18 research outputs found

    Small-Angle Neutron Scattering from Aqueous Dispersions of Single-Walled Carbon Nanotubes with Pluronic F127 and Poly(vinylpyrrolidone)

    No full text
    Amphiphilic block copolymers are excellent dispersants for single-walled carbon nanotubes (SWCNT) in aqueous environments, where their noncovalent attachments do not affect the π chemical bonding. In this small-angle neutron scattering (SANS) study, we investigate whether the coverage of Pluronic F127 polymers around the CNTs depends on the solution concentration in the range of 1–6% (w/w). The observations indicate that at these concentrations the SWCNT surface is fully saturated at about 14 chains per unit length of 100 Å. Furthermore, we seek to verify whether the unusual effect observed in a previous study by contrast variation, interpreted as being due to a dense hydration layer around the polymer chains, also appears using a homopolymer (polyvinylpyrrolidone - PVP) that does not contain poly­(ethylene oxide) (PEO) units. The SANS patterns showed again a minimal intensity value at much higher solvent composition (75% D<sub>2</sub>O) than the expected value of 29% D<sub>2</sub>O. The minimum scattering curve exhibited a nearly <i>q</i><sup>–1</sup> power law at small angles, an indication of rodlike entities. A model of a CNT thin bundle with loosely adsorbed polymer chains around it (core–chains) was reasonably well fitted to the data. The polymer chains are assumed to be surrounded by a water layer with a slightly higher density than bulk water, having partial selectivity for D<sub>2</sub>O

    Micelles from HOOC-PnBA‑<i>b</i>‑PAA‑C<sub>12</sub>H<sub>15</sub> Diblock Amphiphilic Polyelectrolytes as Protein Nanocarriers

    No full text
    We investigate the potential of self-assembled nanostructures of the PnBA-<i>b</i>-PAA amphiphilic diblock polyelectrolyte as candidates for protein nanocarriers. Three PnBA-<i>b</i>-PAA copolymers with different molecular weights and PnBA/PAA weight ratios are tested. The system with the most well-defined core–shell micellar structure is chosen for complexation with lysozyme. Its solutions are found to contain well-defined core–shell micelles that are stable upon increase in solution salt content to physiological levels. Upon mixing with lysozyme we find that the protein globules accumulate preferably at the outer parts of the hydrated corona of the micelles. Increasing the protein concentration, intermicellar aggregation is enhanced in a controllable way. At high salt content the number of proteins per micelle is lower compared with the low salt content, which points to an interaction of predominantly electrostatic nature. While light scattering is very sensitive to complexation, small-angle neutron scattering is able to distinguish between the contributions from individual micelles and aggregates. This work demonstrates the use of scattering techniques to characterize protein–polymer interactions in multiple hierarchical levels

    Relevance of Internal Friction and Structural Constraints for the Dynamics of Denatured Bovine Serum Albumin

    No full text
    A general property of disordered proteins is their structural expansion that results in a high molecular flexibility. The structure and dynamics of bovine serum albumin (BSA) denatured by guanidinium hydrochloride (GndCl) were investigated using small-angle neutron scattering (SANS) and neutron spin–echo spectroscopy (NSE). SANS experiments demonstrated the relevance of intrachain interactions for structural expansion. Using NSE experiments, we observed a high internal flexibility of denatured BSA in addition to center-of-mass diffusion detected by dynamic light scattering. Internal motions measured by NSE were described using concepts based on polymer theory. The contribution of residue-solvent friction was accounted for using the Zimm model including internal friction (ZIF). Disulfide bonds forming loops of amino acids of the peptide backbone have a major impact on internal dynamics that can be interpreted with a reduced set of Zimm modes

    Monomeric Amyloid Beta Peptide in Hexafluoroisopropanol Detected by Small Angle Neutron Scattering - Fig 3

