Solubilization of substituted indole compounds by beta-cyclodextrin in water.

The solubilization of four pairs of substituted indole compounds (SICs) by beta-cyclodextrin (beta-CD) in water was investigated. The results show that 1,2,3,4-tetrahydrocarbazole and N-methyl-1,2,3,4-tetrahydrocarbazole form 1:1 inclusion complexes with beta-CD, while the other six SICs form 1:2 inclusion complexes, respectively. To each pair of SICs with similar structures, the differences between their solubilization in beta-CD/water solutions has been explained by the difference of their contact area within the beta-CD cavity, the difference of their molecule polarity, or the presence of hydrogen bond between SIC molecule and beta-CD molecule.