Nuclear Magnetic Resonance Spectroscopic and Thermodynamic Characterization of Hydroxypropyl-cyclodextrin Inclusion Complexes with Bioactive Molecules from Plant Mother Tinctures

Abstract

H chemical shift changes in BAM NMR spectra allowed the calculation of binding constants, indicating better stability with HP-γ-CD due to its larger cavity size and enhanced flexibility, which favors stronger and more stable inclusion with bioactive molecules. Two-dimensional rotating-frame Overhauser effect spectroscopy experiments provided insight into the binding mode. A simple thermodynamic model highlighted the hydrogen bonding contribution to complexation. Furthermore, the inclusion complex of the carvacrol and eucalyptol mixture showed that carvacrol consistently maintains the most stable complex, even in the presence of both active compounds combined with HP-CD.