Molecular Recognition Study On Supramolecular System .7. Chiral Recognition Of Amino Acids With Alpha-Cyclodextrin Using Competitive Inclusion Method

CYCLODEXTRINS (CDs) have been extensively studied. The studies mainly focused on their inclusion complexation with guest molecules for mimicking the enzyme-substrate specific interaction. The molecular recognition mainly involves several classes of organic compounds, such as hydrocarbon, aliphatic alcohols, aliphatic diols, phenols, cyclohexane derivatives, naphthalene derivatives, and other aromatic compounds, but few amino acid moleculesr1]. We reported the chiral recognition of aromatic amino acids by binuclear copper( I1 ) complexes with cyclodextrins, discussing its contribution to the formation of supramolecular system from the viewpoint of the multiple-point recognition, induced-fit interaction, and the cyclodextrin configuration change due to the formation of binuclear copper( Il ) complex[21. Recently mono[6- ( l-pyridinio) -6-deoxy ]- a- and y- cyclodextrins have also been synthesized to examine the thermodynamics of molecular recognition of aliphatic amino acids, and significant results have been obtained1). However, because both natural cyclodextrins and aliphatic amino acids show very little absorption in ultraviolet and visible regions, general spectrophotometric titration cannot be used to examine their complexation. Calorimetric titration is also difficult to perform due to the very small enthalpy change of the complexation process. Therefore, there are few reports on the molecular recognition and inclusion complexation of aliphatic amino acids with ~~clodextrins[~' 41. In the present work, methyl orange was used as a kind of spectrophotometric molecular probe to determine the stability constants of host-guest inclusion complexes formed by the selective binding of amino acids (guests) with a-cyclodextrin (host) by adopting the competitive inclusion method. The contribution to the formation of inclusion complex is discussed from the viewpoint of the size-fit relationship between the host cavity and the guest molecules.