Experimental and theoretical study of the complexation of Fe3+ and Cu2+ by l‑ascorbic acid in aqueous solution

In this study, the ability of l-ascorbic acid to form complexes with Fe3+ and Cu2+ ions was investigated by using a combination of potentiometric measurements and DFT computations with the aim to recognize the coordination modes of the ligand and the most reliable complexes. Speciation profiles obtained by potentiometric titrations in aqueous solution (i.e., 0.16 M NaCl), and supported by UV–Vis data, show that a complexation occurs at 1:1 and 1:2 Fe(III)-to-ligand ratios and at 1:1, 1:2 and 1:3 Cu(II)-to-ligand ratios. The most plausible structures were firstly hypothesized by considering a general equilibrium that considers the effective ligands which enter in the coordination sphere of the metal ions: the anionic forms of ascorbic acid and hydroxide ion. Computational tools were, thus, exploited to ascertain the feasibility of the hypothesized complexes formation.