Tetrahydrocurcumin encapsulation in cyclodextrins for water solubility improvement: Synthesis, characterization and antifungal activity as a new biofungicide

Abstract

The solubility of the scarcely water-soluble molecule tetrahydrocurcumin (THC), a promising curcumin derivative to be used as biopesticide, was enhanced through the formation of inclusion complexes with different cyclodextrins (CDs). Randomly methylated β-cyclodextrin (MeβCD) gave the best results among the different CDs whose size, substituent or structure was changing. Differential scanning calorimetry as well as 1H- and 2D-Nuclear Magnetic Resonance (NMR) proved the inclusion of THC in MeβCD. Rotating-frame Overhauser effect spectroscopy NMR especially illustrated specific interactions of aromatic protons of THC and protons located inside the CD cavity. The complex formation between THC and MeβCD was studied using the Higuchi and Connor method, giving an association constant of 591 M−1. THC-loaded MeβCD did not show any growth inhibition of the target fungus Fusarium graminearum. However, THC-loaded MeβCD polymers exhibited 25% inhibition of the fungal growth, thus making them promising material for solvent-free, aqueous and bio-based fungicide formulations.

Keywords

• Cyclodextrins, Tetrahydrocurcumin encapsulation
• Methylated β-cyclodextrin
• F. graminearum
• Antifungal activity