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Elucidating the Role of Site-Specific Nitration of alpha-Synuclein in the Pathogenesis of Parkinson's Disease via Protein Semisynthesis and Mutagenesis
No full textParkinsons disease (PD) is characterized by the loss of dopaminergic neurons in the substantia nigra and the presence of intraneuronal inclusions consisting of aggregated and post-translationally modified a-synuclein (a-syn). Despite advances in the chemical synthesis of a-syn and other proteins, the generation of site-specifically nitrated synthetic proteins has not been reported. Consequently, it has not been possible to determine the roles of nitration at specific residues in regulating the physiological and pathogenic properties of a-syn. Here we report, for the first time, the site-specific incorporation of 3-nitrotyrosine at different regions of a-syn using native chemical ligation combined with a novel desulfurization strategy. This strategy enabled us to investigate the role of nitration at single or multiple tyrosine residues in regulating a-syn structure, membrane binding, oligomerization, and fibrils formation. We demonstrate that different site-specifically nitrated a-syn species exhibit distinct structural and aggregation properties and exhibit reduced affinity to negatively charged vesicle membranes. We provide evidence that intermolecular interactions between the N- and C-terminal regions of a-syn play critical roles in mediating nitration-induced a-syn oligomerization. For example, when Y39 is not available for nitration (Y39F and Y39/125F), the extent of cross-linking is limited mostly to dimer formation, whereas mutants in which Y39 along with one or multiple C-terminal tyrosines (Y125F, Y133F, Y136F and Y133/136F) can still undergo nitration readily to form higher-order oligomers. Our semisynthetic strategy for generating site-specifically nitrated proteins opens up new possibilities for investigating the role of nitration in regulating protein structure and function in health and disease.LMN
Study of Electron-Transfer Reactions across an Externally Polarized Water/1,2-Dichloroethane Interface by Scanning Electrochemical Microscopy
No full textLEP
An analytical inverse analysis to determine equi-biaxial tensile properties of strain-hardening UHPFRC from ring-on-ring test
No full textThe equi-biaxial tensile properties of strain-hardening UHPFRC are determined and investigated based on an original analytical inverse analysis of results from ring-on-ring tests. First, the analytical inverse analysis method is developed based on the elastic slab bending and yield line theories. Using this method, a new objective criterion for the determination of the elastic limit stress of strain-hardening UHPFRC is provided, and a point-by-point inverse analysis is used to obtain the strain value at the end of hardening. This method reduces uncertainties regarding assumptions and avoids any iterative procedures. The inverse analysis results are put into perspective with experimental evidence, particularly based on DIC measurements. Moreover, the uniaxial tensile properties are also derived from the inverse analysis of 4PBT results and compared with the equi-biaxial tensile properties from the proposed inverse analysis. The inverse analysis results show a 18% lower elastic limit stress, and almost equivalent tensile strength of UHPFRC subjected to equi-biaxial stresses, compared with the corresponding values from uniaxial stress. Moreover, a relatively small equi-biaxial strain at the end of hardening is highlighted.MCSGIS-G
Soft-probe-scanning electrochemical microscopy reveals electrochemical surface reactivity of E. coli biofilms
No full textInvestigating and understanding dynamic biofilm growth mechanisms is challenging, often because state-of-the-art optical characterization tools provide limited information. Micrometric electrochemical imaging of Escherichia coli biofilms using Soft-Probe-Scanning Electrochemical Microscopy (Soft-Probe-SECM) is herein presented as a complementary technique. A soft microelectrode is scanned over biofilms in a gentle contact mode, which is essential to provide a constant working distance. The on-film reduction of an electro-active compound, here the oxidized form of ferrocene methanol, is used to create in situ biofilm metabolic activity maps by applying the feedback mode of SECM. SECM approach curves of identically grown biofilms suggest that the SECM-based detection of metabolic activity is surface-confined. The analysis could therefore be carried out on entire biofilms as well as on tape-stripped biofilm surface layers. The method is further capable of distinguishing between biofilms containing E. coli cells either with or without ampicillin-resistance. Finally, the SECM detection of the degradation of an E. coli biofilm in the presence of different gentamicin concentrations is presented.GR-LUDCIMELEP
Controlled Reversible Adsorption of Core-Shell Metallic Nanoparticles at the Polarized Water/1,2-Dichloroethane Interface Investigated by Optical Second-Harmonic Generation
No full textWe report the observation of the reversible adsorption of core-shell gold-silver nanoparticles at the polarized water/1,2-dichloroethane interface using the nonlinear optical technique of surface second-harmonic generation. This study unambiguously demonstrates the excellent stability against aggregation of these core-shell nanoparticles, namely, gold core nanoparticles coated with silver layers of variable thickness, in the presence of an electrolyte salt like lithium chloride. Furthermore, it is also demonstrated that the adsorption of the nanoparticles is reversible by modulating the applied potential at water/1,2-dichloroethane interface. The analysis of these results is performed within the Debye-Hückel approximation of the electrostatic interactions between the nanoparticles. This approach shows that the stability of core-shell nanoparticles can be attributed to the formation of a silver oxide layer at the surface of the particles.LEP
