Bulk cellulose plastic materials from processing cellulose powder using back pressure-equal channel angular pressing

Bulk cellulose plastic materials with a continuous morphology were successfully processed from cellulose powder through back pressure-equal channel angular pressing (BP-ECAP) at 150 °C without using any additives. The strong shear deformation during the process caused an efficient deformation of cellulose granular and crystalline structures, resulting in effective chain penetration and strong intermolecular interactions throughout the whole material. The mechanical behaviour of the cellulose plastics was comparable to those of polymer/cellulose composites. Ball milling the cellulose powder prior to processing disrupted the crystalline structures thus resulting in more significant modifications of the molecular motions of the cellulose. The outcome of this research provides a potential methodology for manufacturing renewable and biodegradable bulk materials from cellulose-based agricultural waste.     

Intermolecular interactions and phase structures of plasticized wheat proteins materials

The intermolecular interactions and phase structures of thermally processed wheat proteins with glycerol and water as plasticizers were studied by dynamic mechanical analysis and solid-state high-resolution NMR spectroscopy. The results of phase structures at scales of molecular level to tens of nanometers were correlated with the mechanical properties of the materials. The strong hydrogen bonding intermolecular interactions between the components in wheat proteins and the plasticizers resulted in a significant change in molecular motions of wheat protein materials. The plasticized systems, however, still presented a wide distribution of chain mobility at a scale from the molecular level to 20-30 nm, and the plasticizing effect was different for each wheat protein system. High protein content systems tended to be plasticized relatively easily especially when lipid content is high, but the existence of residual starch would require more plasticizers to reach a similar level of chain mobility. On a scale of 20-30 nm, plasticized vital wheat gluten (WG) and the deamidated wheat proteins (WP-I) were heterogeneous with each component exhibiting its individual mobility, whereas the plasticized insoluble protein system (WP-II) with poor mechanical properties was homogeneous. Both WG and WP-I systems showed excellent mechanical polymeric properties in tensile strength and elasticity despite the heterogeneity. The strong intermolecular hydrogen bonding interactions and soluble protein components in the materials could provide an adhesion among different components and act as a continuous matrix in the systems. Therefore, these materials displayed excellent mechanical properties via coordination effects among different components.     

Solvent effects on the viscoelastic behavior of porcine submaxillary mucin

Rheological methods have been used to investigate the intermolecular interactions of porcine submaxillary mucins (PSM) in solution. PSM is a high molecular weight glycoprotein consisting of a linear, semi-flexible protein backbone to which a large number of oligosaccharides (1–5 saccharide units) are attached as side chains. Concentrated aqueous solutions of PSM containing different amounts of guanidine hydrochloride (GdnHCl) were subjected to both controlled stress and controlled strain rheological analyses. In the absence of GdnHCl, PSM solutions exhibit viscoelastic properties characteristic of a gel: the storage modulus, G′, is much larger than the loss modulus, G″, at all deformation frequencies, and the compliance is 100% recoverable at small stresses, indicative of strong intermolecular interactions. In 3.0 M aqueous GdnHCl, PSM forms a viscoelastic solution, with G″ > G′ at all frequencies and a relatively small recoverable compliance, pointing to disruption of the intermolecular interactions by the chaotropic salt. Intermediate behavior is observed in 1.5 M GdnHCl, characteristic of a marginal gel: G′ ≈ G″ and greater than 50% recoverable compliance. In dilute solution, PSM behaves viscoelastically as a typical polyelectrolyte. However, concentrated solutions are turbid, the turbidity decreasing as GdnHCl is added, indicating that extensive intermolecular association accompanies the gelation process. The results show that although PSM is secreted in nature as a viscous solution, it can form gels that are similar to those of tracheobronchial and gastric mucins, and suggest common features to the gelation mechanism, with the strength of the gel correlated with the length of the oligosaccharide side chains.     

