Anion recognition by hydrogen bonding: urea-based receptors

Abstract

Since 1992 a variety of urea-based anion receptors have been synthesised, of varying complexity and sophistication. This critical review will focus on some distinctive aspects of anion recognition by urea derivatives, with a special reference to: (i) design and synthesis, (ii) methodologies for the investigation of the receptor-anion interaction in solution, (iii) the interpretation of the solution behaviour on the basis of the structural interplay between the receptor and the anion. It will be shown that the efficiency of urea as a receptor subunit depends on the presence of two proximate polarised N-H fragments, capable (i) of chelating a spherical anion or (ii) of donating two parallel H-bonds to the oxygen atoms of a carboxylate or of an inorganic oxoanion, a property which is shared with other diamides, e.g. squaramide. The wide use of urea in the design of neutral anion receptors seems to depends on the ease of its synthesis, in particular through the reaction of a primary amine group with an isocyanate, which allows the high-yield preparation of symmetrically and unsymmetrically substituted derivatives (83 references).

A Small Molecule Mimicking a Phosphatidylinositol (4,5)-Bisphosphate Binding Pleckstrin Homology Domain

“…The head group of PI(4,5)P 2 contains phosphate and hydroxyl functionalities (see Figure 1a) that can be exploited for this purpose. For example, it is well established that ureas can form complementary hydrogen bonding interactions with phosphates (15)(16)(17)(18), while boronic acids have been successfully used for the molecular recognition of diols via the reversible formation of B-O covalent bonds (19,20). Thus, we designed a chemical receptor (PHDM) that utilizes ureas and boronic acids as recognition motifs (see Figure 1b).…”

Computational Discovery of Hydrogen Bond Design Rules for Electrochemical Ion Separation

“…Strong, directional hydrogen bonding is a key paradigm in selective anion recognition 12,[24][25][26][27] , catalysis [28][29][30][31][32] , drug design [33][34][35][36] and materials design [37][38][39] . In anion recognition in particular, HB donors distributed uniformly around a cavity of desired size 12,24,[40][41] have been shown to be suitable for size-selective sensing of symmetric anions, whereas shape-selective sensing is achieved via orienting the same strong HB donors to match locations of HB acceptors in the target anion 12,24,[26][27]42 .…”

Principles, Concepts and Strategies of Stereoselective Synthesis

“…Discriminative interactions and complexations of a chiral host (e.g., extractant) with enantiomers of a chiral guest (racemate that has to be resolved) bearing stereocenter(s) provide an opportunity for the enantiomer recognition and separation. A wide variety of discriminative interactions has been reported, among them anion recognition, [121][122][123] peptide and protein recognition, 124,125 carbohydrate recognition, 126 and recognition of carboxylic acids, 127 amino compounds, 128,129 and neutral molecules. 130 After the addition of a chiral lipophilic host or extractant confined in the organic phase, a host-mediated phase transfer of the substrate occurs.…”