Rybak-Akimova Research Group

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Tufts U.

Mononuclear iron(II) complexes with pentadentate macrocycles:

Synthesis of new mononuclear iron complexes for oxygen and peroxide activation is now in progress. Pyridine-containing macrocycles bearing additional donor atoms in the attached pendant arms are relevant to bleomycins, which are believed to act as antibiotics and anticancer drugs via oxidative DNA cleavage at the iron center. A simple synthetic procedure leading to five-coordinate pyridine-containing macrocyclic complexes of Cu(II) and Ni(II) has been developed. An interesting new rearrangement of the Schiff base Cu(II) macrocycle, a double bond migration dictated by the coordination requirements of the metal ion, was found. This reaction was shown to be mechanistically similar to biochemical transamination catalyzed by vitamin B6. Free pentadentate macrocyclic ligands were isolated from the reduced nickel complexes, and the preparation of their iron complexes is now in progress. A series of acyclic amino pyridine ligands was synthesized, and redox properties of their copper(II) and niclel(II) complexes were correlated with their X-Ray structures. Remarkable stability of a reduced nickel(I) complex with pentadentate acyclic ligand was found. Preliminary studies show that iron complexes with polyamine- and aminopyridine ligands react with hydrogen peroxide, forming transient colored intermediates. Structure and reactivity of these intermediates are under investigations.