Perfluorooctanoic acid rigidifies a model lipid membrane

We report a combined dynamic light scattering and neutron spin-echo (NSE) study on vesicles composed of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine under the influence of varying amounts of perfluorooctanoic acid. We study local lipid bilayer undulations using NSE on time scales up to 200 ns. Similar to the effect evoked by cholesterol, we attribute the observed lipid bilayer stiffening to a condensing effect of the perfluorinated compound on the membrane.Comment: 5 pages, 4 figure

Cytotoxic T lymphocyte-Associated Antigen +49G Variant Confers Risk for Anti-CCP- and Rheumatoid Factor-Positive Type of Rheumatoid Arthritis Only in Combination with CT60∗G Allele

Controversial observations have been published on the association of the cytotoxic T lymphocyte associated antigen gene's variants with rheumatoid arthritis (RA). After genotyping 428 patients and 230 matched controls, the prevalence of the CT60∗G allele was more frequent in RF- and/or anti-CCP-seropositive RApatients, compared to the healthy controls (P < .001). Regression analysis revealed that the CT60∗G allele is a possible predisposing factor for RA in these subgroups. No accumulation of the +49∗G allele was found among patients, and this variant was not found to correlate with RA. Assaying the possible genotype variations, the +49∗G-CT60∗G allelic combination was accumulated in seropositive RA-subtypes, and was associated with the risk of RA (OR = 1.73, P = .001 for the whole RA-population). Although the +49∗G allele did not mean a predisposition to RA alone, in combination with CT60∗G it, also conferred risk, suggesting that the +49A/G variant is associated with the risk of RA only in certain haplotypes

Dynamics of small unilamellar vesicles

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Chem. Phys. 148, 104901 (2018) and may be found at https://doi.org/10.1063/1.5009424.In this paper, we investigate the dynamics of small unilamellar vesicles with the aid of neutron spin-echo spectroscopy. The purpose of this investigation is twofold. On the one hand, we investigate the influence of solubilised cosurfactant on the dynamics of the vesicle’s surfactant bilayer. On the other hand, the small unilamellar vesicles used here have a size between larger vesicles, with dynamics being well described by the Zilman-Granek model and smaller microemulsion droplets which can be described by the Milner-Safran model. Therefore, we want to elucidate the question, which model is more suitable for the description of the membrane dynamics of small vesicles, where the finite curvature of the bilayer is felt by the contained amphiphilic molecules. This question is of substantial relevance for our understanding of membranes and how their dynamics is affected by curvature, a problem that is also of key importance in a number of biological questions. Our results indicate the even down to vesicle radii of 20 nm the Zilman-Granek model appears to be the more suitable one.BMBF, 05K13KT1, Probenumgebung und paralle Charakterisierung bei hochpräzisen Neutronen Spin-Echo (NSE) Messungen an komplexen Systemen der weichen Materi

On the mesoscopic origins of high viscosities in some polyelectrolyte-surfactant mixtures

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Chem. Phys. 143, 074902 (2015) and may be found at https://doi.org/10.1063/1.4928583.Oppositely charged polyelectrolyte (PE) surfactant mixtures allow the control of rheological parameters of a solution even at fairly low concentrations. For example, addition of 0.3 wt. % of anionic surfactant to a 1 wt. % solution of the polycation JR 400 increases the viscosity by 4 orders of magnitude. Recently, we could show that this increase is related to the formation of mixed, rod-like PE/surfactant aggregates which interconnect several polyelectrolyte chains [Hoffmann et al., Europhys. Lett. 104, 28001 (2013)]. In this paper, we refine our structural model of the aggregates to obtain a more consistent picture of their internal structure for different anionic surfactants. Combining small angle neutron scattering (SANS) and neutron spin-echo (NSE) allows us to determine the size of the aggregates. By comparing different contrasts, the internal structure of the aggregates can be elucidated and it is seen that the PE in the aggregates retains a relatively high freedom of movement. We proceeded to investigate the influence of the surfactant concentration and the surfactant type on structure and dynamics of the mixed aggregates. It is seen that the structural parameters of the aggregates depend very little on the surfactant concentration and headgroup. However, it is crucial to incorporate a sufficient amount of PE in the aggregates to increase the viscosity of the aggregates. By comparing viscous samples at 1 wt. % PE concentration with samples at a PE concentration of 0.3 wt. %, where no significant increase in viscosity is observed, we find that similar aggregates are formed already at this lower PE concentrations. However, the amount of PE incorporated in them is insufficient to interconnect several PE chains and therefore, they do not increase viscosity. So, our detailed investigation combining contrast variation SANS and NSE does not only allow to explain the viscosity behavior but also to deduced detailed information regarding the structures and the dynamics especially of the polyelectrolyte within the complexes.BMBF, 05K13KT1, Probenumgebung und paralle Charakterisierung bei hochpräzisen Neutronen Spin-Echo (NSE) Messungen an komplexen Systemen der weichen Materi

