Water-soluble UV/visible light activated Mn-CO-releasing molecules: Synthesis, structure, CO releasing and biological activities evaluation

By reactions of MnBr(CO)5 with 2,2′-bipyridyl-4,4′-dicarboxylic acid and 2,5-pyridinedicarboxylic acid, respectively, we obtained two new Mn-CORMs, [Mn(CO)3(H2O)(HBPDC)] (1) and [Mn(CO)3(CH3CN)(HPYDC)]·CH3CN (2). Complexes 1 and 2 are stable in the absence of light, but they exhibit good CO release ability upon exposure to UV and visible light (blue and green). The CO releasing rate depends on the wavelength of irradiation light, i.e., UV > blue > green, which may make them act as visible light regulated CORMs. It is noteworthy that complexes 1 and 2 possess high water-solubility. TD-DFT studies of complexes 1 and 2 reveal that the metal-to-ligand charge-transfer (MLCT) may be responsible for their CO releasing behaviors triggered by UV and visible light. The cellular viability and anti-inflammatory activities evaluation show that complexes 1 and 2 can inhibit the secretion of NO and TNF-α in LPS-stimulated RAW264.7 macrophages with fine biological compatibility and without apparent cytotoxicity. Furthermore, during the synthesis of complexes 1 and 2, when the pH of solution is hinger than 7, complexes {[Mn(BPDC)]}n (1A) and [Mn(H2O)2(HPYDC)2] (2A) are obtained. Complex 1A is a new 3D Mn-MOF and complex 2A is a zero-dimensional mononuclear compound, which are all without CO ligand.