Novel Reversible Zn2+-Assisted Biological Phosphate “Turn-On” Probing through Stable Aryl-hydrazone Salicylaldimine Conjugation That Attenuates Ligand Hydrolysis

A novel reversible zinc­(II) chemosensing ensemble (2·Zn2+) allows for selective “turn-on” fluorescence sensing of ATP and PPi in aqueous media (detection limits: 2.4 and 1.0 μM, respectively) giving selective binding patterns: ATP ∼ PPi > ADP ≫ AMP > monophosphates ≈ remaining ions tested. The conjugated hydrazone [CNNHR] resists hydrolysis considerably, compared to the imine [CNCH2R, pyridin-2-ylmethanamine] functionality, and generalizes to other chemosensing efforts. Prerequisite Zn2+·[OphenolNimineNpyr] binding is selective, as determined by UV–vis and NMR spectroscopy; ATP or PPi extracts Zn2+ to regenerate the ligand–fluorophore conjugate (PPi: turn-on, 512 nm; detection limit, 1.0 μM). Crystallography, 2-D NMR spectroscopy, and DFT determinations (B3LYP/631g*) support the nature of compound 2. 2-Hydrazinyl-pyridine-salicylaldehyde conjugation is unknown, as such; a paucity of chemosensing-Zn2+ binding reports underscores the novelty of this modifiable dual cation/anion detection platform. A combined theoretical and experimental approach reported here allows us to determine both the potential uniqueness as well as drawbacks of this novel conjugation.