Dynamics of microemulsions bridged with hydrophobically end-capped star polymers studied by neutron spin-echo

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Chem. Phys. 140, 034902 (2014) and may be found at https://doi.org/10.1063/1.4861894.The mesoscopic dynamical properties of oil-in-water microemulsions (MEs) bridged with telechelic polymers of different number of arms and with different lengths of hydrophobic stickers were studied with neutron spin-echo (NSE) probing the dynamics in the size range of individual ME droplets. These results then were compared to those of dynamicic light scattering (DLS) which allow to investigate the dynamics on a much larger length scale. Studies were performed as a function of the polymer concentration, number of polymer arms, and length of the hydrophobic end-group. In general it is observed that the polymer bridging has a rather small influence on the local dynamics, despite the fact that the polymer addition leads to an increase of viscosity by several orders of magnitude. In contrast to results from rheology and DLS, where the dynamics on much larger length and time scales are observed, NSE shows that the linear polymer is more efficient in arresting the motion of individual ME droplets. This finding can be explained by a simple simulation, merely by the fact that the interconnection of droplets becomes more efficient with a decreasing number of arms. This means that the dynamics observed on the short and on the longer length scale depend in an opposite way on the number of arms and hydrophobic stickers.BMBF, 05K10KT1, Verbundprojekt NanoSOFT: Teilprojekt 2: Neutronen Spin-Echo Experimente zur Untersuchung komplexer Soft-Matter Systeme mit extremer Präzissio

Structure and domain dynamics of human lactoferrin in solution and the influence of Fe(III)-ion ligand binding

BackgroundHuman lactoferrin is an iron-binding protein of the innate immune system consisting of two connected lobes, each with a binding site located in a cleft. The clefts in each lobe undergo a hinge movement from open to close when Fe3+ is present in the solution and can be bound. The binding mechanism was assumed to relate on thermal domain fluctuations of the cleft domains prior to binding. We used Small Angle Neutron Scattering and Neutron Spin Echo Spectroscopy to determine the lactoferrin structure and domain dynamics in solution.ResultsWhen Fe3+ is present in solution interparticle interactions change from repulsive to attractive in conjunction with emerging metas aggregates, which are not observed without Fe3+. The protein form factor shows the expected change due to lobe closing if Fe3+ is present. The dominating motions of internal domain dynamics with relaxation times in the 30–50 ns range show strong bending and stretching modes with a steric suppressed torsion, but are almost independent of the cleft conformation. Thermally driven cleft closing motions of relevant amplitude are not observed if the cleft is open.ConclusionThe Fe3+ binding mechanism is not related to thermal equilibrium fluctuations closing the cleft. A likely explanation may be that upon entering the cleft the iron ion first binds weakly which destabilizes and softens the hinge region and enables large fluctuations that then close the cleft resulting in the final formation of the stable iron binding site and, at the same time, stable closed conformation

La France et les révolutions manquées à l'Est

[eng] Abstract The author considers French attitudes towards the developments which took place in Eastern Europe from 1956 to 1989, from three different approaches : the geopolitical situation of France in relation to the Communist empire, the dual character of the Soviet Union — both great military power and conquering ideological system, and the exact timing of each one of the «failed revolutions». The latter were stages in a process during which drastic changes took place. In the late 1980's, France was no longer «in the Second line», as she had been facing the Soviet Union, a position which had allowed de Gaulle's foreign policy some freedom of manœuvre. Like wise , as crises happened in Eastern Europe, marxist and socialist ideology gradually lost its ascendancy over the French intelligentsia. In comparison with the present situation, in which France is again on the front line, with — or facing — Germany, the period of the anti-totalitarian revolutions in Eastern Europe looks like a prehistory, which definitively belongs to the past. [fre] Résumé L'auteur envisage l'attitude française face aux événements survenus en Europe de l'Est entre 1956 et 1989 en faisant intervenir trois dimensions : la situation géopolitique de la France par rapport à l'empire communiste, la double dimension de l'URSS, à la fois grande puissance militaire et système idéologique conquérant, et le moment précis où survient chacune des révolutions manquées. Ces dernières marquent autant d'étapes au cours desquelles la donne initiale se transforme radicalement. A la fin des années 80, la France n'est plus en «seconde ligne» comme elle le fut face à l'URSS, ce qui assurait à la politique étrangère gaulliste une certaine liberté de manœuvre. De même, au fur et à mesure des crises de l'Est, l'idéologie marxiste et socialiste a progressivement perdu son hégémonie dans l'intelligentsia française. Par rapport à la situation actuelle, où la France se retrouve — avec ou face à l'Allemagne — en première ligne, l'époque des révolutions antitotalitaires de l'Est apparaît comme une préhistoire définitivement révolue.