Synthesis, structure, CO releasing, and biological activities of new 1-D chain Mn(I)/Mn(II) visible light activated CO-releasing molecules (CORMs)

Abstract

The manganese tricarbonyl complex {[Mn2(CO)6Mn(H2O)4(BPDC)2]·2H2O}n (1) (BPDC = 2,2′-bipyridyl-4,4′-dicarboxylic acid) was synthesized from the reaction of MnBr(CO)5 with 2,2′-bipyridyl-4,4′-dicarboxylic acid. Various fac-Mn(CO)3 cores based on mononuclear complexes were achieved and only a handful of the Mn(I)-based dinuclear metallastirrups or supramolecular rectangles were reported. Interestingly, our compound is the first example of a CORM with 1-D ladder-like chain and Mn(I)/Mn(II) mixed valence state. Studies show that 1 can release CO under three different wavelengths of light (Green: λ = 520–530 nm; Blue: λ = 465–470 nm; UV: λ = 365–370 nm) and CO releasing rate can be adjusted by changing the wavelength of the irradiation light. Density functional theory (DFT) calculations were conducted to analyze the effect of metal-to-ligand charge transfer (MLCT) on CO releasing behaviors. Furthermore, cellular viability assay and anti-inflammatory activities showed that 1 possessed biological compatibility but no systemic cytotoxicity, and could prevent LPS-induced secretion of TNF-α and NO in RAW264.7 cells. The results suggest that 1 may provide a therapeutic approach for inflammation.