Structural and compositional characteristics of a sulfated galactan from the red alga Gracilariopsis persica

An agar polysaccharide has been isolated from the red seaweed Gracilariopsis persica collected from the Persian Gulf (Iran). Characterization of the structure by chemical and spectroscopic methods showed a basic repeating structure of alternating 3-linked β-d-galactopyranosyl and 4-linked 3,6-anhydro-α-l-galactopyranosyl units. The main polysaccharide components were 3,6-anhydrogalactose (31.8%), galactose (52.1%) and 6-O-methyl-galactose (10.9%). In addition, minor components such as glucose (4.1%) and xylose (1.1%) were detected. The degree of substitution (DS) of sulfate, calculated from S%, was 0.18%. Data from 13C NMR, FT-IR, methylation and desulfation–methylation provided evidence of sulfation at C-2 and C-6 of l-galactose and also C-4 of d-galactose. Gel permeation chromatography (GPC) indicated Mw = 2.22 × 105 g/mol for this polysaccharide.