Mono（2-phenylseleno-2-deoxy）-β-cyclodextrin（2） and mono[2-（p-methoxyphenylseleno）-2-deoxy]-β-cyclodextrin（4）, were newly synthesized and characterized by combustion analyses, IR, 1H NMR and 13 C NMR. Spectrofluorometric titrations have been performed in aqueous phosphate buffer solution（pH 7.20, 0.1 mol/L） at 25 ℃ to give the complex K S and -ΔG° for the stoichiometric 1∶1 inclusion complexation of mono（6-phenylseleno-6-deoxy）-β-cyclodextrin（1）, mono[6-（p-methoxyphenylseleno）-6-deoxy]-β-cyclodextrin（3） and the novel cyclodextrin derivatives 2 and 4 with L- and D-tryptophan. The molecular binding ability and selectivity for L- and D-tryptophan of modified β-cyclodextrins（14） are discussed from the size/shape-fit and geometrical complement relationships between the host cavity and the guest molecule. The results obtained indicate that van der Waals force and hydrophobic interactions dominate the complexation of 1—4 and the aromatic substituents introduced extend the original hydrophobicity of cavity and the molecular binding ability, but reduce the enantioselectivity for L/D-tryptophan guests.
The fluorescence spectra have been studied in phosphate buffer aqueous solution(pH=7.20) to give the stability constants( K s) for the supramolecular system formed by L Pro β CD(1), L Leu β CD(2), and L Ileu β CD(3) with TNS. The results obtained indicate that the binding ability of modified β cyclodextrins(1) with TNS is larger than that of 2 and 3. One possible explanation is that there are different substitutes among the three modified β cyclodextrins.The molecular binding ability is discussed from the size fit concept between the host and the guest molecules. The results indicate that the substitute on the side arm attached to the edge of β CD plays a crucial role in guest inclusion.
