Development of Nitrobenzoxadiazole-Appended Calix[4]arene Conjugate (L) for Selective Sensing of Trivalent Cr3+, Fe3+, and Al3+ Ions in Solution and in the Solid State and Imaging MCF7 cells by {L + Al3+}

A nitrobenzoxadiazole (NBD)-appended calix[4]arene conjugate (L) possessing a cyclic core formed by connecting the 1,3-positions at the lower rim has been designed. The L has been developed as a receptor for the selective recognition of biologically and ecologically relevant trivalent metal ions, viz., Cr3+, Fe3+, and Al3+. The interaction and region of binding of these metal ions by the receptor L have been explored by isothermal titration calorimetry, spectroscopy, microscopy, and density functional theory (DFT) computational studies. The probe L itself exhibits weak fluorescence emission intensity, and the quantum yield is enhanced by ∼4-fold upon addition of the M3+ ion due to the chelate enhanced fluorescence effect. Fluorescence enhancement also takes place in L when it interacts with M3+ even in the solid state and in the MCF7 cancer cells. The binding constant (Kb) for M3+ by L is ∼104 M–1, supporting that these ions bind to L with moderate strength. The detection limit for all the three metal ions is as low as 4–5 μM. The 1H NMR data reflects the region of binding of the M3+ ion to L. The binding is further supported by DFT studies where the space filling structures evidently shows the binding core in L, and the M3+ ion is buried in this core. As a result of this, the microscopy features are almost the same for L and {L + M3+}. The reversible utility of the sensor has been achieved by the addition of H2PO4–. Based on the input–output information, a molecular logic circuit (INHIBIT logic gate) has been built, which will provide an electronic basis for designing a memory device by the concerned experts.

Abstract licence: CC BY-NC-ND

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