| 1. |
- Argatov, Ivan, et al.
(författare)
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Dynamics of post-occlusion water diffusion in stratum corneum
- 2022
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion of water through membranes presents a considerable challenge, as the diffusivity often depends on the local concentration of water. One particular example with strong biological relevance is the stratum corneum (SC) as the primary permeability barrier for the skin. A simple alternative for the constant diffusivity model is provided by the Fujita's two-parameter rational approximation, which captures the experimentally observed fact that the SC diffusion constant for water increases with increasing the water concentration. Based on Fick's law of diffusion, a one-dimensional concentration-dependent diffusion model is developed and applied for the analysis of both the steady-state transepidermal water loss (TEWL) and the non-steady-state so-called skin surface water loss (SSWL) occurred after removal of an occlusion patch from the SC surface. It is shown that some of the age-related changes in the SSWL can be qualitatively explained by the variation of the dimensionless Fujita concentration-dependence parameter.
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| 2. |
- Barrat, Jean-Louis, et al.
(författare)
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Soft matter roadmap
- 2024
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 2515-7639. ; 7:1
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Forskningsöversikt (refereegranskat)abstract
- Soft materials are usually defined as materials made of mesoscopic entities, often self-organised, sensitive to thermal fluctuations and to weak perturbations. Archetypal examples are colloids, polymers, amphiphiles, liquid crystals, foams. The importance of soft materials in everyday commodity products, as well as in technological applications, is enormous, and controlling or improving their properties is the focus of many efforts. From a fundamental perspective, the possibility of manipulating soft material properties, by tuning interactions between constituents and by applying external perturbations, gives rise to an almost unlimited variety in physical properties. Together with the relative ease to observe and characterise them, this renders soft matter systems powerful model systems to investigate statistical physics phenomena, many of them relevant as well to hard condensed matter systems. Understanding the emerging properties from mesoscale constituents still poses enormous challenges, which have stimulated a wealth of new experimental approaches, including the synthesis of new systems with, e.g. tailored self-assembling properties, or novel experimental techniques in imaging, scattering or rheology. Theoretical and numerical methods, and coarse-grained models, have become central to predict physical properties of soft materials, while computational approaches that also use machine learning tools are playing a progressively major role in many investigations. This Roadmap intends to give a broad overview of recent and possible future activities in the field of soft materials, with experts covering various developments and challenges in material synthesis and characterisation, instrumental, simulation and theoretical methods as well as general concepts.
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| 3. |
- Beck, Christian, et al.
(författare)
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Following Protein Dynamics in Real Time during Crystallization
- 2019
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Ingår i: Crystal Growth and Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; , s. 7036-7045
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Tidskriftsartikel (refereegranskat)abstract
- The process of protein crystallization from aqueous protein solutions is still insufficiently understood. During macroscopic crystal formation, occurring often on time scales from a few hours to several days, protein dynamics evolves on the molecular level. Here, we present a proof of concept and a framework to observe this evolving diffusive dynamics on the pico- to nanosecond time scale, associated with cluster or precursor formation that ultimately results in emerging crystals. We investigated the model system of the protein β-lactoglobulin in D2O in the presence of ZnCl2, which induces crystallization by electrostatic bridges. First, the structural changes occurring during crystallization were followed by small-angle neutron scattering. Furthermore, we employed neutron backscattering and spin-echo spectroscopy to measure the ensemble-averaged self- and collective diffusion on nanosecond time scales of protein solutions with a kinetic time resolution on the order of 15 min. The experiments provide information on the increasing number fraction of immobilized proteins as well as on the diffusive motion of unbound proteins in an increasingly depleted phase. Simultaneously, information on the internal dynamics of the proteins is obtained.
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| 4. |
- Beck, Christian, et al.
(författare)
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Nanosecond Tracer Diffusion as a Probe of the Solution Structure and Molecular Mobility of Protein Assemblies: The Case of Ovalbumin
- 2018
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 122:35, s. 8343-8343
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Tidskriftsartikel (refereegranskat)abstract
- Protein diffusion is not only an important process ensuring biological function but can also be used as a probe to obtain information on structural properties of protein assemblies in liquid solutions. Here, we explore the oligomerization state of ovalbumin at high protein concentrations by means of its short-time self-diffusion. We employ high-resolution incoherent quasielastic neutron scattering to access the self-diffusion on nanosecond timescales, on which interparticle contacts are not altered. Our results indicate that ovalbumin in aqueous (D2O) solutions occurs in increasingly large assemblies of its monomeric subunits with rising protein concentration. It changes from nearly monomeric toward dimeric and ultimately larger than tetrameric complexes. Simultaneously, we access information on the internal molecular mobility of ovalbumin on the nanometer length scale and compare it with results obtained for bovine serum albumin, immunoglobulin, and β-lactoglobulin.
