6533b7d8fe1ef96bd126a1ab

RESEARCH PRODUCT

Interactions of N-heteroalkylaminomethylenebisphosphonic acids with Cd(II) ions: Electrochemical and spectroscopic investigations

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The aminomethylenebisphosphonates are known to be excellent chelators for many metal ions. In this work, the coordination properties of three different aminomethylenebisphosphonates with N-substituted heteroalkyl moieties (L1, L2 and L3) and their N-pyridyl derivative (L4) toward cadmium(II) ions are described. Due to their coordination abilities over a broad range of pH, the compounds of this group are good candidates for heavy metal detoxification. To determine the stability constants and the coordination mode of formed aminomethylenebisphosphonate-cadmium(II) complexes, four analytical methods were employed: potentiometry, pulse polarography (DPP), nuclear magnetic resonance spectroscopy (NMR) and electrospray ionization mass spectrometry (ESI-MS). The studies performed revealed that ligands L1, L2 and L3 possessed similar coordination properties, with Cd(II) ions binding below pH 2 to form equimolar complexes and above pH 6 to form bis-complexes. The ligand L4 behaved in a different way, forming six complexes of varied stoichiometry: CdH4L3, CdH3L3, CdHL2, CdL2, CdH2L and Cd3H4L3. The hypothetical competition plot between common complexone d-penicillamine and the studied ligands showed better complexation properties for the aminomethylenebisphosphonates in the pH range 2–6 than for neutral pH, where above neutral pH d-penicillamine bound Cd(II) ions significantly better.