Metal-containing Trifurcate Chemosensing Ensemble for Phytate

A trifurcated receptor system containing three Cu(II)-dipicolylamine ligands has been studied for the molecular sensing of phytate, myo-inositol hexakis(phosphate) sodium salt, through an indicator displacement approach. From the Cu(II) complex, a molecular sensing ensemble system was best constructed with eosin Y as indicator. The addition of phytate to the chemical ensemble system in an aqueous medium of physiological pH resulted in the restoration of fluorescence of eosin Y as it is displaced from the metal complex by the anion added. The ensemble system shows the maximum fluorescence change in the case of phytate, about 70% change in the cases of myo-inositol 1,4,5-tris(phosphate) and pyrophosphate ions, and negligible changes in the cases of monovalent anions (HPO4 2 − , CH3CO2 − , CO3 2 − , Cl− , Br− , ClO4 − , N3 − , NO3 − ) and inositol. A binding study by isothermal titration calorimetry suggests that the Cu(II) complex tends to recognize phytate preferably in a 2:1 binding mode with K 1 of 7.7 × 108 M− 1, accompanied with a large favorable entropy change (TΔS = 19.4 kcal mol− 1) and an unfavorable enthalpy change (ΔH = 7.1 kcal mol− 1) at 303 K. The present chemical ensemble system thus can be used for fluorescence sensing of phytate in the μM range.