Study on the molecular models commonly used in the simulation of dilute polymeric solutions in flow

Three molecular models, commonly used in the simulation of polymeric solutions and melts were employed to describe the rheological behaviour of dilute, elastic and constant viscosity solution formed by bead-and-bond chain molecules immersed into a soft-sphere solvent. The intermolecular interactions for the three models were calculated by the Lennard-Jones potential. The differences amongst the models proceeded from the intramolecular restrictions: the simplest one is a Freely-Joined-Chain (FJC) model with harmonic bond potentials, in the second model bonds are restricted by a finite extensible non-linear elastic (FENE) potential plus a repulsive WCA potential, and the third model is conformed by the United Atom (UA) approach which includes bond, flexion and torsion potentials. Both Couette and Poiseuille flows were simulated using Non-Equilibrium Molecular Dynamics. Deformation displayed by the three chain models; defined in terms of their radius of gyration was calculated and according to results it was found that for Couette flow, the three chains exhibit similar response to deformation. In Poiseulle flow, the FJC and FENE models behave similarly but the UA model presents a larger resistance to deformation. For both flow regimes, the forces involved to deform the chains were estimated in terms of the first normal stress differences. From these estimations it was found that the UA model depicted the stiffest chain, followed by the FENE model, and last the FJC model.     

Effect of vibration on the structure and properties of polymer membranes

The structural memory effect in a wave field has been studied by IR spectroscopy using butadiene-styrene and acrylic latex blend films as polymer membrane models. Notable is the enhancement of interactions between phases in such systems, which can cause changes in their local and translational mobility. The response of disperse polymer systems and their composites to nonlinear vibrations means that their deformation properties are affected by vibration, by analogy with orientation phenomena in solid polymers (where the Rebinder effect can appear), and can be considered as a means for modifying polymers, including the manufacture of nanocomposites, polymer biocarriers, etc.     

Effects of backbone and side chain on the molecular environments of chiral cavities in polysaccharide-based biopolymers

The effects of the backbone and side chain on the molecular environments in the chiral cavities of three commercially important polysaccharide-based chiral sorbents--cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC), amylose tris(3,5-dimethylphenylcarbamate) (ADMPC), and amylose tris[(S)-alpha-methylbenzylcarbamate] (ASMBC)--are studied by attenuated total reflection infrared spectroscopy (ATR-IR), X-ray diffraction (XRD), 13C cross-polarization/magic-angle spinning (CP/MAS) and MAS solid-state NMR, and density functional theory (DFT) modeling. These sorbents are used widely in preparative-scale chiral separations. ATR-IR is used to determine how the H-bonding states of the C=O and NH groups of the polymer depend on the backbone and side chain. The changes in the polymer crystallinity are characterized with XRD. The changes in the polymer helicity and molecular mobility for polymer-coated silica beads (commercially called Chiralcel OD, Chirapak AD, and Chiralpak AS) are probed with 13C CP/MAS and MAS solid-state NMR. The IR wavenumbers and the NMR chemical shifts for the polymer backbone monomers and dimers and the side chains are predicted at the DFT/B3LYP/6-311+g(d,p) level of theory. It is concluded that the molecular environments of the C=O, NH, and phenyl groups show significant differences in intramolecular and intermolecular interactions and in the nanostructures of the chiral cavities of these biopolymers. These results have implications for understanding how the molecular environments of chiral cavities of these polymers affect their molecular recognition mechanisms.     

Effect of protonation and hydrogen bonding on 2, 4, 6-substituted pyrimidine and its salt complex-experimental and theoretical evidence

The short-range properties of alkylpiperazine ionic liquids paired with propionate and lactate anions were analyzed and their affinity for CO₂ molecules studied using density functional theory. Anion–cation interactions led to the development of strong intermolecular hydrogen bonding through the cation amine position, as confirmed through variations in structural and vibrational properties upon pair formation. Topological analysis via the atoms-in-molecules approach revealed the development of intense bond and ring critical points in the intermolecular regions, which is in agreement with charge transfer from lone pairs in anion oxygen atoms of carboxylate groups through antibonding orbitals in cation amine groups. Such anion–cation interactions are weakly dependent on cation alkyl chain length but are remarkably affected by the presence of an anion hydroxyl group. Interactions with CO₂ molecules are stronger for anions than for cations, especially for propionate anions, and are also affected strongly by the anion hydroxyl group.     

