Potentiometric and spectrophotometric studies of MnII and NiII cimetidine complexes

Cimetidine is an important hydrogen histamine receptor which has the ability to chelate metal ions in blood plasma and in different tissues. This study aimed to determine the stability constants for the cimetidine ligand with MnII and NiII metallic ions, synthesizing complexes and characterizing them by infrared spectroscopy, IR, and hydrogen nuclear magnetic resonance, 1H NMR. Cimetidine protonation constant regarding to the imidazole group was log K 7.05 and the stability constants for MnII and NiII complexes, ML2 species were log K 3.75 and 2.97, respectively, in 0.100 mol L-1 KCl. The interpretation of IR and H1 NMR spectra for complexes MnII-cim2 and NiII-cim2 indicated that their formation occurs through the sulfur atoms in the thiol group, nitrogen atoms of imidazole ring, and nitrogen atoms of secondary amine. The nitrile group seems to be involved in the complexation of the NiII-cim2 complex. (author)