Molecular Recognition of Hydrocarbon Guests by a Supramolecular Capsule Formed by the 4:4 Self-Assembly of Tris(Zn2+-Cyclen) and Trithiocyanurate in Aqueous Solution

We have previously reported that the trimeric Zn2+cyclen complex (tris(Zn2+cyclen), [Zn3L1]6+) and the trianion of trithiocyanuric acid (TCA3-) assembled in a 4:4 ratio to form a cuboctahedral supramolecular cage, [(Zn3L1)4(TCA3-)4]12+ (hereafter referred to as a Zncage), in neutral aqueous solution (cyclen=1,4,7,10-tetraazacyclododecane). Herein, we examined the molecular recognition of C1C12 hydrocarbons (CnH(2n+2) (n112)), cyclopentane, cyclododecane, cis-decalin, and trans-decalin by the Zncage 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 Zncage, thereby suggesting that the inner shape of the Zncage was flexible. Computational simulations of Zncageguest complexes provided support for this conclusion. Moreover, the solvent-accessible surface areas (SASA) of the Zncage host, guest molecules, and the Zncage-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 Zncage is also discussed.