Metal-containing trifurcate chemosensing ensemble for phytate

Abstract

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 (HPO42-, CH3CO2-, CO32-, Cl-, Br-, ClO4-, N-3(-), 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 x 10(8) M-1, accompanied with a large favorable entropy change (T Delta S = 19.4 kcal mol(-1)) and an unfavorable enthalpy change (Delta H = 7.1 kcal mol(-1)) at 303 K. The present chemical ensemble system thus can be used for fluorescence sensing of phytate in the mu M range.