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.
The KWS‐1 small‐angle neutron scattering (SANS) instrument operated by the Jülich Centre for Neutron Science (JCNS) at the research reactor FRM II of the Heinz Maier‐Leibnitz Zentrum in Garching near ...Munich has been recently upgraded. The KWS‐1 instrument was updated, from its active collimation apertures to the detector cabling. Most of the parts of the instrument were installed for the first time, including a broadband polarizer, a large‐cross‐section radio‐frequency spin flipper, a chopper and neutron lenses. A custom‐designed hexapod in the sample position allows heavy loads and precise sample positioning in the beam for conventional SANS experiments as well as for grazing‐incidence SANS under applied magnetic field. With the foreseen in situ polarization analysis the main scientific topic of the instrument tends towards magnetism. The performance of the polarizer and flipper was checked with a polarized 3He cell at the sample position. The results of these checks and a comparison of test measurements on a ferrofluid in a magnetic field with polarized and nonpolarized neutrons are presented.
Multi‐domain proteins play critical roles in fine‐tuning essential processes in cellular signaling and gene regulation. Typically, multiple globular domains that are connected by flexible linkers ...undergo dynamic rearrangements upon binding to protein, DNA or RNA ligands. RNA binding proteins (RBPs) represent an important class of multi‐domain proteins, which regulate gene expression by recognizing linear or structured RNA sequence motifs. Here, we employ segmental perdeuteration of the three RNA recognition motif (RRM) domains in the RBP TIA‐1 using Sortase A mediated protein ligation. We show that domain‐selective perdeuteration combined with contrast‐matched small‐angle neutron scattering (SANS), SAXS and computational modeling provides valuable information to precisely define relative domain arrangements. The approach is generally applicable to study conformational arrangements of individual domains in multi‐domain proteins and changes induced by ligand binding.
Segmentally perdeuterated multi‐domain proteins are obtained by Sortase A mediated ligation. Using contrast‐matched small‐angle neutron scattering (SANS) experiments on different samples with selectively perdeuterated domains of the same multi‐domain protein gives insight into domain arrangements and changes induced by ligand binding, thus providing unique information for structural analysis.
Three synthetized polymorphs of calcium carbonate have been tested in combination with the suspension of nanolime particles as potential consolidating agents for contrasting stone decay and overcome ...some of the limitations of nanolime agents when applied to substrates with large porosity. The modifications induced in the pore network of the Maastricht limestone were analyzed with microscopy and in a non-invasive fashion with small angle neutron scattering and synchrotron radiation micro-computed tomography. A reduction in porosity and pore accessibility at the micrometric scale was detected with the latter technique, and ascribed to the improved pore-filling capacity of the consolidation agent containing CaCO
particles. These were found to be effectively bound to the carbonated nanolime, strengthening the pore-matrix microstructure. Penetration depth and positive effect on porosity were found to depend on the particle size and shape. Absence of significant changes in the fractal nature of the pore surface at the nanoscale, was interpreted as indication of the negligible contribution of nanolime-based materials in the consolidation of stones with large porosity. However, the results indicate that in such cases, their effectiveness may be enhanced when used in combination with CaCO
particles, owing to the synergic effect of chemical/structural compatibility and particle size distribution.
Nonionic ethylene oxide (EO)‐based surfactants are widely employed in commercial applications and normally form gel‐like liquid crystalline phases at higher concentrations, rendering their handling ...under such conditions difficult. By incorporating CO2 units in their hydrophilic head groups, the consumption of the petrochemical EO was reduced, and the tendency to form liquid crystals was suppressed completely. This surprising behavior was characterized by rheology and studied with respect to its structural origin by means of small‐angle neutron scattering (SANS). These experiments showed a strongly reduced repulsive interaction between the micellar aggregates, attributed to a reduced hydration and enhanced interpenetration of the head groups owing to the presence of the CO2 units. In addition, with increasing CO2 content the surfactants became more efficient and effective with respect to their surface activity. These findings are important because the renewable resource CO2 is used, and the CO2‐containing surfactants allow handling at very high concentrations, an aspect of enormous practical importance.
Pleasantly sur‐phased: By incorporating CO2 units in the hydrophilic head groups of nonionic surfactants, the tendency to form liquid crystalline phases is suppressed completely, and their viscosity in water remains low up to the highest concentrations. This surprising behavior is characterized by rheology and explained with respect to its structural origin by means of small‐angle neutron scattering (SANS).
We addressed the onset of synergistic activity of the two well-studied antimicrobial peptides magainin 2 (MG2a) and PGLa using lipid-only mimics of Gram-negative cytoplasmic membranes. Specifically, ...we coupled a joint analysis of small-angle x-ray and neutron scattering experiments on fully hydrated lipid vesicles in the presence of MG2a and L18W-PGLa to all-atom and coarse-grained molecular dynamics simulations. In agreement with previous studies, both peptides, as well as their equimolar mixture, were found to remain upon adsorption in a surface-aligned topology and to induce significant membrane perturbation, as evidenced by membrane thinning and hydrocarbon order parameter changes in the vicinity of the inserted peptide. These effects were particularly pronounced for the so-called synergistic mixture of 1:1 (mol/mol) L18W-PGLa/MG2a and cannot be accounted for by a linear combination of the membrane perturbations of two peptides individually. Our data are consistent with the formation of parallel heterodimers at concentrations below a synergistic increase of dye leakage from vesicles. Our simulations further show that the heterodimers interact via salt bridges and hydrophobic forces, which apparently makes them more stable than putatively formed antiparallel L18W-PGLa and MG2a homodimers. Moreover, dimerization of L18W-PGLa and MG2a leads to a relocation of the peptides within the lipid headgroup region as compared to the individual peptides. The early onset of dimerization of L18W-PGLa and MG2a at low peptide concentrations consequently appears to be key to their synergistic dye-releasing activity from lipid vesicles at high concentrations.
