Morshedi M, Boer SA, Thomas M, White NG. Easily-prepared Hydroxy-containing Receptors Recognize Anions in Aqueous Media.
Chem Asian J 2019;
14:1271-1277. [PMID:
30747486 DOI:
10.1002/asia.201900033]
[Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Indexed: 12/20/2022]
Abstract
Despite their ready availability, O-H groups have received relatively little attention as anion recognition motifs. Here, we report two simple hydroxy-containing anion receptors that are prepared in two facile steps followed by anion exchange, without the need for chromatographic purification at any stage. These receptors contain a pyridinium bis(amide) motif as well as hydroxyphenyl groups, and bind mono- and divalent anions in 9:1 CD3 CN:D2 O, showing a selectivity preference for sulfate. Notably, a "model" receptor that does not contain hydroxy groups shows only very weak sulfate binding in this competitive solvent mixture. In the solid state, X-ray crystallographic studies show that the receptors tend to form extended assemblies with anions; however, 1 H and DOSY NMR studies as well as molecular dynamics simulations show that only 1:1 complexes are present in solution. Molecular dynamics simulations suggest that one of the receptors suffers from competing intramolecular hydrogen bonding, while another binds partially-hydrated anions, with the receptor's O-H groups forming hydrogen bonds to water molecules within the anion's coordination sphere.
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