title: pH sensitive tubules of a bile acid derivative: a tubule opening by release of wall leaves.
abstract: Tubules formed by self-assembly of organic molecules have vast potential for nanotechnology applications, and the introduction of sensitivity to stimuli into self-assembly tubules represents a particularly attractive feature. Here we report the preparation and characterization of a molecule obtained by chemical modification of a natural bile acid, a biological surfactant, that self-assembles in pH sensitive tubules in aqueous solutions. The tubules, which are rigid, single-walled and with a diameter of 60 nm, form at pH 8-9 and open up when the pH is increased. The transition is reversible, it occurs in the pH range of 9-10 with an opening mechanism that is remarkably different from those so far proposed in the literature. It involves a release of wall layers similar to leaves, and is determined by a drastic pH-triggered change in the molecular arrangement, which in turn induces a radical modification of the wall curvature. The description of the morphological transformation is provided by means of cryogenic transmission electron microscopy and represents, to our knowledge, the first detailed visualization of pH stimulated tubule opening. UV and circular dichroism spectroscopies are used to investigate the evolution at the molecular level.
authors.affiliation: Dipartimento di Chimica, Università di Roma La Sapienza, P. le A. Moro 5, 00185 Roma, Italy.
authors.forename: M Chiara
authors.initials: MC
authors.lastname: di Gregorio
authors.forename: N Viorel
authors.initials: NV
authors.lastname: Pavel
authors.forename: Aida
authors.initials: A
authors.lastname: Jover
authors.forename: Francisco
authors.initials: F
authors.lastname: Meijide
authors.forename: José
authors.initials: J
authors.lastname: Vázquez Tato
authors.forename: Victor H
authors.initials: VH
authors.lastname: Soto Tellini
authors.forename: Ariel
authors.initials: A
authors.lastname: Alfaro Vargas
authors.forename: Oren
authors.initials: O
authors.lastname: Regev
authors.forename: Yaron
authors.initials: Y
authors.lastname: Kasavi
authors.forename: Karin
authors.initials: K
authors.lastname: Schillén
authors.forename: Luciano
authors.initials: L
authors.lastname: Galantini
mesh_terms: D001647:Bile Acids and Salts / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D010316:Particle Size; D012996:Solutions; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D001647:Bile Acids and Salts; D012996:Solutions; D014867:Water