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Title: Carbohydrates of the brown seaweeds Desmarestia firma and Dictyopteris plagiogramma and of the diatom Coscinodiscus nobilis
Author: Rahman, Manisur
Awarding Body: University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1979
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Plant Sciences