Upper rim modified calix[4]arene towards selective turn-on fluorescence sensor for spectroscopically silent metal ions

Abstract

This work describes the synthesis of a novel sensor calix[4]arene thiosemicarbazone (Lig), consisting of a calix[4]arene thiosemicarbazone moiety capable of detecting Cu2+, Hg2+, Zn2+ colorimetrically and for the selective detection of Zn2+ by “Turn On” fluorescence change in DMSO-H2O (9:1, v/v, pH = 7.2) solution amongst various toxic heavy metal ions. The sensor shows about 240-fold fluorescence enhancements at 474 nm (Stokes shift-140 nm) when bound to a Zn2+ ion with a detection limit of about 15 µM for the Zn2+ ion. Such fluorescence could be visualized by normal unaided eyes offering a simple, visual detection process. DFT theoretical study has been used to further support the high efficiency of the sensor. The binding ability of the Lig with Zn2+ ions has been used to evaluate the biofunctional properties of the synthesized ligand. The synthesized Lig is found to possess the cytotoxic activity and a better penetrating ability towards the A549 human lung cancer cell line.