Covalent capsules: reversible binding in a chiral space

Abstract

Molecular behavior in small spaces is observed fleetingly at enzyme active sites in biology and at a more leisurely pace in the encapsulation complexes of chemistry. In either setting, molecules in the confined space respond to the size, shape and chemical environment of the container. We describe here neutral, extended cylindrical capsules held together by covalent bonds. The capsules act as hosts to congruent guests such as long-chain alkanes (up to C₂₀H₄₂), p-disubstituted aromatics, and two or more hydrogen-bonded guests. The complexes are characterized by NMR spectroscopy, and the exchange of guests in and out of the capsules is slow on the NMR timescale. Interactions between different guests can be arranged in the cylindrical space, creating acid–base complexes within the capsules. The complexes are chiral and persistent in a variety of media.