Chemical composition and C-13 NMR spectroscopic characterisation of ulvansfrom Ulva (Ulvales, Chlorophyta)

The chemical composition and structures of several ulvan extracts isolated from various Ulva species were studied. They were all composed mainly of rh amnose, glucuronic acid, xylose, glucose and sulphate with smaller amounts of iduronic acid and traces of galactose. Proteins were also present, most likely as contaminants. Precise quantification of the uronic acid content b y chemical-enzymatic hydrolysis coupled to HPAEC-PAD analysis and by colori metry was not achieved, most likely due to the incomplete hydrolysis of glu curonan segments, inadequate HPAEC-pulsed-amperometric response factor for iduronic acid and to a possible differential colorimetric response of the t wo uronic acids. C-13 NMR spectroscopic investigation of different ulvans d emonstrated that they were all based on ulvanobiuronic acid 3-sulphate A an d B repeating units [beta-D-GlcpA-(1-> 4)-alpha-L-Rhap3S and alpha-L-IdopA- (1-> 4)-alpha-L-Rha p3S, respectively] as well as contiguous beta 1-> 4 lin ked D-glucuronic acids possibly occurring either in ulvan or as a separate glucuronan. Marked variations in the content of the repeating structures we re seen among the different samples. However, due to the limited number of samples studied, no conclusion was reached concerning the effects of specie s and ecophysiological conditions on the chemistry of ulvan.