Improvement of stability due to a cyclamen aldehyde/β-cyclodextrin inclusion complex

Abstract

Cyclamen aldehyde (Cya) is an essential oil component with an aldehyde group. The current study examined an inclusion complex of Cya and β-cyclodextrin (βCD) and assessed its physicochemical properties, volatility, and stability. Phase solubility diagrams and 1H NMR spectroscopy indicated that Cya and βCD in a co-precipitate (CP) form a complex at a molar ratio of 1/1. Powder X-ray diffraction (PXRD) patterns revealed crystal diffraction peaks due to βCD (2θ = 8.8°, 12.5°, and 20.8°) for the PM and new diffraction peaks (2θ = 11.7° and 17.5°) for the CP. Thermogravimetry (TG) measurements indicated that Cya decreased about 18.2% in a physical mixture (PM) and about 4.4% in the CP. FT-IR and NIR spectroscopies indicated that the spectra produced by the methyl groups and isopropyl group (5908 cm−1) of Cya and by the hydroxyl groups (4756 cm−1) in the cavity of βCD shifted. {1H–1H} NOESY NMR spectra revealed couplings for the protons of the isopropyl group (1.05 ppm) and the protons of the βCD cavity (H-3: 3.66 ppm). These findings indicated that the isopropyl group of Cya is included in the wider opening of the βCD torus. Diffusion-ordered two-dimensional NMR spectroscopy (DOSY) indicated that the CP (Cya/βCD) had a diffusion coefficient of 3.21 × 10−5 cm2/s and that βCD had a diffusion coefficient of 3.25 × 10−5 cm2/s, so the CP (Cya/βCD) had colligate properties like those of βCD. A stability test at a temperature of 40 °C and RH of 82% revealed that Cya decreased about 7.4% in 7 d, but at least 29% of the CP (Cya/βCD) was retained. At a temperature of 25 °C and RH of 84%, Cya decreased about 9.7% in 7 d, but at least 76.5% of the CP (Cya/βCD) was retained. These findings indicated that formation of a complex by the CP (Cya/βCD) should reduce the volatility of Cya and improve its stability.