Cesar A. Tischer

Nanostructural reorganization of bacterial cellulose by ultrasonic treatment.

In this work, bacterial cellulose was subjected to a high-power ultrasonic treatment for different time intervals. The morphological analysis, scanning electron microscopy, and atomic force microscopy revealed that this treatment changed the width and height of the microfibrillar ribbons and roughness of their surface, originating films with new nanostructures. Differential thermal analysis showed a higher thermal stability for ultrasonicated samples with a pyrolysis onset temperature of 208 degrees C for native bacterial cellulose and 250 and 268 degrees C for the modified samples. The small-angle X-ray scattering experiments demonstrated that the treatment with ultrasound increased the thickness of the ribbons, while wide-angle X-ray scattering experiments demonstrated that the average crystallite dimension and the degree of crystallinity also increased. A model is proposed where the thicker ribbons and crystallites result from the fusion of neighboring ribbons due to cavitation effects.

The free reducing oligosaccharides of gum arabic: aids for structural assignments in the polysaccharide

Abstract Gum arabic contains in small quantities, the free reducing sugars, arabinose, ribose, glucose, mannose, galactose, rhamnose, α- d -Galp-(1→3)-αβ- l -Ara, α- l -Araf-(1→4)-β- d -Galp-(1→6)-αβ- d -Gal, β- d -GlcpA-(1→6)-αβ- d -Galp, α- l -Rhap-(1→4)-β- d - GlcpA-(1→6)-αβ- d -Galp, α- l -Rhap-(1→4)-β- d -GlcpA-(1→6)-β- d -Galp-(1→6)-αβ- d -Galp, a branched pentasaccharide with a chain of α- d -Galp-(1→3)-α- l -Araf-(1→3)-β- d -Galp-(1→6)-αβ- d -Galp substituted at O-4 of Gal p ′ with α- l -Ara f units, and a doubly branched heptasaccharide with a chain of α- d -Galp-(1→3)-α- l -Araf-(1→3)-β- d -Galp-(1→6)-αβ- d -Galp, disubstituted, respectively, at O-4 and O-6 of Gal p ′ with α- l -Ara f and α- l -Rha p -(1→4)-β- d -Glc p A groups. A small amount of a related heptasaccharide was also present, with non-reducing end units of β-Ara p , in place of those of α-Gal p . These oligosaccharides were characterized by 1D and 2D NMR spectroscopy, ESI-MS, and in three cases, methylation analysis for final confirmation. The oligosaccharides should represent, with the probable exception of the galactosyl reducing ends, side-chain structures present in the gum arabic polysaccharide.

Structure of the arabinogalactan from gum tragacanth (Astralagus gummifer)

The polysaccharide obtained by ethanol precipitation from an aqueous solution of gum tragacanth contained arabinogalactan and tragacanthic acid, as well as starch ( approximately 0.6%). GC-MS, NMR, and ESI-MS analyses showed the structure of the arabinogalactan to be even more complex than previously determined, with core structures containing Arap, beta-Araf, and alpha-Galp units, as well as known terminal, and 2-O- and 3-O-substituted alpha-Araf units. Analysis was aided by examination of free, reducing oligosaccharides present in the gum. In addition to maltose, maltotriose, maltotetraose, and maltopentaose, the following were characterized: mixed alpha-Araf (1-->2)-alpha-Araf-(1-->4)-Ara and alpha-Araf-(1-->2)-alpha-Araf-(1-->5)-Ara, which correspond to the side chains of the arabinogalactan, beta-Galp-(1-->4)-beta-Galp-(1-->4)-beta-Galp-(1-->4)-Gal; and a mixture of beta-Galp-(1-->4)-beta-Galp-(1-->4)-Gal and beta-Glcp-(1-->4)-beta-Galp-(1-->4)-beta-Galp-(1-->4)-Gal, which did not resemble side-chain structures of the arabinogalactan. The latter are suggested to be related to tragacanthic acid, which has been previously found to contain beta-Galp nonreducing end-units.

