A new strategy for a G-quadruplex fluorescent probe based on a nitro-substituted ruthenium complex is described. G-quadruplex DNA can be distinguished from double-or single-strand DNA by the naked eye. This ability originates from variation of the degree of protection of the nitro group on the complex from water by G-quadruplex and other structure DNAs.

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Due to the essential roles of G‐quadruplex in biological processes, the development of G‐quadruplex luminescent probe is becoming more and more important for further understanding of the functions of G‐quadruplex in biology. We herein reported that a ruthenium complex containing triphenylamine group exhibited “off–on” emission behavior after binding to G‐quadruplex in the presence of luminescence quencher [Fe (CN6)]4−. The Ru‐Fe system consists of a mixture of [Ru (phen)2(TPAD)]2+, where TPAD = N‐4‐(1H‐imidazo [4,5‐f] [1,10]phenanthroline‐2‐yl phenyl)‐N‐phenyl‐benzenamine and [Fe (CN6)]4−, which showed luminescent selectivity toward parallel G‐quadruplex (c‐myc). The detection limit was 159 nM for c‐myc. The ligand TPAD bearing nonplanar triphenylamine group and steric hindrance led to different DNA affinities toward various DNA structures. Luminescence experiments, CD spectra, G4‐FID, FRET (fluorescence resonance energy transfer) measurements, and molecular docking results indicated that different DNA affinities and binding modes of the complex toward various DNA structures result in the luminescence selectivity.

The detection of G-quadruplex is of major interest. Nitro-substituted ruthenium (II) complexes have attracted much attention due to fluorescent sensitivity to environment change. We report here a new nitro-substituted ruthenium (II) complex, [Ru (phen) 2 (hnoip)] 2+ (1) (hnoip = 2-(2-hydroxyl-5-nitrophenyl) imidazo[4,5-f][1,10-phenanthroline]), which displays distinct fluorescent properties in aqueous solution and non-aqueous solvents. This complex exhibits large fluorescence enhancement after binding with G-quadruplex DNA, and displays good fluorescent selectivity over other DNAs. The limit of detection is 6 nM for 22AG in Na + and 43 nM for 22AG in K + , respectively. The results demonstrated that nitro-substituted ruthenium (II) complexes can be utilized to design as G-quadruplex fluorescent probes by protection of the nitro group on the complex from water.

Two ruthenium complexes containing a new phenanthroline‐based ligand pai (pai = 2‐(5‐(1, 10‐ phenanthroline))‐1H‐acenaphtho[1′,2′:4,5]imidazole) were synthesized and characterized. Two ruthenium complexes were found to cleave DNA under irradiation, interact with CT‐DNA by intercalation. Furthermore, DNA topoisomerase inhibition experiments indicated that complex 2 exhibited higher topoisomerase I inhibition activity (IC50 = 10 μM) than complex 1 (IC50 = 40 μM). Molecular modeling studies revealed that complex 2 stabilized Top1cc complex via π‐π interaction and the formation of hydrogen bond. The cytotoxicity of complexes 1 and 2 against Eca‐109 and A549 cells was also evaluate by MTT method, indicating that complex 2 exhibited good anticancer activity against Eca‐109 cells (IC50 = 17.23 ± 0.22 μM), but two ruthenium complexes displayed weak anticancer activity against A549 cells.