Side chain influencing the interaction between β ‐cyclodextrin and vanillin

The reason for low encapsulation efficiency of vanillin compared to p ‐hydroxybenzaldehyde within β ‐cyclodextrin was investigated. Fourier transform infrared spectra proved intermolecular interaction between guest and β ‐cyclodextrin. UV–visible studies indicated that vanillin and p ‐hydroxybenzaldehyde form 1:1 inclusion complexes with β ‐cyclodextrin. Nuclear magnetic resonance and quantum computational methods gave the most favourable orientation in which the guest molecule (vanillin or p ‐hydroxybenzaldehyde) is totally sequestered in the hydrophobic cavity of the cyclodextrin with the phenolic end located near the primary hydroxyls of the β ‐cyclodextrin and the aldehyde group near the secondary hydroxyls with hydrogen bonding formation. Encapsulation efficiency of the β ‐cyclodextrin inclusion with vanillin is about 29% lower than that with p ‐hydroxybenzaldehyde. This result could be attributable to the effect that the side chain methoxy group weakened the guest/host non‐covalent intermolecular interaction, specifically, hydrogen bond interaction. Copyright © 2012 John Wiley & Sons, Ltd.