Rodlike Complexes of a Polyelectrolyte (Hyaluronan) and a Protein (Lysozyme) observed by SANS

We study by Small Angle Neutron Scattering (SANS) the structure of Hyaluronan -Lysozyme complexes. Hyaluronan (HA) is a polysaccharide of 9 nm intrinsic persistence length that bears one negative charge per disaccharide monomer (Mmol = 401.3 g/mol); two molecular weights, Mw = 6000 and 500 000 Da were used. The pH was adjusted at 4.7 and 7.4 so that lysozyme has a global charge of +10 and + 8 respectively. The lysozyme concentration was varied from 3 to 40 g/L, at constant HA concentration (10 g/L). At low protein concentration, samples are monophasic and SANS experiments reveal only fluctuations of concentration although, at high protein concentration, clusters are observed by SANS in the dense phase of the diphasic samples. In between, close to the onset of the phase separation, a distinct original scattering is observed. It is characteristic of a rod-like shape, which could characterize "single" complexes involving one or a few polymer chains. For the large molecular weight (500 000) the rodlike rigid domains extend to much larger length scale than the persistence length of the HA chain alone in solution and the range of the SANS investigation. They can be described as a necklace of proteins attached along a backbone of diameter one or a few HA chains. For the short chains (Mw ~ 6000), the rod length of the complexes is close to the chain contour length (~ 15 nm)

Experimental clues of soft glassy rheology in strained filled elastomers

International audienceTensile stress-relaxation measurements have been performed on a series of cross-linked filled elastomers. The fillers are chosen in order to investigate the effect of the filler-filler and the filler-matrix interactions on the time dependence of the tensile relaxation modulus E(t) after UP and DOWN jumps. For the carbon black filled sample (strong filler-elastomer interaction) E(t) decreases as log(t) when the strain epsilon is strictly larger than 0.2 and reached by UP jumps. For the silica filled samples in the same conditions, and for all samples after a DOWN jump including epsilon = 0.2, the experimental data can be fitted with a power law equation characterized by the exponent m. Thus, in all cases, |dE(t)⁄dt| scales as t^(-α) with α=m+1. Pertinence of the Soft Glassy Rheology (SGR) model for interpreting the present results is examined. It is shown that α could be equivalent to the effective noise temperature x and related to the polymer chain mobility

Solvent contribution to the stability of a physical gel characterized by quasi-elastic neutron scattering

The dynamics of a physical gel, namely the Low Molecular Mass Organic Gelator {\textit Methyl-4,6-O-benzylidene-$\alpha$ -D-mannopyranoside ($\alpha$-manno)} in water and toluene are probed by neutron scattering. Using high gelator concentrations, we were able to determine, on a timescale from a few ps to 1 ns, the number of solvent molecules that are immobilised by the rigid network formed by the gelators. We found that only few toluene molecules per gelator participate to the network which is formed by hydrogen bonding between the gelators' sugar moieties. In water, however, the interactions leading to the gel formations are weaker, involving dipolar, hydrophobic or $\pi-\pi$ interactions and hydrogen bonds are formed between the gelators and the surrounding water. Therefore, around 10 to 14 water molecules per gelator are immobilised by the presence of the network. This study shows that neutron scattering can give valuable information about the behaviour of solvent confined in a molecular gel.Comment: Langmuir (2015

Chain conformation : a key parameter driving clustering or dispersion in polyelectrolyte – colloid systems

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The occurrence of seven-fold helical molecular conformation in cellulose-phosphoric acid complex

International audiencePhosphoric acid is widely used for the swelling and hydrolysis of cellulose. The detailed description of molecular interactions between cellulose and phosphoric acid is essential for understanding and controlling these processes. Here, to obtain structural insights into the swelling behavior, we investigated the structural evolution of cellulose swollen in concentrated phosphoric acid solution using X-ray fiber diffraction and solid-state NMR spectroscopy. We observed the formation of a crystalline complex of cellulose and phosphoric acid at − 40 °C, where cellulose molecules adopt a seven-fold helical conformation. This structure is the second known cellulose-acid crystalline complex and the first cellulosic crystal consisting of seven-fold helical chains. Our observation highlights the conformational flexibility of cellulose molecules in the solvated states and the strong influence of cellulose-acid interactions on the packing and conformation of cellulose molecules

