New [Ru(5,6-dmp/3,4,7,8-tmp)₂(diimine)]²⁺ complexes: non-covalent DNA and protein binding, anticancer activity and fluorescent probes for nuclear and protein components.

A series of Ru(II) complexes of the type [Ru(5,6-dmp)(2)(diimine)](2+)1-3 and [Ru(tmp)(2)(diimine)](2+)4-6, where 5,6-dmp is 5,6-dimethyl-1,10-phenanthroline, tmp is 3,4,7,8-tetramethyl-1,10-phenanthroline and diimine is dipyrido-[3,2-d:2',3'-f]-quinoxaline (dpq), dipyrido[3,2-a:2',3'-c]phenazine (dppz) and 11,12-dimethyl-dipyrido[3,2-a:2',3'-c]phenazine (11,12-dmdppz), has been isolated and the DNA binding mode of the complexes studied by using emission and circular dichroic (CD) spectral techniques. All the complexes exhibit induced circular dichroism upon binding to calf thymus (CT) DNA and show preferential binding to AT and mixed (d(CGCGATCGCG)(2)) sequences rather than to GC sequences. The complex [Ru(tmp)(2)(dpq)](2+)4 exhibits enhancement in luminescence higher than [Ru(5,6-dmp)(2)(dpq)](2+)1 upon binding to DNA. In contrast, [Ru(5,6-dmp)(2)(dppz)](2+)2 and [Ru(5,6-dmp)(2)(dmdppz)](2+)3 exhibit luminescence enhancement higher than [Ru(tmp)(2)(dppz)](2+)5 and [Ru(tmp)(2)(dmdppz)](2+)6 respectively upon DNA binding, illustrating the importance of hydrophobic forces of interaction in determining the DNA binding affinity. Among the complexes, 4 exhibits the highest enhancement in fluorescence intensity upon binding to the protein bovine serum albumin (BSA). The cytotoxicity of the complexes has been studied by screening them against non-small lung carcinoma (NCI-H460) cell line. It is noteworthy that the complex showing the strongest DNA binding affinity exhibits the highest cytotoxicity. The efficiency of the complexes as fluorescent probes for detection of nuclear morphology and proteins has been evaluated by using fluorescence microscopy. Remarkably, 4, which shows strong hydrophobic forces of interaction when bound to DNA and protein, acts as fluorescent probes for detection of nuclear components in the head, and proteins in the tail, of sperms.