Calix[4]arene-Naphthalimide Fluorescent Sensors for Cu2+ and F− Ions: Synthesis and Biological Imaging

Introduction: Calix[n]arenes can be selectively functionalized more easily than other cyclic supramolecules such as crown ethers and cyclodextrins. 1,8-Naphthalimide derivatives of calix[4]arenes are very important and versatile fluorophores widely used in fluorescence detection due to their high absorption coefficients, strong fluorescence, high quantum yields, large Stokes shifts, excellent photostability. Methods: Two Calix[4]arene-based fluorescent probes were synthesized for the detection of Cu2+ and F-. The fluorescence properties of the compounds were evaluated in the presence of various cations and anions using spectroscopic techniques. Their cytotoxicity was tested in Hep-2 and HeLa living cells. Results: The synthesized calix[4]arene derivatives were evaluated in the presence of various cations and anions using different spectroscopic and analytical techniques. In the tests, the fluorescence intensity of 7 decreased significantly in the presence of Cu2+ or F-. A similar quenching effect was observed for 6 only in the presence of Cu2+. The cytotoxic properties of calix[4]arene derivatives were evaluated against Hep-2 and HeLa living cells. The results showed significant cytotoxicity of compounds 6 and 7. Discussion: Confocal microscopy studies revealed that these compounds exhibited strong intracellular fluorescence, indicating efficient cellular uptake by cells. In the presence of Cu2+ or F-, the fluorescence intensity of the diamide derivative decreased significantly, which was attributed to the complexation effect between the ligand and the corresponding ions. Conclusion: Monoamide derivative 6 has the potential to be a fluorescent sensor for Cu2+, and diamide derivative is a fluorescent sensor for Cu2+ and F- ions. Cells treated with compounds 6 or 7 exhibited high intracellular fluorescence.