A novel turn-on fluorometric "reporter-spacer-receptor" chemosensor based on calix[4]arene scaffold for detection of cyanate anion

Herein, a novel calix[4]arene compound, which was modified by the 2-(2-aminophenyl)benzothiazole fragment with cyanate recognition function was designed based on the reporter-spacer-receptor sensing system. The construction was done via two-step reaction, and the desired sensor 4 was characterized by FT-IR, H-1-, C-13-NMR, and fluorescence spectroscopy along with HRMS data. The sensor candidate showed distinct fluorometric cyanate detection by means of reporter feature of selected benzothiazole constituent. In the presence of cyanate, the sensor gave a turn-on-type fluorescence at 482 nm with a large stokes' shift. Furthermore, it was observed that our fluoroionophore 4 is highly selective toward cyanate over remaining anions such as sulfate, phosphate, fluoride, chloride, bromide, iodide, chlorate, and nitrate in 10% aqueous solution of DMSO. The 1:2 stoichiometric ratio of the 4-cyanate complex was given the best fit with Job's plot based on the titration data. The association constant (K-a) of sensor 4 with cyanate is determined to be 1.64 x 10(5) M-2. The obtained limit of detection (LOD) value for cyanate anion, 312 nM, clearly revealed the remarkable sensitivity of the chemosensor 4. This supramolecular method provides a highly adaptive technique for the detection of cyanate and so cyanide ions by current international standard methods.