Encapsulation-Induced Remarkable Stability of a Hydrogen-Bonded Heterocapsule

Remarkably enhanced stability of the self-assembled hydrogen-bonded heterocapsule 12 by the encapsulation of 1,4-bis(1-propynyl)benzene 3a was found with Ka=1.14x109M1 in CDCl3 and Ka2=1.59x108M2 in CD3OD/CDCl3 (10% v/v) at 298K. The formation of 3a@(12) was enthalpically driven (H degrees<0 and S degrees<0) and there was a unique inflection point in the correlation between H degrees versus S degrees as a function of polar solvent content. The ab initio calculations revealed that favorable guestcapsule dispersion and electrostatic interactions between the acetylenic parts (triple bonds) of 3a and the aromatic inner space of 12, as well as less structural deformation of 12 upon encapsulation of 3a, play important roles in the remarkable stability of 3a@(12).