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Regioselective modification is an effective approach to synthesize polysaccharides with different structure features and improved properties. In this study, regioselective sulfation of Artemisia sphaerocephala polysaccharide (SRSASP) was prepared by using triphenylchloromethane (TrCl) as protecting precursor. The decrease in fractal dimension (df) values (1.56-2.04) of SRSASP was observed in size-exclusion chromatography combined with multi angle laser light scattering (SEC-MALLS) analysis. Compared to sample substituted at C-6, SRSASP showed a more expanded conformation of random coil, which was attributed to the breakup of hydrogen bonds and elastic contributions. Circular dichroism (CD), methylene blue (MB) and congo red (CR) spectrophotometric method and atomic force microscopy (AFM) results confirmed the conformational transition and stiffness of the chains after sulfation. SRSASP exhibited enhanced antioxidant activities in the DPPH, superoxide and hydroxyl radical scavenging assay. Sulfation at C-2 or C-3 was favorable for the chelation which might prevent the generation of hydroxyl radicals. It concluded that the degree of substitution and substitution position were the factors influencing biological activities of sulfated polysaccharides., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The conventional extraction methods for polysaccharides were time-consuming, laborious and energy-consuming. Microwave-assisted extraction (MAE) technique was employed for the extraction of Artemisia sphaerocephala polysaccharides (ASP), which is a traditional Chinese food. The extracting parameters were optimized by Box-Behnken design. In microwave heating process, a decrease in molecular weight (M(w)) was detected in SEC-LLS measurement. A d(f) value of 2.85 indicated ASP using MAE exhibited as a sphere conformation of branched clusters in aqueous solution. Furthermore, it showed stronger antioxidant activities compared with hot water extraction. The data obtained showed that the molecular weights played a more important role in antioxidant activities.