Carbohydrate constituents of the marine algae of Sri Lanka part ii. composition and sequence of uronate residues in alginates from some brown seaweeds

The ratio of mannuronic acid residues to guluronic acid residues (M/G ratio) of sodium alginate extracted from Cystoseira trinodis, Turbinaria conoidcs and Sargassum sp. was determined using high resolution ¹H-NMR spectroscopy. The intensities of the signals due to H-5 of guluronate residues and H-1 of both guluronate and mannuronate residues were used. The alginate samples were found to be rich in guluronate residues, and the polymer chains are likely to be composed of long blocks of guluronate residues, short blocks of mannuronate residues and a small proportion of blocks containing both uronide residues.