Structural and physical characterization of octenylsuccinyl β-cyclodextrin

Beta-cyclodextrin (β-CD) was partially substituted by 2-octen-1-ylsuccinic anhydride, via its oxyanion prepared from a reaction with NaH in N,N-dimethyl formamide. 13C and 1H NMR spectra revealed that the substitution occurred mainly on C-2 hydroxyl group of glycosyl units. In the reaction mixture, three major derivatives with different average degree of substitution (DS) (0.723, 0.493, and 0.178) were detected by thin layer chromatography. The substitution increased as addition of the anhydride and reaction time increased, but decreased with reaction temperature. The octenylsuccinyl β-CD was highly soluble not only in water (>40%, w/w) but also in aqueous solutions of alcohol (>30% solubility in 50% ethanol) and salt (>40% in 1% NaCl or CaCl2). The solubility decreased with increasing acidity of the solution. In an acidic citrate buffer solution (pH 3 or 5), β-CD derivative of low DS (0.178) showed a higher solubility (>30%) than that of high DS (0.518, 1–4%). The octenylsuccinyl derivatives had raised abilities for complexation and dissolution for trans-retinol. Solubility of the retinol in water became 6.57 mg/ml with an octenylsuccinyl β-CD complexation (DS 0.518, 100 mg/ml). The β-CD derivatives could also act as emulsifiers, forming a stable emulsion with linoleic acid.