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).

Remarkable hexafunctional anion receptor with operational urea-based inner cleft and thiourea-based outer cleft: Novel design with high-efficiency for sulfate binding

“…5c) to encapsulate a sulfate anion within its inner cleft , yielding the binding energies as −151 and −77 kcal/mol in gas and solvent phase, respectively. The calculated binding energies for thiourea-bound complex ( ΔE  = −203 kcal/mol) and for urea-bound complex ( ΔE  = −151 kcal/mol) are comparable to our previous report on sulfate binding with a tris -thiourea ( ΔE  = −200 kcal/mol) and a tris -urea ( ΔE  = −173 kcal/mol) in gas phase 33 . The higher binding energy for the thiourea-bound complex (Fig.…”

“…The shift changes for NH resonances (Fig. 3), however, were not consistent with a purely 1:1 binding model as commonly observed for related molecules 33 . Therefore, they were analyzed with a 1:2 ( L :sulfate) binding model using the EQNMR program 46 , displaying the binding constants (in log K ) of 3.06(2) and 2.56(4) for L  + SO 4 2−  = [ L (SO 4 )] 2− and [ L (SO 4 )] 2−  + SO 4 2−  = [ L (SO 4 ) 2 ] 4− , respectively.…”

“…Our previous work has shown that the M06-2X functional accurately predicts the binding energy trends for non-covalent interactions between anions and organic receptors 33 . To this end, the initial equilibrium geometry for the free receptor L was first optimized at the M06-2X/6-31G(d,p) level of theory 53 .…”

Consistent Binding Aptitude of Halides and Oxyanions via Cooperative vs. Non‐Cooperative Binding Modes by Neutral Napthyl Bis‐Urea Receptors

“…Tripodal receptor having structurally flexible preorganized cavity with urea functionalization is a renowned area for anion binding and recognition . Thus in the realm of supramolecular chemistry, synthetic design of a ligand accomplished of strong biding towards anions of different dimensionality (spherical, tetrahedral, planar) is an area of immense interest . To facilitate the binding of anion, most of the commonly reported urea functionalized scaffolds consists of electron withdrawing group making the receptor more electron deficient in nature .…”

A Couple of Tripodal and Dipodal Fluorescent Sensors for Sequential “On‐Off‐On” Response to Cu2+ and ATP/ADP Recognition in Aqueous Solution

“…[24][25][26][27][28] Besides that, tris (2-amino-ethyl) amine (tren) is another most used scaffold for the design of three-dimensional receptors. By attachment of functional groups to the tren unit to modify the binding sites and even the receptors' conformation, those acyclic tripodal receptors have been reported to exhibit specific binding ability towards different types of guests, such as tetrahedral oxoanions (NO 3 À , PO 4 3À and SO 4 2À ), [29][30][31][32][33] halide ions (F À and Cl À ), [34][35][36][37] divalent oxalate (C 2 O 4 2 À ), [38] and metal ions (Cu 2 + and Hg 2 + ). [38][39][40] Until now, the exploration of tripodal ligands for nucleoside polyphosphates recognition is still rare.…”