pH-dependent coordination mode of new bleomycin synthetic analogues with copper(II), iron(II), and zinc(II)

The bleomycin mimic ligands L1 and L2 are synthesized and their pH-dependent complexations with Cu(II), Fe(II) and Zn(II) are investigated via pH-metric titrations. The protonation constants for both ligands show the considerable influence exerted by the carbamide group. The complexation of L1 with Cu(II) forms (Cu(II)(H(sub -1)L1H(super 1+)))2+ at pH < 5 and (Cu(II)(H(sub -1)L1))1+ at pH > 6. Meanwhile, L1 and Zn(II) give (Zn(II)L1)2+ at pH < 6 and (Zn(II)(H(sub 1-)L1))1+ at pH > 8. Finally, the complexation of L2 with Cu(II) yields (Cu(II)(H(sub -1)L2))1+.