Carbohydrate Complexes with Lead(II) Ion. Interaction of Pb(II) with β-d-Glucurono-6,3-lactone, d-Glucono-1,5-lactone, and Their Acid Anions and the Effects of Metal Ion Binding on the Sugar Hydrolysis

Abstract

Abstract The interaction of Pb(II) ion with β-d-glucurono-6,3-lactone, d-glucuronic acid, d-glucono-1,5-lactone, and their acid anions has been investigated in aqueous solution and solid compounds of the type Pb(d-glucurono-6,3-lactone)(NO3)2, Pb(d-glucuronic acid)(NO3)2, Pb(II)–d-glucuronate, Pb(d-glucono-1,5-lactone)(NO3)2, and Pb(II)–d-gluconate have been isolated. These compounds are characterized by means of FT-IR, 1H and 13C NMR spectroscopy and molar conductivity measurements. Among these Pb–sugar complexes, the crystal structure of the Pb(II)–d-gluconate is known through X-ray diffraction measurements, in which the lead(II) ion is hexa-coordinated, binding to four d-gluconate anions via a carboxylato oxygen and an α-hydroxyl group of the two anions (chelation) and to a carboxylato oxygen atom of the other two sugar anions (unidentately). Spectroscopic evidence suggested that in the Pb–lactone or Pb–acid adducts, the metal ion could be bonded to a lactone or acid molecule through one of the carbonyl oxygen atom and other sugar donor group as well as to two bridging nitrato groups. In the Pb(II)–d-glucuronate, the metal ion could be bonded to four sugar moieties (similar to that of the Pb(II)–d-gluconate) via a carboxylato oxygen atom and other sugar donor group of the two anions and to a carboxylato oxygen atom of the other two acid anions, resulting into a hexa-coordinated lead(II) ion. The β-anomer sugar configuration is predominant in the free d-glucurono-6,3-lactone, d-glucuronic acid, d-glucuronate anion and in these Pb–sugar complexes.