Nitric oxide (NO) has key regulatory roles in various biological and medical processes. The control of its local concentration, which is crucial for obtaining the desired effect, can be achieved with exogenous NO donors. Release of NO from metal-nitrosyl complexes upon exposure to light is a strategy that could allow for the site-specific delivery of the reactive species NO to physiological targets. The photodissociation of NO from two nitrosylruthenium(II) isomer complexes {cis- and trans-[Ru(OAc)(2mqn)2NO]} was demonstrated by matrix-assisted laser desorption ionization time-of-flight mass spectrometry spectra, and electron paramagnetic resonance spectra further prove the photoinduced NO release by spin trapping of NO free radicals upon photoirradiation. Real-time NO release was quantitatively measured by electrochemistry with an NO-specific electrode. The quantitative control of NO release from [Ru(OAc)(2mqn)2NO] in aqueous solutions was done by photoirradiation at different wavelengths. Both isomers show photoinduced damage on plasmid DNA, but the trans isomer has higher cytotoxicity and photocytotoxicity activity against the HeLa tumor cell line than that of the cis isomer. Nitrosylruthenium(II) complex, with 8-quinolinol derivatives as ligands, has a great potential as a photoactivated NO donor reagent for biomedical applications.
Photoisomerization from cis-2 [Ru(OAc)(2cqn)2NO] (H2cqn=2-chloro-8-quinolinol) to cis-1 isomer was studied
quantitatively and the effect of wavelength on isomerization was investigated. The main absorption band in UV-Vis
region for cis-1 and cis-2 isomer was observed from 350 nm to 500 nm, and the kinetic study showed that the
photoisomerization from cis-2 to cis-1 isomer was first-order and the rate constant (k) is 0.00022 (s-1) at 420 nm, 0.00018 (s-1) at 475 nm, 0.00011 (s-1) at 550 nm, respectively. Density functional theory (DFT) calculation suggested that the electronic transition from a ligand based orbital to an antibonding overlap of the Ru(d) and π* NO(p) orbitals control the photo induced reactivity of [Ru(OAc)(2cqn)2NO] complexes. The study provides basic information to design
the molecular optical switches and advance optoelectronic materials based on nitrosylruthenium(II) complexes.
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