Aza-Crown-Based Macrocyclic Probe Design for "PET-off" Multi-Cu 2+ Responsive and "CHEF-on" Multi-Zn 2+ Sensor: Application in Biological Cell Imaging and Theoretical Studies.

The work represents a rare example of an aza-crown-based macrocyclic chemosensor, H 2 DTC (H 2 DTC = 1,16-dihydroxy-tetraaza-30-crown-8) for the selective detection of both Zn 2+ and Cu 2+ in HEPES buffer medium (pH 7.4). H 2 DTC exhibits a fluorescence response for both Zn 2+ and Cu 2+ ions. The reversibility of the chemosensor in its binding with Zn 2+ and Cu 2+ ions is also examined using a Na 2 EDTA solution. H 2 DTC exhibits a chelation-enhanced fluorescence (CHEF) effect in the presence of Zn 2+ ions and a quenching effect (CHEQ) in the presence of paramagnetic Cu 2+ ions. Furthermore, the geometry and spectral properties of H 2 DTC and the chemosensor bound to Zn 2+ have been studied by DFT and TDDFT calculations. The limit of detection (LOD) values are 0.11 × 10 -9 and 0.27 × 10 -9 M for Cu 2+ and Zn 2+ , respectively. The formation constants for the Zn 2+ and Cu 2+ complexes have been measured by pH-potentiometry in 0.15 M NaCl in 70:30 (v:v) water:ethanol at 298.1 K. UV-vis absorption and fluorometric spectral data and pH-potentiometric titrations indicate 1:1 and 2:1 metal:chemosensor species. In the solid state H 2 DTC is able to accommodate up to four metal ions, as proved by the crystal structures of the complexes [Zn 4 ( DTC )(OH) 2 (NO 3 ) 4 ] ( 1 ) and {[Cu 4 ( DTC) (OCH 3 ) 2 (NO 3 ) 4 ]·H 2 O} n ( 2 ). H 2 DTC can be used as a potential chemosensor for monitoring Zn 2+ and Cu 2+ ions in biological and environmental media with outstanding accuracy and precision. The propensity of H 2 DTC to detect intracellular Cu 2+ and Zn 2+ ions in the triple negative human breast cancer cell line MDA-MB-468 and in HeLa cells has been determined by fluorescence cell imaging.