Labile Zinc-Assisted Biological Phosphate Chemosensing and Related Molecular Logic Gating Interpretations

Herein, molecular fluorescence ‘OFF–ON’ behavior with aqueous addition of biological phosphate and Zn²⁺ is studied with Zn₂(<i>slys</i>)₂Cl₂ [H₂<i>slys</i> = 6-amino-2-{(2-hydroxybenzylidene)­amino}­hexanoic acid], a fluorescent water-soluble complex, using various spectroscopic tools (e.g., ³¹P NMR, UV–vis, emission, and CD spectroscopy) at the micromolar level. Adduct-dependent fluorescence intensity changes can be interpreted as a two-input (cation/anion) implication molecular logic gating system. A displacement study of PPi from the dizinc complex is also reported. Diphosphate and triphosphate addition/displacements were also studied. ³¹P NMR spectroscopy shows gradual NMR peak shifts from bound ADP/GDP to free ADP/GDP with increasing [PPi]. In the emission spectrum, fluorescence quenching is shown: CD signal maxima decrease with addition of PPi. These displacement events are also tested with triphosphates (ATP, GTP), and their binding strength/displacement ability over ADP/GDP is quantified: PPi > ATP ≈ GTP (3.35 ± 0.77 × 10⁴ M^–1 for PPi, 7.73 ± 1.79 × 10³ M^–1 for ATP, 9.21 ± 2.88 × 10³ M^–1 for GTP over <b>1</b>·ADP). Many anions and cations were also screened for selectivity. Tubulin polymerization was assayed in the presence of <b>1</b> and its copper analogue which reflected a slight inhibition in polymerization