An Adaptive Cholic Acid Dimer for Selective Encapsulation

A novel cleft-type cholic acid dimer was synthesized from native bile acid through a six-step reaction sequence. Structural characterization was performed using FTIR, 1D NMR (¹H, ¹³C and DEPT135), 2D NMR (¹H,¹H COSY; ¹H,¹³C HSQC; ¹H,¹³C HMBC) and ESI-MS (+). The dimer could entrap both polar and nonpolar guests within its invertible pockets, adapting to changes in solvent polarity. Specifically, UV-Vis absorption and in silico simulations revealed a moderately stable 1:1 host-guest complex for the dimer with Cresol Red sodium salt in an organic solvent. The docked dimer-pyrene complex, investigated by molecular modeling studies, demonstrated an identical 1:1 binding ratio and moderate stability in the micromolar concentration range. Steady-state fluorescence investigations implied that the quenching of pyrene emission by the dimer in an aqueous environment was chiefly a collisional or dynamic pathway rather than the generation of a ground-state dimer-pyrene assembly.