| 1. |
- Buchanan, Claire, et al.
(author)
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Comprehensive multidimensional study of the self-assembly properties of a three residue substituted beta(3) oligoamide
- 2021
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In: Pure and Applied Chemistry. - : Walter de Gruyter. - 0033-4545 .- 1365-3075. ; 93:11, s. 1327-1341
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Journal article (peer-reviewed)abstract
- Substituted (beta(3) oligoamides form a unique self-assembling system where each monomer folds into a helix containing approximately three (beta(3) amino acids per turn, yielding a geometrically well-defined cylindrical building block that, when N-acylated, is able to self-assemble head-to-tail into nanorods that can reach several 100 mu m length. It was shown in previous works that self-assembly can be achieved with a three residue long oligoamide as well that lacks any intramolecular H-bonds, yet it crystallizes in a helix-like conformation. The self-assembly properties of these small oligoamides are however elusive, suggesting a more complex system than the self-assembly of the H-bond stabilized helical monomers. Here we focus on the self-assembly behaviour of a three residue oligoamide, Ac-beta(3)[LIA] where the letters denote the side chain of the analogous a amino acid. Ac-beta(3)[LIA] can yield highly inhomogeneous suspensions in water with a broad range of large fibrous structures that seem to be very stable, yet occasionally fibre growth is only observed upon heating. The small size of the monomer suggests a highly dynamic equilibrium yet all previous attempts failed to clearly identify low molecular weight species. Therefore a special methodology was employed in this study to characterize the suspensions at different size ranges: SANS that is optimal to measure the small oligomers and cross sectional diameter of the assemblies, DLS that is sensitive to the large populations and therefore the length of the superstructures, and NMR that is sensitive to monomeric and small oligomeric form, in conjunction with IR spectroscopy to probe the folding and AFM to image the morphology of the assemblies. Temperature ramping was used to perturb the system to probe the dynamicity of the self-assembly. It was found that the anomalous self-assembly behaviour of Ac-beta(3)[LIA] is caused by its two stable conformations, a helix-building "horseshoe" fold and a linear conformer. The latter is exclusively found in monomeric form in solution whereas the horseshoe fold is stable in solid phase and in fibrous assemblies. Small oligomers were absent. Thus the self assembly of Ac-beta(3)[LIA] is arrested by the activation energy need of the conformation change; fibre growth might be triggered by conditions that allow increased conformational freedom of the monomers. This observation may be used to develop strategies for controlled switchable self-assembly.
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| 2. |
- Cao, Cheng, et al.
(author)
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The Protein Corona Leads to Deformation of Spherical Micelles
- 2021
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In: Angewandte Chemie International Edition. - : John Wiley & Sons. - 1433-7851 .- 1521-3773. ; 60:18, s. 10342-10349
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Journal article (peer-reviewed)abstract
- The formation of a non-specific protein corona around nanoparticles (NPs) has been identified as one of the culprits for failed nanomedicine. The amount and type of adsorbed protein from the blood plasma are known to determine the fate of NPs and the accessibility of targeting ligands. Herein, we show that the adsorbed protein may not only enlarge the NPs and change their surface properties but also, in the case of soft NPs such as polymer micelles, lead to deformation. Poly(1-O-methacryloyl -beta-D-fructopyranose)-b-poly(methylmethacrylate) (P(1-O-MAFru)-b-PMMA) block co-polymers were self-assembled into NPs with a spherical core-shell morphology as determined by small angle neutron scattering (SANS). Upon incubation with albumin, TEM, SANS, and small angle X-ray scattering (SAXS) revealed the adsorption of albumin and deformation of the NPs with a spheroid geometry. Removal of the protein led to the reversal of the morphology back to the spherical core-shell structure. Structural studies and cell studies of uptake of the NPs imply that the observed deformation may influence blood circulation time and cell uptake.
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| 3. |
- Raghuwanshi, Vikram Singh, et al.
(author)
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Deuterated Bacterial Cellulose Dissolution in Ionic Liquids
- 2021
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In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 54:14, s. 6982-6989
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Journal article (peer-reviewed)abstract
- Understanding the dissolution mechanism of deuterated bacterial cellulose (DBC) is important to engineer advanced material applications such as in quantifying and visualizing biomolecules at the cellulose interface for diagnostics. Small-angle neutron scattering (SANS) is applied to evaluate the distribution and volume fraction of dissolved DBC chains in 1-ethyl-3-methylimidazolium acetate (EMIM-Ac) ionic liquid (IL-h) solvent in three different ways: (i) DBC in IL-h, (ii) DBC in a mixture of N,N-dimethylformamide (DMF) with IL-h (IL-h/DMF), and (iii) modified DBC by dissolution in IL-h with dichloromethane (DCM), (DCM-DBC). EMIM-Ac is a highly viscous solvent, and the incorporation of DMF reduces its viscosity. DCM incorporation into EMIM-Ac leads to partial acetylation of the cellulose chains. The DBC dissolves differently in all the modified solvents studied. The DBC and DCM-DBC dissolution in IL-h shows the presence of surface fractals (power law relation of intensity to a scattering vector, q, of q-3.4) indicating compact aggregated DBC structures. The DBC structure is more open in the DMF/IL-h solvent, which is reflected in the SANS curve mass fractal analysis with a power law of q-2.5. At intermediate values of the scattering vector, a q-1 power law is observed, indicative of rigid segments of dissolved DBC chains. Analysis of the intensity in this range provides insights as to the dissolution mechanism. The observed higher intensity measured in the solutions of DBC and DCM-DBC in IL-h can be attributed to the tight binding adsorption of the acetate ions on the DBC surface. Moreover, the unique aspect of this experiment, using deuterated cellulose in a mixture of deuterated DMF with protiated EMINM-Ac, provides direct proof for formation of a shell layer of IL-h surrounding the DBC surface. The results obtained shed light on the dissolution mechanism of cellulose in EMIM-Ac, highlighting its potential application in engineering biosensors and bio-diagnostics.
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| 4. |
- Russo, Daniela, et al.
(author)
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Conformation of Myoglobin-Poly(Ethyl Ethylene Phosphate) Conjugates Probed by SANS : Correlation with Polymer Grafting Density and Interaction.
- 2021
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In: Macromolecular Bioscience. - : John Wiley & Sons. - 1616-5187 .- 1616-5195. ; 21:2
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Journal article (peer-reviewed)abstract
- One can take advantage of the influence of a polymer conjugated with a protein to control the thermal stability and the deployment of the protein. Here, the structural properties are reported of the protein-polymer conjugate myoglobin (Mb)-poly(ethyl ethylene phosphate) (PEEP) in the native and unfolded conformations, in order to understand the respective roles of the protein and of the polymer size in the stability of the conjugate. The effect is also investigated of the grafting density of the linear biodegradable polyphosphoesters covalently attached to the protein. It is observed that, while the conjugation process at room temperature does not modify the secondary and tertiary structure of the Mb, the unfolding process, as a function of temperature, depends on the grafting density. Small angle neutron scattering reveals that, at room temperature, conjugation does not alter the size of the native protein and that the thickness of the polymer shell around the protein increases as a function of grafting density and of polymer molecular weight. The denatured form of all conjugates is described by an unfolded chain and a correlation length due to the presence of local stiffness.
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