| 1. |
- di Gregorio, Maria Chiara, et al.
(författare)
-
pH Sensitive Tubules of a Bile Acid Derivative: a Tubule Opening by Release of Wall Leaves
- 2013
-
Ingår i: Physical Chemistry Chemical Physics. - 1463-9084. ; 15:20, s. 7560-7566
-
Tidskriftsartikel (refereegranskat)abstract
- Tubules formed by self-assembly of organic molecules have a vast potential in nanotechnology applications and the introduction of sensitivity to stimuli into self-assembly tubules represents a particularly attractive feature. Here we report on 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, that 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 performed by means of cryogenic transmission electron microscopy and represent, 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.
|
|
| 2. |
- Gubitosi, Marta, et al.
(författare)
-
Sugar-Bile Acid-Based Bolaamphiphiles: From Scrolls to Monodisperse Single-Walled Tubules.
- 2014
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:22, s. 6358-6366
-
Tidskriftsartikel (refereegranskat)abstract
- The introduction of a mannose residue on carbon 3 of lithocholic acid gives rise to an asymmetric and rigid bolaamphiphilic molecule, which self-assembles in water to form elongated tubular aggregates with an outer diameter of about 20 nm. These tubular structures display a temporal evolution, where the average tube diameter decreases with time, which can be followed by time-resolved small-angle X-ray scattering experiments. Cryogenic transmission electron microscopy images collected as a function of time show that at short times after preparation tubular scrolls are formed via the rolling of layers, after which a complex transformation of the scrolls into single-walled tubules takes place. At long time scales, a further evolution occurs where the tubules both elongate and become narrower. The observed self-assembly confirms the tendency of bile acids and their derivatives to form supramolecular aggregates with an ordered packing of the constituent molecules. It also demonstrates that scrolls can be formed as intermediate structures in the self-assembly process of monodisperse single-walled tubules.
|
|
| 3. |
- Gubitosi, Marta, et al.
(författare)
-
Tailoring Supramolecular Nanotubes by Bile Salt Based Surfactant Mixtures.
- 2015
-
Ingår i: Angewandte Chemie (International edition). - : Wiley. - 1521-3773. ; 54:24, s. 7018-7021
-
Tidskriftsartikel (refereegranskat)abstract
- An approach for tailoring self-assembled tubular structures is described. By controlling the relative composition of a two-component surfactant mixture comprising the natural bile salt lithocholate and its bolamphiphilic derivative, it was possible to finely tune the nanotube cross-section of the mixed tubular aggregates that self-associated spontaneously in aqueous solution at pH 12. The diameter was found to vary up to 50 % when the stoichiometric ratio of the two bile salts was changed. The tuning of supramolecular nanochannels with such remarkable precision is of significant interest for technological applications of these materials.
|
|
| 4. |
- Schillén, Karin, et al.
(författare)
-
Supramolecular assembly of thermoresponsive steroidal surfactant with oppositely charged thermoresponsive block copolymer
- 2017
-
Ingår i: Physical Chemistry Chemical Physics. - 1463-9084. ; 19:2, s. 1504-1515
-
Tidskriftsartikel (refereegranskat)abstract
- Supramolecular rearrangements are crucial in determining the response of stimuli sensitive soft matter systems such as those formed by mixtures of oppositely charged amphiphiles. Here mixtures of this kind were prepared by mixing the cationic block copolymer pAMPTMA30-b-pNIPAAM120 and an anionic surfactant obtained by the modification of the bile salt sodium cholate. As pure components, the two compounds presented a thermoresponsive self-assembly at around 30–35 °C; a micelle formation in the case of the copolymer and a transition from fibers to tubes in the case of the bile salt derivative. When both were present in the same solution they associated into mixed aggregates that showed complex thermoresponsive features. At room temperature, the core of the aggregate was comprised of a supramolecular twisted ribbon of the bile salt derivative. The block copolymers were anchored on the surface of this ribbon through electrostatic interactions between their charged blocks and the oppositely charged heads of the bile salt molecules. The whole structure was stabilized by a corona of the uncharged blocks that protruded into the surrounding solvent. By increasing the temperature to 30–34 °C the mixed aggregates transformed into rods with smooth edges that associated into bundles and clusters, which in turn induced clouding of the solution. Circular dichroism allowed us to follow progressive rearrangements of the supramolecular organization within the complex, occurring in the range of temperature of 20–70 °C.
|
|
| 5. |
- Travaglini, Leana, et al.
(författare)
-
On the self-assembly of a tryptophan labeled deoxycholic acid
- 2014
-
Ingår i: Physical Chemistry Chemical Physics. - 1463-9084. ; 16:36, s. 19492-19504
-
Tidskriftsartikel (refereegranskat)abstract
- Self-assembly of peptides and bile acids has been widely investigated because of their biological role and their potential as a tool for the preparation of nanostructured biomaterials. We herein report both the synthesis and the self-association behavior of a compound that combines the aggregation properties of bile acid- and amino acid-based molecules. The derivative has been prepared by introducing a L-tryptophan residue into the C-3 position of the deoxycholic acid skeleton and resulted in an amphoteric fluorescent labeled bile acid that shows a pH-dependent self-assembly. Under alkaline conditions it assembles into 28 nm diameter tubules, thus showing a completely different behavior compared to the precursor bile acid, which forms micelles under similar conditions. Upon heating the tubules break and turn into micelles, leading to an increase in the exposure to water of the tryptophan residue. On the other hand, in acidic solutions it aggregates into elongated micelles that further self-assemble forming a gel network, when an electrolyte is added.
|
|
