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

The work represents a rare example of an aza-crown-based macrocyclic chemosensor, H (H = 1,16-dihydroxy-tetraaza-30-crown-8) for the selective detection of both Zn and Cu in HEPES buffer medium (pH 7.4). H exhibits a fluorescence response for both Zn and Cu ions. The reversibility of the chemosensor in its binding with Zn and Cu ions is also examined using a NaEDTA solution. H exhibits a chelation-enhanced fluorescence (CHEF) effect in the presence of Zn ions and a quenching effect (CHEQ) in the presence of paramagnetic Cu ions. Furthermore, the geometry and spectral properties of H and the chemosensor bound to Zn have been studied by DFT and TDDFT calculations. The limit of detection (LOD) values are 0.11 × 10 and 0.27 × 10 M for Cu and Zn, respectively. The formation constants for the Zn and Cu 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 is able to accommodate up to four metal ions, as proved by the crystal structures of the complexes [Zn()(OH)(NO)] () and {[Cu((OCH)(NO)]·HO} (). H can be used as a potential chemosensor for monitoring Zn and Cu ions in biological and environmental media with outstanding accuracy and precision. The propensity of H to detect intracellular Cu and Zn ions in the triple negative human breast cancer cell line MDA-MB-468 and in HeLa cells has been determined by fluorescence cell imaging.