Transition metal complexes of two new imino-dihydroxamic acids

Two new iminodihydroxamic acids [N-benzyl-iminobis(propionohydroxamic acid) and N-benzyl-iminobis(butyrohydroxamic acid)] were prepared and studied as specific binders for the transition M2+ ions due to their potential interest as inhibitors of metalloproteinases. Their architecture is based on aliphatic backbones, as spacers connecting two hydroxamate chelating units, with an N-benzyl group inserted in that skeleton to simulate the protein lipophilic subset. Herein, we first report the synthetic procedure that basically involves the formation of the corresponding intermediates with two nitrile groups, which were then converted to the CONHOH moieties. Then, the acid–base and the chelating properties of these ligands towards Cu2+, Ni2+ and Zn2+ ions, studied by potentiometric and spectrophotometric techniques, are described. Both the ligands form quite stable complexes with these metal ions, presenting a preferential M2+ coordination to the hydroxamate over the amine groups, according to the order Zn2+≥Ni2+>Cu2+.