Reactions of Cr3+ with aspartic acid within a wide pH range

Formation of the metal complexes of aspartic acid (Asp) with the chromium metal ion (Cr3+) in solutions using potentiometric titrations is presented within a wide pH range (∼3.5 to ∼10.5) at 25°C and I=0.10 M NaNO3. Concentration distribution diagrams revealed that the main complex formed within this pH range is the bis Cr 3+ complex. Literature stability constant values for the Cr–Asp complexes were used to construct concentration distribution diagrams. Complexes taken into consideration were the simple one-to-one complex, the bis-complex, and the bis-mono-protonated complex, namely, Cr–Asp, Cr(Asp)2, and Cr(Asp)2H. The corresponding Log β values of these complexes were 12.46, 21.86, and 24.30, respectively. UV–Vis spectra demonstrate Cr 3+–Asp binding. The UV–Vis spectra were collected from a system that reached a high level of equilibrium state (50 days’ equilibrium time).