Molecular Recognition of Hydrocarbon Guests by a Supramolecular Capsule Formed by the 4:4 Self-Assembly of Tris(Zn~(2+)-Cyclen) and Trithiocyanurate in Aqueous Solution

摘要

We have previously reported that the trimeric Zn~(2+)-cyclen complex (tris(Zn~(2+)-cyclen), [Zn_(3)L~(1)]~(6+)) and the trianion of trithiocyanuric acid (TCA~(3-)) assembled in a 4:4 ratio to form a cuboctahedral supramolecular cage, [(Zn_(3)L~(1))_(4)(TCA~(3-))_(4)]~(12+) (hereafter referred to as a Zn-cage), in neutral aqueous solution (cyclen velence 1,4,7,10-tetraazacyclododecane). Herein, we examined the molecular recognition of C_(1)-C_(12) hydrocarbons (C_(n)H_(2n+2) (n approx= 1-12)), cyclopentane, cyclododecane, cisdecalin, and trans-decalin by the Zn-cage under normal atmospheric pressure. This cage complex was also able to encapsulate guest molecules that had larger volumes than that of the inner cavity of the Zn-cage, thereby suggesting that the inner shape of the Zn-cage was flexible. Computational simulations of Zn-cage-guest complexes provided support for this conclusion. Moreover, the solvent-accessible surface areas (SASA) of the Zn-cage host, guest molecules, and the Zn-cage-guest complexes were calculated and the data were used to explain the order of stability determined by the guest-replacement experiments. The storage of volatile molecules in aqueous solution by the Zn-cage is also discussed.