Synthesis and characterization of a new series of unsymmetrical macrocyclic binuclear vanadyl(IV) complexes: Electrochemical, antimicrobial, DNA binding and cleavage studies

A new series of unsymmetrical macrocyclic binuclear bis-phenoxo bridged oxidovanadium(IV) complexes have been synthesized and characterized by elemental and spectral techniques. A cyclic voltammetric investigation of these binuclear (VO)-O-IV complexes evidenced that two successive quasi-reversible one electron transfer reduction waves (E-pc(1) = -0.54 to -0.67 V, E-pc(2) = -0.80 to -0.85 V) are obtained. In the positive potential region (+0.50 to +1.00 V) two quasi-reversible oxidation couples are observed for all the complexes. The first one electron oxidation is observed around (E-pc(1)) +0.63 to +0.78 V and the second around (E-pc(2)) +0.82 to +0.97 V. The ESR spectra of all the binuclear (VO)-O-IV complexes showed a single broad-band resonance at ca. g = 1.97-2.11 with the half field signal at 1500G (M = 2), which suggest magnetic interactions between two (VO)-O-IV ions through the phenolate bridge. DNA binding experiments show that the aromatic diimine containing macrocyclic (VO)-O-IV complexes display better DNA interactions than the aliphatic diimine containing (VO)-O-IV analogues. These complexes significantly promote the oxidative cleavage of supercoiled plasmid DNA under physiological conditions in the presence of H2O2. All the complexes show noticeable growth inhibition of some plant pathogenic fungal species and human pathogenic bacterial species. (C) 2009 Elsevier Ltd. All rights reserved.