Water Dynamics in a Concentrated Poly( N -isopropylacrylamide) Solution at Variable Pressure

Using quasi-elastic neutron scattering (QENS), we study the dynamics of water in a concentrated poly(N-isopropylacrylamide) solution over a large temperature range across the demixing transition at pressures of 0.1 and 130 MPa. The QENS spectra extending in frequency from 1 to 3 × 103 GHz and in momentum transfer from 0.45 to 1.65 Å–1 reveal the relaxation of hydration water as well as multiple dynamic processes in bulk water. At the cloud point, the fraction of hydration water decreases abruptly at 0.1 MPa, whereas at 130 MPa, it decreases smoothly. The susceptibility spectra of hydration water occur at lower frequencies than those of pure water and the dependence of the relaxation times on momentum transfer can be described by a jump-diffusion model. At a pressure of 0.1 MPa, the hydration water remaining in the two-phase region is more constrained than at 130 MPa. We attribute these findings to the pressure-dependent hydration interactions

The influence of a medium pressure on the structure and dynamics of a bovine pancreatic trypsin inhibitor protein

A new hydrostatic pressure cell designed for small angle neutron scattering SANS and quasi elastic neutron scattering QENS experiments on biomolecular solutions has been developed at the Laboratoire Leon Brillouin. SANS and QENS experiments on bovine pancreatic trypsin inhibitor BPTI , a small protein, have been performed and show us that this pressure cell is well adapted to this kind of experiments. Interesting results about the influence of pressure 1 6200 bar on structure and dynamics of BPTI have been obtaine

Membrane stiffness and myelin basic protein binding strength as molecular origin of multiple sclerosis

Myelin basic protein (MBP) and its interaction with lipids of the myelin sheath plays an important part in the pathology of multiple sclerosis (MS). Previous studies observed that changes in the myelin lipid composition lead to instabilities and enhanced local curvature of MBP-lipid multilayer structures. We investigated the molecular origin of the instability and found that the diseased lipid membrane has a 25% lower bending rigidity, thus destabilizing smooth >1µm curvature radius structures such as in giant unilamellar vesicles. MBP-mediated assembling of lipid bilayers proceeds in two steps, with a slow second step occurring over many days where native lipid membranes assemble into well-defined multilayer structures, whereas diseased lipid membranes form folded assemblies with high local curvature. For both native and diseased lipid mixtures we find that MBP forms dense liquid phases on top of the lipid membranes mediating attractive membrane interactions. Furthermore, we observe MBP to insert into its bilayer leaflet side in case of the diseased lipid mixture, whereas there is no insertion for the native mixture. Insertion increases the local membrane curvature, and could be caused by a decrease of the sphingomyelin content of the diseased lipid mixture. These findings can help to open a pathway to remyelination strategies

Magnetic small-angle neutron scattering from self-assembled iron oxide nanoparticles influenced by field

Self-assembly of magnetic nanoparticles, in general, is of interest due to the broad range of applications in material science and biomedical engineering [1,2]. Parameters that affect self-assembly in nanoparticles include particle size, the applied magnetic field profile, concentration and synthesis routines [3]. A range of different sizes of iron oxide nanoparticles between 17 and 27 nm were investigated using polarized small-angle neutron scattering (SANS) at the KWS-1 instrument operated by the Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany. Nanoparticles were dispersed in toluene and measured at room temperature in a range of applied fields between ±2.2 T. The observed self-assembly strongly depended on both nanoparticle size and applied field. For smaller particles (diameter ≤ 20 nm), there was no indication of self-assembly even at high concentration (1% v/v), while 27 nm nanoparticles assemble into linear chains even in low concentrations (0.42% v/v) and low field.The smallest nanoparticles (d = 17 nm) were studied by contrast variation; by altering the isotopic composition of the toluene solvent, the magnetization profile within the cores of the nanoparticles could be extracted with high-resolution when using a spin-polarized incident neutron beam [4]. For larger nanoparticle, the structural and form factors were obtained by sector analysis of the 2-D SANS patterns (Fig. 1(a) and (b)). The extracted structure factors suggest that the chains grow longer and straighter and align more closely with the field direction up until application of the maximum field (Fig. 1(c)). This is understood in terms of a minimization of the dipole energy of the nanoparticles in the presence of the applied field and neighbouring particles. The implications for the control of self-assembly of more complex nanoparticles will be discussed.[1] G. Ozina, K. Hou, B. Lotsch, L. Cademartiri, D.Puzzo, F. Scotognella, A. Ghadimi, J. Thomson, Materials Today, Vol. 12, p.12 (2009)[2] P. Tartaj, Current Nanoscience, Vol. 2, p.43 (2006) [3] Z. Fu, Y. Xiao, A. Feoktystov, V. Pipich, M. Appavou, Y. Su, E. Feng, W. Jin and T. Brückel, Nanoscale, Vol. 8, p.18541 (2016)[4] A. Wiedenmann, Journal of Applied Crystallography, Vol. 33, p.428 (2000

