Catalytic synthesis of sulfated polysaccharides. II: Comparative studies of solution conformation and antioxidant activities

Sulfated derivatives of Artemisia sphaerocephala polysaccharide (ASP) with high degree of substitution (DS) were synthesized using 4-dimethylaminopyridine (DMAP)/dimethylcyclohexylcarbodiimide (DCC) as catalyst. Size exclusion chromatography combined with multi-angle laser light scattering (SEC-LLS) results showed a decrease in fractal dimension (df) values of sulfated ASP (SASP). Compared to ASP and SASP with low DS (0.51–1.01), SASPcata2 exhibited an internal structure between rigid rod and random coil with a DS of 1.24. DS had greater influence on its conformation in aqueous solution. Circular dichroism (CD), methylene blue (MB) and Congo red (CR) spectrophotometric method and atomic force microscopy (AFM) results confirmed that the degradation of ASP and SO3H groups improved significantly the stiffness of the chains due to the electrostatic effect. Furthermore, antioxidant experiments revealed that high DS could enhance the scavenging activities of radicals and reducing power of SASP in vitro. The extended chain conformation was beneficial to enhance the biological activity of sulfated polysaccharides.