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| 5. |
- Beck, Christian, et al.
(författare)
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Neutron spectroscopy on protein solutions employing backscattering with an increased energy range
- 2019
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; 562, s. 31-35
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Tidskriftsartikel (refereegranskat)abstract
- Novel cold neutron backscattering spectrometers contribute substantially to the understanding of the diffusive dynamics of proteins in dense aqueous suspensions. Such suspensions are fundamentally interesting for instance in terms of the so-called macromolecular crowding, protein cluster formation, gelation, and self-assembly. Notably, backscattering spectrometers with the highest flux can simultaneously access the center-of-mass diffusion of the proteins and the superimposed internal molecular diffusive motions. The nearly complete absence of protein-protein collisions on the accessible nanosecond observation time scale even in dense protein suspensions implies that neutron backscattering accesses the so-called short-time limit for the center-of-mass diffusion. This limit is particularly interesting in terms of a theoretical understanding by concepts from colloid physics. Here we briefly review recent progress in studying protein dynamics achieved with the latest generation of backscattering spectrometers. We illustrate this progress by the first data from a protein solution using the backscattering-and-time-of-flight option BATS on IN16B at the ILL and we outline future perspectives.
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| 6. |
- Beck, Christian, et al.
(författare)
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Notes on Fitting and Analysis Frameworks for QENS Spectra of (Soft) Colloid Suspensions
- 2022
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 272, s. 01004-01004
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Tidskriftsartikel (refereegranskat)abstract
- With continuously improving signal-to-noise ratios, a statistically sound analysis of quasi-elasticneutron scattering (QENS) spectra requires to fit increasingly complex models which poses several challenges.Simultaneous fits of the spectra for all recorded values of the momentum transfer become a standard approach.Spectrometers at spallation sources can have a complicated non-Gaussian resolution function which has to bedescribed most accurately. At the same time, to speed up the fitting, an analytical convolution with this resolutionfunction is of interest. Here, we discuss basic concepts to efficient approaches for fits of QENS spectra basedon standard MATLAB and Python fit algorithms. We illustrate the fits with example data from IN16B, BASIS,and BATS.
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| 7. |
- Beck, Christian, et al.
(författare)
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Short-Time Transport Properties of Bidisperse Suspensions of Immunoglobulins and Serum Albumins Consistent with a Colloid Physics Picture.
- 2022
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 126:38, s. 7400-7408
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Tidskriftsartikel (refereegranskat)abstract
- The crowded environment of biological systems such as the interior of living cells is occupied by macromolecules with a broad size distribution. This situation of polydispersity might influence the dependence of the diffusive dynamics of a given tracer macromolecule in a monodisperse solution on its hydrodynamic size and on the volume fraction. The resulting size dependence of diffusive transport crucially influences the function of a living cell. Here, we investigate a simplified model system consisting of two constituents in aqueous solution, namely, of the proteins bovine serum albumin (BSA) and bovine polyclonal gamma-globulin (Ig), systematically depending on the total volume fraction and ratio of these constituents. From high-resolution quasi-elastic neutron spectroscopy, the separate apparent short-time diffusion coefficients for BSA and Ig in the mixture are extracted, which show substantial deviations from the diffusion coefficients measured in monodisperse solutions at the same total volume fraction. These deviations can be modeled quantitatively using results from the short-time rotational and translational diffusion in a two-component hard sphere system with two distinct, effective hydrodynamic radii. Thus, we find that a simple colloid picture well describes short-time diffusion in binary mixtures as a function of the mixing ratio and the total volume fraction. Notably, the self-diffusion of the smaller protein BSA in the mixture is faster than the diffusion in a pure BSA solution, whereas the self-diffusion of Ig in the mixture is slower than in the pure Ig solution.
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| 8. |
- Beck, Christian, et al.
