Encapsulation of ethylene gas into α-cyclodextrin and characterisation of the inclusion complexes

Molecular encapsulation of various apolar compounds with α-cyclodextrin (α-CD) is becoming a widely applied technique to produce food, pharmaceutical and agricultural materials. Encapsulated ethylene in the form of inclusion complexes (ICs) with cyclodextrin, which is in powder form, could be used in fruit ripening and other aspect of plant growth regulation. In this research, ethylene was complexed with an α-CD under 0.2–1.5 MPa for 12–120 h. Ethylene concentration in the inclusion complexes (ICs) varied from 0.98 to 1.03 mol ethylene/mole CD. Pressure and time did not increase ethylene concentrations in the complexes, but did yield significantly higher amounts of the crystal complex. The physico-chemical properties of the ethylene-α-CD complexes at various concentration of ethylene were characterised using X-ray diffractometry (XRD), nuclear magnetic resonance spectroscopy (CP–MAS 13C NMR), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Complex formation was confirmed by sharp peaks in the XRD diffractograms, crystal images by SEM, double bond of ethylene gas and chemical shifts at C4, C3 and C5 in NMR spectra, intensity changes of C–H bending and CC stretching in the FTIR spectra, and water loss and physico-chemical property modifications in the DSC and TGA scans.