The free reducing oligosaccharides of angico branco (Anadenanthera colubrina) gum exudate: an aid for structural assignments in the heteropolysaccharide.

A novel method is described for the determination of sequential side-chain structures in the complex, high-arabinose polysaccharide of the gum exudate of angico branco (Anadenanthera colubrina), using as basis the structurally similar reducing oligosaccharides present in small quantities. Of the ten detected, eight were characterized as disaccharides (2, 3, and 9), linear trisaccharides (1 and 4), branched pentasaccharides (5 and 6), and a doubly branched heptasaccharide (8). The oligosaccharides are substituents of the polysaccharide, which has a (1-->3)-linked beta-D-galactopyranosyl main chain, and with two exceptions they had 6-O-substituted galactopyranosyl reducing ends, probably corresponding to its main-chain units. Characterization was effected through their 1D and 2D NMR correlation spectra, which were better resolved and more readily interpretable than those of the polysaccharide. These spectral data were supported by monosaccharide composition and rotation values. Controlled Smith degradations and methylation analyses were carried out when it was necessary. These data were confirmed by field-desorption MS.

New structural features of the polysaccharide from gum ghatti (Anogeissus latifola).

Methylation and 13C NMR analyses were carried out on the high-arabinose, acidic heteropolysaccharide of gum ghatti and the products obtained on three successive, controlled Smith degradations. The side chains contained mainly 2-O- and 3-O-substituted Araf units. Of these the second degradation eliminated remaining alpha-Araf units, and their beta anomers became evident. The proportion of Galp units gradually increased in the form of nonreducing end- and Galp units, although 3,6-di-O- and 3,4,6-tri-O-substituted Galp units diminished. After three degradations groups with consecutive 3-O-substituted beta-Galp units were formed. The proportion of periodate-resistant 3-O- and 2,3-di-O-substituted Manp units was maintained. As a guide to side-chain structures in the polysaccharide, seven of the 10 free reducing oligosaccharide fractions (PC) present in the gum were isolated and examined (NMR, ESIMS, and sometimes methylation analysis). Characterized are alpha-Araf-(1 --> 2)-Ara and three Ara-containing oligosaccharide fractions containing 2-O- and 3-O-substituted units. These gave respectively, ESIMS molecular ions arising from Ara(2), beta-Araf oligosaccharides with four units, beta-Araf oligosaccharides with seven units, and Hex(2)-Ara(4). Alpha-Rhap-(1 --> 4)-GlcA, alpha-Rhap-(1 --> 4)-beta-GlcpA-(1 --> 6)-Gal, and alpha-Rhap-(1 --> 4)-beta-GlcpA-(1 --> 6)-beta-Galp-(1 --> 6)-Gal represented other side chains.

Structural characterization and emulsifying properties of polysaccharides of Acacia mearnsii de Wild gum.

Polysaccharides (GNF) from Acacia mearnsii de Wild gum exudates, collected from trees growing in the south of Brazil, were characterized ((13)C and HSQC NMR, GC-MS, colorimetric assays). A commercial gum arabic (GAC) was analyzed similarly and compared with GNF. There were differences, consistent with distinct behavior in tensiometry tests and as emulsion stabilizer. GNF had a higher protein content than GAC, with small differences in the monosaccharide composition, the greater one being the lower uronic acid content of GNF (4%), compared with GAC (17%). GNF had a much broader molecular mass distribution, M(w)/M(n), and a lower M(w). GNF was more efficient in lowering the surface tension of water and saline solutions and was more efficient in emulsifying castor oil droplets. Results were discussed taking into account structural and molecular differences between the studied gums. It was concluded that polysaccharides from A. mearnsii de Wild are candidates as substitutes of currently commercialized arabic gums (Acacia senegal and Acacia seyal) having, depending on their application, improved properties.

Bacterial cellulose and hyaluronic acid hybrid membranes: Production and characterization.

