Marta Kačuráková

FT-IR study of plant cell wall model compounds: pectic polysaccharides and hemicelluloses

Pectic polysaccharides and hemicelluloses extracted from plants were studied in highly hydrated films on BaF2 discs. Distinctive absorption band maxima in the mid-infrared region at 1200‐800 cm 21 were shown to be useful for the identification of polysaccharides with different structure and composition. Two series of the hexopyranose and pentopyranose monosaccharides, which are the structural units of the plant cell wall polysaccharides, were also studied by FT-IR spectroscopy in solution (i.e. comparable to the amorphous state of the polymers). Their spectral data showed that the main IR band positions are influenced by the relative position of axial and equatorial (OH) groups on the pyranoid ring. q 2000 Elsevier Science Ltd. All rights reserved.

Hydration properties of xylan‐type structures: an FTIR study of xylooligosaccharides

An FTIR study of the effect of hydration as a function of relative humidity on the structurally different xylooligosaccharide models is presented. The IR spectral pattern changes are strongly affected by the type and position of the glycosidic linkages and reflects the hydration properties of the models.

Quaternized xylans: synthesis and structural characterization

Abstract Quaternization xylans were prepared by treating xylans differing in structural and molecular properties with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHMAC) in aqueous NaOH under mild reaction conditions. The degree of substitution with quaternary ammonium groups can be monitored by altering the amount of CHMAC at optimum molar ratios of NaOH/CHMAC in the range 1·2-1·6, without changing the structure of the xylan backbones. Hot water pretreatment of the xylans in the alkaline activation step significantly enhances their reactivity. The presence of alkylammonium substituents was revealed by IR and NMR spectroscopy. The applicability of quaternized xylans as a retention aid in papermaking is demonstrated on thermomechanical pulp. Xylans, therefore, represent an important renewable resource for the production of novel cationic biopolymers.

Amphiphilic beechwood glucuronoxylan derivatives

Long alkyl chains (C 12 ) have been introduced onto glucuronoxylan and its sulfoethyl derivative via O-alkylation using 1-bromododecane in dimethylsulfoxide. The new amphiphilic xylan derivatives were characterized by chemical, elemental, and spectral analyses. They reduce the surface tension and exhibit remarkable emulsifying and protein foam-stabilizing properties. The results indicate that the development of new biopolymeric surfactants may be based on heteroxylans that are abundant in hardwoods and annual plants, and represent an unexploited renewable polysaccharide resource.

The glycoprotein character of multiple forms of Aspergillus polygalacturonase.

Comparisons of known primary structures of polygalacturonases show that extent and localization of potential N-glycosylation sites differ. Some sites are similar in position and adjacent to strictly conserved residues at the potential active site. The presence of N-acetylglucosamine and mannose in the molecules of two homogeneous, major Aspergillus sp. polygalacturonase forms was confirmed by IR spectroscopy. The purification method, based on interaction of the carbohydrate part with concanavalin A immobilized on chlorotriazine bead cellulose, was optimized. Deglycosylation with N-glycosidase F under denaturating and nondenaturating conditions led to molecular mass decreases followed by complete inactivation of the polygalacturonase enzyme activity. These results show the importance of glycosylation in these protein forms, while the comparative patterns establish both variability and some similarities in overall glycosylation architectures.

Chemical modification of beechwood xylan with p-carboxybenzyl bromide

Xylan isolated from beechwood was alkylated with p-carboxybenzyl bromide in aqueous alkali. The alkylation by varying stochiometry and reaction temperature yielded carboxybenzylated xylan derivatives with a degree of substitution which ranged from 0.05 to 0.25. The reaction products were characterized by elementary analysis and FTIR and UV spectroscopy. As tested by HPGPC, no degradation of the xylan chains resulted up to a reaction temperature of 40°C. The derivatives show moderate surface activity.

Characterization of Pectins Isolated from Mongolian Plants

Abstract Pectic polysaccharides (HP, RP) were extracted from Mongolia hawthorn berries and from rhubarb stalks by hot aqueous oxalic acid treatment. Both polysaccharides contained approximately 78% of galacturonate. HP displayed a low degree of esterification (DE) and arabinose/galactose molar ratio 1.7:1. RP was higher in DE and contained these sugars in a molar ratio 0.5:1. Rhamnose, fucose, xylose, glucose, mannose, 2-O-methylxylose, and 2-O-methylfucose were found in lower amounts. Results from 13C NMR spectroscopy and methylation analysis indicated the presence of branched arabinans, (1−>4)-and (1−>3,6)-linked galactans and hemicelluloses of the xylan and glucan types. The pectins differed in theirmolecular properties. HP exhibited a low molecular weight (M W = 45,000), whereas RP had a broad M W-distribution with M W= 360,000. Independently of these differences, the binding capacity of both pectins towards divalent cations was influenced by the DE only and increased in the order: Ca2+ < Cd2+ < Pb2+ ...

Infrared study of intramolecular hydrogen bonds in methyl mono- and di-O-substituted β-d-xylopyranosides

Abstract The strength of the intramolecular hydrogen bonds of the methyl mono- and di- O -methyl-β- d -xylopyranosides, methyl mono- and di- O -benzyl-β- d -xylopyranosides, benzyl di- O -benzyl-β- d -xylopyranosides, and mono- and di- O -acetyl-β- d -xylopyranosides was measured in terms of the frequency of the hydroxyl stretching vibration. The spectral data of the compounds measured in a carbon tetrachloride solution indicated the existence of intramolecular hydrogen bonds and conformational equilibria of the pyranoid ring in 4 C 1 and 1 C 4 chair forms resulting from the hydrogen bond properties, and position, number and steric effects of the substituents.