<title>DNA dynamics by using highly luminescent phosphine complex of osmium (II)</title>

Abstract

A new highly luminescent "molecular light switch" has been prepared using osmium (II) metal and nonchromophoric phosphine (dppe) and chromophoric (dppz) ligands to study the dynamics ofDNA, where dppe is cis-1,2-bis(diphenylphosphino)-ethylene and dppz is dipyrido{3,2-a:2',3'-c]phenazine. The complex, [Os(dppe)2(dppz)]2, shows a quantum yield in acetonitrile about twofold larger than analogous ruthenium compound, [Ru(bpy)2(dppz)]2t The anisotropy of [Os(dppe)2(dppz)]2 was found to be near 0.2 at -60°C in glycerol. This compound emits at 610 nm on exciting at metal to ligand charge transfer (MLCT) band (390 nm). The lifetimes are 550 and 3 15 ns in argon and air equilibrated acetonitrile samples respectively. This new class of fluorophore using MLCT complex is useable for measurement of DNA dynamics over a larger time scales, which is not possible with conventional DNA dyes, such as ethidium bromide or acridine derivatives.

DNA Binding and Photocleavage in Vitro by New Dirhodium(II) dppz Complexes: Correlation to Cytotoxicity and Photocytotoxicity

“…Emissive transition metal complexes bound to DNA have been explored extensively as reporters of structure, − sequence, nucleotide reactivity, hybridization, cross-linking, drug binding, electron transfer, − and nucleic acid solvation environment and dynamics in duplexes. − [Ru(L) 2 (dppz)] 2+ (L = bpy (2,2‘-bipyridine), phen (1,10-phenanthroline); dppz = dipyrido[3,2- a :2‘,3‘- c ]phenazine) complexes exhibit the “light switch” effect, whose luminescence is “turned on” in the presence of DNA. − The DNA photocleavage by [Ru(bpy) 3 ] 2+ and related Ru(II) complexes, including intercalated [Ru(bpy) 2 (dppz)] 2+ , is only observed in the presence of O 2 , and it likely proceeds via the formation of 1 O 2 through energy transfer from the excited state of the complex . Since the first reports of the “light switch” effect, numerous mononuclear and bimetallic dppz complexes containing a wide variety of metal centers were reported and typically exhibit strong binding to DNA owing to the intercalation of the dppz ligand ( K b values range from ∼10 4 to ∼10 8 M -1 ). ,− It was shown that bimetallic complexes of dppz also bind strongly to DNA, but the two metal centers in the systems reported to date are not in close proximity and their photoreactivity toward nucleic acids was not explored. , …”