Correlation models for the inclusion complexation of aliphatic compounds with α- and β-cyclodextrins

Complexation free energies of aliphatic compounds with alpha- and beta-cyclodextrins were analyzed in terms of theoretical and empirical parameters that account for the role of van der Waals, hydrophobic, electrostatic, charge transfer interactions and steric effects. Two multivariate correlations were obtained to describe the inclusion behavior of 73 aliphatic guests in beta-cyclodextrin and 37 species in -cyclodextrin. For the first time, these models have dealt with the inclusion complexation of neutral, anionic and cationic aliphatic species. Results indicate that the most important factor involved in the inclusion of aliphatic guests is van der Waals interaction, whereas charge transfer appears as a key factor that differentiates the inclusion complexation between neutral and ionic species. Additionally, steric effects affect the inclusion complexation with alpha-cyclodextrin, whose smaller cavity is subjected to steric hindrance when there are voluminous guests.