Studies on molecular recognition in supramolecular systems. Part 31: Circular dichroism spectral studies of molecular and chiral recognition of aliphatic alcohols buy 6-modified #beta#-cyclodextrins

摘要

The stability constants (K_S) for the inclusion complexation of novel mono[6-O-(1-benzotriazole)]-#beta#-cyclodextrin (2) and mono(6-benzylseleno-6-deoxy)-#beta#-cyclodextrin (3) with a series of chiral and achiral (cyclo)alkanols have been determined at 25 deg C in aqueous phosphate buffer solution at pH 7.20 by circular dichroism titration. It was revealed that 2 and 3 can fairly strictly recognize not only the size/shape but also the chirality of guest molecules. Thus, the log K_S value, or the Gibbs free energy change (-#DELTA#G~O), incrases linearly with increasing number of carbon atoms (N_C) in cycloalkanol, affording comparable increments per methylene nuit: -d#DELTA#G~)/dN_C = 2.0 and 2.2 kJ mol~(-1) for 2 and 3, respectively. Furthermore, 2 and 3 displayed moderate to excellent isomer selectivities of up to 15.3 for the guest alcohols examined, while moderate enantioselectivities of 1.1-1.4 were obtained with chiral borneol and methanol guests upon complexation with 2 and 3. The present results obtained with 2 and 3 elucidate the effects of substituents on the complexation behavior as well as some of the faactors governing size, shape, and chiral selectivities.