Two heptadentate Co(III) and Mn(III) complexes with partially deprotonated cyclen derivative bearing four hydroxypropyl pendants: structure, DNA binding and DNA cleavage

Two new complexes, (Co III ) 2 (H 3 L − ) 2 (0.5H 2 O) 2 (ClO 4 ) 4 (I) and (Mn III ) 2 (H 3 L − ) 2 (0.5H 2 O) 2 (ClO 4 ) 4 (II), were synthesized and crystallographically characterized [H 4 L = 1,4,7,10‐tetra‐(2‐hydroxypropyl)‐l,4,7,10‐tetraazacyclododecane] using electrospray ionization mass spectrometry and X‐ray photoelectron spectrometery. The characterizations confirmed that the valences of the metal ions increased from divalent to trivalent due to deprotonation of one OH group (H 4 L was in the form of H 3 L − ). Owing to the instability of Co(III) and Mn(III) in both air and in solution, they preferred to exist in divalent form. The two heptadentate complexes are extraordinary in that the chiral pendants of the complexes are different in configuration. Spectroscopic studies, viscosity measurements, thermal denaturation experiments and circular dichroism spectra demonstrated that the complexes were prone to interact with DNA by groove binding. At micromolar concentrations and under physiological conditions, the two complexes were able to oxidatively cleave the supercoiled pUC19 plasmid DNA into its nicked and linear forms. Mechanistic studies using various additives suggest the complexes had structures different from those of other inorganic complexes. These are the first reported inorganic complexes not containing planar aromatic ligands and yet binding at the major groove. Copyright © 2012 John Wiley & Sons, Ltd.