Cu(II) complexes of a bio-compatible aminoguanidine Schiff base: Histidine sensing and DNA-binding studies

Abstract

Two Cu(II) complexes of pyridoxal-aminoguanidine Schiff base ligand with formula [Cu(HL)Cl]2(OAc)2·4H2O (1) and [Cu(HL)Cl(NCS)].H2O (2) are reported. The ligand and the complexes were characterized by their elemental analyses, ESI-MS, Uv–Vis, IR spectroscopy and cyclic voltammetric measurements. Single crystal structures of complex 1 and 2 were solved by X-ray diffraction. In both the Cu(II) complexes Cu(II) ions are in a square pyramidal geometry having geometry index (τ) value of 0.11 for complex 1 and 0.15 for complex 2. Both the complexes bind to calf-thymus DNA with binding constant comparable to ethidium bromide. Circular dichroism studies revealed an intercalative mode of binding for both the complexes. In addition, the complexes also show promising cleavage of pUC19 supercoiled plasmid DNA with 1 showing the highest cleavage activity of ∼ 99%. In addition, both the complexes selectively recognize l-histidine amino acid. The low detection limit values (0.085 μM and 0.19 μM for complexes 1 and 2, respectively) ascertain the making of an efficient l-histidine biosensor. The absorption, emission and mass spectral results establish the formation of Cu(His)2 complex, with liberation of the fluorescent free ligand as the mechanism of sensing.