β-D-(1→4), β-D-(1→3) 'mixed linkage' xylans from red seaweeds of the order Nemaliales and Palmariales

Xylans from five seaweeds belonging to the order Nemaliales (Galaxaura marginata, Galaxaura obtusata, Tricleocarpa cylindrica, Tricleocarpa fragilis, and Scinaia halliae) and one of the order Palmariales (Palmaria palmata) collected on the Brazilian coasts were extracted with hot water and purified from acid xylomannans and/or xylogalactans through Cetavlon precipitation of the acid polysaccharides. The beta-D-(1 -> 4), beta-D-(1 -> 3) 'mixed linkage' structures were determined using methylation analysis and ID and 2D NMR spectroscopy. The presence of large sequences of beta-(1 -> 4)-linked units suggests transient aggregates of ribbon- or helical-ordered structures that would explain the low optical rotations. (C) 2011 Elsevier Ltd. All rights reserved.