Ion sensing of sister sensors based-on calix[4]arene in aqueous medium and their bioimaging applications

Here, sister calix[4]arene derivatives containing two NBD (7-nitro-benzofurazan) units in 1,3-(distal) derivatives (sensors 4&8) were prepared and characterized by H-1, C-13 NMR, FTIR, elemental analysis, and fluorescence spectroscopy. The ion binding properties of multi-channel sensors 4&8 were performed in the presence of various cations and anions. Both sensor compounds, 4&8, showed on-off' type fluorescence response towards Cu2+ cation and H2PO4-&F - anions with high selectivity in aqueous solution (CH3CN/H2O, 4/1, v/v). The connected spectroscopic parameters were investigated as the complex stoichiometry, binding constant etc. for a better result. Moreover, the lowest detection limit of 4 for sensing Cu2+ and H2PO4-&F- were obtained 2.4 x 10(-8), 9.1 x 10(-7), 9.7 x 10(-7) mol/L respectively. the lowest detection limit of Cu2+ and H2PO4-&F- by 8 was obtained as 2.9 x 10(-8), 9.7 x 10(-7), 8.9 x 10(-7) mol/L respectively. The confocal microscope was performed to investigate the sensor properties of 4&8 towards ions on living cells. Sensors 4 and 8 showed fluorescence properties on the A549 cell line, while it was observed to turn off the fluorescence intensity in cells treated with H2PO4-F- and Cu2+ ions. Besides, compounds 4 and 8 can be used to identify H2PO4-F- and Cu2+ ions in living cells.

Automated summary

In this study, sister calix[4]arene derivatives with two NBD units were successfully synthesized as sensors for selective ion detection. The sensors showed excellent on-off fluorescence response towards Cu2+ cations and H2PO4- & F- anions in aqueous solution, with high selectivity and low detection limits. These compounds can be used for identifying specific ions in living cells through confocal microscopy.