Bidentate Coordination of 2-Aminopyridine (2Apy) in cis-[Ru(phen)(2)(2Apy)](2+) Aiming at Photobiological Studies

This study describes the synthesis and characterization of the photoluminescent and water-soluble complex cis-[Ru-(phen)(2)(2Apy)](2+) (Ru2Apy, phen=1,10-phenanthroline and 2Apy = 2-aminopyridine), which exhibits spectroscopic and physicochemical properties favorable for biological applications. H-1-NMR, photoluminescence, and UV-vis spectroscopy experiments show bidentate coordination of the 2Apy ligand, which leads to a blue shift in the emission spectrum and places the (MLCT)-M-3 in proximity to the (MC)-M-3 excited states, thus enabling a photochemical pathway. Under continuous light irradiation at 450 nm, Ru2Apy opens the coordinating site of the NH2 group in 2Apy to form the monoacetonitrile complex cis-[Ru-phen)(2) (2Apy)(CH3CN))(2+), with a quantum yield of 0.457. Further irradiation leads to a second photoprocess to form the bisacetonitrile cis-[Ru(phen)(2)(CH3CN)(2)](2+) complex, with a quantum yield of 0.002. Ru2Apy binds to human serum albumin via non-covalent interactions with K-b = 4.63 x10(-9) mol L-1, Delta H = - 3.4 x 10(-3) kcal mol(-1), and Delta S = 8.7 kcal mol(-1)K(-1), and displays a moderate inhibition of AChE with an IC50 of 13.2 +/- 2.0 mu mol L-1. The complex also exhibited high uptake into HeLa cells with no cytotoxicity. Furthermore, the emissive response of Ru2Apy was be used to assess, in real-time, the aggregation of A beta(1-40) in a dose-dependent manner.