Photoactivatable CO-Releasing Properties of {Ru(CO)₂}-Core Pyridylbenzimidazole Complexes and Reactivity towards Lysozyme

The photoinduced CO-releasing properties of [RuL^Py(CO)₂Cl₂] (1), [Ru(L^Py2Bz-ĸ²N¹,N²)(CO)₂Cl₂] (2), and [Ru(L^Py2Bz–Et-ĸ³N¹,N²,N³)(CO)₂(Cl)]·PF₆ (3) [L^Py = 2-(2-pyridyl)benzimidazole, L^Py2Bz = 2,6-bis(benzimidazole-2′-yl)pyridine, and L^Py2Bz–Et = 2,6-bis(1-ethyl-benzimidazol-2′-yl)pyridine] in both DMSO and reduced myoglobin solution are reported. Complexes 1 and 2 release CO upon illumination at 365 nm. The bidentate chelation mode of L^Py2Bz in 2 is changed into a meridional tridentate mode upon the ethylation of the benzimidazolic NH groups, 3. The extension of the conjugation system and the shift of the MLCT band into the visible region in 3 give rise to the Ru^II dicarbonyl complex capable of releasing CO at 468 nm. During illumination of 2, the chelation mode of L^Py2Bz is changed from ĸ²N¹,N² to ĸ³N¹,N²,N³, as monitored by solution NMR spectroscopic studies. The spectral properties were studied by TD-DFT calculations. The interaction of 1–3 with hen-egg-white lysozyme, as a biocompatible carrier, has been studied by ESI-MS and UV/Vis spectroscopy in the dark and upon illumination. Stable protein adducts containing the Ru^II(CO)₂ moiety, capable of photoinduced release of CO, are formed.