Malonyl-based Chemosensors: Selective Detection of Fe Ion in Aqueous Medium.

Two novel malonyl-based chemosensors, N,N'-bis(ethyl-4'-benzoate)-1,3-propanediamide (1) and N,N'-bis(ethyl-3'-benzoate)-1,3-propanediamide (2), have been synthesized and screened towards various biologically important metal ions such as Na, Mg, K, Ca, Al, Cr, Mn, Fe, Fe, Co, Ni, Cu, Zn, Ag, Cd, Hg, Ti, and Pb. The emission spectral studies of both 1 and 2 displayed 84 - 91% turn-off emission responses selectively with Fe ion in aqueous buffer (MeCN/HO, 1:4, v/v, pH = 7.4) solution. Chemosensors 1 and 2 exhibited remarkable sensing ability towards Fe ion over other metal ions with limit of detection (LOD) of 4.28 and 4.33 μM, respectively. The binding stoichiometry of 1 and 2 with Fe ion was studied by Benesi-Hildebrand fitting, Stern-Volmer plot and Job's plots, revealing that both chemosensors (1 - 2) bind with Fe metal ion in 1:1 stoichiometric ratio with the apparent association constant (K) 8.90 × 10 and 11.16 × 10 M, respectively. Furthermore, the interactions of chemosensors (1 - 2) with metal ion were also investigated by using density functional theory (DFT) at B3LYP hybrid functional using 6-31G and LanL2DZ basis sets.