Nickel and Cobalt Complexes of Non-protein L-Norvaline and Antioxidant Ferulic Acid: Potentiometric and Spectrophotometric Studies

Binary and mixed-ligand complexes of Ni2+ and Co2+ involving L-norvaline (Nva) and ferulic acid (FA) have been investigated in aqueous solutions by pH potentiometry and UV–visible spectrophotometric techniques, at 298.15 K and fixed ionic strength (0.15 mol⋅dm−3, NaNO3). The overall stability constants of the Ni2+ and Co2+ complexes with the ligands studied were obtained by the HYPERQUAD2008 program from the pH-potentiometric data. As a result of the numerical treatment, a model composed of seven species NiNva+, NiNva2, NiNvaH−1, NiNva−−2, NiFA, NiFAH−−1 and NiNvaFA− was obtained for the Ni2++Nva+FA system, whereas for the Co2++Nva+FA system the complexes CoNva+, CoNva2, CoNvaH−1, CoNvaH−−2, CoFA, CoFAH−−1, and CoNvaFA− were obtained. The complex species distributions in certain pH ranges were calculated by the HySS2009 simulation program. Spectroscopic UV–visible measurements were carried out to give qualitative information about the complexes formed in these solutions