Synthesis and anion recognition studies of new ureylbenzamide-based receptors

<p>A new group of ureylbenzamide-based receptors (<b>1</b>–<b>4</b>) has been synthesized; its binding affinity and capacity to form supramolecular complexes in solution with different anions have been investigated. For designing these receptors, it was considered a combination of the positions of the urea and amide groups (<i>ortho</i> and <i>meta</i>), and the chromophore groups naphthyl and nitrophenyl, yielding four receptors. The position and chromophore structure affected the acidity of the urea and amide hydrogens in the order <b>4</b>><b>3</b>><b>2</b>><b>1</b>. All the spectroscopic studies showed a significant change of <b>1</b> and <b>2</b> compared with <b>3</b> and <b>4</b> in the presence of different TBAX salts in acetonitrile. The <sup>1</sup>H-NMR spectra show a preferential interaction of the anions with the urea group in receptors <b>1</b> and <b>2</b> due to the less steric hindrance, while there is a cooperative interaction of amide group in receptors <b>3</b> and <b>4</b> due to the closeness of both groups.</p>