Carbohydrate constituents of Lessonia trabeculata

D-mannitol was the only low-molecular weight carbohydrate isolated from ethanolic extracts of Lessonia trabeculata blades. After sequential extraction with water, acid and alkali, laminaran, fucose-containing polysaccharides and alginic acid were also isolated. Fucose-containing polysaccharide from the acidic extract was separated into three fractions by ion exchange chromatography. Alginic acid was the major polysaccharide obtained in the sequential extraction.     

The acidic polysaccharide from Palmaria decipiens (Palmariales,Rhodophyta)

Palmaria decipiens, one of the most abundant red seaweeds of the chilean Antarctic, was collected in King George Island. The hot water extract (26% yield) showed by acid hydrolysis to contain xylose, galactose and traces of glucose. Fractionation with cetrimide gave a soluble neutral xylan and an insoluble fraction. The insoluble fraction afforded an acidic polysaccharide that contained 4.8% of uronic acids, 2.8% of sulfate and 18.9% of protein. Polyacrylamide gel electrophoresis showed that it was homogeneous. The GLC and HPLC analysis of the total acidic hydrolysis products showed that the acidic polysaccharide was composed of the neutral sugars galactose and xylose in the molar ratio 8.2:1.0 and of galacturonic and glucuronic acid in the ratio 1.5:1.0. The second-derivative FT-IR spectrum showed the characteristic amide I, II and III bands of proteins. Alkaline cleavage with 0.1 M NaOH indicated the presence of a glycoprotein with O-glycosidic linkage.Results found in this work suggest that the acidic polysaccharide extracted from Palmaria decipiens is an acidic xylogalactan-protein complex.     

Carrageenophyte identification by second-derivative Fourier transform infrared spectroscopy

The second-derivative mode of the Fourier transform I.R. spectra of dried algal material has been applied to distinguish the carrageenans-producingStenogramme interrupta from the isomorphous speciesRhodymenia howeana. Spectra of the tetrasporophyteS. interrupta showed bands assigned to a -carrageenan type polysaccharide, while the gametophytic and cystocarpic plants showed the characteristic absorptions of -and -carrageenans. Results were confirmed by hot water extraction of samples of the three nuclear phases ofS. interrupta and characterization of the extracts by chemical analysis.Author for correspondence     

Heterogeneity of carrageenans from Chondrus crispus.

Carrageenans extracted from gametophytic and sporophytic Chondrus crispus were analysed by hydrolysis, KCl fractionation and 1H NMR spectroscopy. The carrageenan from gametophytic plants is composed predominantly of two KCl insoluble fractions which contain kappa-carrageenan as the major component with 1-carrageenan and sulphated galactans as minor components. The precursor mu- and v-carrageenans were not found in the soluble fraction. The extract from sporophytic plants is composed mainly of a KCl soluble fraction which could be separated into 10 fractions by ion-exchange chromatography. The major component did not show a lambda-type structure but one of a xi-carrageenan.     

A sulfated galactan with antioxidant capacity from the green variant of tetrasporic Gigartina skottsbergii (Gigartinales, Rhodophyta)

The water soluble polysaccharide produced by the green variant of tetrasporic Gigartina skottsbergii was found to be composed of D-galactose and sulfate groups in a molar ratio of 1.0:0.65. (1)H and (13)C NMR spectroscopy studies of the desulfated polysaccharide showed a major backbone structure of alternating 3-linked β-D-galactopyranosyl and 4-linked α-D-galactopyranosyl units, and minor signals ascribed to 3-O-methyl-substitution on the latter unit. Ethylation analysis of the polysaccharide indicated that the sulfate groups are mainly located at position O-2 of 4-linked α-D-galactopyranosyl residue and partially located at positions O-6 of the same unit and at position O-2 of 3-linked β-D-galactopyranosyl residue, and confirmed the presence of 3-O-methyl-galactose in minor amounts (4.4%). The sulfated d-galactan presents a similar structure to λ carrageenan but with much lower sulfation at position O-6 of the α-residue and at position O-2 of β-residue. The antioxidant capacity of the sulfated d-galactan was evaluated by the peroxyl radicals (ORAC method), hydroxyl radicals, chelating activity, and ABTS(+) assays. Kinetic results obtained in these assays were compared with those obtained for the commercial λ carrageenan. The antioxidant activity toward peroxyl radicals was higher for commercial λ carrageenan, this agrees with its higher content of sulfate group. The kinetics of the reaction of both polysaccharides with hydroxyl and ABTS(+) radicals showed a complex mechanism, but the antioxidant activity was higher for the polysaccharide from the green variant of tetrasporic Gigartina skottsbergii.     

