Ruthenium–Cyclopentadienyl–Cycloparaphenylene Complexes: Sizable Multicharged Cations Exhibiting High DNA-Binding Affinity and Remarkable Cytotoxicity
Two novel sizable multicharged cationic complexes, of the formulae [(η6–-[12]CPP)[Ru(η5–-Cp)]12]Χ12 and [(η6–-[11]CPP)[Ru(η5–-Cp)]11]Χ11, CPP = cycloparaphenylene, Cp = cyclopentadienyl, X = [PF6]−, (1), (3) and [Cl]−, (2), (4), were synthesized and characterized using NMR techniques, high-resolution mass spectrometry, and elemental analyses. Complexes (1) and (3) were stable in acetone and acetonitrile solutions over 48 h. In contrast, the water-soluble (2) and (4) begin to decompose in aqueous media after 1 h, due to the [Cl]− tendency for nucleophilic attack on ruthenium of the {Ru(η5–-Cp)} units. Fluorescence quenching experiments conducted during the stability window of (2) with the d(5′-CGCGAATTCGCG-3′)2-EtBr adducts revealed remarkably high values for Ksv = 1.185 × 104 ± 0.025 M−1 and Kb = 3.162 × 105 ± 0.001 M−1. Furthermore, the cytotoxic activity of (2) against A2780, A2780res, and MCF-7 cancer cell lines shows that it is highly cytotoxic with IC50 values in the range of 4.76 ± 1.85 to 16 ± 0.81 μΜ.
