DNA cleavage promoted by trigonal-bipyramidal zinc(II) and copper(II) complexes formed by asymmetric tripodal tetradendate 2-[bis(2-aminoethyl)amino]ethanol

Asymmetric trigonal-bipyramidal Zn(II) complex 1 formed by 2-[bis(2-aminoethyl)amino]ethanol (L) was found to be able to promote the cleavage of supercoiled plasmid DNA pBR322 to the nicked and linear DNA via a hydrolytic manner but only in neutral Tris–HCl buffer, no cleavage was observed in HEPES or NaH2PO4/Na2HPO4 buffer. However, the copper complex 2 of L, possessing the similar coordination geometry, can only promote DNA cleavage via an oxidative mechanism in the presence of ascorbic acid. ESI-MS study implies that complex 1 exist mainly as [Zn(L)]2+/[Zn(L–H)]+ in neutral Tris–HCl buffer. Moreover, there is no discriminable species for complex 1 in HEPES or NaH2PO4/Na2HPO4 buffer. A phosphate activation mechanism via phosphate coordinating to Zn(II) center of [Zn(L)]2+/[Zn(L–H)]+ to form the stable trigonal-bipyramidal structure is proposed for the hydrolytic cleavage promote by complex 1. For complex 2, the abundance of [Cu(L)Cl]+ is higher than that of [Cu(L)]2+/[Cu(L–H)]+ in Tris–HCl buffer. The lower phosphate binding/activating ability of Cu(II) in complex 2 may be the origin for its incapability to promote the hydrolytic DNA cleavage. However, the readily accessible redox potential of Cu(II) makes complex 2 promote the oxidative DNA cleavage. Although the DNA cleavage promoted by complex 1 has no specificity, trigonal-bipyramidal Zn(II) complexes formed by asymmetric tripodal polyamine with ethoxyl pendent should be a novel potential model for practical artificial nuclease.