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

Abstract 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. 1 H‐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 3 MLCT in proximity to the 3 MC excited states, thus enabling a photochemical pathway. Under continuous light irradiation at 450 nm, Ru2Apy opens the coordinating site of the NH 2 group in 2Apy to form the monoacetonitrile complex cis ‐[Ru(phen) 2 (2Apy)(CH 3 CN)) 2+ , with a quantum yield of 0.457. Further irradiation leads to a second photoprocess to form the bis‐acetonitrile cis ‐[Ru(phen) 2 (CH 3 CN) 2 ] 2+ complex, with a quantum yield of 0.002. Ru2Apy binds to human serum albumin via non‐covalent interactions with K b =4.63×10 −9 mol L −1 , ΔH=−3.4×10 −3 kcal mol −1 , and ΔS=8.7 kcal mol −1 K −1 , and displays a moderate inhibition of AChE with an IC 50 of 13.2±2.0 μmol 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 Aβ 1–40 in a dose‐dependent manner.