Monodisperse unilamellar nanotubes (NTs) and nanoribbons (NRs) were transformed to multilamellar NRs and NTs in a well‐defined fashion. This was done by using a step‐wise approach in which ...self‐assembled cationic amino acid amphiphile (AAA) formed the initial NTs or NRs, and added polyanion produced an intermediate coating. Successive addition of cationic AAA formed a covering AAA layer, and by repeating this layer‐by‐layer (LBL) procedure, multi‐walled nanotubes (mwNTs) and nanoribbons were formed. This process was structurally investigated by combining small‐angle neutron scattering (SANS) and cryogenic‐transmission electron microscopy (cryo‐TEM), confirming the multilamellar structure and the precise layer spacing. In this way the controlled formation of multi‐walled suprastructures was demonstrated in a simple and reproducible fashion, which allowed to control the charge on the surface of these 1D aggregates. This pathway to 1D colloidal materials is interesting for applications in life science and creating well‐defined building blocks in nanotechnology.
Multi‐walled nanotubes and nanoribbons of amino acid amphiphiles are fabricated by using a layer‐by‐layer technique, where successive rigid amphiphile layers are glued together by oppositely charged polyelectrolyte. The resulting well‐defined 1D structures are attractive as potential biocompatible delivery systems and building blocks in nanotechnology.
Extracellular polysaccharides are widely produced by bacteria, yeasts, and algae. These polymers are involved in several biological functions, such as bacteria adhesion to surface and biofilm ...formation, ion sequestering, protection from desiccation, and cryoprotection. The chemical characterization of these polymers is the starting point for obtaining relationships between their structures and their various functions. While this fundamental correlation is well reported and studied for the proteins, for the polysaccharides, this relationship is less intuitive. In this paper, we elucidate the chemical structure and conformational studies of a mannan exopolysaccharide from the permafrost isolated bacterium Psychrobacter arcticus strain 273-4. The mannan from the cold-adapted bacterium was compared with its dephosphorylated derivative and the commercial product from Saccharomyces cerevisiae. Starting from the chemical structure, we explored a new approach to deepen the study of the structure/activity relationship. A pool of physicochemical techniques, ranging from small-angle neutron scattering (SANS) and dynamic and static light scattering (DLS and SLS, respectively) to circular dichroism (CD) and cryo-transmission electron microscopy (cryo-TEM), have been used. Finally, the ice recrystallization inhibition activity of the polysaccharides was explored. The experimental evidence suggests that the mannan exopolysaccharide from P. arcticus bacterium has an efficient interaction with the water molecules, and it is structurally characterized by rigid-rod regions assuming a 14-helix-type conformation.
Nanolimes are dispersions of nanosized Ca(OH)
2
particles in alcohols often used for the consolidation of various types of cultural heritage objects. The consolidation effect is based on the ...transformation of Ca(OH)
2
into CaCO
3
phases during carbonation process. The detection of microstructural changes consequent to a consolidating treatment (essential to evaluate its effectiveness) was approached adopting the innovative combination of two advanced techniques, covering a range in pore size from the nanometric to the millimetric scale: small-angle neutron scattering (SANS) and synchrotron X-ray micro-computed tomography (µ-CT). The changes in the 3D microstructure of samples of Maastricht limestone, a well-known weak stone material considered as a sort of ‘standard’ in cultural heritage conservation studies, pure and treated with nanolime dispersions, have been described in a fully non-invasive fashion, overcoming the limitation of previous approaches. The application of nanolime resulted to have a limited positive effect in reducing the fine porosity. Its time evolution was attributed to the progress of the carbonation reaction. On the contrary, the treatment produced positive effects on the porosity in the size range covered with µ-CT, reducing the pore accessibility between 30 and 65 µm, suggesting an improvement of the mechanical properties. The combined use of SANS and µ-CT represents and novel methodological approach in support of cultural heritage conservation works.
The formation of supported lipid bilayers (SLB) on hydrophilic substrates through the method of unilamelar vesicle fusion is used routinely in a wide range of biophysical studies. In an effort to ...control and better understand the fusion process on the substrate, many experimental studies employing different techniques have been devoted to the elucidation of the fusion mechanism. In the present work, we follow the kinetics of membrane formation using time-resolved (TR) neutron reflectivity, focusing on the structural changes near the solid/liquid interface. A clear indication of stacked bilayer structure is observed during the intermediate phase of SLB formation. Adsorbed lipid mass decrease is also measured in the final stage of the process. We have found that it is essential for the analysis of the experimental results to treat the shape of adsorbed lipid vesicles on an attractive substrate theoretically. The overall findings are discussed in relation to proposed fusion mechanisms from the literature, and we argue that our observations favor a model involving enhanced adhesion of incoming vesicles on the edges of already-formed bilayer patches.
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