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 Māori) was characterised using capillary viscometry, multi-angle laser light scattering and dynamic light scattering techniques. The intrinsic viscosity [η][η] of the native polymer was ∼2020 ± 23 mL/g (in Milli-Q water). The weight-average molar mass Mw and the root-mean square (Rg2)z1/2radius 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 ∼3 × 106 Da and ∼144 nm respectively. The z-average diameter of the samples obtained by dynamic light scattering was ∼75 nm. Based on the Smidsrød-Haug’s stiffness parameter B   (∼0.015); the exponent of (Rg2)z1/2 versus Mw (∼0.60); and the shape-factor (p  ) of (Rg2)z1/2/Rh (∼1.8), the results suggest that the polymer molecule adopted a semi-flexible (extended) random coil conformation in 0.1 M NaCl solution.

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