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

Structural Characterization of Pluronic Micelles Swollen with Perfume Molecules

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

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Stretchable hydrogels of chitosan/hyaluronic acid induced by polyelectrolyte complexation around neutral pH

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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