COORDINATION CHEMISTRY OF VITAMIN-C .2. INTERACTION OF L-ASCORBIC-ACID WITH ZN (II), CD(II), HG(II), AND MN (II) IONS IN THE SOLID-STATE AND IN AQUEOUS-SOLUTION

The reaction of L-ascorbic acid with the zinc group and manganese ions has been investigated in aqueous solution at pH 6-7. The solid salts of the type M (L-ascorbate)2 .2H2O, where M = Zn(II), Cd(II) and Mn(II) were isolated and characterized by C-13 NMR and Fourier Transform infrared (FT-IR) spectroscopy. Spectroscopic evidence showed that in aqueous solution, the bindings of the Zn(II) and Mn(II) ions are through the ascorbate anion O-3 and O(2)-H groups (chelation), while the Cd(II) ion binding is via the O-3 atom only. In the solid state, the binding of these metal ions would be through two acid anions via O-3, O-2 of the first and O-1, O-3 of the second anion as well as to two H2O molecules, resulting in a six-coordinated metal ion. The Hg(II) ion interaction leads to the oxidation of the ascorbic acid in aqueous solution.