Stability constants and complex formation equilibria between iron, calcium, and zinc metal ions with vitamin B9 and glycine

The complexation equilibria of folic acid (FA) and glycine (Gly) were studied in aqueous solutions at room temperature (ca. 298.15 K) and in fixed ionic strength (0.15 mol.dm−3 NaNO3), by means of potentiometry technique. The ferric (Fe3+), ferrous (Fe2+), calcium (Ca2+), and zinc (Zn2+) complex-forming capacities of FA and Gly, and their overall stability constants in aqueous solutions were obtained by applying the potentiometric data in Hyperquad 2008 computer program. From the determined stability constants of the metal complex species, the concentration distribution of the various metal ion complex species involving FA and Gly in solutions was estimated using HySS 2009 software. The complex species distribution diagrams were explained and discussed. Supplementary, the Gibbs free energies and the molecular structures of the formed complexes were evaluated and predicted using Gaussian 09 software molecular modeling and calculations. GRAPHICAL ABSTRACT