title: Resolving self-assembly of bile acids at the molecular length scale.
abstract: The self-assembly behavior of the naturally occurring steroidal bile compounds cholic, deoxycholic, ursodeoxycholic, and lithocholic acid was studied by combining atomic force microscopy (AFM), polarized optical microscopy (POM), Fourier-transform infrared spectroscopy (FTIR), absorption spectroscopy (UV-vis), circular dichroism (CD), and wide-angle X-ray scattering (WAXS). Molecular solutions of these mono-, di-, and trihydroxyl substituted bile acids spontaneously evolved into supramolecular aggregates upon the incremental addition of H(2)O as a poor solvent. Highly crystalline nanostructured multilayered assemblies were formed, which revealed a very rich polymorphism of micro- and macro-structures depending on the chemical structure of the bile acid and the properties of the cosolvent (EtOH or DMSO) used. In particular, AFM allowed resolving the crystalline structure to an unprecedented level. It was thus possible to establish that bile acids associate into H-bonded chiral dimer building blocks, which organize in 2D layers of nanostructured lamellar surface topologies with unique facial amphiphilicity. The detailed understanding of the hierarchical organization in bile acid assemblies may contribute to develop strategies to design bioinspired materials with tailor-made nanostructured surface topologies.
authors.affiliation: Food and Soft Materials Science, Institute of Food, Nutrition and Health, ETH Zurich, Schmelzbergstrasse 9, LFO E23, CH-8092 Zürich, Switzerland.
authors.forename: Larissa
authors.initials: L
authors.lastname: Schefer
authors.forename: Antoni
authors.initials: A
authors.lastname: Sánchez-Ferrer
authors.forename: Jozef
authors.initials: J
authors.lastname: Adamcik
authors.forename: Raffaele
authors.initials: R
authors.lastname: Mezzenga
mesh_terms: D001647:Bile Acids and Salts / Q000737:chemistry*; D019281:Dimerization; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation
chemical_list: D001647:Bile Acids and Salts