Ruthenium(II) Complexes of 6,7-Dicyanodipyridoquinoxaline:  Synthesis, Luminescence Studies, and DNA Interaction

Abstract

The hexaflurophosphate and chloride salts of a series of ruthenium(II) complexes incorporating a new dipyridophenazine-based ligand, dicnq (6,7-dicyanodipyrido[2,2-d:2',3'-f]quinoxaline), are synthesized in good-to-moderate yields. These mono ([Ru(phen)2(dicnq)]2+; phen = 1,10-phenanthroline), bis ([Ru(phen)(dicnq)2]2+), and tris ([Ru(dicnq)3]2+) complexes are fully characterized by elemental analysis, infrared, FAB-MS, 1H NMR, and cyclic voltammetric methods. Results of absorption titration and thermal denaturation studies reveal that these complexes are moderately strong binders of calf-thymus (CT) DNA, with their binding constants spanning the range (1-3) x 10(4) M-1. On the other hand, under the identical set of experimental conditions of light and drug dose, the DNA (pBR 322)-photocleavage abilities of these ruthenium(II) complexes follow the order [Ru(phen)2(dicnq)]2+ > [Ru(phen)(dicnq)2]2+ >> [Ru(dicnq)3]2+, an order which is the same as that observed for their MLCT emission quantum yields. Steady-state emission studies carried out in nonaqueous solvents and in aqueous media with or without DNA reveal that while [Ru(dicnq)3]2+ is totally nonemissive under these solution conditions, both [Ru(phen)2(dicnq)]2+ and [Ru(phen)(dicnq)2]2+ are luminescent and function as "molecular light switches" for DNA. Successive addition of CT DNA to buffered aqueous solutions containing the latter two complexes results in an enhancement of the emission in each case, with the enhancement factors at saturation being approximately 16 and 8 for [Ru(phen)2(dicnq)]2+ and [Ru(phen)(dicnq)2]2+, respectively. These results are discussed in light of the relationship between the structure-specific deactivations of the MLCT excited states of these metallointercalators and the characteristic features of their DNA interactions, and attempts are made to compare and contrast their properties with those of analogous dipyridophenazine-based complexes, including the ones reported in the preceding paper.

DNA Interaction, Photocleavage and Topoisomerase I Inhibition by Ru(II) Complex with a New Ligand Possessing Phenazine Unit

“…The DNA viscosity was calculated according to η i =(t i -t 0 )/ t 0 , where η i is the corresponding values of DNA viscosity; t i is the flow time of the solutions in the presence or absence of the complex; and t 0 is the flow time of buffer alone. Data were presented as (η/η 0 ) 1/3 vs. binding ratio [8], where η is the viscosity of DNA in the presence of complex and η 0 is the viscosity of DNA alone.…”

“…The Ru(II) complex, [Ru(bpy) 2 (pyidppz)] 2+ displayed resolvable 1 H NMR spectra (Fig. S1), and all proton chemical shifts were assigned based on the comparison with those of similar compounds [7][8][9][10][11][12][13][14][15][16][17][18][36][37][38][39][40][41][42][43][44]. A singlet peak for the complex appears at ca.13.9, which assigned to the proton on the nitrogen atom of the imidazole.…”

“…These complexes with DNA Blight switches^behavior usually exhibit negligible background emission in aqueous solution but display strong luminescence after binding to DNA in intercalation mode [1,[7][8][9][10][11][12][13][14][15][16][17][18]. An important complex of this type is [Ru(bpy) 2 dppz] 2+ (dppz = dipyrido[3,2-a;2′,3′-c]phenazine), whose Blight switch^effect involves the protonation of the phenazine nitrogens in excited-state [7,19].…”

Effects of Anthracene and Pyrene Units on the Interactions of Novel Polypyridylruthenium(II) Mixed‐Ligand Complexes with DNA

“…In the case of the corresponding mixed- 2 , typical of PF 6 salts of polypyridylruthenium(ii) complexes. [18][19][20]33] …”

Ternary Zinc(II)-Dipeptide Complexes for the Hydrolytic Cleavage of DNA at Physiological pH

“…4, curves d and e, resp. ), which indicated either denaturation or conformational change of DNA [20]. In contrast, basically no effect was observed upon addition of the dipeptides; the slight increase in optical density upon increasing the Zn 2 concentration was probably be due to counter-ion effects.…”