A novel β-cyclodextrin dimer, 2,2'-o-phenylenediseleno-bridged bis(β-cyclodextrin) (2), has been synthesized by reaction of mono-[ 2-O-( p-tolylsulfonyl )]-β-cydodextrin and poly(o-phenylenediselenide). The complexation stability constants (Kβ) and Gibbs free energy changes ( - ΔG°) of dlmer 2 with four fluorescence dyes, that is, ammonium 8-anilino-l-naphthalenesulfonate ( ANS ), sodium 6-( p-toluidino )-2-naphthalenesulfonate (TNS), Acridine Red (AR) and Rhodamine B (RhB)have been determined in aqueous phosphate buffer solution (pH =7.2, 0.1 mol·L^-1) at 25℃ by means of fluorescence spectroscopy. Using the present results and the previously reported corresponding data of ^-cyclodextrin (1) and 6, 6'-o-phenylenediseleno-bridged his ( β-cydodextrin ) ( 3 ), binding ability and molecular selectivity are compared, indicating that the bis (β-cydodextrin)s 2 and 3 possess much higher binding ability toward these dye molecules than parent β-cydodextrin 1, but the complex stability constant for 2 linked from the primary side is larger than that of 3 linked from the secondary side,which is attributed to the more effective cooperative binding of two hydrophobie cavities of host 3 and the size/shape-fit relationship between host and guest. The binding constant (Ks) upon inclusion complexation of host 3 and AR is enhanced by factor of 27.3 as compared with that of 1. The 2D ^1H NOESY spectrum of host 2 and RhB is performed to confirm the binding mode and explain the relative weak binding ability of 2.
A novel modified cyclodextrin, mono[6-O-6-(4- carboxyl-phenyl)]-b-CD (1), has been synthesized by the reaction of mono[6-(p-toluenesulfonyl)]- b-CD with 4-hydro- xybenzoate, and its molecular self-assembly behavior in both solution and solid state was studied by means of crystallography, NMR spectroscopy and microcalorimetry. The results indicate that the bezoic acid groups are successively penetrated intermolecularly into the adjacent b-CD cavities to form helical columnar supramolecules in the solid state. As compared with crystal, the similar self-assembly behavior of 1 in aqueous solution has also been confirmed by the 1H ROESY spectroscopy. Thermodynamically, the formation of polymeric supramolecules by modified CD in aqueous solution is mainly driven by entropy changes.
FAN Zhi, ZHAO Yanli & LIU Yu Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China Correspondence should be addressed to Liu Yu (e-mail: yuliu@public. tpt.tj.cn)
The self-assembly behavior of mono(6-phenolic-6-deoxy)-β-cyclodextrin (1) both in solu- tion and the solid state is comparatively studied by X-ray crystallography and 1H NMR spectroscopy. The results obtained show that the phenolic groups in the crystal 1 can successively penetrate into the adjacent β-cyclodextrin cavities from the secondary side to form head-to-tail linear polymeric su- pramolecule with a 2-fold screw axis. The self-assembly behavior also can be determined in D2O so- lution, giving a self-association constant of 240 mol?1?L. Using the present and previous structures reported for the relevant β-cyclodextrin derivatives, i.e., mono(6-anilino-6-deoxy)-β-cyclodextrin (2), mono(6-phenylselenyl-6-deoxy)-β-cyclodextrin (3), and mono(6-phenylthio-6-deoxy)-β-cyclodextrin (4), we further reveal the factors governing the formations of supramolecular assemblies.
