Structural characterization of cold extracted fraction of soluble sulfated polysaccharide from red seaweed Gracilaria birdiae

Water soluble polysaccharide from Gracilaria birdiae cultivated along the northeast coast of Brazil was characterized by infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. The composition of the polysaccharide in wt% was determined as: β-d-galp (50.3%), 3,6-anhydro-α-l-galp (40.5%) and -α-l-galp-6 sulfate (9.2%). The ratio of l/d units (β-d-galp units and 3,6-anhydro-α-l-galp + α-l-galp-6 sulfate) is that of an ideal agarose. The sulfate content calculated by S% accounts for 6.4%. 1D and 2D NMR techniques were employed in order to assign the spin system of polysaccharide without partial degradation. The structure is composed of → 4-3,6-anhydro-α-l-galp (1 → 3)β-d-galp 1 → segments, with the possibility of a α-l-galp unit substituted at the 6-position by sulfate ester.