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Surfactant vesicles containing monomers in the interior of the bilayer were used to template hollow polymer nanocapsules. This study investigated the formation of surfactant/monomer assemblies by two loading methods, concurrent loading and diffusion loading. The assembly process and the resulting aggregates were investigated with dynamic light scattering, small angle neutron scattering, and small-angle X-ray scattering. Acrylic monomers formed vesicles with a mixture of cationic and anionic surfactants in a broad range of surfactant ratios. Regions with predominant formation of vesicles were broader for compositions containing acrylic monomers compared with blank surfactants. This observation supports the stabilization of the vesicular structure by acrylic monomers. Diffusion loading produced monomer-loaded vesicles unless vesicles were composed from surfactants at the ratios close to the boundary of a vesicular phase region on a phase diagram. Both concurrent-loaded and diffusion-loaded surfactant/monomer vesicles produced hollow polymer nanocapsules upon the polymerization of monomers in the bilayer followed by removal of surfactant scaffolds.

Surfactants and hydrophobic monomers spontaneously assemble into vesicles containing monomers within the bilayer. The joint action of monomers and surfactants is essential in this synergistic self-assembly. Polymerization in the bilayer formed hollow polymer nanocapsules.

Lignin, a major polymeric component of plant cell walls, forms aggregates in vivo and poses a barrier to cellulosic ethanol production. Here, neutron scattering experiments and molecular dynamics simulations reveal that lignin aggregates are characterized by a surface fractal dimension that is invariant under change of scale from $~$1--1000 \AA{}. The simulations also reveal extensive water penetration of the aggregates and heterogeneous chain dynamics corresponding to a rigid core with a fluid surface.

Lignocellulosic biomass, which is an abundant renewable natural resource, has the potential to play a major role in the generation of renewable biofuels through its conversion to bioethanol. Unfortunately, it is a complex biological composite material that shows significant recalcitrance, making it a cost-ineffective feedstock for bioethanol production. Small-angle neutron scattering (SANS) was employed to probe the multi-scale structure of cellulosic materials. Cellulose was extracted from milled native switchgrass and from switchgrass that had undergone a dilute acid pretreatment method in order to disrupt the lignocellulose structure. The high-Q structural feature (Q > 0.07 A−1) can be assigned to cellulose fibrils based on a comparison of cellulose purified by solvent extraction of native and dilute acid pretreated switchgrass and a commercial preparation of microcrystalline cellulose. Dilute acid pretreatment results in an increase in the smallest structural size, a decrease in the interconnectivity of the fibrils and no change in the smooth domain boundaries at length scales larger than 1000 A.

The oil/water interfacial assembly of tobacco mosaic virus (TMV) has been studied in situ by tensiometry and small-angle X-ray and neutron scattering (SAXS and SANS). TMV showed different orientations at the perfluorodecalin/water interface, depending on the initial TMV concentration in the aqueous phase. At low TMV concentration, the rods oriented parallel to the interface, mediating the interfacial interactions at the greatest extent per particle. At high TMV concentrations, the rods were oriented normal to the interface, mediating the interfacial interactions and also neutralizing inter-rod electrostatic repulsion. We found that the inter-rod repulsive forces between TMVs dominated the in-plane packing, which was strongly affected by the ionic strength and the bulk solution but not by the pH in the range of pH = 6-8.

An extensive study of the factors that affect the interfacial assembly of bionanoparticles at the oil/water (O/W) interface is reported. Bionanoparticles, such as viruses, have distinctive structural properties due to the unique arrangement of their protein structures. The assembly process of such bionanoparticles at interfaces is governed by factors including the ionic strength and pH of the aqueous layer, concentration of the particles, and nature of the oil phase. This study highlights the impact of these factors on the interfacial assembly of bionanoparticles at the O/W interface using native turnip yellow mosaic virus (TYMV) as the prototype. Robust monolayer assemblies of TYMV were produced by self-assembly at the O/W interface using emulsions and planar interfaces. TYMV maintained its structure and integrity under different assembly conditions. For the emulsion droplets, they were fully covered with TYMV as evidenced by transmission electron microscopy (TEM) and scanning force microscopy (SFM). Tensiometry and small-angle neutron scattering (SANS) further supported this finding. Although the emulsions offered a complete coverage by TYMV particles, they lacked long-range ordering due to rapid exchange at the interface. By altering the assembly process, highly ordered, hexagonal arrays of TYMV were obtained at planar O/W interfaces. The pH, ionic strength, and viscosity of the solution played a crucial role in enhancing the lateral ordering of TYMV assembled at the planar O/W interface. This interfacial ordering of TYMV particles was further stabilized by introduction of a positively charged dehydroabietyl amine (DHAA) in the organic phase which held the assembly together by electrostatic interactions. The long-range array formation was observed using TEM and SFM. The results presented here illustrate that the interfacial assembly at the O/W interface is a versatile approach to achieve highly stable self-assembled structures.

