Guest Penetration Deep within the Cavity of Calix[4]arene Hosts: The Tight Binding of Nitric Oxide to Distal (Cofacial) Aromatic Groups

Abstract

Nitric oxide in solitary confinement: Conformationally mobile p-tert-butylcalix[4]arene methyl ether captures nitric oxide (NO) with unprecedented efficiency (K>5×108 M−1) upon oxidative activation. X-ray crystallographic and NMR spectroscopic studies confirm that NO penetrates deep into the interior of the quasi-cylindrical cavity of the 1,3-alternate conformer (see picture).