Molecular characteristics of a novel water-soluble polysaccharide from the New Zealand black tree fern (Cyathea medullaris)

A water-soluble polysaccharide fraction isolated from the fronds of the black tree fern (Cyathea medullaris or 'Mamaku' in Maori) was characterised using capillary viscometry, multi-angle laser light scattering and dynamic light scattering techniques. The intrinsic viscosity [eta] of the native polymer was similar to 2020 +/- 23 mL/g (in Milli-Q water). The weight-average molar mass M(w) and the root-mean square (R(g)(2))(Z)(1/2) radius of the polymer molecules in 0.1 M NaCl, determined using a size-exclusion chromatography coupled to a multi-angle laser light scattering (SEC-MALLS), were similar to 3 x 10(6) Da and similar to 144 nm respectively. The z-average diameter of the samples obtained by dynamic light scattering was similar to 75 nm. Based on the Smidsrod-Haug's stiffness parameter B (similar to 0.015); the exponent of (R(g)(2))(Z)(1/2) versus M(w) (similar to 0.60); and the shape-factor (p) of (R(g)(2))(Z)(1/2)/R(h) (similar to 1.8), the results suggest that the polymer molecule adopted a semiflexible (extended) random coil conformation in 0.1 M NaCl solution. (C) 2010 Elsevier Ltd. All rights reserved.