The properties of natural silk fibers: deformation study and NMR data

Natural silk (Bombyx mori) fibers with low humidity (0.07 g H2O/g dried silk) after temperature influence were studied for mechanical longitudinal deformation. On the basis of the stress-strain curves, some estimates of tensile properties for silk fibers were obtained. It was found that the maximal tension (sigma(max) in tensile-linear field of deformation of silk fibers decreases with increasing fiber diameter. The results showed that the heating of fibers (100 degrees C) results in a diminishing of the sigma(max)-value. Scanning electron microscopy pictures for cross section and longitudinal fiber surface were obtained. Natural silk fibers were studied by the NMR relaxation method (free induction decay curves) and the second moments of NMR-line shape in silk samples were calculated. The intra- and intermolecular contributions into the second moment were analyzed. The results showed a strong interaction of water molecules with macromolecules and a low molecular mobility. Some characteristics of interactions between silk macromolecules and water molecules as well as the role of intermolecular links in the change of the structure-function properties of natural silk under the action of external factors are discussed.     

Comparison of membrane organization in mitochondria from yeast and rat liver by nuclear magnetic resonance spectroscopy

Summary Proton magnetic resonance (PMR) and carbon-13 magnetic resonance (CMR) spectra of intact, unsonicated yeast and rat liver motochondria show differences which may be correlated with the composition of the membranes. High resolution PMR and CMR signals in intact yeast mitochondria have been assigned to regions of fluid lipid-lipid interaction on the basis of spectra of extracted lipid and protein, and the temperature dependence of NMR signals from the intact membrane. PMR spectra suggest that about 20% of total yeast phospholipid is in regions where both intramolecular fatty acid chain mobility and lateral diffusion of entire phospholipid molecules are possible. No such regions appear to exist in rat liver mitochondria. For both yeast and rat liver mitochondria, comparison of PMR and CMR spectra suggests that about 50% of phospholipid appears to be in regions where intramolecular fatty acid chain motion is considerable, but lateral diffusion is restricted. The remaining phospholipid appears to have little inter- or intramolecular mobility. Since NMR observation of lipid extracts from membranes indicates that phospholipid-sterol interactions do not account for the spectra of intact mitochondria, these effects are interpreted in terms of extensive lipid-protein interactions.     

The formation of strong intermolecular interactions in immiscible blends of poly(vinyl alcohol) (PVA) and lignin

The intermolecular interactions of lignin with a hydrophilic polymer, poly(vinyl alcohol) (PVA), were studied using thermal analyses and FT-IR spectroscopy of a series of PVA/hardwood kraft lignin blend fibers prepared by thermal extrusion. Although two phases are observed in this blend system, some of the lignin was closely associated with the PVA in the PVA-rich phase. The crystallinity of the PVA fraction was reduced with increasing lignin content. An interaction energy density of -9.34 cal cm(-1), calculated from melting point depression data, suggests that strong intermolecular interactions exist between PVA and lignin. FT-IR analysis indicates the formation of strong intermolecular hydrogen bonds between the hydroxyl groups of PVA and lignin. Although the PVA/lignin blend system is immiscible in the bulk, the results herein show the existence of some specific intermolecular interaction between PVA and lignin.     

