With the constantly improving performance of neutron spin echo (NSE) spectrometers it becomes possible to perform measurements on increasingly complex samples and to study more and more delicate ...effects. To properly study such effects, proper background correction becomes increasingly important. In this paper, we will review different methods to subtract the buffer from NSE measurements and study the effect of small errors in the subtraction of the background. In the large dynamic range of modern neutron spin-echo spectrometers multiple effects become visible in a single measurement. Specifically, for vesicles both membrane undulations and translational diffusion have an effect on the intermediate scattering function in the NSE time window and here, we will investigate how taking this into account differently affects the results obtained from data analysis.
We review the work done on complexes between biopolyelectrolytes such as ionically modified cellulose or chitosan and oppositely charged surfactants. Around equimolarity of the charges one typically ...observes precipitation but for other mixing ratios one may form long-time stable complexes, where structure and rheology depend on the mixing ratio, total concentration and the molecular constitution of the components. In addition, it may be the case that the structures are formed under non-equilibrium situations and therefore depend on the preparation path. The binding is shown to occur cooperatively and the micelles present often retain their shape irrespective of the complexation. However, the rather stiff biopolyelectrolytes may lead to an interconnection between different aggregates thereby forming a network with the corresponding rheological properties. In general, the structure and the properties of the aggregates are rather versatile and correspondingly one can create a wide range of different surfactant-biopolyelectrolyte systems by appropriately choosing the composition. This is very interesting as it allows for formulations with a large range of tuneable properties with ecologically friendly polyelectrolytes for many relevant applications.
Work on the formation of complexes composed of biopolyelectrolytes such as ionically modified cellulose or chitosan and oppositely charged surfactants is reviewed.
Reported here is the synthesis of perfectly sequence defined, monodisperse diblock copolypeptides of hydrophilic elastin-like and hydrophobic resilin-like polypeptide blocks and characterization of ...their self-assembly as a function of structural parameters by light scattering, cryo-TEM, and small-angle neutron scattering. A subset of these diblock copolypeptides exhibit lower critical solution temperature and upper critical solution temperature phase behavior and self-assemble into spherical or cylindrical micelles. Their morphologies are dictated by their chain length, degree of hydrophilicity, and hydrophilic weight fraction of the ELP block. We find that (1) independent of the length of the corona-forming ELP block there is a minimum threshold in the length of the RLP block below which self-assembly does not occur, but that once that threshold is crossed, (2) the RLP block length is a unique molecular parameter to independently tune self-assembly and (3) increasing the hydrophobicity of the corona-forming ELP drives a transition from spherical to cylindrical morphology. Unlike the self-assembly of purely ELP-based block copolymers, the self-assembly of RLP–ELPs can be understood by simple principles of polymer physics relating hydrophilic weight fraction and polymer–polymer and polymer–solvent interactions to micellar morphology, which is important as it provides a route for the de novo design of desired nanoscale morphologies from first principles.
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On the capital market, price movements of stock corporations can be observed independent of overall market developments as a result of company-specific news, which suggests the occurrence of a sudden ...risk event. In recent years, numerous concepts from statistical physics have been transferred to econometrics to model these effects and other issues, e.g., in socioeconomics. Like other studies, we extend the approaches based on the "buy" and "sell" positions of agents (investors' stance) with a third "hold" position. We develop the corresponding theory within the framework of the microcanonical and canonical ensembles for an ideal agent system and apply it to a capital market example. We thereby design a procedure to estimate the required model parameters from time series on the capital market. The aim is the appropriate modeling and the one-step-ahead assessment of the effect of a sudden risk event. From a one-step-ahead performance comparison with selected benchmark approaches, we infer that the model is well-specified and the model parameters are well determined.
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Recent developments in the field of oppositely charged polyelectrolyte-surfactant complexes (PESCs) have been reviewed. Among the many developments in that field in particular very interesting is ...certainly the discovery of still new types of structural arrangements that arise from the complexity of the prevailing interactions, both in terms of electrostatics, as well as steric and specific interactions. More complex structures often arise from the architecture of the polyelectrolyte, such as the use of block copolymers or hydrophobically modified polyelectrolytes. However, also the surfactant plays a role in the PESC structure and for instance bilayer forming surfactants can be induced by polyelectrolyte to form multilamellar assemblies. Of course, PESCs may exhibit responsiveness to changes of pH, temperature, chemical environment etc. and this even in a complex fashion as the polyelectrolyte and surfactant may respond here in a different fashion. Interesting observations also concern the control of rheological properties by PESCs that depend strongly on the properties of the polyelectrolyte and the extension of the formed mixed aggregates, as well as their bridging. An old topic is coacervate formation in such systems, but one that currently receives renewed attention, as various aspects here are still not fully understood and at the same time they are very promising for further applications in separation/sequestration. Often overlooked is the fact that PESCs are typically not static entities but instead highly dynamic systems and recent neutron spin-echo (NSE) measurements indicate that the local dynamics of polyelectrolyte chains is only little affected by the incorporation within such aggregates. Therefore PESCs are still a highly fascinating class of self-assembled structures, where a large number of interesting developments may still be expected in the future.