Chemical modifications of carboxylated chitosan

C-6-carboxylated chitosan obtained by oxidation of chitosan was selectively modified in order to obtain derivatives similar to bacterial antigens. Selective O-acetylation of 6-carboxyl chitosan afforded a modified polysaccharide with the 2-amino group available for further modifications to create carbonyl groups. A deaminative degradation reaction allowed the formation of oligosaccharides with terminal aldehyde groups. Reductive alkylation with lactose introduced lactityl branches which were oxidized with galactose oxidase to give aldehyde groups in its -galactose residues.     

Characterization of a neutral polysaccharide with antioxidant capacity from red wine

A neutral fraction (PS-SI) (0.3 g/L) with MW of 74 kDa, which contained galactose, arabinose, mannose, and glucose in the molar ratio of 1.0:0.6:0.4:0.2 was obtained by treatment of the whole polysaccharide extracted from red wine with cetrimide, followed by gel permeation chromatography. Spectroscopic and methylation analyses indicated that PS-SI is a mixture of neutral polysaccharides, consisting mainly of β (1→3)-linked galactopyranosyl residues, with side chains of galactopyranosyl residues at positions O-6. Arabinofuranosyl residues linked α (1→5), α-mannopyranosyl and glucosyl residues appear to be components of different polysaccharides. The in vitro antioxidant capacity of fractions of wine polysaccharide was studied by hydroxyl radical scavenging and ORAC assays. Fraction PS-SI presented the strongest effect on hydroxyl radicals (IC₅₀ = 0.21).     

Sulfation of agarose from subantarctic Ahnfeltia plicata (Ahnfeltiales,Rhodophyta): studies of its antioxidant and anticoagulant properties in vitro and its copolymerization with acrylamide

Aqueous extraction of Ahnfeltia plicata collected in the Magellan ecoregion afforded agarose devoid of sulfate groups. This neutral agarose was subjected to sulfation with SO₃-pyridine complex, giving an aqueous soluble derivative with 35.5 % sulfate groups. Analysis by Fourier transform infrared spectroscopy (FT-IR) and by ¹H and ¹³C NMR spectroscopy indicated that this derivative was sulfated at positions C-6 of the β-galactopyranosyl residue and C-2 of the α-3,6-anhydrogalactopyranosyl residue and partially sulfated at position C-2 of the β residue. The antioxidant capacity of sulfated agarose was evaluated by the oxygen radical absorbance capacity (ORAC) method, ABTS radical cation, hydroxyl radicals, and chelating assays. This capacity of sulfated agarose toward peroxyl radicals was higher than that of commercial λ-carrageenan, while native agarose presented good activity, with an ORAC value similar to that of commercial κ-carrageenan. Sulfated agarose presented good antioxidant capacity toward other radicals. Copolymerization of sulfated agarose with acrylamide was achieved using ceric ammonium nitrate as initiator. NMR spectroscopy indicated grafting of polyacrylamide at position C-4 of β-galactopyranosyl residues.     

Agars from Chilean Gelidiaceae

Cystocarpic, tetrasporic and vegetative thalli of Gelidium chilense were extracted with water at 95 °C. The contents of 3,6-anhydro-galactose and sulfate group of the hydrocolloids correspond to those of an agar-type polysaccharide. The percentages of 6-O-methyl-galactose and of pyruvic acid ranged between 5.7–6.2% and 0.42–0.54%, respectively. The gel melting and gelation temperatures of Gelidium chilense, G. rex and G. lingulatum agars were determined. A correlation between 6-O-methylgalactose content and gelation temperatures was not observed. It was found by anion-exchange chromatography that 19.8% of tetrasporic and 4.9% of vegetative G. chilense agars are unsulfated polymers. Structural studies on the neutral fraction from tetrasporic G. chilense agar by partial hydrolysis and ¹H NMR spectroscopy have shown that it is mainly composed of agarose. Methylation analysis, oxidative hydrolysis and partial hydrolysis, followed by ¹H NMR spectroscopy, have shown that the neutral fraction of the agar from tetrasporic Gelidium rex is agarose. The results obtained in this work are compared with previously reported data on studies of agars from Chilean Gelidium species.     

Second-derivative Fourier transform infrared spectra of seaweed galactans

The Fourier transform infrared spectra of agar, agarose, -, -, and -carrageenan, and ofChondrus canaliculatus, Iridaea ciliata, I. membranacea, I. laminarioides andGracilaria chilensis polysaccharides were recorded in the 4000–400 cm^-1 region. The bands in the second derivative mode are sharper and more bands are resolved than in the normal spectra.Agar, agarose andG. chilensis phycocolloids exhibit diagnostic bands at 790 and 713 cm^-1. -, - and -carrageenans, and native carrageenan-type polysaccharides fromC. canaliculatus andIridaea species exhibit bands at around 1160, 1140, 1100, 1070, 1040, 1008, 610, and 580 cm^-1. Therefore, FT-IR spectroscopy in the second-derivative mode may be applied to differentiate between agar- and carrageenan-types seaweed galactans.