Complex formation constant of ferric ion with Gly, Pro-Hyp and Gly-Pro-Hyp.

The complexes of protein hydrolysates with iron ions may provide one solution for treating iron deficiency because they can work as iron absorption promoters. The chelating ability of some protein hydrolyzates is the key for their iron absorption promotion. Collagen is the most abundant protein in the nature, and collagen peptides are reported to have the ability to promote iron absorption. Collagen's basic tri-peptide unit, , glycine-proline-hydroxyproline (Gly-Pro-Hyp) and its digestion products, glycine (Gly) and proline-hydroxyproline (Pro-Hyp), have been studied against the ferric metal ion. The complexation abilities were determined potentiometrically at three different temperatures of 25 °C, 37 °C, and 40 °C. The ionic strength was maintained using 0.15 mol dm NaCl. Potentiometric data were refined using Hyperquad 2008, and the species distributions were simulated using HySS2009. The complexes of [MA H ], with = 1 to 3 and = -4 to 2, were refined from three ligands at different temperatures and in the pH range from 2 to 11. The complex formation constant (log ) indicated that the complex of Gly-Pro-Hyp was the most stable followed by Pro-Hyp and Gly complexes. Thermodynamic analysis revealed that the formation of the complexes of [MA H ], with = 1 to 3 and = 0, was spontaneous since the Δ value was negative; this means that Gly, Pro-Hyp and Gly-Pro-Hyp have good iron chelating abilities and therefore, they can act as promising iron absorption promoters. The thermodynamic properties of these complexes were also studied, and the base for the usage of these complexes was provided.