[Study on the inclusion complexation interaction of beta-cyclodextrin and beta-carotene by UV-Vis spectra]

Beta-cyclodextrin (beta-CD), a kind of cyclic oligosaccharides, was found to possess a strong inclusion ability with beta-carotene. The inclusion compounds of beta-CD with beta-carotene were prepared by the coprecipitation method, and studied by UV-Vis spectra of different mole ratio beta-CD/beta-carotene in the H2O+ ethanol solution (H2O for beta-CD, and ethanol for beta-carotene). Equilibrium constant of inclusion compound was determined by UV-Vis spectra. The results indicate that 3.25 moles of beta-CD can include one mole beta-carotene to form inclusion compound by Van der Waals force and hydrophobic interaction etc. The optimum synthesis conditions of inclusion compound of beta-CD with beta-carotene is that the mole ratio of beta-CD/beta-carotene is 3.25:1 (mol/mol), the concentration ratio of beta-CD H2O solution/beta-carotene solution is 12:1 (mol x L(-1)/mol x L(-1)), and the time and temperature of inclusion reaction are 2 h and 30 degrees C, respectively. Equilibrium constant of inclusion compound (Ka) is 9.46 x 10(11) L x mol(-1). The selective binding ability of beta-CD with beta-carotene has been discussed from the viewpoint of size/shape-fitting and geometry fitting between the host cavity and the guest molecule. The resistance to oxidation and photooxidation, and the solubility in H2O of beta-carotene were increased by inclusion with beta-CD.