpy)]_n·2nH₂O (2) (bpy=2,2′-bipyridine) are also reported. A comparison of the coordinative behavior of galactaric acid and other aldonic and alduronic acids is also discussed.