In this study, the effect of the addition of hyaluronic acid (HA) on bacterial cellulose (BC) production, under static conditions was evaluated in terms of the properties of the resulting BC hybrid membranes. HA was added to the fermentation process in three distinct time points: first day (BC-T0), third day (BC-T3) and sixth day (BC-T6). Analyses of FT-IR and CP/MAS (13)C NMR confirmed the presence of HA in bacterial cellulose membranes. The crystal structure, crystallinity index (Ic) surface roughness, thermal stability and hybrophobic/hydrophilic character changed. Membranes with higher roughness were produced with HA added on the first and third day of fermentation process. The surface energy of BC/HA membranes was calculated and more hydrophilic membranes were produced by the addition of HA on the third and sixth day, also resulting in more thermally stable materials. The results demonstrate that bacterial cellulose/hyaluronic acid hybrid membranes can be produced in situ and suggest that HA interacts with the sub-elementary bacterial cellulose fibrils, changing the properties of the membranes. The study and understanding of the factors that affect those properties are of utmost importance for the safe and efficient use of BC as biomaterials in numerous applications, specifically in the biological field.

Chemotyping glucans from lichens of the genus Cladonia

Abstract α- d -Glucans were isolated from the Cladonia spp., C. clathrata, C. connexa, C. crispatula, C. furcata, C. ibitipocae, C. imperialis, C. penicillata, and C. signata, to evaluate their possible significance in chemotyping. Each was isolated in water-insoluble form via successive alkaline extraction and freeze-thawing. They were then individually investigated using 13C and 1H-NMR spectroscopy (including COSY, TOCSY and HMQC techniques), methylation analysis, and Smith degradation, and their specific rotations and monosaccharide compositions determined. Each α- d -glucan contained alternating (1→3) and (1→4)-linkages (1:1 ratio), as determined by the relative areas of their respective H-1 signals at δ 5.14 and 5.23. Also, the respective relative areas of C-1 signals at δ 99.2 and 100.1, and those of C-3 of 3-O-(δ 82.6) and C-4 of 4-O-substituted (δ 78.9) units, were similar for each glucan. The presence of α- d -glucans of the nigeran type appears to be typical of Cladonia spp.

Glycosphingolipids from Magnaporthe grisea cells: expression of a ceramide dihexoside presenting phytosphingosine as the long-chain base

Magnaporthe grisea is a fungal pathogen that infects rice leaves and causes rice blast, a devastating crop disease. M. grisea produces active elicitors of the hypersensitive response in rice that were previously identified as ceramide monohexosides (CMHs). Using several chromatographic approaches, mass spectrometry, and nuclear magnetic resonance, we identified ceramide mono- and dihexosides (CDH) in purified lipid extracts from M. grisea cells. As described by other authors, CMH consists of a ceramide moiety containing 9-methyl-4,8-sphingadienine in amidic linkage to 2-hydroxyoctadecenoic or 2-hydroxyhexadecenoic acids and a carbohydrate segment consisting of one residue of glucose. CDHs, however, contain beta-galactose (1-->4)-linked to beta-glucose as sugar units and phytosphingosine as the long-chain base, bound to a C24 alpha-hydroxylated fatty acid. To our knowledge, this is the first report on the occurrence of CDH in a fungal species and illustrates the existence of an alternative path of ceramide glycosylation in fungal cells.

A new triterpene with antinociceptive activity from Maytenus robusta

A new triterpene 3,15-dioxo-21α-hydroxy friedelane has been isolated from methanol extract of Maytenus robusta and its structure elucidated on the basis of spectral analysis. Stigmasterol, friedelin, friedelanol and 3,15-dioxo friedelane were also obtained. 3,15-dioxo-21α-hydroxy friedelane was analyzed against the writhing test in mice and exhibited potent dose-dependent effects with an ID50 value of 12.5 ± 2.1 µmol kg−1 and a maximal inhibition of 85.90%. It was about 10-fold more active than aspirin and paracetamol, used as reference drugs.