A Comparative Study on the Binding Behaviors of β-Cyclodextrin and Its Two Derivatives to Four Fanlike Organic Guests

Four fanlike organic compounds, 1-ethoxybenzene (EOB), 1-butoxybenzene (BOB), 1-dodecyloxybenzene (DOB), and 1-(dodecyloxy)-2-methoxybenzene (DOMB), were chosen as guests, and β-cyclodextrin (β-CD) and its two derivatives, mono(2-O-2-methyl)-β-CD and mono(2-O-2-hydroxy-propyl)-β-CD, were chosen as hosts. Energy changes involved in host−guest inclusion processes were clearly obtained by applying semiempirical PM3 calculations. According to this, probable structures of the host−guest inclusion complexes were proposed. The inclusion systems in aqueous solution were investigated by UV−vis spectroscopy and nuclear magnetic resonance (1H NMR) titration, and the formation constants (K) of the inclusion complexes were determined using the Benesi−Hildebrand equation. Moreover, two solid inclusion complexes of β-CD with EOB and DOB were prepared and characterized by Fourier transform infrared spectra, X-ray powder diffraction, 1H NMR, electrospray ionization mass spectrometry, and thermogravimetric analyses. Results showed that the host−guest stoichiometries in the inclusion complexes were all 1:1 both in solid state and in aqueous solution. As for the same host, the values of K increased in the order EOB < BOB < DOB, in strong association with the fan handle in the fanlike molecules; that is to say, the K values increased with increasing carbon chain length of substituent on benzene ring. In addition, the K values of DOMB complexes were larger than those of DOB complexes for the same CD, indicating that the introduction of an extra o-methoxyl group on DOB further stabilized the CD inclusion complexes. The decomposition activation energies of EOB−β-CD and DOB−β-CD were very similar but significantly larger than that of free β-CD.