title: Oligomeric cholates: amphiphilic foldamers with nanometer-sized hydrophilic cavities.
abstract: The hydroxyl at the C-3 of cholic acid was converted to an amino group, and the resulting amino-functionalized cholic acid was used as a monomer to prepare amide-linked oligomeric cholates. These cholate oligomers fold into helical structures with nanometer-sized hydrophilic internal cavities in solvent mixtures consisting of mostly nonpolar solvents such as carbon tetrachloride or ethyl acetate/hexane and 2-5% of a polar solvent such as methanol or DMSO. The conformations of the foldamers were studied by UV, fluorescence, fluorescence quenching, and fluorescence resonance energy transfer. The nature of the polar/nonpolar solvents and their miscibility strongly influenced the folding reaction. Folding was cooperative, as evidenced by the sigmoidal curves in solvent denaturation experiments. The folded conformers became more stable with an increase in the chain length. The folding/unfolding equilibrium was highly sensitive toward the amount of polar solvent. One percent variation in the solvent composition could change the folding free energies by 0.5-1.4 kcal/mol.
authors.affiliation: Department of Chemistry, Iowa State University, Ames, Iowa 50011-3111, USA. zhaoy@iastate.edu
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Zhenqi
authors.initials: Z
authors.lastname: Zhong
mesh_terms: D000577:Amides / Q000737:chemistry; D020355:Cholates / Q000138:chemical synthesis / Q000737:chemistry*; D031541:Fluorescence Resonance Energy Transfer; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000577:Amides; D020355:Cholates