Vlasta Sasinková

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.

Antioxidative and antimutagenic activity of yeast cell wall mannans in vitro.

Antioxidative and antimutagenic effect of yeast cell wall mannans, in particular, extracellular glucomannan (EC-GM) and glucomannan (GM-C.u.) both from Candida utilis, mannan from Saccharomyces cerevisiae (M-S.c.) and mannan from Candida albicans (M-C.a.) was evaluated. Luminol-dependent photochemical method using trolox as a standard showed that EC-GM, GM-C.u., M-S.c. and M-C.a. have relatively good antioxidative properties. EC-GM exhibited the highest antioxidative activity, followed by GM-C.u. and M-S.c. M-C.a. showed the least antioxidative activity. These mannans were experimentally confirmed to exhibit different, statistically significant antimutagenic activity in reducing damage of chloroplast DNA of the flagellate Euglena gracilis induced by ofloxacin and acridine orange (AO). We suggest that the antimutagenic effect of EC-GM, GM-C.u., M-S.c. and M-C.a. against ofloxacin is based on their ability to scavenge reactive oxygen radicals. With AO, the reduction of the chloroplast DNA lession could be a result of the absorptive capacity of the mannans. The important characteristics of mannans isolated from the yeast cell walls, such as good water solubility, relatively small molecular weight (15-30kDa), and antimutagenic effect exerted through different mode of action, appear to be a promising features for their prospective use as a natural protective (antimutagenic) agents.

Influence of the drying method on the physical properties and immunomodulatory activity of the particulate (1→3)-β-d-glucan from Saccharomyces cerevisiae

Abstract The particulate (1→3)-β- d -glucan isolated from Saccharomyces cerevisiae cell walls was recovered from the aqueous medium as water-insoluble particles by different drying methods: solvent exchange (GE), lyophilisation (GL), and spray drying (GS). The samples were characterised by optical microscopy, FT-IR spectroscopy, swelling capacity, and rheological behaviour of aqueous dispersions. The immunological activity of the glucan samples was examined using the assay for the mitogenic and comitogenic activities. The drying method affected the microstructure of the glucan particles leading to differences in their physical properties (particle size and shape, swelling capacity, interparticle hydrogen bonding) as well as in the flow and viscoelastic properties. In comparison to GL and GE, the GS particles preserved the ellipsoid shape of yeast cells and exhibited a very low extent of interparticle hydrogen bonds. The rather liquid-like GS dispersion showed a several times lower apparent viscosity than the gel-like GE and GL dispersions. The results suggest that the physical state of the variously dried particulate glucan samples influenced significantly also their immunomodulatory activity which was found to be about twice higher with GS than with the GL and GE samples. The results indicated that for application of the particulate (1→3)-β- d -glucan as immunomodulator/adjuvans in form of aqueous suspension it is important to use spray-dried preparations.

Characterization of immunomodulatory polysaccharides from Salvia officinalis L.

Crude polysaccharide fractions, rich mainly in arabinogalactans (A), pectin (B) and glucuronoxylan-related polymers (D), have been obtained from aerial parts of sage (Salvia officinalis L.) by sequential extraction with various reagents. Arabinogalactans displayed on HPLC a dominance of lower molecular-mass polymers (MW < 10,000), while pectin and glucuronoxylan-related polysaccharides showed predominance of polymers with MW > 50,000. Individual polysaccharide fractions were examined for their immunomodulatory activity in the in vitro comitogenic thymocyte test. The polysaccharide fractions tested possessed the capacity to induce rat thymocyte proliferation in the order D>B>A. Besides, fraction D possessed a significant comitogenic effect, and the SIcomit/SImit ratio 3-4 indicates potential adjuvant properties of this glucuronoxylan-rich material.

Cyclodextrin derivative of hyaluronan

Conversion of hyaluronan (HA) to its β-cyclodextrin derivative (HA-β-CD) was accomplished by direct coupling of β-cyclodextrin (β-CD) molecules with carboxylic acid groups of the HA macromolecule. The intermolecular dehydration, yielding the HA-β-CD derivative, was performed by the action of diethyl azodicarboxylate and triphenylphosphine under mild, neutral conditions. The physico-chemical characteristics of the novel (bio)material, determined both in solution and solid state, were compared with those of native HA. The specific action of a hyaluronidase was exploited to advantage in studying the depolymerization kinetics of the two types (HA and HA-β-CD) of macrobiomolecules.