Cytosine nucleobases were successfully incorporated into the side chain of the self-assembling amyloid peptide fragment HHQALVFFA to give ccAQLVFFA. At a pH range of 3-4, where cytosine is expected to be partially protonated, small-angle X-ray scattering analyses revealed the nucleobase peptide assembles to be well-defined nanotubes with an outer diameter of 24.8 nm and wall thicknesses of 3.3 nm. FT-IR and X-ray diffraction confirmed beta-sheet-rich assembly with the characteristic cross-beta architecture of amyloid. The beta-sheet registry, determined by measuring (13)CO-(13)CO backbone distances with solid-state NMR and linear dichroism, placed the cytosine bases roughly perpendicular to the nanotube axis, resulting in a model where the complementary interactions between the cytosine bases increases beta-sheet stacking to give the nanotube architecture. These scaffolds then extend the templates used to encode biological information beyond the nucleic acid duplexes and into covalent networks whose self-assembly is still defined by a precise complementarity of the side-chain registry.

Amino acid cross-strand pairing interactions along a beta-sheet surface have been implicated in protein beta-structural assembly and stability, yet the relative contributions have been difficult to evaluate directly. Here we develop the central core sequence of the Abeta peptide associated with Alzheimer's disease, Abeta(16-22), as an experimental system for evaluating these interactions. The peptide allows for internal comparisons between electrostatic and steric interactions within the beta-sheet and an evaluation of these cross-strand pair contributions to beta-sheet registry. A morphological transition from fibers to hollow nanotubes arises from changes in beta-sheet surface complementarity and provides a convenient indicator of the beta-strand strand registry. The intrinsic beta-sequence and pair correlations are critical to regulate secondary assembly. These studies provide evidence for a critical desolvation step that is not present in most models of the nucleation-dependent pathway for amyloid assembly.

The interface between water and mixed surfactant solutions of CH(3)(CH(2))(19)OH and CF(3)(CF(2))(7)(CH(2))(2)OH in hexane was studied with interfacial tension and X-ray reflectivity measurements. Measurements of the tension as a function of temperature for a range of total bulk surfactant concentrations and for three different values of the molal ratio of fluorinated to total surfactant concentration (0.25, 0.28, and 0.5) determined that the interface can be in three different monolayer phases. The interfacial excess entropy determined for these phases suggests that two of the phases are condensed single surfactant monolayers of CH(3)(CH(2))(19)OH and CF(3)(CF(2))(7)(CH(2))(2)OH. By studying four different compositions as a function of temperature, X-ray reflectivity was used to determine the structure of these monolayers in all three phases at the liquid-liquid interface. The X-ray reflectivity measurements were analyzed with a layer model to determine the electron density and thickness of the headgroup and tailgroup layers. The reflectivity demonstrates that phases 1 and 2 correspond to an interface fully covered by only one of the surfactants (liquid monolayer of CH(3)(CH(2))(19)OH in phase 1 and a solid condensed monolayer of CF(3)(CF(2))(7)(CH(2))(2)OH in phase 2). This was determined by analysis of the electron density profile as well as by direct comparison to reflectivity studies of the liquid-liquid interface in systems containing only one of the surfactants (plus hexane and water). The liquid monolayer of CH(3)(CH(2))(19)OH undergoes a transition to the solid monolayer of CF(3)(CF(2))(7)(CH(2))(2)OH with increasing temperature. Phase 3 and the transition regions between phases 1 and 2 consist of a mixed monolayer at the interface that contains domains of the two surfactants. In phase 3 the interface also contains gaseous regions that occupy progressively more of the interface as the temperature is increased. The reflectivity determined the coverage of the surfactant domains at the interface. A simple model is presented that predicts the basic features of the domain coverage as a function of temperature for the mixed surfactant system from the behavior of the single surfactant systems.

