Ruthenium-Cyclopentadienyl-Cycloparaphenylene Complexes: Sizable Multicharged Cations Exhibiting High DNA-Binding...

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 K_sv = 1.185 × 10⁴ ± 0.025 M^-1 and K_b = 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.