Novel reversible Zn2+-assisted biological phosphate "turn-on" probing through stable aryl-hydrazone salicylaldimine conjugation that attenuates ligand hydrolysis

Abstract

A novel reversible zinc(II) chemosensing ensemble (2·Zn 2+) 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+·[O phenolNimineNpyr] 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. © 2013 American Chemical Society.