Determination of formation constants of some metal complexes of compounds containing naphthoquinone structure

Naphthoquinone derivative compounds and/or metal complexes have an important place in drug research since they show various broad-spectrum pharmacological activities such as antibacterial, antifungal, anticancer, anti-inflammatory, and cytotoxic. For this reason, it is important to determine the formation constants of the complexes that the compounds containing the naphthoquinone structure will form with various metal ions. Within the scope of this study, four compounds containing naphthoquinone structure were synthesized and the formation constants of the complexes to be formed by Zn(II), Ni(II), and Pt(II) ions of these compounds were determined by means of HYPERQUAD computer program using the data obtained as a result of potentiometric titrations in the hydro-organic solvent system at 0.1 °C ± 25.0 and 0.1 M NaCl ionic intensity and dimethyl sulfoxide:water (50:50 v/v). In conclusion of the potentiometric titrations, it was determined that the ligands would form 1:1 complexes with these metal ions under the specified conditions. It is considered that the possible complexes that are expected to form with metal ions of all four ligand types containing naphthoquinone structure to be formed through the coordinate covalent bonds that will form between the carbonyl oxygen, amine nitrogen, and thiocarbonyl sulfur of thiourea and metal ions in the 1,4-naphthoquinone ring system. From the calculations carried out by HYPERQUAD computer program, it was found that the complexes formed by the ligands and Zn(II), Ni(II), and Pt(II) ions were 1:1, and as a result of these complexations, it was determined that ML, MHL, MH2L, MH3L, and MH4L types were formed and consumed at different pH ranges for the compounds.