Unraveling the Structural Puzzle of the Giant Glutenin PolymerAn Interplay between Protein Polymerization, Nanomorphology, and Functional Properties in Bioplastic Films

A combination of genotype, cultivation environment, and protein separation procedure was used to modify the nanoscale morphology, polymerization, and chemical structure of glutenin proteins from wheat. A low-polymerized glutenin starting material was the key to protein–protein interactions mainly via SS cross-links during film formation, resulting in extended β-sheet structures and propensity toward the formation of nanoscale morphologies at molecular level. The properties of glutenin bioplastic films were enhanced by the selection of a genotype with a high number of cysteine residues in its chemical structure and cultivation environment with a short grain maturation period, both contributing positively to gluten strength. Thus, a combination of factors affected the structure of glutenins in bioplastic films by forming crystalline β-sheets and propensity toward the ordered nanostructures, thereby resulting in functional properties with high strength, stiffness, and extensibility

Formation of Inverse Topology Lyotropic Phases in Dioleoylphosphatidylcholine/Oleic Acid and Dioleoylphosphatidylethanolamine/Oleic Acid Binary Mixtures

The addition of saturated fatty acids (FA) to phosphatidylcholine lipids (PC) that have saturated acyl chains has been shown to promote the formation of lyotropic liquid-crystalline phases with negative mean curvature. PC/FA mixtures may exhibit inverse bicontinuous cubic phases (<i>Im</i>3<i>m</i>, <i>Pn</i>3<i>m</i>) or inverse topology hexagonal phases (H_II), depending on the length of the acyl chains/fatty acid. Here we report a detailed study of the phase behavior of binary mixtures of dioleoylphosphatidylcholine (DOPC)/oleic acid (OA) and dioleoylphosphatidylethanolamine (DOPE)/oleic acid at limiting hydration, constructed using small-angle X-ray diffraction (SAXD) data. The phase diagrams of both systems show a succession of phases with increasing negative mean curvature with increasing OA content. At high OA concentrations, we have observed the occurrence of an inverse micellar <i>Fd</i>3<i>m</i> phase in both systems. Hitherto, this phase had not been reported for phosphatidylethanolamine/fatty acid mixtures, and as such it highlights an additional route through which fatty acids may increase the propensity of bilayer lipid membranes to curve. We also propose a method that uses the temperature dependence of the lattice parameters of the H_II phases to estimate the spontaneous radii of curvature (<i>R</i>₀) of the binary mixtures and of the component lipids. Using this method, we calculated the <i>R</i>₀ values of the complexes comprising one phospholipid molecule and two fatty acid molecules, which have been postulated to drive the formation of inverse phases in PL/FA mixtures. These are −1.8 nm (±0.4 nm) for DOPC­(OA)₂ and −1.1 nm (±0.1 nm) for DOPE­(OA)₂. <i>R</i>₀ values estimated in this way allow the quantification of the contribution that different lipid species make to membrane curvature elastic properties and hence of their effect on the function of membrane-bound proteins

Experimental Confirmation of Transformation Pathways between Inverse Double Diamond and Gyroid Cubic Phases

A macroscopically oriented double diamond inverse bicontinuous cubic phase (Q_II^D) of the lipid glycerol monooleate is reversibly converted into a gyroid phase (Q_II^G). The initial Q_II^D phase is prepared in the form of a film coating the inside of a capillary, deposited under flow, which produces a sample uniaxially oriented with a ⟨110⟩ axis parallel to the symmetry axis of the sample. A transformation is induced by replacing the water within the capillary tube with a solution of poly­(ethylene glycol), which draws water out of the Q_II^D sample by osmotic stress. This converts the Q_II^D phase into a Q_II^G phase with two coexisting orientations, with the ⟨100⟩ and ⟨111⟩ axes parallel to the symmetry axis, as demonstrated by small-angle X-ray scattering. The process can then be reversed, to recover the initial orientation of Q_II^D phase. The epitaxial relation between the two oriented mesophases is consistent with topology-preserving geometric pathways that have previously been hypothesized for the transformation. Furthermore, this has implications for the production of macroscopically oriented Q_II^G phases, in particular with applications as nanomaterial templates

