Molecular binding thermodynamics of spherical guests by β-cyclodextrins bearing aromatic substituents

The molecular binding behaviors of two beta-cyclodextrin (beta-CD) derivatives bearing 1,2,3-triazole moieties, i.e. mono-6-deoxy-6-{4-(8-oxymethylquinolino)[1,2,3]triazolyl}-beta-CD (1) and mono-6-deoxy-6-{4-(8-oxymethylnaphthol)[1,2,3]triazolyl}-beta-CD (3), and their analogs without 1,2,3-triazole moieties, i.e. mono-6-deoxy-6-(8-oxymethylquinolino)-beta-CD (2) and mono-6-deoxy-6-(8-oxymethylnaphthol)-beta- (4) toward spherical guests (+/-)-borneol and (+/-)-camphor were investigated to elucidate how substituent moiety of host affects the binding abilities by 2D NMR as well as microcalorimetric titrations in aqueous phosphate buffer solution (pH 7.20) at 298.15 K. The binding modes of host-guest interactions obtained from 2D NMR displayed that host CDs without triazole moieties gave better induce-fit efficiency between hosts and guests, leading to stronger binding abilities. Thermodynamically, the inclusion complexation was driven by enthalpy with the stoichiometry of 1:1. Another factor contributed to the enhanced binding abilities was the enthalpy gain with the smaller entropy loss. (C) 2013 Elsevier B.V. All rights reserved.