A Potentiometric and Spectroscopic Investigation of Copper(II)– and Zinc(II)–Orotate Complex Equilibria Under Physiological Conditions

A quantitative study of zinc(II) and copper(II) complex formation with orotic acid has been performed under physiological conditions (37°C; 0.15 mol-dm−3 NaCl) using the glass electrode potentiometric technique. Several species have been identified within the pH range 2–10 for the metal-to-ligand concentration ratios investigated. Three mononuclear complexes, ML, ML2, and ML2H−1, have been characterized with both metals. In addition, the polynuclear species M3L2H−2 has been found with copper(II). Formation constants for all these species have been calculated with the help of the SUPERQUAD computer program. UV absorption and IR spectroscopic measurements combined with speciation calculations have been used to confirm corresponding structures.