Study on inclusion interaction of hydrophilic 2-chloromandelic acid with hydroxypropyl-β-cyclodextrin

The inclusion interaction between hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and hydrophilic 2-chloromandelic acid (CMA) was studied by ultraviolet (UV) absorption spectrophotometer. A reliable determination of the complex stoichiometry was provided by the continuous variation technique. H-1 NMR spectrum and Thermo-gravimetric/differential thermal analyzer (TG/DTA) techniques were explored to further characterize the inclusion complex, and molecular modeling was used to investigate the mechanism of inclusion interaction. The results showed that HP-beta-CD reacted with R,S-CMA to form inclusion complexes, with 1:1 stoichiometry and inclusion stability constants K-R and K-S were 24 and 39 L/mol determined from UV data by the method of Benesi-Hildebrand's. Molecular modeling confirmed experimental observation and indicated that the hydrogen bonding interaction plays an important role in the interactive inclusion between HP-beta-CD and CMA. Besides, compared with the HP-beta-CD, molecular modeling showed R, S-CMA interact with beta-CD through different binding modes, in which Vander Waals is the main intermolecular force between beta-CD and R-CMA (or S-CMA) while without obvious hydrogen bonding interaction.