Refineries in plains and valleys. Debating the environmental problems of oil infrastructure in Switzerland (1958-1966)
No full textAs oil consumption surged in Western Europe after 1945, its environmental and sanitary consequences became visible to consumers for whom they had remained largely hidden until then. Indeed, refineries had long been located in the producing countries or, in Europe, near the sea. This changed with the creation of new infrastructure that both reacted to and helped sustain the rising demand. In the late 1950s and early 1960s, major pipelines were built across Europe, making it economically sound to plan the construction of refineries inland. However, little is known about the public reactions to these new refineries. This presentation will shed light on this topic by focusing on one country. Unlike France, Italy or Germany, Switzerland saw the building of its first refineries as a result of these late 1950s developments,. Over a few years, six different locations were discussed. All were controversial, and in all cases concerns over pollution featured prominently in the debates. Critics often referred to local wind patterns or criticised the idea of refining oil in “steep valleys”. Drawing on archives from local and national authorities, as well as various other sources, the presentation will discuss the differences between the projects, such as the players involved, the topography and local environments and the communication strategies of proponents and opponents. By doing so, the study will disentangle the various factors that led to the building of two refineries and the cancellation of the other plans, thus highlighting one aspect of the contingency of the process that made oil a major source of energy.LHS
Optimal radial basis for density-based atomic representations
No full textThe input of almost every machine learning algorithm targeting the properties of matter at the atomic scale involves a transformation of the list of Cartesian atomic coordinates into a more symmetric representation. Many of the most popular representations can be seen as an expansion of the symmetrized correlations of the atom density and differ mainly by the choice of basis. Considerable effort has been dedicated to the optimization of the basis set, typically driven by heuristic considerations on the behavior of the regression target. Here, we take a different, unsupervised viewpoint, aiming to determine the basis that encodes in the most compact way possible the structural information that is relevant for the dataset at hand. For each training dataset and number of basis functions, one can build a unique basis that is optimal in this sense and can be computed at no additional cost with respect to the primitive basis by approximating it with splines. We demonstrate that this construction yields representations that are accurate and computationally efficient, particularly when working with representations that correspond to high-body order correlations. We present examples that involve both molecular and condensed-phase machine-learning models.COSM
Oxygen transport through dense La0.6Sr0.4Fe0.8Co0.2O3-d perovskite-type permeation membranes
No full textIn this study, we examine the parameters that govern the overall oxygen flux through a permeation membrane. The chemical diffusion (D) and the surface exchange (k) coefficients for oxygen in La0.6Sr0.4Fe0.8Co0.2O3-d were determined as a function of temperature using a specially designed electrochemical cell combined with impedance spectroscopy. Typically, D=1.7 10-5 cm2/s and k=3.6 10-4 cm/s in air at 900°C. These values were compared with literature 18O/16O isotope exchange data. Oxygen permeation measurements were also performed on the same material in an air/Ar gradient, in the temperature range of 800 to 1000°C. At 900°C, the oxygen flux across a 1.53 mm thick membrane was 8.0 10-8 mol/(cm2s). The measured fluxes were compared with fluxes calculated on the basis of the D and k values using expressions derived from Fick’s law. Comparison showed that the flux is controlled by both bulk diffusion and surface exchange, even for such thick membranes, and that the apparent k? varies significantly from one experiment to another.LEN
QFT without infinities and hierarchy problem
No full textThe standard way to do computations in Quantum Field Theory (QFT) often results in the requirement of dramatic cancellations between contributions induced by a "heavy" sector into the physical observables of the "light" (or low energy) sector - the phenomenon known as "technical hierarchy problem". This procedure uses divergent multi-loop Feynman diagrams, their regularisation to handle the UV divergences, and then renormalisation to remove them. At the same time, the ultimate outcome of the renormalisation is the mapping of several finite parameters defining the renormalisable field theory into different observables (e.g. all kinds of particle cross-sections). In this paper, we first demonstrate how to relate the parameters of the theory to observables without running into intermediate UV divergences. Then we go one step further: we show how in theories with different mass scales, all physics of the "light" sector can be computed in a way that does not require dramatic cancellations induced by the physics of the "heavy" sector. The existence of such a technique suggests that the "hierarchy problem" in renormalisable theories is not really physical, but rather an artefact of the conventional procedure to compute correlation functions. If the QFT is defined by the "divergencies-free" method all fine-tunings in theories with well-separated energy scales may be avoided. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/). Funded by SCOAP3.LPP