Complexation of sodium cholate and sodium deoxycholate by β-cyclodextrin and derivatives

The complexation behavior of two bile salts-sodium cholate (NaC) and sodium deoxycholate (NaDC)- with beta-cyclodextrin (beta-CD), 6-deoxy-6-amino-beta-cyclodextrin (beta-CDNH2), and dimer I (N,N'-bis(6-deoxy-beta-cyclodextrin)pyromellic acid diamide) was studied by NMR techniques. Complexes formed between beta-CD and beta-CDNH2 with NaC and NaDC have 1:1 and 2:1 (host:guest) stoichiometries, respectively. Complexes with beta-CDNH2 show higher equilibrium constants than those with beta-CD because of the electrostatic effect of the protonated amine group. Dimer I showed 1:2 and n:n stoichiometries with NaC and NaDC, respectively. ROESY spectra stated that bile salts enter first with their 5-C ring forward the inner cavity by the side of the secondary hydroxyl groups of cyclodextrins. In the complexes formed with beta-CDNH2, the steroid body of the bile salt enters deeper in the cavity, while the carboxylated side chain is extended toward the protonated amine group at C-6, allowing an electrostatic interaction between both groups. In the case of the 2:1 stoichiometry, the second cyclodextrin complexes ring A of the steroid body.