A new and stable quadruple hydrogen-bonded capsule, tetracarboxylcavitand.meso-tetra(2-pyridyl)porphyrin (1 x 2) has been synthesized and spectroscopically characterized. 1 x 2 can encapsulate small molecules of various size from methane to cyclopentane. The guest and host exchange rates were evaluated by EXSY.

New capsule-shaped hosts “cavitand-linked porphyrin” metal complexes (Mcp: M = H2, Ni, Zn, and Pd) have been synthesized to mimic the substrate binding functions of metalloenzymes such as cytochrome P-450cam. Crystal structures of cavitand 1·MeOH·CHCl3, [Zntpp(MeOH)], [Nicp]·MeOH·2CHCl3·3H2O, [Zncp(MeOH)]·2CHCl3·3H2O, and [Pdcp]·MeOH·2CHCl3·3H2O have been determined. One methanol molecule, originating from crystallization solvent is encapsulated in each host cavity, and coordinates to Zn in Zncp but not in Ni- and Pdcp. Encapsulation of various small hydrocarbon molecules in CDCl3 solutions of Mcps have been evaluated by determining binding constants and thermodynamic parameters obtained from 1H NMR titrations. All Mcps encapsulate hydrocarbons smaller than propane under atmospheric pressure. The guest size selectivity is primarily influenced by cavity size, and partly by metal insertion. The metal ion radius does not affect guest size selectivity. Encapsulation of coordinating guest molecules (MeOH, EtOH, MeCN, and H2O) in Mcps has also been investigated. Only Zncp favors coordination of non-hydrocarbon guests such as MeOH. We concluded that accommodation of different size guests by Mcps depends upon guest sizes and coordination of functional groups depends upon both the identity of the porphyrin’s metal ion and guest sizes.

An accommodating host: A new capsule‐shaped host molecule, the cavitand–porphyrin shown, reversibly encapsulates single hydrocarbon molecules smaller than propane (see picture). With the exception of acetylene, the binding affinities are inversely correlated with the size of the guest hydrocarbons.

Ein gastfreundlicher Wirt: Ein neues, kapselförmiges Wirtmolekül, das gezeigte Cavitandporphyrin, schließt reversibel einzelne Kohlenwasserstoffmoleküle kleiner als Propan ein (siehe Bild). Mit Ausnahme von Acetylen korrelieren die Bindungsaffinitäten invers mit der Größe des Gast‐Kohlenwasserstoffs.