Molecular Recognition Study on Supramolecular Systems. 20. Molecular Recognition and Enantioselectivity of Aliphatic Alcohols by L-Tryptophan-Modified beta-Cyclodextrin.
L-Tryptophan-modified beta-cyclodextrin (L-Trp-beta-CD) has been synthesized and its molecular recognition behavior investigated through fluorescence and circular dichroism spectrometry, as well as fluorescence lifetime measurement in the presence and absence of various alcohols as guest molecules. Employing the indolyl group as a spectral probe, spectrofluorometric and spectropolarimetric titrations have been performed in aqueous phosphate buffer solution at pH 7.20 to calculate the complex stability constants for 1:1 inclusion complexation of L-Trp-beta-CD with several series of alcohols at 25 degrees C. The results obtained indicate that L-Trp-beta-CD can recognize not only size/shape and hydrophobicity but also the enantiomeric and geometrical isomers of the guest alcohols, showing a 230-fold molecular selectivity (13.5 kJ mol(-)(1)) for 2-adamantanol over cyclopentanol among the cyclic alcohols examined. Moderate enantiomeric selectivities of 1.2 and 1.9 for (-)-isomers of borneol and menthol, respectively, and geometrical selectivity of 2.0 for geraniol over nerol have also been observed.
Liu
Yu
Y
Inoue Photochirogenesis Project, ERATO, JST, 4-6-3 Kamishinden, Toyonaka, Osaka 565-0085, Japan, Department of Chemistry, Nankai University, Tianjin, 300071, China, and Department of Molecular Chemistry, Faculty of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Han
Bao-Hang
BH
Sun
Shi-Xin
SX
Wada
Takehiko
T
Inoue
Yoshihisa
Y