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DOI: 10.1098/rsta.2019.0455
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DOI: 10.1021/acs.analchem.1c00527
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12 Citations
Résumé:

Aggregation mechanisms of amyloid β peptides depend on multiple intrinsic and extrinsic physicochemical factors (e.g., peptide chain length, truncation, peptide concentration, pH, ionic strength, temperature, metal concentration, etc.). Due to this high number of parameters, the formation of oligomers and their propensity to aggregate make the elucidation of this physiopathological mechanism a challenging task. From the analytical point of view, up to our knowledge, few techniques are able to quantify, in real time, the proportion and the size of the different soluble species during the aggregation process. This work aims at demonstrating the efficacy of the modern Taylor dispersion analysis (TDA) performed in capillaries (50 μm i.d.) to unravel the speciation of β-amyloid peptides in low-volume peptide samples (∼100 μL) with an analysis time of ∼3 min per run. TDA was applied to study the aggregation process of Aβ(1-40) and Aβ(1-42) peptides at physiological pH and temperature, where more than 140 data points were generated with a total volume of ∼1 μL over the whole aggregation study (about 0.5 μg of peptides). TDA was able to give a complete and quantitative picture of the Aβ speciation during the aggregation process, including the sizing of the oligomers and protofibrils, the consumption of the monomer, and the quantification of different early- and late-formed aggregated species.

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Ref Arxiv: 2108.09487
DOI: 10.1111/jace.18090
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Ref Arxiv: 2106.12669
DOI: 10.1021/acs.macromol.1c01394
WoS: 000703552500031
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21 Citations
Résumé:

Using molecular dynamics simulations, we study the static and dynamic properties of spherical nanoparticles (NPs) embedded in a disordered and polydisperse polymer network. Purely repulsive and weakly attractive polymer–NP interactions are considered. It is found that for both types of particles, the NP dynamics at intermediate and long times is controlled by the confinement parameter C = σN/λ, where σN is the NP diameter and λ is the dynamic localization length of the cross-links. Three dynamical regimes are identified: (i) for weak confinement (C ≲ 1), the NPs can freely diffuse through the mesh; (ii) for strong confinement (1 ≲ C ≲ 3), NPs proceed by means of activated hopping; (iii) for extreme confinement (C ≳ 3), the mean-squared displacement shows on intermediate time scales a quasi-plateau because the NPs are trapped by the mesh for very long times. Escaping from this local cage is a process that depends strongly on the local environment, thus giving rise to an extremely heterogeneous relaxation dynamics. The simulation data are compared with the two main theories for the diffusion process of NPs in gels. Both theories give a very good description of the C dependence of the NP diffusion constant but fail to reproduce the heterogeneous dynamics at intermediate time scales.

Ref HAL: hal-03355624_v1
DOI: 10.1063/5.0060408
WoS: WOS:000684667000002
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In a recent computer study, we have shown that the combination of spatially heterogeneous dynamics and kinetic facilitation provides a microscopic explanation for the emergence of excess wings in deeply supercooled liquids. Motivated by these findings, we construct a minimal empirical model to describe this physics and introduce dynamic facilitation in the trap model, which was initially developed to capture the thermally-activated dynamics of glassy systems. We fully characterise the relaxation dynamics of this facilitated trap model varying the functional form of energy distributions and the strength of dynamic facilitation, combining numerical results and analytic arguments. Dynamic facilitation generically accelerates the relaxation of the deepest traps, thus making relaxation spectra strongly asymmetric, with an apparent "excess" signal at high frequencies. For well-chosen values of the parameters, the obtained spectra mimic experimental results for organic liquids displaying an excess wing. Overall, our results identify the minimal physical ingredients needed to describe excess processes in relaxation spectra of supercooled liquids.

Ref HAL: hal-03355608_v1
DOI: 10.1103/PhysRevLett.127.088002
WoS: WOS:000686914500008
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A theoretical treatment of deeply supercooled liquids is difficult because their properties emerge from spatial inhomogeneities that are self-induced, transient, and nanoscopic. I use computer simulations to analyse self-induced static and dynamic heterogeneity in equilibrium systems approaching the experimental glass transition. I characterise the broad sample-to-sample fluctuations of salient dynamic and thermodynamic properties in elementary mesoscopic systems. Findings regarding local lifetimes and distributions of dynamic heterogeneity are in excellent agreement with recent single molecule studies. Surprisingly broad thermodynamic fluctuations are also found, which correlate well with dynamics fluctuations, thus providing a local test of the thermodynamic origin of slow dynamics.