A hydrazone based probe for selective sensing of Al(iii) and Al(iii)-probe complex mediated secondary sensing of PPi:...

A hydrazone-based conjugate Nap-hyz-pyz (H₃L3) with potential N₂O₂ donor atoms was found to act as a dual channel (colori- and fluori-metric) sensor towards Al³⁺ and PPi in H₂O-MeOH (6 : 4, v/v) at pH 7.2 (40 mM HEPES buffer) at 25 °C. The formation constants, K_f = (3.49 ± 1.77) × 10⁴ and (3.78 ± 0.1) × 10⁴ M^-1, of the sensor towards Al³⁺ were determined by absorption and fluorescence titrations, respectively. The 1 : 1 stoichiometry of the reaction was determined by Job's method and confirmed by ESI-MS⁺ (m/z) studies. The LOD for Al³⁺, as determined by the 3σ method, was found to be 114.54 nM. Most strikingly, the addition of ∼115 μM PPi to the Nap-hyz-pyz-Al³⁺ ensemble (20 μM ligand and 74 μM Al³⁺) leads to complete quenching of fluorescence. The fluorescence response of Nap-hyz-pyz towards Al³⁺ was not perturbed by the presence of 5 equivalents or more of other ions and inorganic anions. The structure of the [Al(L³)(H₂O)] complex was delineated by DFT calculations. TD-DFT studies were performed to investigate various spectral transitions. Based on changes in the fluorescence intensities of Nap-hyz-pyz in the presence of Al³⁺ and PPi at 487 nm, INHIBIT and molecular logic gates were constructed and interpreted. The probe was found to be bio-compatible and cell permeable with no or negligible cytotoxicity; thus, it provides a good opportunity for in vitro cell imaging studies of these ions. The presence of ATP or Pi did not interfere with the fluorescent detection of PPi. Thus, these evident and excellent sensing capabilities of Nap-hyz-pyz towards Al³⁺ and PPi were further scrutinized in HepG2 cell lines.