Experimental Confirmation of Transformation Pathways between Inverse Double Diamond and Gyroid Cubic Phases

A macroscopically oriented double diamond inverse bicontinuous cubic phase (Q_II^D) of the lipid glycerol monooleate is reversibly converted into a gyroid phase (Q_II^G). The initial Q_II^D phase is prepared in the form of a film coating the inside of a capillary, deposited under flow, which produces a sample uniaxially oriented with a ⟨110⟩ axis parallel to the symmetry axis of the sample. A transformation is induced by replacing the water within the capillary tube with a solution of poly­(ethylene glycol), which draws water out of the Q_II^D sample by osmotic stress. This converts the Q_II^D phase into a Q_II^G phase with two coexisting orientations, with the ⟨100⟩ and ⟨111⟩ axes parallel to the symmetry axis, as demonstrated by small-angle X-ray scattering. The process can then be reversed, to recover the initial orientation of Q_II^D phase. The epitaxial relation between the two oriented mesophases is consistent with topology-preserving geometric pathways that have previously been hypothesized for the transformation. Furthermore, this has implications for the production of macroscopically oriented Q_II^G phases, in particular with applications as nanomaterial templates

Effect of Clay Surface Charge on the Emerging Properties of Polystyrene–Organoclay Nanocomposites

A series of polystyrene–clay nanocomposites, based on two natural clay types (Na–Montmorillonite and Hectorite) and two synthetic clays (Laponite and Li–Fluorohectorite), were prepared via in situ intercalative polymerization after surface modification with an organic ammonium cation (CTAB). The structural characteristics of the organically modified clays as well as the nanocomposites were investigated by means of wide-angle X-ray scattering (WAXS), and the thermal properties were studied with TGA. In the organically modified clays, the silicate interlayer spacing increases, and the magnitude seems to be directly correlated with the amount of clay surface charge. In the nanocomposites, polymer intercalation is also observed, but partial exfoliation is present, modifying significantly the morphology of the material. The degree of dispersion of the clay platelets, as well as the resulting properties of the nanocomposites, were found again to be systematically, and almost linearly, correlated with the intrinsic surface charge of the clays, which varied between 44 and 120 meq/100 g. Increased dispersion was seen in the nanocomposites made from clays with low surface charge, here Hectorite and Laponite, suggesting that these can be suitable alternatives to the more employed Montmorillonite for enhancement of thermal properties. The thermal stability was found to be better for the nanocomposites than for the pure polystyrene

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

We show experimentally that gaseous CO₂ 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 CO₂ 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 H₂O, 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 CO₂ 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

Nanostructural Morphology of Plasticized Wheat Gluten and Modified Potato Starch Composites: Relationship to Mechanical and Barrier Properties

In the present study, we were able to produce composites of wheat gluten (WG) protein and a novel genetically modified potato starch (MPS) with attractive mechanical and gas barrier properties using extrusion. Characterization of the MPS revealed an altered chain length distribution of the amylopectin fraction and slightly increased amylose content compared to wild type potato starch. WG and MPS of different ratios plasticized with either glycerol or glycerol and water were extruded at 110 and 130 °C. The nanomorphology of the composites showed the MPS having semicrystalline structure of a characteristic lamellar arrangement with an approximately 100 Å period observed by small-angle X-ray scattering and a B-type crystal structure observed by wide-angle X-ray scattering analysis. WG has a structure resembling the hexagonal macromolecular arrangement as reported previously in WG films. A larger amount of β-sheets was observed in the samples 70/30 and 30/70 WG-MPS processed at 130 °C with 45% glycerol. Highly polymerized WG protein was found in the samples processed at 130 °C versus 110 °C. Also, greater amounts of WG protein in the blend resulted in greater extensibility (110 °C) and a decrease in both E-modulus and maximum stress at 110 and 130 °C, respectively. Under ambient conditions the WG-MPS composite (70/30) with 45% glycerol showed excellent gas barrier properties to be further explored in multilayer film packaging applications