Analytical Sciences

Malonyl-based Chemosensors: Selective Detection of Fe³⁺ Ion in Aqueous Medium

Monu KUMAR, Neha GUPTA, and Amit Pratap SINGH

Department of Applied Sciences, National Institute of Technology Delhi, New Delhi-110 040, India

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⁺, Mg²⁺, K⁺, Ca²⁺, Al³⁺, Cr³⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ag⁺, Cd²⁺, Hg²⁺, Ti³⁺, and Pb²⁺. The emission spectral studies of both 1 and 2 displayed 84 – 91% turn-off emission responses selectively with Fe³⁺ ion in aqueous buffer (MeCN/H₂O, 1:4, v/v, pH = 7.4) solution. Chemosensors 1 and 2 exhibited remarkable sensing ability towards Fe³⁺ 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 Fe³⁺ ion was studied by Benesi–Hildebrand fitting, Stern–Volmer plot and Job’s plots, revealing that both chemosensors (1 – 2) bind with Fe³⁺ metal ion in 1:1 stoichiometric ratio with the apparent association constant (K_a) 8.90 × 10³ and 11.16 × 10³ M⁻¹, 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.

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