Potentiometric Study of the Dissociation and the Metal Complex-formation Competence of 5-(3,3-dimethyl-1-triazeno)-imidazole-4-carboxamide (Dacarbazine).

A potentiometric investigation has been carried out to disclose the coordination properties of Dacarbazine, 5-(3,3-dimethyl-1-triazeno)-imidazole-4-carboxamide (abbreviated DTIC) with particular transition metal ions (Zn2+, Cu2+, Ni2+ and Co2+). The coordination of DTIC with these metal ions results in several complexes emerging in solution. The aim of this work is to determine the protonation constants of the DTIC and to show the extent of its coordination with (Zn2+, Cu2+, Ni2+ and Co2+), in other words, establish the stability of the complexes formed between the DTIC and these metal ions by the determination of their stability constants. Experimental environments were organized to attain the coordination and measurements in aqueous solutions at 25±0.1 ºC and an ionic background of 0.1 mol.dm-3 NaCl. The HYPERQUAD computer program was used to determine both the protonation and stability constants for the ligand and metal-ligand complexes respectively. DTIC has five protonation constants that can be obtained under experimental conditions used; 10.54, 20.15, 26.99, 32.02 and 36.01. The results are interpreted in terms of the basicity of the donor atoms and structural composition of the ligand. All the complexes produced in the solution are exhibited in speciation diagrams.