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

Area of Science:

• Supramolecular Chemistry
• Photochemistry
• Computational Chemistry

Background:

• Benzaldehydes are versatile organic compounds with applications in various fields.
• Cyclodextrins (CDs) are cyclic oligosaccharides widely used as host molecules in supramolecular chemistry.
• Understanding host-guest interactions is crucial for designing novel functional materials.

Purpose of the Study:

• To investigate the inclusion complexation of four substituted benzaldehydes (2HMB, 4HMB, DMB, HDMB) with different cyclodextrins (α-CD, β-CD, HP-α-CD, HP-β-CD).
• To elucidate the binding interactions and thermodynamics of these complexation processes.
• To determine the preferred binding orientation of benzaldehydes within cyclodextrin cavities.

Main Methods:

• UV-Visible spectroscopy to monitor complex formation.
• Steady-state and time-resolved fluorescence spectroscopy to study binding dynamics.
• PM3 computational methods for geometry optimization and interaction energy calculations.

Main Results:

• All benzaldehydes formed 1:1 inclusion complexes with the studied cyclodextrins.
• Dual fluorescence behavior was observed for all benzaldehydes in aqueous and CD media.
• The 4-hydroxy-3,5-dimethoxybenzaldehyde (HDMB)/CD complex showed significantly higher stability.
• Negative enthalpy changes indicated spontaneous complexation.
• PM3 optimizations revealed that methoxy/hydroxyl groups are entrapped in the cyclodextrin cavity, while the aldehyde group remains exposed.

Conclusions:

• The study successfully characterized the inclusion complexation of substituted benzaldehydes with cyclodextrins.
• The findings highlight the selectivity of cyclodextrins towards specific guest molecules, particularly HDMB.
• The observed binding mode provides insights into the design of host-guest systems for molecular recognition and encapsulation.