Electrochemical performance of Ti3C2Tx MXene in aqueous media: towards ultrasensitive H2O2 sensing

An extensive characterization of pristine and oxidized Ti3C2Tx (T: =O, -OH, -F) MXene showed that exposure of MXene to an anodic potential in the aqueous solution oxidizes the nanomaterial forming TiO2 layer or TiO2 domains with subsequent TiO2 dissolution by F- ions, making the resulting nanomaterial less electrochemically active compared to the pristine Ti3C2Tx. The Ti3C2Tx could be thus applied for electrochemical reactions in a cathodic potential window i.e. for ultrasensitive detection of H2O2 down to nM level with a response time of approx. 10 s. The manuscript also shows electrochemical behavior of Ti3C2Tx modified electrode towards oxidation of NADH and towards oxygen reduction reactions.

Influence of tiopronin, captopril and levamisole therapeutics on the oxidative degradation of hyaluronan

The ability to protect hyaluronic acid (HA) from oxidative degradation by cupric ions and ascorbate (production of (•)OH and peroxy-type radicals) during acute phase joint inflammation has been investigated using the following drugs: tiopronin, captopril, and levamisole. Radical scavenging activity, i.e. the propensity for donation of electrons was assessed for the drugs by ABTS and DPPH assays. The kinetics of HA degradation have been measured in the presence of each drug using rotational viscometry. The results of ABTS and DPPH assays show the highest radical scavenging activity for captopril, followed by tiopronin. For levamisole, no effect was observed. Captopril and tiopronin prevented HA degradation induced by (•)OH radicals in a similar manner, while tiopronin was more effective in scavenging peroxy-type radicals. On the other hand, levamisole was shown to be a pro-oxidant. Recovered HA fragments were characterized using FT-IR analysis, the incorporation of a sulphur atom from captopril and tiopronin but not from levamisole into the HA molecule was demonstrated.

Hydrogen peroxide generation by the Weissberger biogenic oxidative system during hyaluronan degradation.

By applying the enzyme catalase, our study on hyaluronan degradation confirms the generation of hydrogen peroxide using the Weissberger biogenic oxidative system (WBOS), which is composed of ascorbate and cupric ions. Dynamic viscosities of hyaluronan (HA) solutions influenced by WBOS in the absence and presence of catalase were analysed by rotational viscometry. Molar masses of HAs were determined by size-exclusion chromatography with multi-angle laser-light scattering. Our results show that catalase dose-dependently inhibited the degradation of HA macromolecules, which presumably confirms the generation of H2O2 in the reaction system. This has implications in range of biomedical applications such as arthritic joint treatment, tissue engineering, ocular and cosmetic surgery.

Structure and properties of water‐soluble p‐carboxybenzyl polysaccharide derivatives

A series of water-soluble and water-insoluble heteroxylans, citrus pectin, and both starch components, amylose and amylopectin, were hydrophobically modified by introducing low amounts of p-carboxybenzyl groups at constant reaction conditions. The achieved degree of substitution ranged from 0.03 to 0.22. The derivatives were characterized by chemical and spectral analyses. They exhibited tensioactive properties evaluated by various surface-activity tests. The results indicate a weak surface tension-lowering effect and low foamability of all derivatives. However, significant emulsifying and protein foam-stabilizing effects were found for most of the studied derivatives, the most pronounced for the modified pectin and acidic xylans. The rheological behavior of the derivatives was investigated by rotational and oscillation rheometry. The results indicated that the hydrophobic interactions lowered significantly the apparent viscosity of the xylan dispersions and introduced changes, particularly in their flow properties.

Effect of Salt Stress on the Production and Properties of Extracellular Polysaccharides Produced by Cryptococcus laurentii

The composition, main structural features and molecular properties of exopolysaccharides (EP) produced by Cryptococcus laurentii var. laurentii CCY 17-3-16 under optimal (EPo) and NaCl-stress conditions (EPs) as well as their subfractions isolated by gel chromatography were studied using chemical, FT-IR and NMR spectroscopy methods. The results showed that under stress conditions the yeast produced EP with a lower content of protein and phosphorus. In comparison to EPo, the EPs exhibited a substantially larger proportion of high molecular mass populations. NMR analysis of EPs revealed a higher degree of branching with single xylose side chains of the heteromannan components. The increase of the molecular mass and degree of branching of the macromolecular chains of the heteromannan components might in part be related to the function of EPs to protect the yeast cells from water loss and maintain growth conditions under the salt stress.