Conductometric, Spectrophotometric and Computational Investigation of Binary and Ternary Complexes of Co(II) and Cu(II) Bivalent Metal Ions with L-Valine Amino Acid and Paracetamol Drug

The conductivity and spectrophotometry techniques were employed to evaluate the binary and ternary complexes of the divalent metal ions Co(II) and Cu(II) with the physiologically relevant amino acid L-Valine (Val) and the analgesic paracetamol. The conductivity experiments were generated by direct conductivity equation from conductivity titration data, while the spectrophotometry experiments were performed using the continuous variations approach (Job's method). Both techniques were accomplished in an aqueous solution with a constant concentration of 0.004 M of divalent metal ions at (40.0 ± 0.1) °C. The binary complexes of Co(II) and Cu(II) have a 1:1 binding ratio of metal to paracetamol (M:para). However, the binary complexes of Co(II) and Cu(II) have metal: Val binding ratios of either 1:1 or 2:1. In addition, the Cu(II) binary complexes of both ligands have a higher stability constant than Co(II) binary complexes of paracetamol and Val ligands, which was in good agreement with the Rossotti-Willime order. The ternary complexes of Co(II) and Cu(II) have a 1:1:1 binding ratio of metal to paracetamol: L-valine, (M:para:Val). The stability constants were in order: The ternary metal complexes > The binary metal-L-Val complexes > The binary metal-para complexes. DFT (Density Functional Theory) simulations were used in order to gain a better understanding of the molecular interactions of Co(II) and Cu(II) divalent metal ions with L-Val and paracetamol. Calculations were made on the electronic structure, HOMOs and LUMOs, and molecular geometry of complexes and their corresponding ligands. The findings unequivocally demonstrate that the metal ion is bound to both the amide nitrogen in the paracetamol ligand and the oxygen atom of the carbonyl group. Moreover, the metal ion is bound to the nitrogen atom of the amine NH2 group and the oxygen atom of the hydroxyl group for the L-Val ligand.