Synchrotron X-ray reflectivity is used to study the electron density as a function of depth through the bulk nitrobenzene-water interface at four different temperatures. The measured interfacial width differs from the predictions of capillary wave theory with a progressively smaller deviation as the temperature is raised. Computer simulations suggest the presence of both molecular layering and dipole ordering parallel to the interface. Either layering or a bending rigidity, that can result from dipole ordering, can explain these measurements.

The interface between bulk water and bulk hexane solutions of n-alkanols (H(CH(2))(m)OH, where m=20, 22, 24, or 30) is studied with x-ray reflectivity, x-ray off-specular diffuse scattering, and interfacial tension measurements. The alkanols adsorb to the interface to form a monolayer. The highest density, lowest temperature monolayers contain alkanol molecules with progressive disordering of the chain from the -CH(2)OH to the -CH(3) group. In the terminal half of the chain that includes the -CH(3) group the chain density is similar to that observed in bulk liquid alkanes just above their freezing temperature. The density in the alkanol headgroup region is 10% greater than either bulk water or the ordered headgroup region found in alkanol monolayers at the water-vapor interface. We conjecture that this higher density is a result of water penetration into the headgroup region of the disordered monolayer. A ratio of 1:3 water to alkanol molecules is consistent with our data. We also place an upper limit of one hexane to five or six alkanol molecules mixed into the alkyl chain region of the monolayer. In contrast, H(CH(2))(30)OH at the water-vapor interface forms a close-packed, ordered phase of nearly rigid rods. Interfacial tension measurements as a function of temperature reveal a phase transition at the water-hexane interface with a significant change in interfacial excess entropy. This transition is between a low temperature interface that is nearly fully covered with alkanols to a higher temperature interface with a much lower density of alkanols. The transition for the shorter alkanols appears to be first order whereas the transition for the longer alkanols appears to be weakly first order or second order. The x-ray data are consistent with the presence of monolayer domains at the interface and determine the domain coverage (fraction of interface covered by alkanol domains) as a function of temperature. This temperature dependence is consistent with a theoretical model for a second order phase transition that accounts for the domain stabilization as a balance between line tension and long range dipole forces. Several aspects of our measurements indicate that the presence of domains represents the appearance of a spatially inhomogeneous phase rather than the coexistence of two homogeneous phases.

X-ray reflectivity is used to study the interaction of C2 domains of cytosolic phospholipase A(2) (cPLA(2)alpha-C2) with a Langmuir monolayer of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) supported on a buffered aqueous solution containing Ca(2+). The reflectivity is analyzed in terms of the known crystallographic structure of cPLA(2)alpha-C2 domains and a slab model representing the lipid layer to yield an electron density profile of the lipid layer and bound C2 domains. This new method of analysis determines the angular orientation and penetration depth of the cPLA(2)alpha-C2 domains bound to the SOPC monolayer, information not available from the standard slab model analysis of x-ray reflectivity. The best-fit orientation places the protein-bound Ca(2+) ions within 1 A of the lipid phosphate group (with an accuracy of +/-3 A). Hydrophobic residues of the calcium-binding loops CBL1 and CBL3 penetrate deepest into the lipid layer, with a 2 A penetration into the tailgroup region. X-ray measurements with and without the C2 domain indicate that there is a loss of electrons in the headgroup region of the lipid monolayer upon binding of the domains. We suggest that this is due to a loss of water molecules bound to the headgroup. Control experiments with a non-calcium buffer and with domain mutants confirm that the cPLA(2)alpha-C2 binding to the SOPC monolayer is Ca(2+)-dependent and that the hydrophobic residues in the calcium-binding loops are critical for membrane binding. These results indicate that an entropic component (due to water loss) as well as electrostatic and hydrophobic interactions contributes to the binding mechanism.