Unusual rheological properties of a new associative polysaccharide in salt media

New amphiphilic polysaccharides based on alginate-grafted-Poly (ε-caprolactone) or alg-g-PCL bearing two kinds of PCL chains with different molar masses (1250 and 530 gmol⁻¹) with various amounts from 3% to 15% were prepared. Rheological properties in aqueous solutions of such systems have been investigated as a function of polymer concentration, added salt and temperature in semi-dilute regime. Strong hydrophobic intermolecular associations were clearly demonstrated in pure water whatever the PCL chain length and extend of modification. Increasing polymer concentration, grafting rate and/or PCL chains length can lead to a structured liquid behaviour. Rheological properties of the most organized system have been found independent to the temperature (until 60 °C). In salt media, a strong dependence of hydrophobic interactions to the length of PCL chains was observed. For M_PCL = 1250 g.mol⁻¹ the screening of charges promotes the establishment of intermolecular interactions and leads to a strong physical gel for the highest grafting rates. For M_PCL = 530 g mol⁻¹, ionic strength leads to a decrease of rheological properties when increasing grafting rate. This result may indicate an increase of hydrophobic clusters even in the entangled regime. This unusual behaviour opens the ways for the preparation of suitable hydrogels for drug release.     

Thermal mobility of β-O-4-type artificial lignin

Several lignin model polymers and their derivatives comprised exclusively of β-O-4 or 8-O-4' interunitary linkages were synthesized to better understand the relation between the thermal mobility of lignin, in particular, thermal fusibility and its chemical structure; an area of critical importance with respect to the biorefining of woody biomass and the future forest products industry. The phenylethane (C6-C2)-type lignin model (polymer 1) exhibited thermal fusibility, transforming into the rubbery/liquid phase upon exposure to increasing temperature, whereas the phenylpropane (C6-C3)-type model (polymer 2) did not, forming a char at higher temperature. However, modifying the Cγ or 9-carbon in polymer 2 to the corresponding ethyl ester or acetate derivative imparted thermal fusibility into this previously infusible polymer. FT-IR analyses confirmed differences in hydrogen bonding between the two model lignins. Both polymers had weak intramolecular hydrogen bonds, but polymer 2 exhibited stronger intermolecular hydrogen bonding involving the Cγ-hydroxyl group. This intermolecular interaction is responsible for suppressing the thermal mobility of the C6-C3-type model, resulting in the observed infusibility and charring at high temperatures. In fact, the Cγ-hydroxyl group and the corresponding intermolecular hydrogen bonding interactions likely play a dominant role in the infusibility of most native lignins.     

Chemical relaxation of co-operative conformational transitions of linear biopolymers

The kinetics and chemical relaxation of co-operative conformational changes of linear (bio)polymers (e.g. helix-coil transitions of polypeptides) are discussed on the basis of the linear ISING model. Chemical relaxation is in general shown to be described by 4N−5 relaxation times if the polymer chain consists of N elementary reaction sites. It is pointed out that nevertheless substantial simplifications of the theory can be achieved in many special cases of practical interest. Sufficiently short chains exhibit first-order kinetics resulting in a single relaxation time whereas for certain medium chain lengths zero-order kinetics plays a principal role in the relaxation process. For the particularly interesting case of very long chains a set of four relaxation equations is derived. The corresponding relaxation times are calculated assuming strong co-operativity and slow nucleation rates. However, it is almost exclusively the largest one of these relaxation times which actually controls the conformational change as turns out by means of a new approach to compute amplitude factors.     

Mechanical denaturation of globular protein in the solid state

A method for taking stress-strain diagrams in microsamples prepared from glutaraldehyde-treated monocrystals and amorphous films of hen egg-white lysozyme has been developed. Analysis of the diagrams has shown that the deformation obeys Hooke's law within 0-2%. Upon further deformation of a crystalline sample (up to 6-10%), when a critical stress, sigma(cr), is reached, the protein molecules in the sample denature and become greatly extended. Depending on the crystal type and crystallographic direction, the sample length increases 2-4 times. The critical stress is essentially dependent on the factors affecting intra- and intermolecular interactions: temperature, hydration level and urea concentration. Mechanisms for mechanical denaturation are proposed.     

