Molecular Recognition by Modified Cyclodextrins and Their Application to Molecular Sensing

Abstract

Cyclodextrins (CDs) capable of accommodating a guest molecule into their hydrophobic cavity are excellent entities for exploring molecular association phenomena. However, the molecular recognition ability of CDs is rather limited owing to their relatively rigid structure. This deficiency can be overcome by introducing pendant residues to CDs. That is hydrophobic pendant residues attached at the primary or the secondary hydroxyl side of CDs acted as hydrophobic caps enhancing hydrophobicity of the CD cavity or spacers narrowing the CD cavity to adapt it for accommodating a small guest. This induced-fit type guest binding usually induces drastic changes in spectroscopic properties of modified residues when they are spectroscopically active. The spectroscopic changes can be used as a measure for molecular recognition and, with regard to this, modified CDs should act as a molecular sensing probe. Selectivity and sensitivity of individual modified CDs upon detecting guests are different from one another, depending on the modified residues. The modified CDs-based sensing probes may be effective in detecting spectroscopically inert substanCes such as bile acids.