Molecular Recognition Process in Resorcinarene-based Coordination Capsules

Abstract

Cu and Ag capsules can take up various organic molecules. Their molecular recognition possibly involves partial dissociation and slippage. We investigated molecular recognition processes in the Cu and Ag capsules by CD and ¹ H NMR spectroscopy and employed 4,4'-diacetoxy biphenyl carrying two benzothiadiazole groups as a probe. CD and ¹ H NMR measurements reveal that the host-guest complexation proceeds under second-order reactions and that these capsules undergo the partial dissociation to take up the probe in [D₁ ]chloroform and [D₈ ]THF. The slippage also contributes to host-guest complexation for a Cu capsule that carries p-methoxyphenyl groups on the 2,2'-bipyridiyl arms. DFT calculations suggest that π/π stacking interactions between the electron-rich p-methoxyphenyl group and the electron-poor 2,2'-bipyridyl arm elongate the capsule, allowing the guest to access the cavity without the partial dissociation.

Keywords: host-guest; kinetics; molecular recognition; resorcinarene; supramolecular chemistry.