Water soluble host–guest chemistry involving aromatic N-oxides and sulfonateresorcinarene

Abstract

<p>Resorcinarenes decorated with sulfonate groups are anionic in nature and water soluble with a hydrophobic electron-rich interior cavity. These receptors are shown to bind zwitterionic aromatic mono-N-oxides and cationic di-N-oxide salts with varying spacer lengths. Titration data fit a 1:1 binding isotherm for the mono-N-oxides and 2:1 binding isotherm for the di-N-oxides. The first binding constants for the di-N-oxides (K<sub>1</sub>: 10<sup>4</sup> M<sup>−1</sup>) are higher compared to the neutral mono-N-oxide (K: 10<sup>3</sup> M<sup>−1</sup>) due to enhanced electrostatic attraction from a receptor with an electron-rich internal cavity and cationic and electron deficient N-oxides. The interaction parameter α reveals positive cooperativity for the di-N-oxide with a four-carbon spacer and negative cooperativity for the di-N-oxides that have spacers with more four carbons. This is attributed to shape complementarity between the host and the guest.</p>