(författare)
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Temperature and salt controlled tuning of protein clusters
- 2021
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Ingår i: Soft Matter. - : Royal Society of Chemistry. - 1744-683X .- 1744-6848. ; :37, s. 8506-8516
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Tidskriftsartikel (refereegranskat)abstract
- The formation of molecular assemblies in protein solutions is of strong interest both from a fundamental viewpoint and for biomedical applications. While ordered and desired protein assemblies are indispensable for some biological functions, undesired protein condensation can induce serious diseases. As a common cofactor, the presence of salt ions is essential for some biological processes involving proteins, and in aqueous suspensions of proteins can also give rise to complex phase diagrams including homogeneous solutions, large aggregates, and dissolution regimes. Here, we systematically study the cluster formation approaching the phase separation in aqueous solutions of the globular protein BSA as a function of temperature (T), the protein concentration (c(p)) and the concentrations of the trivalent salts YCl3 and LaCl3 (c(s)). As an important complement to structural, i.e. time-averaged, techniques we employ a dynamical technique that can detect clusters even when they are transient on the order of a few nanoseconds. By employing incoherent neutron spectroscopy, we unambiguously determine the short-time self-diffusion of the protein clusters depending on c(p), c(s) and T. We determine the cluster size in terms of effective hydrodynamic radii as manifested by the cluster center-of-mass diffusion coefficients D. For both salts, we find a simple functional form D(c(p), c(s), T) in the parameter range explored. The calculated inter-particle attraction strength, determined from the microscopic and short-time diffusive properties of the samples, increases with salt concentration and temperature in the regime investigated and can be linked to the macroscopic behavior of the samples.
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| 9. |
- Braun, Michal K., et al.
(författare)
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Crowding-Controlled Cluster Size in Concentrated Aqueous Protein Solutions : Structure, Self- and Collective Diffusion
- 2017
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 8:12, s. 2590-2596
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the concentration-controlled formation of clusters in β-lactoglobulin (BLG) protein solutions combining structural and dynamical scattering techniques. The static structure factor from small-angle X-ray scattering as well as de-Gennes narrowing in the nanosecond diffusion function D(q) from neutron spin echo spectroscopy support a picture of cluster formation. Using neutron backscattering spectroscopy, a monotonous increase of the average hydrodynamic cluster radius is monitored over a broad protein concentration range, corresponding to oligomeric structures of BLG ranging from the native dimers up to roughly four dimers. The results suggest that BLG forms compact clusters that are static on the observation time scale of several nanoseconds. The presented analysis provides a general framework to access the structure and dynamics of macromolecular assemblies in solution.
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| 10. |
- Braun, Michal K., et al.
(författare)
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Reentrant Phase Behavior in Protein Solutions Induced by Multivalent Salts: Strong Effect of Anions Cl– Versus NO3–
- 2018
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 122:50, s. 11978-11985
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the effects of the two anions Cl– and NO3– on the phase behavior of bovine serum albumin (BSA) in solution with trivalent salts are compared systematically. In the presence of trivalent metal salts, negatively charged proteins such as BSA in solution undergo a reentrant condensation (RC) phase behavior, which has been established for several proteins with chlorides of trivalent salts. Here, we show that replacing Cl– by NO3– leads to a marked change in the phase behavior. The effect is investigated for the two different cations Y3+ and La3+. The salts are thus YCl3, Y(NO3)3, LaCl3, and La(NO3)3. The experimental phase behavior shows that while the chloride salts induce both liquid–liquid phase separation (LLPS) and RC, the nitrate salts also induce LLPS, but RC becomes partial with La(NO3)3 and disappears with Y(NO3)3. The observed phase behavior is rationalized by effective protein–protein interactions which are characterized using small-angle X-ray scattering. The results based on the reduced second virial coefficients B2/B2HS and 1/I(q → 0) demonstrate that the NO3– salts induce a stronger attraction than the Cl– salts. Overall, the effective attraction, the width of the condensed regime in the RC phase diagram, and the nature of LLPS follow the order LaCl3 < YCl3 < La(NO3)3 < Y(NO3)3. Despite the decisive role of cations in RC phase behavior, isothermal titration calorimetry measurements indicate that replacing anions does not significantly influence the cation binding to proteins. The experimental results observed are discussed based on an “enhanced Hofmeister effect” including electrostatic and hydrophobic interactions between protein–cation complexes.
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