Tailoring Ligand Environment toward Development of Colorimetric and Fluorescence Indicator for Biological Mn(II) Imaging

Mn(2+) ion plays an essential role in all forms of life. Paramagnetic nature of Mn(2+) and its close resemblance with Ca(2+) and Mg(2+) are two key limiting factors responsible for the least development of fluorescence probes suitable for bioimaging. In literature we have found only a few Mn(2+) selective fluorescent sensor and their applications. These probes are mainly based on linear polydentate and macrocyclic ligands. Systematic tuning of ligand environment allows colorimetric and fluorescence recognition of traces Mn(2+) in real sample and fluorescence indicator in living RAW264.7 cells. Two probes, one based on fluorescein (FHDB) and the other based on rhodamine (RDDB) showed turn-on response toward Mn(2+) in DMSO and acetonitrile, respectively. Colorimetric detection of Mn(2+) ion is also possible in the presence of other metal ions. The new sensing probe RDDB shows higher sensitivity as well as faster response compared to the reported systems. The detection limit of RDDB is 5 × 10(-8) M and FHDB is 1 × 10(-7) M. DFT studies strongly support the experimental facts.