Molecular binding behavior of a bispyridinium-containing bis(β-cyclodextrin) and its corresponding [2]rotaxane towards bile salts

Abstract

Bispyridinium-bridged bis(β-cyclodextrin) (1) and its corresponding [2]rotaxane (2) were synthesized by a ‘click’ reaction, in which two different types of macrocycles, cucurbit[7]uril and β-cyclodextrin, are employed as the wheel component and bulky stopper, respectively. Moreover, the molecular binding behaviors of hosts 1 and 2 with four bile salts, namely, the sodium salts of cholic acid (CA), deoxycholic acid (DCA), glycocholic acid (GCA), and taurocholic acid (TCA), were comparatively investigated by ¹H NMR spectroscopy and isothermal titration calorimetry experiments. The spectroscopic and microcalorimetric results can jointly demonstrate a cucurbituril-mediated binding process; that is, the introduction of cucurbit[7]uril has a pronounced impact on the electrostatic attraction and hydrogen-bonding interaction between the bispyridinium spacer in the host molecules and the hydrophilic terminal group in the guest molecules, ultimately giving a significant change in the thermodynamic origins of these supramolecular complexes.