The structure of methyl alpha-D-galacturonic acid methyl ester

Pectin-organophilized ZnO nanoparticles as sustainable fillers for high-density polyethylene composites

A series of nanocomposites made of high-density polyethylene (HDPE) and 10 wt% zinc oxide nanoparticles (ZnO NPs) were produced by extrusion and injection molding. The nanoparticles were prepared via a green way using the pectin-based banana peel extract as the stabilizer and a proper dispersion-providing agent. The fillers were well-dispersed in the matrix and the composites exhibited improved functional characteristics such as increased thermal stability and mechanical properties. The presence of the pectin-organophilized filler had a significant impact on the crystallization process of HDPE. The kinetics of the degradation process was also altered in comparison to the pure polymer. The fire properties of the composites were enhanced as the amount of the gas products produced during their degradation was reduced, what was confirmed by thermogravimetric analysis coupled with gas products analyses (TGA/FTIR/QMS). The structure and morphology of the materials were characterized by scanning electron microscope (SEM), infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). Additionally, the mechanical properties were tested by tensile tests. An in-depth analysis revealed that the HDPE-pectin-ZnO interactions are crucial for the structural and performance properties of the final composite. The used biopolymer reacts with ZnO via ionic interaction and through hydrogen bond in the case of HDPE.

Synthesis of N-(β-D-glycuronopyranosyl)alkanamides and 1-(β-D-glycuronopyranosyl)-4-phenyl-[1,2,3]-triazoles as N-glycoprotein linkage region analogs: examination of the effect of C5 substituent on the N-glycosidic torsion (ΦN) based on X-ray crystallography

The torsion angle around the N-glycoprotein linkage region (GlcNAc-Asn) is an important factor for presenting sugar on the cell surface which is crucial for many biological processes. Earlier studies using model and analogs showed that this important torsion angle is greatly influenced by substitutions in the sugar part. In the present work, uronic acid alkanamides and triazole derivatives have been designed and synthesized as newer analogs of N-glycoprotein linkage region to understand the influence of the carboxylic group on linkage region torsion as well as on molecular packing. Crystal structure of N-(β-D-galacturonopyranosyl)acetamide is solved with the space group of P22121. Comparison of the torsion angle and molecular packing of this compound with N-(β-D-galactopyranosyl)acetamide showed that changing the C6-hydoxymethyl group to the carboxylic acid group has minimum influence on the N-glycosidic torsion angle, ΦN and significant influence on the molecular packing.

Chain−Chain Interactions for Methyl Polygalacturonate: Models for High Methyl-Esterified Pectin Junction Zones

The ability of pectins to form gels in the presence of calcium is well-known, and it implies the interaction of carboxylate groups and bivalent ions. However, even when most of the galacturonic units are methyl esterified, pectins are able to form gels but only under certain experimental conditions. In this case, hydrogen bonding and hydrophobic interactions are believed to be responsible for gel formation, and it is likely, as in the other mechanisms of polysaccharide gel formation, that stable junction zones consist of cooperatively ordered chains linked together throughout nonbonded interactions to provide a three-dimensional network. To investigate the junction zones in HM-pectin gels, we investigated, by molecular modeling, all of the ways to associate two, and then three, fully methyl-esterified galacturonic acid chains. Two models are obtained: the first one is based on a packing of parallel chains; it agrees with the hypothetical model derived from fiber diffraction study; the second one displays an antiparallel orientation of the chains; it presents a better arrangement of the chains and, theoretically, a much lower potential energy. In both cases, all of the favorable associations occur within a network of hydrogen bonds and of hydrophobic contacts.

Molecular motions of D-alpha-galacturonic acid (GA) and methyl-D-alpha-galacturonic acid methyl ester (MGAM) in the solid state-A proton NMR study

The molecular motions of D-alpha-galacturonic acid monohydrate (GA) and its derivative methyl-alpha-D-galacturonic acid methyl ester monohydrate (MGAM) in the solid state have been studied using 1H NMR. Both protonated and deuterium exchanged samples have been used. Spin-lattice relaxation times in the laboratory and rotating frames as well as second moments have been measured over the temperature range 90-370 K. Analysis of results has shown that in GA spin-lattice relaxation is chiefly by hydroxyl groups and water of crystallization. In MGAM, methyl groups dominate spin-lattice relaxation in the laboratory frame at the low temperature. Hydroxyl groups and water of crystallization contribute to the spin-lattice relaxation in the laboratory frame in the high temperature region. In the rotating frame motion of hydroxyl groups and water of crystallization provide the main relaxation pathway. Changes in the static second moment with temperature can be reasonably well predicted using values of correlation time and motionally averaged second moments obtained by fitting the spin-lattice relaxation data. 13C CPMAS spectra for GA and MGAM are also described.

Structural studies on the bacterial cell wall peptidoglycan pseudomurein. I. Conformational energy calculations on the glycan strands in C1 conformation and comparison with murein

Conformational energy calculations have been used to explore the conformations which may be realized for the sugar moiety of murein and pseudomurein. For the building blocks of the pseudomurein sugar strands, i.e. for the monosaccharides beta-D-N-acetylglucosamine (NAG) and alpha-L-N-acetyltalosaminuronic acid (NAT), both in C1 ring conformation, as well as for their 1,3 and 1,4 linked disaccharides, the favoured conformations were obtained. The helical parameters of sugar strands of both linkage types, which describe the regular structure of the corresponding polysaccharides, poly-(1,3-NAT-NAG) and poly-(1,4-NAT-NAG), were calculated. Both types of polysaccharides poly-(NAG-NAT) considered in this study favoured extended conformations, which in the case of 1,3 linked polymers showed less gain of length per saccharide unit compared to 1,4 linked poly-(NAG-NAT) residues. For a 1,3 linked sugar moiety of pseudomurein every pair of neighbouring peptides attached to glycan chain pointed in favoured conformations approximately to opposite sides of the strands, whereas in a 1,4 linked poly-(NAG-NAT) the peptides protruded approximately to the same side of the glycan moiety. A comparison between pseudomurein and murein revealed that the sugar moieties of both peptidoglycans have similar features in respect to their overall structure, i.e. both favoured more or less extended structures. In contrast to these data the shapes of the resulting polysaccharide moieties were remarkably different. In poly-(1,3-NAG-NAT) the glycan chains possessed a zig-zag-like arrangement, whereas for glycan chains of the murein type relatively flat structures were preferred. These remaining differences in the conformational arrangement between both peptidoglycans depend strongly on the C1 chair conformation of NAT. It is, therefore, attractive to speculate about an hypothetical pseudomurein sugar chain configuration comprising beta-L-N-acetyltalosaminuronic acid in its 1C conformation.