title: Between peptides and bile acids: self-assembly of phenylalanine substituted cholic acids.
abstract: Biocompatible molecules that undergo self-assembly are of high importance in biological and medical applications of nanoscience. Peptides and bile acids are among the most investigated due to their ability to self-organize into many different, often stimuli-sensitive, supramolecular structures. With the aim of preparing molecules mixing the aggregation properties of bile acid and amino acid-based molecules, we report on the synthesis and self-association behavior of two diastereomers obtained by substituting a hydroxyl group of cholic acid with a l-phenylalanine residue. The obtained molecules are amphoteric, and we demonstrate that they show a pH-dependent self-assembly. Both molecules aggregate in globular micelles at high pH, whereas they form tubular superstructures under acid conditions. Unusual narrow nanotubes with outer and inner cross-section diameters of about 6 and 3 nm are formed by the derivatives. The diasteroisomer with α orientation of the substituent forms in addition a wider tubule (17 nm cross-section diameter). The ability to pack in supramolecular tubules is explained in terms of a wedge-shaped bola-form structure of the derivatives. Parallel or antiparallel face-to-face dimers are hypothesized as fundamental building blocks for the formation of the narrow and wide nanotubes, respectively.
authors.affiliation: Department of Chemistry, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Leana
authors.initials: L
authors.lastname: Travaglini
authors.forename: Andrea
authors.initials: A
authors.lastname: D'Annibale
authors.forename: Maria Chiara
authors.initials: MC
authors.lastname: di Gregorio
authors.forename: Karin
authors.initials: K
authors.lastname: Schillén
authors.forename: Ulf
authors.initials: U
authors.lastname: Olsson
authors.forename: Simona
authors.initials: S
authors.lastname: Sennato
authors.forename: Nicolae V
authors.initials: NV
authors.lastname: Pavel
authors.forename: Luciano
authors.initials: L
authors.lastname: Galantini
mesh_terms: D001647:Bile Acids and Salts / Q000737:chemistry*; D002793:Cholic Acids / Q000737:chemistry*; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D008823:Micelles; D018625:Microscopy, Atomic Force; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D010649:Phenylalanine / Q000737:chemistry*; D013500:Surface Tension; D013696:Temperature
chemical_list: D001647:Bile Acids and Salts; D002793:Cholic Acids; D008823:Micelles; D010455:Peptides; D010649:Phenylalanine