Tomás S. Plivelic

The yellow mini-hutch for SAXS experiments at MAX IV Laboratory

I911-SAXS is the new SAXS (Small-Angle-X-ray-Scattering) beamline at the MAX IV Laboratory in Lund, Sweden. It is one of the 5 stations of the hard X-ray Cassiopeia beamline (I911) at the 1.5 GeV ring MAX II. I911-4 was converted into a multipurpose SAXS station which opened to the scientific community in May 2011. The SAXS users community at this laboratory comes from diverse fields of research with different needs and requirements at the end-station. This results in different set-ups routinely being installed in the easy-accessible experimental mini-hutch. The beam can be focused at sample-to-detector distances between a few hundred millimetres and more than two meters. This versatility permits a selection of q-ranges between 0.006 A−1 and 2 A−1. The recent acquisition of a fast readout, low noise pixel detector (PILATUS 1M) and the implementation of a hight-throughput solution SAXS are the latest beamline upgrades.

Wheat gluten polymer structures : The impact of genotype environment and processing on their functionality in various applications

ABSTRACT For a number of applications, gluten protein polymer structures are of the highest importance in determining end-use properties. The present article focuses on gluten protein structures in the wheat grain, genotype- and environment-related changes, protein structures in various applications, and their impact on quality. Protein structures in mature wheat grain or flour are strongly related to end-use properties, although influenced by genetic and environment interactions. Nitrogen availability during wheat development and genetically determined plant development rhythm are the most important parameters determining the gluten protein polymer structure, although temperature during plant development interacts with the impact of the mentioned parameters. Glutenin subunits are the main proteins incorporated in the gluten protein polymer in extracted wheat flour. During dough mixing, gliadins are also incorporated through disulfide-sulfhydryl exchange reactions. Gluten protein polymer size and complexi...

Molecular structure of citric acid cross-linked starch films

The effect of citric acid (CA) on starch films has been examined. A new method to detect cross-linking of starch by CA in solution-cast films by molecular weight measurements is described. Furthermore, we managed to distinguished between free, mono- and di-esterified CA and quantify di-ester content within starch films by using a modification in the method of complexometric titration with copper(II)-sulfate. Cross-linking of starch by CA occurred at low temperature, 70°C, which we assumed is so far the lowest temperature reported where cross-linking reaction occurred. This is essential for starch coating applications within paper industry since no high temperatures for curing will be required. However, curing at 150°C and high CA concentrations, 30 pph, increased cross-linking reaction. Furthermore, the physical properties like water solubility, gel content and glass transition temperature, were highly reflected by changes in the molecular structure i.e. cross-linking and hydrolysis, as well as CA content and curing temperature.

Structure and morphology of wheat gluten films: from polymeric protein aggregates toward superstructure arrangements.

Evaluation of structure and morphology of extruded wheat gluten (WG) films showed WG protein assemblies elucidated on a range of length scales from nano (4.4 Å and 9 to 10 Å, up to 70 Å) to micro (10 μm). The presence of NaOH in WG films induced a tetragonal structure with unit cell parameters, a = 51.85 Å and c = 40.65 Å, whereas NH(4)OH resulted in a bidimensional hexagonal close-packed (HCP) structure with a lattice parameter of 70 Å. In the WG films with NH(4)OH, a highly polymerized protein pattern with intimately mixed glutenins and gliadins bounded through SH/SS interchange reactions was found. A large content of β-sheet structures was also found in these films, and the film structure was oriented in the extrusion direction. In conclusion, this study highlights complexities of the supramolecular structures and conformations of wheat gluten polymeric proteins in biofilms not previously reported for biobased materials.

Rod Packing in Chiral Nematic Cellulose Nanocrystal Dispersions Studied by Small-Angle X-ray Scattering and Laser Diffraction

The packing of cellulose nanocrystals (CNC) in the anisotropic chiral nematic phase has been investigated over a wide concentration range by small-angle X-ray scattering (SAXS) and laser diffraction. The average separation distance between the CNCs and the average pitch of the chiral nematic phase have been determined over the entire isotropic-anisotropic biphasic region. The average separation distances range from 51 nm, at the onset of the anisotropic phase formation, to 25 nm above 6 vol % (fully liquid crystalline phase) whereas the average pitch varies from ≈15 μm down to ≈2 μm as ϕ increases from 2.5 up to 6.5 vol %. Using the cholesteric order, we determine that the twist angle between neighboring CNCs increases from about 1° up to 4° as ϕ increases from 2.5 up to 6.5 vol %. The dependence of the twisting on the volume fraction was related to the increase in the magnitude of the repulsive interactions between the charged rods as the average separation distance decreases.