International audience; Transparent wood biocomposites based on PMMA combine high optical transmittance with excellent mechanical properties. One hypothesis is that despite poor miscibility the polymer is distributed at the nanoscale inside the cell wall. Smallangle neutron scattering (SANS) experiments are performed to test this hypothesis, using biocomposites based on deuterated PMMA and "contrast-matched" PMMA. The wood cell wall nanostructure soaked in heavy water is quantified in terms of the correlation distance d between the center of elementary cellulose fibrils. For wood/ deuterated PMMA, this distance d is very similar as for wood/ heavy water (correlation peaks at q ≈ 0.1 Å −1). The peak disappears when contrast-matched PMMA is used, indeed proving nanoscale polymer distribution in the cell wall. The specific processing method used for transparent wood explains the nanocomposite nature of the wood cell wall and can serve as a nanotechnology for cell wall impregnation of polymers in large wood biocomposite structures.

X-ray reflectivity measurements are used to determine the configuration of the C2 domain of protein kinase Calpha (PKCalpha-C2) bound to a lipid monolayer of a 7:3 mixture of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine and 1-stearoyl-2-oleoyl-sn-glycero-3-phosphoserine supported on a buffered aqueous solution. The reflectivity is analyzed in terms of the known crystallographic structure of PKCalpha-C2 and a slab model representation of the lipid layer. The configuration of lipid-bound PKCalpha-C2 is described by two angles that define its orientation, theta = 35 degrees +/- 10 degrees and phi =210 degrees +/- 30 degrees, and a penetration depth (=7.5 +/- 2 A) into the lipid layer. In this structure, the beta-sheets of PKCalpha-C2 are nearly perpendicular to the lipid layer and the domain penetrates into the headgroup region of the lipid layer, but not into the tailgroup region. This configuration of PKCalpha-C2 determined by our x-ray reflectivity is consistent with many previous findings, particularly mutational studies, and also provides what we believe is new molecular insight into the mechanism of PKCalpha enzyme activation. Our analysis method, which allows us to test all possible protein orientations, shows that our data cannot be explained by a protein that is orientated parallel to the membrane, as suggested by earlier work.

Green photosynthetic bacteria adjust the structure and functionality of the chlorosome - the light absorbing antenna complex - in response to environmental stress factors. The chlorosome is a natural self-assembled aggregate of bacteriochlorophyll (BChl) molecules. In this study we report the regulation of the biogenesis of the Chlorobaculum tepidum chlorosome by carbon assimilation in conjunction with temperature changes. Our studies indicate that the carbon source and thermal stress culture of Cba. tepidum grows slower and incorporates less BChl c in the chlorosome. Compared with the chlorosome from other cultural conditions we investigated, the chlorosome from the carbon source and thermal stress culture displays: (a) smaller cross-sectional radius and overall size; (b) simplified BChl c homologues with smaller side chains; (c) blue-shifted Qy absorption maxima and (d) a sigmoid-shaped circular dichroism (CD) spectra. Using a theoretical model we analyze how the observed spectral modifications can be associated with structural changes of BChl aggregates inside the chlorosome. Our report suggests a mechanism of metabolic regulation for chlorosome biogenesis., 32 pages, 14 figures

Small-Angle Neutron Scattering (SANS) is well-suited to study structure and function of protein in solution by exploiting the natural scattering contrast difference between proteins and other biomolecules such as lipids and nucleic acids. The combination of high neutron flux and low experimental background makes the Bio-SANS instrument at ORNL's High Flux Isotope Reactor (HFIR) an ideal tool to study proteins and other biomolecules within complex biological assemblies and composites, in situ and in-vivo. The procedures used for protein solution scattering at the Bio-SANS are presented here. The scattering signal is collected by a newly-developed Linear Position-Sensitive Detector (LPSD), which has a count rate capability of at least one million neutrons per second. It enables the Bio-SANS to utilize the full potential of the intense cold neutron source at HFIR. The detector-to-sample distance is adjustable from ∼1m to ∼15.3m to provide q-range from 0.0009 1/A to 0.7 1/A. The data collected at different distances are corrected against dark current, pixel efficiency, sample transmission and geometry to produce 1D profiles to be merged into a full scattering data set. A calibrated standard sample or direct beam intensity is used to obtain the absolutely scaled intensity of protein scattering. A few examples are presented here to demonstrate the procedure and the capability. They include scattering from protein crowded by another protein, membrane protein in a membrane-mimic environment, etc.