Social Self-Sorting: Alternating Supramolecular Oligomer Consisting of Isomers

The isomers of cinnamoyl alpha-CDs (2-CiO-alpha-CD and 3-CiO-alpha-CD) organize by themselves to give different types of supramolecular complexes in aqueous solutions. 2-CiO-alpha-CD was found to form a double-threaded dimer, which was characterized by single crystal X-ray analysis. The molecular sizes of supramolecular complexes consisting of CiO-alpha-CDs were estimated by pulsed field gradient spin-echo NMR, which gives the diffusion coefficient (D). D of 2-CiO-alpha-CD was found to be 2.3 x 10(-10) m(2)/s at concentrations over 10 mM and D was saturated. It should be noted that the hydrodynamic radius derived from D of 2-CiO-alpha-CD was found to be 9.6 angstrom, which closely matched the result from the single crystal X-ray analysis. D of 3-CiO-alpha-CD, however, was smaller than that of 2-CiO-alpha-CD at concentrations over 32 mM, indicating that 3-CiO-alpha-CD formed a supramolecular oligomer. Two-dimensional (2D)-ROESY spectra of the mixture of 2-CiO-alpha-CD and 3-CiO-alpha-CD did not show a correlation between the same species; rather, correlation peaks between 2-CiO-alpha-CD and 3-CiO-alpha-CD were observed. D's of a mixture of 2-CiO-alpha-CD and 3-CiO-alpha-CD were found to be larger than those of 2-CiO-alpha-CD and 3-CiO-alpha-CD, respectively, indicating that the mixture of 2-CiO-alpha-CD and 3-CiO-alpha-CD formed an alternative supramolecular oligomer and not a self- or random- supramolecular complex. CDs recognize a guest molecule and the substitutional position of a guest molecule on CD, suggesting that CDs have social self-sorting capability.