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During wheat seeds development, storage proteins are synthetized and subsequently form dense protein phases, also called Protein Bodies (PBs). The mechanisms of PBs formation and the supramolecular assembly of storage proteins in PBs remain unclear. In particular, there is an apparent contradiction between the low solubility in water of storage proteins and their high local dynamics in dense PBs. Here, we probe the interplay between short-range attraction and long-range repulsion of a wheat gliadin isolate by investigating the dynamics of liquid-liquid phase separation after temperature quench. We do so using time-resolved small angle light scattering, phase contrast microscopy and rheology. We show that gliadins undergo liquid-liquid phase separation through Nucleation and Growth or Spinodal Decomposition depending on the quench depth. They assemble into dense phases but remain in a liquid-like state over an extended range of temperatures and concentrations. The analysis of phase separation kinetics reveals that the attraction strength of gliadins is in the same order of magnitude as other proteins. We discuss the respective role of competing interactions, protein intrinsic disorder, hydration and polydispersity in promoting local dynamics and providing this liquid-like behavior despite attractive forces. ispartof: SCIENTIFIC REPORTS vol:8 issue:1 ispartof: location:England status: published

Viruses come in various shapes and sizes, and a number of viruses originate from extremities, e.g. high salinity or elevated temperature. One challenge for studying extreme viruses is to find efficient purification conditions where viruses maintain their infectivity. Asymmetrical flow field-flow fractionation (AF4) is a gentle native chromatography-like technique for size-based separation. It does not have solid stationary phase and the mobile phase composition is readily adjustable according to the sample needs. Due to the high separation power of specimens up to 50 A mu m, AF4 is suitable for virus purification. Here, we applied AF4 for extremophilic viruses representing four morphotypes: lemon-shaped, tailed and tailless icosahedral, as well as pleomorphic enveloped. AF4 was applied to input samples of different purity: crude supernatants of infected cultures, polyethylene glycol-precipitated viruses and viruses purified by ultracentrifugation. All four virus morphotypes were successfully purified by AF4. AF4 purification of culture supernatants or polyethylene glycol-precipitated viruses yielded high recoveries, and the purities were comparable to those obtained by the multistep ultracentrifugation purification methods. In addition, we also demonstrate that AF4 is a rapid monitoring tool for virus production in slowly growing host cells living in extreme conditions.

Phase separation in aqueous biopolymer mixtures results in the formation of an interface, separating two aqueous bulk phases. The properties of that interface are key parameters to understand and predict phenomena, such as the phase-separation process and deformation of droplets in a flow field. In these processes, the structures and sizes of the morphologies depend on the balance between viscous and interfacial forces. Normally, one assumes that the interfacial tension is the only important parameter regarding the interfacial forces. However, we will show that in these water-in-water emulsions, bending rigidity and interfacial permeability also play an important role. Spinning drop experiments show that at long time scales the interface is permeable to both dissolved biopolymers and water. From droplet relaxation experiments, we could conclude that, for shorter time scales, water is the only ingredient that can diffuse through the interface. Due to this permeability, these methods cannot be used to calculate the interfacial tension accurately, without taking into account the permeability of the interface. Including the permeability, we give a full description for the relaxation time of deformed droplets. From this description, the interfacial tension and the permeability of the interface can be deduced simultaneously. We also incorporate the permeability and the bending rigidity into the description of the kinetics of phase separation. From this theoretical description, we predict four different regimes to occur in the phase-separation process depending on the size of the domains. For the scaling of the domain size with time, we find an exponent of (1)/(4) for bending- and permeability-dominated coarsening, an exponent of (1)/(3) for bending-dominated coarsening, an exponent of (1)/(2) for interfacial tension- and permeability-dominated coarsening, and an exponent of 1 for interfacial tension-dominated coarsening. The crossover between the different regimes depends on two different critical radii, R(c), equal to (2k/gamma)(1/2) and R(lambda), equal to etalambda(eff). Taking values for the interfacial properties, we find these critical radii to be larger than a micrometer, indicating that both bending rigidity and permeability are of importance during phase separation.

The present work provides a critical review of polymer crystallization studies using SALS; experimental methods, analysis techniques, observations and their relations with respect to other techniques are discussed. Furthermore, the fact that nucleation might be accompanied by large scale density fluctuations has been investigated for the flow-induced crystallization of iPB. SALS was applied to measure density and orientation fluctuations, whereas complementary results were obtained from optical microscopy. The observations from both crystallization and melting experiments seem to indicate that the detected density fluctuations result from the presence of weakly anisotropic structures, ratjer than being an indication of densification before the onset of crystallization. ispartof: Macromolecular materials and engineering vol:293 issue:4 pages:255-273 status: published

We discuss the coarsening of domains in bicontinuous structure of aqueous polymer mixtures, driven by hydrodynamic flow. Taking into account the bending energy as a contribution to the interfacial energy, we derive a general expression for the coarsening rate in these mixtures. Examining the limiting behavior of small and large length scales, we find two regimes. For small length scales, the size of the domains (¿) scales with time (t) as ¿ t1/3, while at large length scales, the domain size scales with time as ¿ t. The crossover between the two regimes occurs at a particular length scale, the critical radius Rc, which is dependent on the bending rigidity k, and the interfacial tension of a flat interface ¿0 (Rc = ). In the case of aqueous biopolymer mixtures, we predict this particular length scale to be in the micron range. This new general expression for the coarsening of domains in aqueous polymer mixtures can explain experimental results [Lorén et al. Macromolecules 2001, 34, 8117], which show the two regimes of coarsening with a crossover at 4 µm.

International audience; The evolution of the global orientation parameter for a series of aqueous hydroxypropylcellulose solutions both during and following the cessation of a steady-state shear Bow is reported. Time-resolved orientation measurements were made in situ through a novel X-ray rheometer coupled with a two-dimensional electronic X-ray camera, and using an intense X-ray source at the LURE synchrotron. After the cessation of flow, the global orientation decreases from the steady state orientation level to zero following shear flow at a low shear rate or to a small but finite value after flow at a high shear rate. The decrease of orientation with time shows different behaviour, dependent upon the previously applied shear rate.

The dynamic variation of optical birefringence during solution polycondensation of rigid rodlike molecules in a simple shear flow is obtained. At relatively high shear rates (413 s-1) and late stages of the polymerization the orientation of the molecules is found to be significant. Molecular orientation is important in such reactions since it increases the polymerization rate and alters the molecular weight distribution (Agarwal, U. S.; Khakhar, D. V. Nature 1992, 360, 53). The birefringence at different shear rates (gamma) over the course of the polymerization is found to depend only on gamma/D(r), where D(r) is the rotational diffusivity. The predictions of the theory of Marrucci and Grizzuti (J. Polym. Sci., Polym. Lett. Ed. 1983, 21, 83), however, show large deviations in comparison to the experimental birefringence measurements. The experiments are carried out using terephthaloyl chloride and p-phenylenediamine to produce poly(p-phenyleneterephthalamide) in a mixed solvent at low temperatures. A two-reactor system is used in which the second reactor is designed to give a uniform simple shear flow and to allow for measurement of birefringence during polymerization.