Intercalation and Retention of Carbon Dioxide in a Smectite Clay promoted by Interlayer Cations

A good material for CO2 capture should possess some specific properties: (i) a large effective surface area with good adsorption capacity, (ii) selectivity for CO2, (iii) regeneration capacity with minimum energy input, allowing reutilization of the material for CO2 adsorption, and (iv) low cost and high environmental friendliness. Smectite clays are layered nanoporous materials that may be good candidates in this context. Here we report experiments which show that gaseous CO2 intercalates into the interlayer nano-space of smectite clay (synthetic fluorohectorite) at conditions close to ambient. The rate of intercalation, as well as the retention ability of CO2 was found to be strongly dependent on the type of the interlayer cation, which in the present case is Li+, Na+ or Ni2+. Interestingly, we observe that the smectite Li-fluorohectorite is able to retain CO2 up to a temperature of 35°C at ambient pressure, and that the captured CO2 can be released by heating above this temperature. Our estimates indicate that smectite clays, even with the standard cations analyzed here, can capture an amount of CO2 comparable to other materials studied in this context.

A Multitechnique Study of Structure and Dynamics of Polyfluorene Cast Films and the Influence on Their Photoluminescence

This article describes the microstructure and dynamics in the solid state of polyfluorene-based polymers, poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO), a semicrystalline polymer, and poly[(9,9-dioctyl-2,7-divinylene-fluorenylene)-alt-co-{2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene}, a copolymer with mesomorphic phase properties. These structures were determined by wide-angle X-ray scattering (WAXS) measurements. Assuming a packing model for the copolymer structure, where the planes of the phenyl rings are stacked and separated by an average distance of approximately 4.5 A and laterally spaced by about approximately 16 A, we followed the evolution of these distances as a function of temperature using WAXS and associated the changes observed to the polymer relaxation processes identified by dynamical mechanical thermal analysis. Specific molecular motions were studied by solid-state nuclear magnetic resonance. The onset of the side-chain motion at about 213 K (beta-relaxation) produced a small increase in the lateral spacing and in the stacking distance of the phenyl rings in the aggregated structures. Besides, at about 383 K (alpha-relaxation) there occurs a significant increase in the amplitude of the torsion motion in the backbone, producing a greater increase in the stacking distance of the phenyl rings. Similar results were observed in the semicrystalline phase of PFO, but in this case the presence of the crystalline structure affects considerably the overall dynamics, which tends to be more hindered. Put together, our data explain many features of the temperature dependence of the photoluminescence of these two polymers.

Swelling transition of a clay induced by heating.

Clays are of paramount importance for soil stability, but also in applications ranging from oil recovery to composites and hydrogels. Generically, clays are divided into two subclasses: macroscopically swelling, ‘active’ clays that have the capacity for taking up large amounts of water to form stable gels, and ‘passive’ or non-swelling clays; the former stabilize soils whereas the latter are known to lead to landslides. However, it has been unclear so far what mechanisms underlie clay swelling. Here, we report the first observation of a temperature-induced transition from a passive to an active, swelling clay. We propose a simple description of the swelling transition; while net attractive interactions are dominant at low temperatures so that the clay particles remain attached to each other in stacks, at higher temperatures it is energetically favourable for the clay to swell due to the entropy that is gained by counterions which are liberated during swelling.

X-ray Studies of Carbon Dioxide Intercalation in Na-Fluorohectorite Clay at Near-Ambient Conditions

We show experimentally that gaseous CO(2) intercalates into the interlayer space of the synthetic smectite clay Na-fluorohectorite at conditions not too far from ambient. The mean interlayer repetition distance of the clay when CO(2) is intercalated is found to be 12.5 Å for the conditions -20 °C and 15 bar. The magnitude of the expansion of the interlayer upon intercalation is indistinguishable from that observed in the dehydrated-monohydrated transition for H(2)O, but the possibility of water intercalation is ruled out by a careful analysis of the experimental conditions and repeating the measurements exposing the clay to nitrogen gas. The dynamics of the process is observed to be dependent on the pressure, with a higher intercalation rate at increased pressure. The rate of CO(2) intercalation at the studied conditions is found to be several orders of magnitude slower than the intercalation rate of water or humidity at ambient pressure and temperature.

Structural architecture and solubility of native and modified gliadin and glutenin proteins: non-crystalline molecular and atomic organization

Wheat gluten (WG) and its components, gliadin and glutenin proteins, form the largest polymers in nature, which complicates the structural architecture of these proteins. Wheat gluten, gliadin and glutenin proteins in unmodified form showed few secondary structural features. Structural modification of these proteins using heat, pressure and the chemical chaperone glycerol resulted in a shift to organized structure. In modified gliadin, nano-structural molecular arrangements in the form of hexagonal closed packed (HCP) assemblies with lattice parameter of (58 A) were obvious together with development of intermolecular disulphide bonds. Modification of glutenin resulted in highly polymerized structure with proteins linked not only by disulphide bonds, but also with other covalent and irreversible bonds, as well as the highest proportion of β-sheets. From a combination of experimental evidence and protein algorithms, we have proposed tertiary structure models of unmodified and modified gliadin and glutenin proteins. An increased understanding of gliadin and glutenin proteins structure and behavior are of utmost importance to understand the applicability of these proteins for various applications including plastic materials, foams, adhesives, films and coatings.