A ruthenium nitrosyl cyclam complex with appended anthracenyl fluorophore

Abstract

The complex trans-[Ru(NO)(H2O)(L)](ClO4)3 (L = (1-anthracen-9-ylmethyl)-1,4,8,11-tetraazacyclotetradecane) (RuNOL) was synthesized and characterized, and its photophysics and reactivity were investigated. The FTIR spectrum displays a νNO band at 1840 cm−1, indicating a nitrosonium character. 1H and 13C signals in 1D and 2D NMR spectra were assigned and are consistent with the trans configuration. The UV–Vis spectrum displays maximal absorption bands at 341 nm (log ε 3.74), 363 nm (log ε 3.91), 378 nm (log ε 3.97) and 397 nm (log ε 3.91). Coordination of the [RuNO] moiety to the L ligand strongly quenches the anthracenyl fluorescence, and thus RuNOL exhibits only very weak emission at 390, 418, 440 and 472 nm. Electrochemical studies indicate that cathodic peak potentials at +1.10 V(Ic), −0.1 V(IIc) and −0.4 V(IIIc) (vs Ag/AgCl) are related to An+/An, {RuNO}6/7 and {RuNO}7/8 reduction processes, respectively. The pKa of coordinated water was estimated as 2.8 ± 0.2 by DPV. The emission of the pendant fluorophore increases upon electrochemical or chemical reduction of RuNOL, and the resulting switch-ON fluorescence is possibly due to NO release from the target complex. Spectroscopic titrations with DNA resulted in hypochromism and red shifts and allowed estimation of binding constants of 1.9 × 103 (L) and 1.8 × 103 (RuNOL). Molecular docking showed that RuNOL complex has a great affinity with DNA. The RuNOL complex showed low cytotoxicity toward MCF-7 and NIH-3T3 and was ineffective in healthy HUVEC and A7r5 cell lines in the range of concentration of 1 × 10−7–1 × 10−4 mol L−1.