    No full text
    <p>Exemplary structure of Aβ monomers: (a) Aβ<sub>1–42</sub> dHFIP<sub>0.8</sub>D<sub>2</sub>O<sub>0.2</sub> (PDB code 1IYT)[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0150267#pone.0150267.ref020" target="_blank">20</a>] with two α helices from residues Ser8-Gly25 and Lys28-Gly38, which is connected by a type I β-turn. (b) Aβ<sub>1–40</sub> in TFE<sub>0.4</sub>H<sub>2</sub>O<sub>0.6</sub> (PDB code 1AML)[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0150267#pone.0150267.ref021" target="_blank">21</a>] with two α helices from Gln15-Asp23 and from Ile31-Met35 connected with a type I β-turn.</p

    Crowding the Environment of Single-Chain Nanoparticles: A Combined Study by SANS and Simulations

    No full text
    We present an investigation by combining small-angle neutron scattering (SANS) and coarse-grained molecular dynamics (MD) simulations on the conformational properties of single-chain nanoparticles (SCNPs) in crowded macromolecular solutions. By using linear chains as crowders, SANS shows a crossover from almost unperturbed SCNP conformations in dilute conditions toward a continuous collapse of the macromolecule with increasing crowding. This collapse starts when the total concentration of the solution reaches the value of the overlap concentration of the pure SCNP solutions. MD simulations suggest the generalizability of these experimental findings and extend them to the case when the SCNPs themselves are used as crowdersa situation which in real systems leads to unavoidable formation of aggregates, as shown here by SANS and DLS. Exploiting the simulations, we have calculated the contact probability and the distance between monomers as functions of the contour distance between them; the results suggest that crumpled globular conformations are generally adopted by SCNPs in crowded macromolecular solutions. In the case of linear crowders, the SCNPs show, at fixed monomer concentration, a nonmonotonic dependence of their collapse on the length of the crowders

    Time resolved DLS experiment of Aβ<sub>1–42</sub> and Aβ<sub>1–40</sub> in dHFIP.

    No full text
    <p>The samples were measured between 0.5 h and 14 days after initial incubation at 20°C. For Aβ<sub>1–40</sub> the value of <i>τ</i> = 10000 μs is subtracted to focus on the two smaller species. For both samples correlations are normalized to 1 for <b><i>τ</i>→0</b> to get a better overview over the data. Original measurements are found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0150267#pone.0150267.s002" target="_blank">S1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0150267#pone.0150267.s003" target="_blank">S2</a> Figs.</p

    Influence of PEGylation on Domain Dynamics of Phosphoglycerate Kinase: PEG Acts Like Entropic Spring for the Protein

    No full text
    Protein–polymer conjugation is a widely used technique to develop protein therapeutics with improved pharmacokinetic properties as prolonged half-life, higher stability, water solubility, lower immunogenicity, and antigenicity. Combining biochemical methods, small angle scattering (SAXS/SANS), and neutron spin–echo spectroscopy, here we examine the impact of PEGylation (i.e., the covalent conjugation with poly­(ethylene glycol) or PEG) on structure and internal domain dynamics of phosphoglycerate kinase (PGK) to elucidate the reason for reduced activity that is connected to PEGylation. PGK is a protein with a hinge motion between the two main domains that is directly related to function. We find that secondary structure and ligand access to the binding sites are not affected. The ligand induced cleft closing is unchanged. We observe an additional internal motion between covalent bonded PEG and the protein compatible with Brownian motion of PGK in a harmonic potential. Entropic interaction with the full PEG chain leads to a force constant of about 8 pN/nm independent of PEG chain length. This additional force preserves protein structure and has negligible effects on the functional domain dynamics of the protein. PEGylation seems to reduce activity just by acting as a local crowder for the ligands. The newly identified interaction mechanism might open possibilities to improve rational design of protein–polymer conjugates

    Internal Nanosecond Dynamics in the Intrinsically Disordered Myelin Basic Protein

