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The natural environment of proteins is a crowded environment as in cells, extracellular fluids, or during processing. Semidilute polymer solutions have been a source of rich structural and dynamical properties and mimic a crowded environment, but a proper understanding of protein dynamics in the crowded environment is far lagging. Such a study not only realizes protein's natural environment in a crowded solution in the cell or during processing but also manifests the underlying protein−polymer interaction. By dispersing model globular proteins like α-lactalbumin (La) and hemoglobin (Hb), in aqueous solution of poly(ethylene oxide) (PEO) we mimic a crowded environment and use state-of-the-art neutron spin echo (NSE) and small-angle neutron scattering (SANS) techniques to observe the corresponding protein dynamics in semidilute polymer solution. NSE can access the fast diffusion process (D fast ) prior to the slow diffusion process on long times and length scales (D γ ). The protein dynamics in a crowded environment can be described analogous to the diffusion in a periodic potential. The fast dynamics corresponds to diffusion inside a trap built by the polymer mesh while the slower process is the long time diffusion on macroscopic length scales also observed by other techniques. We observe the onset of fractional diffusion for higher concentrated polymer solutions.

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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13628-016-0032-3) contains supplementary material, which is available to authorized users.

An optical method allowing the characterization of melt flow instabilities typically occurring during an extrusion process of polymers and polymer compounds is presented. It is based on a camera‐acquired image of the extruded compound with a reference length scale. Application of image processing and transformation of the calibrated image to the frequency domain yields the magnitude spectrum of the instability. The effectiveness of the before mentioned approach is shown on Styrene‐butadiene rubber (SBR) compounds, covering a wide range of silica filler content, extruded through a Göttfert capillary rheometer. The results of the image‐based analysis are compared with the results from the sharkskin option, a series of highly sensitive pressure transducers installed inside the rheometer. A simplified version of the code used to produce the optical analysis results is included as supplementary material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48806.

In this work, we present an extension to the Adam-Gibbs (AG) model to describe the segmental dynamics of miscible polymer blends with strong interactions. We studied the segmental dynamics of crosslinked styrene butadiene rubber (SBR)/butadiene rubber (BR) blends of different microstructure, chain-end functionalization and composition both unfilled and filled with precipitated silica by means of broadband dielectric spectroscopy (BDS). Contrary to what is observed for athermal miscible blends, the dynamics shows only a single segmental relaxation process due to the strong intermolecular interaction given by the crosslinks. The temperature dependence of the relaxation times has been described and analysed within the framework of a modified AG approach that takes into account the strong interactions between blend components due to the presence of the crosslinks. The accuracy of the proposed model facilitates a deepened understanding of the dynamics of polymer blend systems based on the dynamics of its neat components.