Molecular motion of spin labeled side chains in the C-terminal domain of RGL2 protein: a SDSL-EPR and MD study

Five singly spin labeled side chains at surface sites in the C-terminal domain of RGL2 protein have been analyzed to investigate the general relationship between nitroxide side chain mobility and protein structure. At these sites, the structural perturbation produced by replacement of a native residue with a nitroxide side chain appears to be very slight at the level of the backbone fold. The primary determinants of the nitroxide side chain mobility are backbone dynamics and tertiary interactions. On the exposed surfaces of alpha-helices, the side chain mobility is not restricted by tertiary interactions but appears to be determined by backbone dynamics, while in loop sites, the side chain mobility is even higher. For a better understanding of the changes in the EPR spectral line shape, molecular dynamics simulations were performed and found in agreement with EPR spectral data.     

The use of liquid polyacrylamide in electrophoresis: III. Properties of liquid polyacrylamide in the presence of cellulose acetate

Solutions of uncross-linked liquid polyacrylamide (LPA) stabilized by cellulose acetate are shown to represent efficient molecular sieves for RNA and for sodium dodecyl sulfate-protein complexes. Endosmosis and evaporation have to be considered to obtain corrected estimates of mobilities of the macro-ions. The efficiency of molecular sieving is strongly influenced by the chain length of the single polymer molecules. This can be shown both in terms of the steepness of the relationship between logarithm of molecular weight and mobility and in the relationship between log (K_R) and log molecular weight. Comparable chain length effects are found in cross-linked polyacrylamide, suggesting a common mechanism of action of the two electrophoretic sieving media. The correlation of polymer viscosity and of the impedance towards migration of macro-ions, as demonstrated by LPA-electrophoresis, suggests the participation of hydrodynamic interactions in the molecular sieving process.     

Binding of cationic conjugated polymers to DNA: atomistic simulations of adducts involving the Dickerson's dodecamer

We here describe the investigation at the atomistic level of the structure, stability, and dynamics of several complexes resulting from the interaction of oxidized poly(3,4-ethylenedioxythiophene) with the well-known Dickerson's dodecamer sequence. Four specific arrangements have been selected as referential structures for molecular dynamics simulations, and the resulting independent trajectories tend to converge in two distinguishable models with the strongest interactions. The first one presents a coiled DNA strand enveloping the oligomer chain, whereas in the second model, the conducting polymer chain and the disorganized DNA strand are facing side-by-side. Analysis of the intermolecular interactions indicates that the electrostatic interactions involving the negatively charged DNA phosphates and the positively charged units of the oligomer are much more frequent in the first model. In addition, aside from these electrostatic interactions, specific O · · · H and S · · · H hydrogen bonds, π-π stacking, and N-H · · · π interactions have been detected. Among all of these four specific interactions, we show that the π-π stacking is the most abundant and shows the best stability, whereas O · · · H hydrogen bonds are also frequent with long lifetimes. At the end, we have to underline that these specific interactions are predominant for the thymine and the guanine, which is in perfect agreement with previous experimental observations.     

Effect of pressure on islet amyloid polypeptide aggregation: revealing the polymorphic nature of the fibrillation process

