Encapsulation-induced remarkable stability of a hydrogen-bonded heterocapsule.

Remarkably enhanced stability of the self-assembled hydrogen-bonded heterocapsule 1⋅2 by the encapsulation of 1,4-bis(1-propynyl)benzene 3 a was found with Ka =1.14×10(9) M(-1) in CDCl3 and Ka2 =1.59×10(8) M(-2) in CD3 OD/CDCl3 (10 % v/v) at 298 K. The formation of 3 a@(1⋅2) was enthalpically driven (ΔH°<0 and ΔS°<0) and there was a unique inflection point in the correlation between ΔH° versus ΔS° as a function of polar solvent content. The ab initio calculations revealed that favorable guest-capsule dispersion and electrostatic interactions between the acetylenic parts (triple bonds) of 3 a and the aromatic inner space of 1⋅2, as well as less structural deformation of 1⋅2 upon encapsulation of 3 a, play important roles in the remarkable stability of 3 a@(1⋅2).