An Ir(III) complex capable of discriminating homocysteine from cysteine and glutathione with luminescent signal and imaging studies.

A new cationic Ir(III) complex with aldehyde and amino groups was synthesized and characterized. The Ir(III) complex has rich photophysical properties. The reaction of the aldehyde group in the Ir(III) complex with homocysteine (Hcy) afforded thiazinane derivatives which resulted in obvious changes in the luminescence spectra. After addition of Hcy to the Ir(III) complex containing 4,4'-diamino-2,2'-bipyridine, the luminescence intensity at ca. 580-610 nm decreased, and a new band at ca.490-520 nm appeared and enhanced strongly with a large blue shift of ca.90 nm, and the luminescent color changed from orange red to green. Based on this ratiometric probe, it can sensitively and selectively recognize Hcy by the ratio of emission intensity at two wavelengths to the concentrations of Hcy. While after addition of cysteine (Cys) or glutathione (GSH), the luminescence band showed a mild decrease in intensity with an unnoticeable shift. These different phenomena make it capable of discriminating homocysteine from cysteine and glutathione. The cytotoxicity and imaging of the complex were also studied in this work. The complex exhibited very low cytotoxicity on HeLa cells and showed sensitivity toward Hcy in living cells. These advantages provide it a good candidate for the application in the analytical and bioanalytical field.