Type II diabetes mellitus is a disease which is characterized by peripheral insulin resistance coupled with a progressive loss of insulin secretion that is associated with a decrease in pancreatic islet beta-cell mass and the deposition of amyloid in the extracellular matrix of beta-cells, which lead to islet cell death. The principal component of the islet amyloid is a pancreatic hormone called islet amyloid polypeptide (IAPP). High-pressure coupled with FT-IR spectroscopic and AFM studies were carried out to elucidate further information about the aggregation pathway as well as the aggregate structures of IAPP. To this end, a comparative fibrillation study of IAPP fragments was carried out as well. As high hydrostatic pressure (HHP) is acting to weaken or even prevent hydrophobic self-organization and electrostatic interactions, application of HHP has been used as a measure to reveal the importance of these interactions in the fibrillation process of IAPP and its fragments. IAPP preformed fibrils exhibit a strong polymorphism with heterogeneous structures, a large population of which are rather sensitive to high hydrostatic pressure, thus indicating a high percentage of ionic and hydrophobic interactions and loose packing of these species. Conversely, fragments 1-19 and 1-29 are resistant to pressure treatment, suggesting more densely packed aggregate structures with less void volume and strong cooperative hydrogen bonding. Furthermore, the FT-IR data indicate that fragment 1-29 has intermolecular beta-sheet conformational properties different from those of fragment 1-19, the latter exhibiting polymorphic behavior with more disordered structures and less strongly hydrogen bonded fibrillar assemblies. The data also suggest that hydrophobic interactions and/or less efficient packing of amino acids 30-37 region leads to the marked pressure sensitivity observed for full-length IAPP.     

Simulations of the erythrocyte cytoskeleton at large deformation. I. Microscopic models.

Three variations of a polymer chain model for the human erythrocyte cytoskeleton are used in large deformation simulations of microscopic membrane patches. Each model satisfies an experimental observation that the contour length of the spectrin tetramers making up the erythrocyte cytoskeleton is roughly square root of 7 times the end-to-end distance of the tetramer in vivo. Up to modest stress, each brushy cytoskeletal network behaves, consistently, like a low-temperature, planar network of Hookean springs, with a model-dependent effective spring constant, keff, in the range of 20-40 kBT/s(o)2, where T is the temperature and s(o) is the force-free spring length. However, several features observed at large deformation distinguish these models from spring networks: 1) Network dimensions do not expand without bound in approaching a critical isotropic tension (square root of 3 keff) that is a characteristic limit of Hookean spring nets. 2) In surface compression, steric interactions among the chain elements prevent a network collapse that is otherwise observed in compression of planar triangulated networks of springs. 3) Under uniaxial surface tension, isotropy of the network disappears only as the network is stretched by more than 50% of its equilibrium dimensions. Also found are definitively non-Hookean regimes in the stress dependence of the elastic moduli. Lastly, determinations of elastic moduli from both fluctuations and stress/strain relations prove to be consistent, implying that consistency should be expected among experimental determinations of these quantities.     

pH effect on the mechanical performance and phase mobility of thermally processed wheat gluten-based natural polymer materials

The mechanical properties, phase composition, and molecular motions of thermally processed wheat gluten- (WG-) based natural polymer materials were studied by mechanical testing, dynamic mechanical analysis (DMA), and solid-state NMR spectroscopy. The performance of the materials was mainly determined by the denaturization and cross-linking occurring in the thermal processing and the nature or amount of plasticizers used. The pH effect also played an important role in the materials when water was used as the only plasticizer (WG-w). Alkaline conditions modified the chemical structure of WG, possibly via deamidation; enhanced the thermal cross-linking of WG macromolecules to form a more stable aggregation structure; and promoted intermolecular interactions between water and all components in WG (proteins, starch, and lipid), resulting in a strong adhesion among different components and phases. The saponification of lipid under alkaline conditions also enhanced the hydrophilicity of lipid and the miscibility among lipid, water, and WG components. However, when glycerol was used with water as a plasticizer (WG-wg), the phase mobility and composition of the materials mainly depended on the content of glycerol when the water content was constant. During thermal processing under either acidic or alkaline conditions, glycerol was unlikely to thermally cross-link with WG as suggested previously. The advanced mechanical performance of the WG-wg materials was attributed to the nature of hydrogen-bonding interactions between glycerol and WG components in the materials. This caused the whole material to behave like a strengthened "cross-linked" structure at room temperature due to the low mobility of glycerol. The pH effect on phase mobility and compositions of WG-wg systems was not as significant as that for WG-w materials.