An insight into the morphology of DNA compaction induced by homobinuclear Ru(II) polypyridyl complexes

Binuclear Ru(II) polypyridyl complexes [Ru₂(NN)₄(BIPMB)]⁴⁺ (1-4), where N-N = 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), dipyrido [3,2-d:2',3'-f] quinoxaline (dpq), and dipyrido[3,2-a:2',3'-c]phenazine (dppz), have been synthesized using suitable precursors and bridging ligand (BIPMB), where BIPMB = 3,3'-bis-{(imidazol-1-yl)-[4,5-f]-1,10-phenanthroline) methyl}-1,1'-biphenyl. The binding mode and affinity of complexes 1-4 with Calf Thymus DNA (CT-DNA) were determined by absorption and steady-state fluorescence spectroscopy. The decrease in viscosity of CT-DNA on sequential addition of these complexes indicated DNA condensation and the result was corroborated by circular dichroism (CD). The nanosized globular aggregates of CT-DNA induced by complexes 1-4 were observed by dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. The gel electrophoretic mobility studies revealed the small orderly particles of supercoiled plasmid pBR322 DNA induced by these complexes. Additionally, the morphology and size of compact plasmid DNA condensates were studied by DLS and atomic force microscopy (AFM). The complexes were moderately cytotoxic against MCF-7 cells.