Not just a fluidifying effect : omega-3 phospholipids induce formation of non-lamellar structures in biomembranes

Polyunsaturated omega-3 fatty acid docosahexaenoic acid (DHA) is found in very high concentrations in a few peculiar tissues, suggesting that it must have a specialized role. DHA was proposed to affect the function of the cell membrane and related proteins through an indirect mechanism of action, based on the DHA-phospholipid effects on the lipid bilayer structure. In this respect, most studies have focused on its influence on lipid-rafts, somehow neglecting the analysis of effects on liquid disordered phases that constitute most of the cell membranes, by reporting in these cases only a general fluidifying effect. In this study, by combining neutron reflectivity, cryo-transmission electron microscopy, small angle neutron scattering, dynamic light scattering and electron paramagnetic resonance spectroscopy, we characterize liquid disordered bilayers formed by the naturally abundant 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and different contents of a di-DHA glycero-phosphocholine, 22:6-22:6PC, from both a molecular/microscopic and supramolecular/mesoscopic viewpoint. We show that, below a threshold concentration of about 40% molar percent, incorporation of 22:6-22:6PC in the membrane increases the lipid dynamics slightly but sufficiently to promote the membrane deformation and increase of multilamellarity. Notably, beyond this threshold, 22:6-22:6PC disfavours the formation of lamellar phases, leading to a phase separation consisting mostly of small spherical particles that coexist with a minority portion of a lipid blob with water-filled cavities. Concurrently, from a molecular viewpoint, the polyunsaturated acyl chains tend to fold and expose the termini to the aqueous medium. We propose that this peculiar tendency is a key feature of the DHA-phospholipids making them able to modulate the local morphology of biomembranes

Pressure-Dependence of Poly( N -isopropylacrylamide) Mesoglobule Formation in Aqueous Solution

Above their cloud point, aqueous solutions of the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM) form large mesoglobules. We have carried out very small-angle neutron scattering (VSANS with q = 0.21–2.3 × 10–3 Å–1) and Raman spectroscopy experiments on a 3 wt % PNIPAM solution in D2O at atmospheric and elevated pressures (up to 113 MPa). Raman spectroscopy reveals that, at high pressure, the polymer is less dehydrated upon crossing the cloud point. VSANS shows that the mesoglobules are significantly larger and contain more D2O than at atmospheric pressure. We conclude that the size of the mesoglobules and thus their growth process are closely related to the hydration state of PNIPAM

Tough Supramolecular Hydrogel Based on Strong Hydrophobic Interactions in a Multiblock Segmented Copolymer

We report the preparation and structural and mechanical characterization of a tough supramolecular hydrogel, based exclusively on hydrophobic association. The system consists of a multiblock, segmented copolymer of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dimer fatty acid (DFA) building blocks. A series of copolymers containing 2K, 4K, and 8K PEG were prepared. Upon swelling in water, a network is formed by self-assembly of hydrophobic DFA units in micellar domains, which act as stable physical cross-link points. The resulting hydrogels are noneroding and contain 75–92 wt % of water at swelling equilibrium. Small-angle neutron scattering (SANS) measurements showed that the aggregation number of micelles ranges from 2 × 102 to 6 × 102 DFA units, increasing with PEG molecular weight. Mechanical characterization indicated that the hydrogel containing PEG 2000 is mechanically very stable and tough, possessing a tensile toughness of 4.12 MJ/m3. The high toughness, processability, and ease of preparation make these hydrogels very attractive for applications where mechanical stability and load bearing features of soft materials are required