Carbohydrates of the brown seaweeds Desmarestia firma and Dictyopteris plagiogramma and of the diatom Coscinodiscus nobilis

Rahman, Manisur

(1980)

Rahman, Manisur (1980) Carbohydrates of the brown seaweeds Desmarestia firma and Dictyopteris plagiogramma and of the diatom Coscinodiscus nobilis.

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Abstract

Dictyopteris plagiogramma: The carbohydrates of this weed have been chemically studied for the first time. Sequential extraction of the weed gave a mixture of laminaran and 'fucan' in the aqueous extract and a mixture of alginic acid and 'fucan' in the alkaline extracts. A pure laminaran was separated on a DE-52 cellulose column and shown to comprise a (1>3)-linked B-glucan containing 1.4% mannitol. The 'fucan' contained fucose, glucuronic acid, xylose, galactose, mannose and half ester sulphate. A variety of fractionation procedure gave 'fucans' with varying proportions of constituents and half ester sulphate. The alginic acid from the sequential extraction was shown to be highly degraded, but an alkaline extract of a fresh sample of weed contained a less degraded alginate in which the mannuronic/guluronic acid ratio was ca. 60:40. Methylation and periodate oxidation studies established the similarity of linkage pattern with other 'fucans'. Alkaline desulphation of Dictyopteris 'fucan' and 3 fucans' from other seaweeds revealed, after hydrolysis, the presence of a monosaccharide which was characterised as a 6 deoxyhexose indicating that SO=4was attached to the fucose molecule at C-2 and/or C-3. Sodium methoxide treatment of the desulphated fucan followed by identification of 2-0-methyl fucose confirmed that SO=4 was attached to the interchain fucose residue at C-2. Desmarestia firma: The sequential alkaline extract from this weed was also shown to comprise 16% of a highly degraded alginic acid and 1.8% of crude 'fucan'. Direct alkaline extraction yielded 19.8% of relatively higher viscosity alginate. Coscinodiscus nobilis: After culturing the diatom under bacteria free conditions, 50 mg of extracellular polysaccharide and 30 mg of diatom were recovered. The former was shown to comprise a highly branched hetero-polysaccharide containing fucose, rhamnose, mannose, D-glucose, xylose, D-glucuronic acid, galactose (trace) and half ester sulphate. The positions of linkages between the monosaccharides have been established and evidence for the linkages between D-glucuronic acid and monosaccharides was obtained. The extracellular polysaccharides contained also a chrysolaminaran, but this may have been derived from dead cells. Fucose and mannose occur also in a separate polymer. The diatom contained polysaccharide material consisting of glucose, mannose, fucose and uronic acid residues.

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This is a Accepted version
This version's date is: 1980
This item is not peer reviewed

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Item TypeThesis (Doctoral)
TitleCarbohydrates of the brown seaweeds Desmarestia firma and Dictyopteris plagiogramma and of the diatom Coscinodiscus nobilis
AuthorsRahman, Manisur
Uncontrolled KeywordsPlant Sciences; Biological Sciences; Brown; Carbohydrates; Coscinodiscus; Desmarestia; Diatom; Dictyopteris; Firma; Nobilis; Plagiogramma; Seaweeds; Seaweeds
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ISBN978-1-339-61563-9

Deposited by () on 01-Feb-2017 in Royal Holloway Research Online.Last modified on 01-Feb-2017

Notes

Digitised in partnership with ProQuest, 2015-2016. Institution: University of London, Royal Holloway College (United Kingdom).


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