Selective Recognition Behavior of Arginine and Histidine Using an Anionic Luminescent Metal-Organic Material Stabilized by Cationic Amine: Steady State and Time-Resolved Luminescence Studies

Abstract

A new Eu-based metal-organic material, [Eu(CAM)₂(H₂O)] 0.5H₂Pip·H₂O, [CAM = chelidamate and H₂Pip = diprotonated piperazine], 1, was synthesized by hydrothermal technique. Structure elucidation of compound 1 was done by single-crystal X-ray diffraction. The connectivity between Eu³⁺ ions and chelidamate ligands forms anionic dimeric metal-organic structures stabilized by interdimer OH···O hydrogen bond interactions involving the free hydroxyl groups and carboxylate oxygen atoms. The OH···O hydrogen bonds connect each dimeric unit with four other dimeric units to form a supramolecular 2D structure with rhombus grid topology. The 2D anionic hydrogen-bonded structures are further stabilized through NH···O hydrogen bond interactions by involving piperazinediium ion to form an overall 3D supramolecular assembly. pH-dependent luminescence studies of compound 1 confirmed its stable nature in the pH range of 1–11. Luminescence turn-off behaviors of compound 1 were observed in the presence of two amino acids, for example, L-arginine (Arg) and L-histidine (His), in water. Luminescence decay processes and lifetime values confirmed that the quenching of luminescence of compound 1 by arginine is due to both static and dynamic quenching, but in the case of histidine, the quenching is purely static in nature.