| 1. |
- Del Giudice, Alessandra, et al.
(författare)
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Self-Assembly of Model Amphiphilic Peptides in Nonaqueous Solvents : Changing the Driving Force for Aggregation Does Not Change the Fibril Structure
- 2020
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 36:29, s. 8451-8460
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Tidskriftsartikel (refereegranskat)abstract
- Within the homologous series of amphiphilic peptides AnK, both A8K and A10K self-assemble in water to form twisted ribbon fibrils with lengths around 100 nm. The structure of the fibrils can be described in terms of twisted β-sheets extending in the direction of the fibrils, laminated to give a constant cross section of 4 nm by 8 nm. The finite width of the twisted ribbons can be reasonably explained within a simple thermodynamic model, considering a free energy penalty for the stretching of hydrogen bonds along the twisted β-sheets and an interfacial free energy gain for the lamination of the hydrophobic β-sheets. In this study, we characterize the self-assembly behavior of these peptides in nonaqueous solutions as a route to probe the role of hydrophobic interaction in fibril stabilization. Both peptides, in methanol and N,N-dimethylformamide, were found to form fibrillar aggregates with the same β-sheet structure as in water but with slightly smaller cross-sectional sizes. However, the gel-like texture, the slow relaxation in dynamic light scattering experiments, and a correlation peak in the small-angle X-ray scattering pattern highlighted enhanced interfibril interactions in the nonaqueous solvents in the same concentration range. This could be ascribed to a higher effective volume of the aggregates because of enhanced fibril growth and length, as suggested by light scattering and cryogenic transmission electron microscopy analyses. These effects can be discussed considering how the solvent properties affect the different energetic contributions (hydrophobic, electrostatic, and hydrogen bonding) to fibril formation. In the analyzed case, the decreased hydrogen bonding propensity of the nonaqueous solvents makes the hydrogen bond formation along the fibril a key driving force for peptide assembly, whereas it represents a nonrelevant contribution in water.
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| 2. |
- Schillén, Karin, et al.
(författare)
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Interaction between Bile Salt Sodium Glycodeoxycholate and PEO-PPO-PEO Triblock Copolymers in Aqueous Solution
- 2016
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Ingår i: RSC Advances. - 2046-2069. ; 6, s. 69313-69325
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Tidskriftsartikel (refereegranskat)abstract
- The interactions of the anionic bile salt NaGDC with three triblock copolymers based on poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), denoted P65, P123 and F127, were investigated using high-sensitive differential scanning calorimetry (DSC), turbidimetry, dynamic and static light scattering and small angle X-ray scattering (SAXS). P65 and P123 had the same hydrophilic PEO block lengths, whereas F127 and P123 had the same hydrophobic PPO block length. In water, the block copolymers self-assembled and formed spherical micelles at a critical micelle temperature, which depended on both the PPO/PEO composition ratio and the molecular weight of the copolymer. The mixed systems were studied at a constant P65, P123 or F127 concentration (i.e., 1.0 wt% or 5.0 wt%) with varying nNaGDC/npolymer molar ratio (MR) from 0 to 12. The DSC measurements presented endothermic enthalpy values (correlated to the amount of PPO that dehydrates in the aggregation process) that were suppressed at high MR. At 50 °C, the NaGDC molecules associated to the PPO core – PEO corona interface of the copolymer micelle forming a negatively charged block copolymer micelle–NaGDC complex. The complexes began to disintegrate upon NaGDC addition. Their resistance to disruption followed the stability order as inferred from the CMT values. At 20 °C, the unassociated block copolymer chains interacted with the NaGDC micelles and formed small NaGDC-rich complexes with a radius of ∼2 nm as determined by SAXS.
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| 3. |
- Schillén, Karin, et al.
(författare)
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Supramolecular assembly of thermoresponsive steroidal surfactant with oppositely charged thermoresponsive block copolymer
- 2017
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Ingår i: Physical Chemistry Chemical Physics. - 1463-9084. ; 19:2, s. 1504-1515
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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.
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| 4. |
- Travaglini, Leana, et al.
(författare)
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A tryptophan-substituted cholic acid : expanding the family of labelled biomolecules
- 2015
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 483:Online 31 March 2015, s. 142-149
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of a novel cholic acid derivative bearing in the C-3 position a residue of tryptophan linked through an amide bond is herein described. Acidic or basic conditions are needed for the solubilization of the derivative in water. In alkaline solutions the molecule shows a self-association similar to the one of its natural precursor leading to the formation of ellipsoidal micelles which does not involve significant Trp–Trp interactions. On the contrary, in acidic conditions strong interactions between the tryptophan moieties occur, leading to the formation of a gel at low temperature. These interactions are broken upon heating and small micelles similar to those observed at high pH are formed. In both cases, fluorescence spectra suggest a polar environment for the amino acid fluorophore not remarkably affected by the self-assembly.
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| 5. |
- Travaglini, Leana, et al.
(författare)
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On the self-assembly of a tryptophan labeled deoxycholic acid
- 2014
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Ingår i: Physical Chemistry Chemical Physics. - 1463-9084. ; 16:36, s. 19492-19504
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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.
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| 6. |
- Travaglini, Leana, et al.
(författare)
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Twisted nanoribbons from a RGD-bearing cholic acid derivative
- 2017
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Ingår i: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 0927-7765. ; 159, s. 183-190
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Tidskriftsartikel (refereegranskat)abstract
- In light of the biomedical interest for self-assembling amphiphiles bearing the tripeptide Arg-Gly-Gly (RGD), a cholic acid derivative was synthesized by introducing an aromatic moiety on the steroidal skeleton and the RGD sequence on the carboxylic function of its chain 17–24, thus forming a peptide amphiphile with the unconventional rigid amphiphilic structure of bile salts. In aqueous solution, the compound self-assembled into long twisted ribbons characterized by a very low degree of polydispersity in terms of width (≈25 nm), thickness (≈4.5 nm) and pitch (≈145 nm). It was proposed that in the ribbon the molecules are arranged in a bilayer structure with the aromatic moieties in the interior, strongly involved in the intermolecular interaction, whereas the RGD residues are located at the bilayer-water interface. The nanostructure is significantly different from those generally provided by RGD-containing amphiphiles with the conventional peptide-tail structure, for which fibers with a circular cross-section were observed, and successfully tested as scaffolds for tissue regeneration. From previous work on the use of this kind of nanostructures, it is known that features like morphology, rigidity, epitope spacing and periodicity are important factors that dramatically affect cell adhesion and signaling. Within this context, the reported results demonstrate that bile salt-based peptide surfactants are promising building blocks in the preparation of non-trivial RGD-decorated nanoaggregates with well-defined morphologies and epitope distributions.
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