Novel colorimetric and fluorescent off–on enantiomers with high selectivity for Fe3+ imaging in living cells

Abstract Two novel colorimetric and fluorescent off–on enantiomers ( R / S - RBOL ) were developed to detect Fe 3+ in aqueous and biological samples through probing the integrated changes in fluorescence, circular dichroism (CD) and circularly polarized luminescence (CPL). The fluorescence intensity of R / S - RBOL is linearly proportional to the Fe 3+ concentration in the range of 0–20 equiv., bringing out a detection limit of 1.83 × 10 −7  M. The Job's plot indicates a 1:1 binding stoichiometry of RBOL :Fe 3+ , which is further confirmed by ESI-MS analysis. Moreover, the RBOL s exhibit a dual-readout response in colour and fluorescence, rendering them suitable to sense Fe 3+ in living cells with low cytotoxicity. In order to shed some light on the detection mechanism, the coordination between R / S - RBOL and Fe 3+ is unravelled by DFT calculations. From the free RBOL to the RBOL –Fe 3+ complex, the spiro-lactam ring is opened to interact with Fe 3+ via the lactam N and O, imine N and hydroxyl O atoms in the form of a ferric six-coordinate structure.