Further evidence of liquid-like correlations in polyelectrolyte solutions

Elastic, quasi elastic light scattering and viscosity experiments were used to investigate polyelectrolytic polysaccharide succinoglycan solutions at low solute concentration $C_{\rm p}$, and salt concentration $C_{\rm s}$. The highest degree of “organization” in the solution necessary to describe the observations is a simple liquid type correlation, manifested by broad angular static and dynamic scattering maxima of visible light for solutions at very low ionic strength. Letting the solutions stand undisturbed for a few days did not lead to a sharpening of the broad maxima, nor did lowering the temperature. The positions of these maxima scale roughly as $C^{1/2}_{\rm p}$. By adding salt, the maxima were found to maintain roughly the same position. The reciprocal diffusion coefficient $D^{-1}(q)$ corresponding to the liquid-like correlation state followed the intensity maxima, as has often been demonstrated for similar systems. No “slow mode” or “extraordinary regime” of diffusion was found associated with the static and dynamic light scattering maxima although extreme care in filtration of solution was necessary to avoid a spurious slow diffusional mode due to aggregates

Mesostructural changes in cellulose within wood cell wall upon hydrothermal treatment at 200 °C

Funding Information: This study was supported by JSPS KAKENHI Grant Number JP17J05156 (T.K.). The dried wood specimens were obtained through collaborative research using wood collection databases with Research Institute for Sustainable Humanosphere (RISH) (Y.M. and T.K.). We thank Prof. Junji Sugiyama and Hajime Sorimachi (Kyoto University, Japan) for advising us on the selection of wood specimens. We thank the support of Prof. Yukie Saito (The University of Tokyo, Japan) and The University of Tokyo Chichibu Forest and Arboricultural Research Institute (UTCF) during the sampling of beech green wood specimens. We acknowledge Glyco@Alps (ANR-15-IDEX-02) for the financial support. The wide-angle X-ray detector (WOS) was funded by the French National Research Agency (ANR) under the ‘Investissement d’Avenir’ program (Grant No. ANR-11-EQPX-0010). ESRF is acknowledged for the provision of beamtimes (experiment numbers A02-1-892 and A02-1-864, D2AM beamline). Publisher Copyright: © 2023, The Author(s).Hydrothermal treatment between 150 °C and 230 °C is widely used in wood processing, from the steam treatment of timber for better dimensional stability and durability to the pretreatment for enzymatic saccharification and chemical pulping. Understanding the ultrastructural changes of wood cell walls through hydrothermal treatments is crucial for controlling and optimizing these hydrothermal treatment-based processes. Here, we studied the ultrastructure of wood cell walls of 24 hardwood species using simultaneous small- and wide-angle X-ray scattering measurements before and after the hydrothermal treatment at 200 °C. Most hardwoods show similar equatorial scattering features, representing the structure in the cross-section of the cell walls. In a water-saturated native state, there is a prominent correlation peak between 0.1 and 0.2 Å−1 and a second peak between 0.2 and 0.4 Å−1. The hydrothermal treatment above 160 ˚C drastically altered the structure at this nanometric scale: the two native correlation peaksdisappeared, coincident with a buildup of a correlation peak in the 0.03–0.04 Å−1 range. The hydrothermal treatment likely removed the cell wall matrix component between the microfibrils through autohydrolysis and phase separation, leading to the collapse of microfibrils with each other in the normal wood. In cellulose-rich cell walls, such as the G-layer in tension wood, cellulose microfibrils are already collated in the native state.Peer reviewe