Issue 23, 2015

Synthesis and anion binding studies of tris(3-aminopropyl)amine-based tripodal urea and thiourea receptors: proton transfer-induced selectivity for hydrogen sulfate over sulfate

Abstract

Tris(3-aminopropyl)amine-based tripodal urea and thiourea receptors, tris([(4-cyanophenyl)amino]propyl)urea (L1) and tris([(4-cyanophenyl)amino]propyl)thiourea (L2), have been synthesized and their anion binding properties have been investigated for halides and oxoanions. As investigated by 1H NMR titrations, each receptor binds an anion with a 1 : 1 stoichiometry via hydrogen-bonding interactions (NH⋯anion), showing the binding trend in the order of F > H2PO4 > HCO3 > HSO4 > CH3COO > SO42− > Cl > Br > I in DMSO-d6. The interactions of the receptors were further studied by 2D NOESY, showing the loss of NOESY contacts of two NH resonances for the complexes of F, H2PO4, HCO3, HSO4 or CH3COO due to the strong NH⋯anion interactions. The observed higher binding affinity for HSO4 than SO42− is attributed to the proton transfer from HSO4 to the central nitrogen of L1 or L2 which was also supported by the DFT calculations, leading to the secondary acid–base interactions. The thiourea receptor L2 has a general trend to show a higher affinity for an anion as compared to the urea receptor L1 for the corresponding anion in DMSO-d6. In addition, the compound L2 has been exploited for its extraction properties for fluoride in water using a liquid–liquid extraction technique, and the results indicate that the receptor effectively extracts fluoride from water showing ca. 99% efficiency (based on L2).

Graphical abstract: Synthesis and anion binding studies of tris(3-aminopropyl)amine-based tripodal urea and thiourea receptors: proton transfer-induced selectivity for hydrogen sulfate over sulfate

Supplementary files

Article information

Article type
Paper
Submitted
22 Jan 2015
Accepted
29 Jan 2015
First published
29 Jan 2015
This article is Open Access
Creative Commons BY license

RSC Adv., 2015,5, 17606-17614

Synthesis and anion binding studies of tris(3-aminopropyl)amine-based tripodal urea and thiourea receptors: proton transfer-induced selectivity for hydrogen sulfate over sulfate

M. Emami Khansari, C. R. Johnson, I. Basaran, A. Nafis, J. Wang, J. Leszczynski and Md. A. Hossain, RSC Adv., 2015, 5, 17606 DOI: 10.1039/C5RA01315A

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