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•Polyelectrolyte-surfactant complexes (PESCs) can have largely different structures.•PESCs are versatile systems for rheological control.•Coacervate formation by PESCs is interesting for liquid-liquid extraction.•Polyelectrolyte chains in PESCs are highly mobile.
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Myelin basic protein (MBP) is intrinsically disordered in solution and is considered as a conformationally flexible biomacromolecule. Here, we present a study on perturbation of MBP structure and ...dynamics by the denaturant guanidinium chloride (GndCl) using small-angle scattering and neutron spin–echo spectroscopy (NSE). A concentration of 0.2 M GndCl causes charge screening in MBP resulting in a compact, but still disordered protein conformation, while GndCl concentrations above 1 M lead to structural expansion and swelling of MBP. NSE data of MBP were analyzed using the Zimm model with internal friction (ZIF) and normal mode (NM) analysis. A significant contribution of internal friction was found in compact states of MBP that approaches a non-vanishing internal friction relaxation time of approximately 40 ns at high GndCl concentrations. NM analysis demonstrates that the relaxation rates of internal modes of MBP remain unaffected by GndCl, while structural expansion due to GndCl results in increased amplitudes of internal motions. Within the model of the Brownian oscillator our observations can be rationalized by a loss of friction within the protein due to structural expansion. Our study highlights the intimate coupling of structural and dynamical plasticity of MBP, and its fundamental difference to the behavior of ideal polymers in solution.
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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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Protein–polymer conjugation is a widely used technique to develop protein therapeutics with improved pharmacokinetic properties as prolonged half-life, higher stability, water solubility, lower ...immunogenicity, and antigenicity. Combining biochemical methods, small angle scattering (SAXS/SANS), and neutron spin–echo spectroscopy, here we examine the impact of PEGylation (i.e., the covalent conjugation with poly(ethylene glycol) or PEG) on structure and internal domain dynamics of phosphoglycerate kinase (PGK) to elucidate the reason for reduced activity that is connected to PEGylation. PGK is a protein with a hinge motion between the two main domains that is directly related to function. We find that secondary structure and ligand access to the binding sites are not affected. The ligand induced cleft closing is unchanged. We observe an additional internal motion between covalent bonded PEG and the protein compatible with Brownian motion of PGK in a harmonic potential. Entropic interaction with the full PEG chain leads to a force constant of about 8 pN/nm independent of PEG chain length. This additional force preserves protein structure and has negligible effects on the functional domain dynamics of the protein. PEGylation seems to reduce activity just by acting as a local crowder for the ligands. The newly identified interaction mechanism might open possibilities to improve rational design of protein–polymer conjugates.
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This manuscript presents the preparation and study of a new double-network hydrogel system, comprising an amphiphilic, pH-responsive first polymer conetwork synthesized
via
reversible ...addition-fragmentation chain transfer (RAFT) polymerization, and a second hydrophilic polymer network prepared
via
free radical photopolymerization. The amphiphilic character of the first conetwork led to its phase separation on the nanoscale, as indicated by small-angle neutron scattering (SANS) in deuterium oxide, whereas the presence of segments consisting of tertiary amine-bearing monomer repeating units resulted in pH-dependent equilibrium swelling in water. Finally, the introduction of a second, reinforcing network into the structure of the first conetwork produced a double-network hydrogel system with mechanical properties (compressive stress and strain at break, and low-strain elastic modulus) superior to those of the first conetwork. Thus, the present complex hydrogel system bears three important functions: high mechanical properties to endure an environment with high stresses, hydrophobic pockets to solubilize non-polar substances within an overall aqueous milieu, and an ability to respond to changes in pH. Such multi-functional water-swollen polymer systems can pave the way toward next-generation biomaterials.
Double-networks based on amphiphilic polymer conetworks synthesized using RAFT polymerization were prepared, exhibiting pH-responsiveness, nanophase separation and enhanced mechanical properties.
In this study, the phase behavior, structure and properties of systems composed of the cationic, cellulose-based polycation JR 400 and the anionic surfactants sodium dodecylbenzenesulfonate (SDBS) or ...sodium dodecylethoxysulfate (SDES), mainly in the semidilute regime, were examined. This system shows the interesting feature of a very large viscosity increase by nearly 4 orders of magnitude as compared to the pure polymer solution already at very low concentrations of 1 wt %. By using rheology, dynamic light scattering (DLS), and small-angle neutron scattering (SANS), we are able to deduce systematic correlations between the molecular composition of the systems (characterized by the charge ratio Z = +polymer/−surfactant), their structural organization and the resulting macroscopic flow behavior. Mixtures in the semidilute regime with an excess of polycation charge form highly viscous network structures containing rodlike aggregates composed of surfactant and polyelectrolyte that are interconnected by the long JR 400 chains. Viscosity and storage modulus follow scaling laws as a function of surfactant concentration (η ∼ c s 4; G 0 ∼ c s 1.5) and the very pronounced viscosity increase mainly arises from the strongly enhanced structural relaxation time of the systems. In contrast, mixtures with excess surfactant charges form solutions with viscosities even below those of the pure polymer solution. The combination of SANS, DLS, and rheology shows that the structural, dynamical, and rheological properties of these oppositely charged polyelectrolyte/surfactant systems can be controlled in a systematic fashion by appropriately choosing the systems composition.
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