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Polysaccharide gels assembled from the anionic biopolymers pectin and carrageenan have been studied using transmission electron microscopy (TEM). Gels were formed in several different ways: for pectin, hydrogen bonding was used to form junction zones between strands, whereas for carrageenan systems, several different ion types were used to form ionotropic networks. Using this approach, several distinct network architectures were realized. In addition to preparing gelled samples for electron microscopy, a set of samples was taken without performing the additional treatment necessitated by the TEM measurements, and these were studied directly by small-angle X-ray scattering (SAXS). Taking careful consideration of the relative merits of different image sizes and available processing techniques, the real-space images acquired by TEM were used via radial integration of the Fourier transform to produce simulated scattering patterns. These intensity-versus-wavevector plots were compared with the results of SAXS experiments carried out on the unadulterated gels using synchrotron radiation. Although information regarding chain thicknesses and flexibilities was found to be modified by labeling and changes in the dielectric constant and mechanical properties of the surroundings in the TEM, the studies carried out here show that careful protocols can produce data sets where information acquired above ∼20 nm is broadly consistent with that obtained by SAXS studies carried out on unadulterated samples. The fact that at larger length scale the structure of these water-rich networks seems largely preserved in the TEM samples suggests that three-dimensional (3D) TEM tomography experiments carried out with careful sample preparation will be valuable tools for measuring network architecture and connectivity; information that is lost in SAXS owing to the intrinsic averaging nature of the technique.

The present article describes the synthesis of the N-(Lys-Gly-Tyr-Gly)-chitosan using the water-soluble active ester method, the preparation of the N-(Lys-Gly-Tyr-Gly)-chitosan-gellan hybrid fibers, and the reinforcement of the hybrid fibers by enzymatic cross-linking between the N-grafted peptides chains of chitosan. The cationic polysaccharide chitosan was treated with Boc-Lys(Z)-Gly-Tyr(Bzl)-Gly (4-hydroxyphenyl)dimethylsulfonium methyl sulfate ester in DMF-0.15 M acetic acid to incorporate the peptides into the side chain amino groups of chitosan followed by the acidic removals of the Z and Bzl groups. The degrees of N substitution were estimated to be 2.0 and 10 molar % by changing the molar ratios of the amino groups of the parent chitosan and the active ester. The resulting cationic N-(Lys-Gly-Tyr-Gly)-chitosan was spun into the hybrid fibers with the anionic polysaccharide gellan in water. The tensile strengths of the N-(Lys-Gly-Tyr-Gly)-chitosan hybrid fibers were superior to those of the original chitosan-gellan fibers. The mechanical strengths of the hybrid fibers further increased upon enzymatic oxidation using tyrosinase. Based on these results, we concluded that the covalent cross-linking due to the enzyme oxidation between the grafted peptides significantly contributed to reinforcement of the polysaccharide hybrid fibers. The present results afford a new methodology for the reinforcement achieved by the polymer modification inspired by a biological process.

It has been reported that caroubin, a protein mixture obtained from carob seeds, has rheological properties similar to those of gluten. Comparative studies of the effects of hydration and temperature on caroubin and gluten were carried out with the aid of NMR, FTIR, scanning electron microscopy, and differential scanning calorimetry techniques. The results show that caroubin has a more ordered structure than gluten and that hydration has little effect on its secondary structure when compared to gluten. Caroubin is more easily accessible to water than gluten, suggesting that caroubin is more hydrophilic in nature. On hydration, caroubin, like gluten, forms fibrillar structures and sheets.

Molecular structure determination in concentrated solutions is generally considered unfeasible. This conclusion, drawn from experience with linear flexible chains, relates to the complete interpenetration of coils and their ensuing entanglement. Such deep interpenetration is prevented by the obstacles of branching units in branched macromolecules. The present study with branched (and one linear cellulose) polysaccharides demonstrates that different architectures can be distinguished via their different repulsive interactions. The procedure displayed in this article permits the estimation of true molar mass and true radius of gyration at finite concentration c. It furthermore allows, within upper and lower limits, an estimation of the growing size, when association takes place. Results from starches, glycogen, dextran, and cellulose, in aqueous media are discussed. The cellulose was dissolved in a recently developed aqueous cadmium complex. Association can lead to gel formation and/or to phase separation. The former is characterized by repulsive interactions which only slightly decrease when the gel point is approached. Phase separation, on the other hand, results from a decrease of the repulsive interaction induced, for instance, by another polymer. The effect is demonstrated with starches containing different amounts of amylose, where pure amylose forms unstable solutions and precipitates in time as a semicrystalline solid.

Scanning electron microscopy (SEM) and chemical analysis were used to observe the cell wall changes that occur in cork with "mancha amarela", when compared to a standard cork. To mimic the microbial attack exhibited in cork with mancha amarela, the standard cork was treated enzymatically with commercial pectinase and hemicellulase preparations. The tissues treated with pectinase were comparable with those attacked with mancha amarela. Both were composed by deformed and wrinkly cells and exhibited cell wall separation at the middle lamella level, which suggests solubilization/removal of the pectic polysaccharides. The cork cell wall material, prepared as alcohol-insoluble residue, was fractionated by hot water (Pect(H)()2(O)) and hot dilute acid (Pect(acid)). The relatively large amount of hexuronic acid and the occurrence of Ara in the SPect(H)()2(O) and SPect(acid) allow to confirm, as far as we know, for the first time the presence of pectic polysaccharides in the cell walls of cork from Quercus suber L. They accounted for ca. 1.5% of the cork and may consist of polymers with long side chains of arabinosyl residues. These polymers have to be taken into account in any realistic model of the cork cell wall. Cork with mancha amarela contained a smaller amount of pectic polysaccharides (ca. 0.5%), which confirms that the cellular separation observed by SEM is related to the degradation/removal of the middle lamella pectic polysaccharides.