CIRCULAR-DICHROISM, ULTRAVIOLET, AND PROTON NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPIC STUDIES OF THE CHIRAL RECOGNITION MECHANISM OF BETA-CYCLODEXTRIN

The chiral recognition mechanism of beta-cyclodextrin was studied by UV-visible, circular dichroism, and proton nuclear magnetic resonance spectroscopic methods. The D and L enantiomers of DNP-valine, DNP-leucine, and DNP-methionine were used as model solutes. The results indicate that the dinitrophenyl group, which forms stable inclusion complexes with the beta-cyclodextrin cavity and places the other functional groups around the chiral center in association with the hydroxyl groups at the edge of the cavity, plays a very important role in the chiral recognition. The alkyl groups of amino acids, which form a secondary inclusion complex with another beta-cyclodextrin cavity (in the case of DNP-L-amino acids) or are sterically repulsed by the hydroxyl groups at the edge of the cavity (in the case of DNP-D-amino acids), are also major contributors to the chiral recognition process. The dissociation constants of the inclusion complexes of beta-cyclodextrin with these model compounds were also obtained from the changes of UV absorbance, elipticity, and chemical shifts, respectively. It was found that the DNP-L-amino acids always have smaller dissociation constants than the D-enantiomers.