Characterisation and properties of the inclusion complex of 24-epibrassinolide with β-cyclodextrin

This paper reports the first study of an inclusion complex of abrassinosteroid with β-cyclodextrin. The formation of inclusion complexesbetween 24-epibrassinolide and β-cyclodextrin was confirmed by theirphysicochemical properties and the compounds were analysed by differentialscanning calorimetry, powder X-ray diffraction, nuclear magnetic resonancespectrometry and scanning electron microscopy. Theoretical calculations usingthe MM+ HyperChem force field showed a preference for inclusion of thesidechain of the epibrassinolide molecule into the β-cyclodextrin cavity toform a 1:1 inclusion complex, although complexes involving inclusion ofthe steroidal nucleus also possess a favourable interaction energy. Rice laminainclination assay, employing IAC-103 and IAC-104 cultivars, showed an improvedactivity for the epibrassinolide-cyclodextrin complex compared to theepibrassinolide itself. The results suggest that brassinosteroid complexationwith cyclodextrins may enhance the biological activity of these plant growthregulators.