    No full text
    Intrinsically disordered proteins lack a well-defined folded structure and contain a high degree of structural freedom and conformational flexibility, which is expected to enhance binding to their physiological targets. In solution and in the lipid-free state, myelin basic protein belongs to that class of proteins. Using small-angle scattering, the protein was found to be structurally disordered similar to Gaussian chains. The combination of structural and hydrodynamic information revealed an intermediary compactness of the protein between globular proteins and random coil polymers. Modeling by a coarse-grained structural ensemble gave indications for a compact core with flexible ends. Neutron spin–echo spectroscopy measurements revealed a large contribution of internal dynamics to the overall diffusion. The experimental results showed a high flexibility of the structural ensemble. Displacement patterns along the first two normal modes demonstrated that collective stretching and bending motions dominate the internal modes. The observed dynamics represent nanosecond conformational fluctuations within the reconstructed coarse-grained structural ensemble, allowing the exploration of a large configurational space. In an alternative approach, we investigated if models from polymer theory, recently used for the interpretation of fluorescence spectroscopy experiments on disordered proteins, are suitable for the interpretation of the observed motions. Within the framework of the Zimm model with internal friction (ZIF), a large offset of 81.6 ns is needed as an addition to all relaxation times due to intrachain friction sources. The ZIF model, however, shows small but systematic deviations from the measured data. The large value of the internal friction leads to the breakdown of the Zimm model

    Eumelanin Buildup on the Nanoscale: Aggregate Growth/Assembly and Visible Absorption Development in Biomimetic 5,6-Dihydroxyindole Polymerization.

    No full text
    Establishing structure–property relationships in the black insoluble eumelanins, the key determinants of human pigmentation and skin photoprotective system, is a considerable conceptual and experimental challenge in the current drive for elucidation of the biological roles of these biopolymers and their application as advanced materials for organoelectronics. Herein, we report a new breakthrough toward this goal by the first detailed investigation on the nanoscale level of the oxidative polymerization of 5,6-dihydroxyindole (DHI), a model process of eumelanin synthesis. On the basis of a combined use of spectrophotometry, dynamic light scattering (DLS), and small-angle neutron scattering (SANS) investigations, it was possible to unveil the dynamics of the aggregation process before precipitation, the key relationships with visible light absorption and the shape of fundamental aggregates. The results indicated a polymerization mechanism of the type: Polymer<sub><i>n</i></sub> + DHI<sub><i>x</i></sub> = Polymer<sub><i>n</i>+<i>x</i></sub>, where DHI<sub><i>x</i></sub> indicates monomer, dimer, or low oligomers (<i>x</i> ≤ 5). During polymerization, visible absorption increases rapidly, reaching a plateau. Particle growth proceeds slowly, with formation of 2-D structures ∼55 nm thick, until precipitation occurs, that is, when large aggregates with a maximum hydrodynamic radius (<i>R</i><sub>h</sub>) of ∼1200 nm are formed. Notably, markedly smaller <i>R</i><sub>h</sub> values, up to ∼110 nm, were determined in the presence of poly­(vinyl alcohol) (PVA) that was shown to be an efficient aggregation-preventing agent for polymerizing DHI ensuring water solubilization. Finally, it is shown that DHI monomer can be efficiently and partially irreversibly depleted from aqueous solutions by the addition of eumelanin suspensions. This behavior is suggested to reflect oxidant-independent competing pathways of polymer synthesis and buildup <i>via</i> monomer conversion on the active aggregate surface contributing to particle growth. Besides filling crucial gaps in DHI polymerization, these results support the attractive hypothesis that eumelanins may behave as a peculiar example of living biopolymers. The potential of PVA as a powerful tool for solution chemistry-based investigations of eumelanin supramolecular organization and for technological manipulation purposes is underscored

    Small-Angle Neutron Scattering Reveals the Nanostructure of Liposomes with Embedded OprF Porins of Pseudomonas aeruginosa

    No full text
    The use of liposomes as drug delivery systems emerged in the last decades in view of their capacity and versatility to deliver a variety of therapeutic agents. By means of small-angle neutron scattering (SANS), we performed a detailed characterization of liposomes containing outer membrane protein F (OprF), the main porin of the Pseudomonas aeruginosa bacterium outer membrane. These OprF-liposomes are the basis of a novel vaccine against this antibiotic-resistant bacterium, which is one of the main hospital-acquired pathogens and causes each year a significant number of deaths. SANS data were analyzed by a specific model we created to quantify the crucial information about the structure of the liposome containing OprF, including the lipid bilayer structure, the amount of protein in the lipid bilayer, the average protein localization, and the effect of the protein incorporation on the lipid bilayer. Quantification of such structural information is important to enhance the design of liposomal delivery systems for therapeutic applications
    corecore