Spectral and molecular modeling studies on hydroxybenzaldehydes with native and modified cyclodextrins

The inclusion complexation of 2-hydroxy-3-methoxybenzaldehyde (2HMB), 4-hydroxy-3-methoxybenzaldehyde (4HMB), 3,4-dimethoxybenzaldehyde (DMB) and 4-hydroxy-3,5-dimethoxybenzaldehyde (HDMB) with α-CD, β-CD, HP-α-CD and HP-β-CD were carried out by UV-Visible, steady-state and time-resolved fluorescence and PM3 methods. All the benzaldehydes shows dual fluorescence in aqueous and CD mediums and 1:1 inclusion complexes were formed with CDs. PM3 geometry optimizations results indicate that the HDMB/CD complex is significantly more favorable than the other complexes. The negative enthalpy changes suggest that the inclusion complexation processes are spontaneous. The geometry of the most stable complex shows that methoxy/OH group of HMBs is entrapped in the less polar CD cavities, while the aldehyde group present in the upper part of the CDs cavities.