Lanthanide-Based Polymers with Charged Ligand Backbones: Triple-Stranded Chain Structures and their DNA Cleavage Studies

Four rare-earth metal complexes, [Ln(Ccbp)(3)(H2O)(3)](n) (Ln=La (1), Ce (2), Pr (3) and Nd (4)) are synthesised from the ligand H(2)CcbpBr (H(2)CcbpBr=4-carboxy-1-(4-carboxybenzyl)pyridinium bromide) and the respective lanthanide metal ions. Complexes 1-4 are isostructural in that every three Ccbp(-) ligands juxtapose two Ln(3+) ions in a monodentate coordination mode to form triple-stranded one-dimensional chain structures. Each central Ln(3+) atom further associates with three H2O molecules, furnishing a monocapped square-antiprism geometry. Agarose gel electrophoresis studies indicate that 1-4 are capable of cleaving DNA in the presence of H2O2, most probably via an oxidative cleavage mechanism. Complexes 1 and 2 exhibited catalytic efficiencies (k(max)/K-M) of 37.69 and 34.11h(-1)mM(-1), and are approx. 15- and 20-fold more effective than those of complexes 3 (k(max)/K-M=1.75h(-1)mM(-1)) and 4 (k(max)/K-M=2.21h(-1)mM(-1)).