| Aralia chinensis L.belongs to Aralia,Araliaceae.Its root bark and stem bark can be used as medicines,with the functions of blood sugar lowering,analgesia,anti-tumor and anti-aging.Studies have shown that its medicinal ingredients were mainly polysaccharides,and saponins,etc.In recent years,A.chinensis polysaccharides have gained wide attention,and the introduction of various functional groups can not only lower the side effect of polysaccharide drugs but also improve the physical and chemical character and activity of them.Among the modification methods,sulfation was the most popular one.Sulfated polysaccharide derivatives have received more and more attention due to their excellent physical and chemical properties and biological activities.Therefore,chemical modified A.chinensis stem-bark polysaccharides(SASCP)by the chlorosulfonic acid-pyridine method(CSA-Py)were prepared.The preliminary in vitro antioxidant activity was explored.The main conclusions were as follows:(1)Response surface methodology(RSM)to optimize the preparation process and structural characterization of SACSPA.chinensis stem-bark polysaccharides(ACSP)were modified by CSA-Py to obtain SACSP.The synthesis conditions of SACSP were optimized by RSM.The optimum conditions were as follows: CSA/Py was 2.51,reaction time was 4.70 h,and reaction temperature was 65.02 °C.The theoretical maximum of the degree of substitution(DS)is 1.57.Under the optimal conditions,2.5: 1 as CSA/Py,65° C as the reaction temperature,and 5 h as the reaction time were selected to perform the repeated test.DS under these conditions was 1.56,which was in line with model expectations.The structure of the SACSP was characterized by X-ray photoelectron spectroscopy(XPS)and Fourier transform infrared spectroscopy(FT-IR).The results showed that the sulfate group has been successfully introduced into ACSP.Gas chromatography-mass spectrometry(GC-MS)analysis of monosaccharide composition showed that SACP consisted of arabinose,glucose,galactose,and mannose.The average molecular weight(Mw)of SACSP detected by Size Exclusion Chromatography with Laser Light Scattering(SEC-LLS)showed that Mw of SACSP was 1.98×105 g/mol,Mn of SACSP was 6.13×104 g/mol and Mw/Mn of SACSP was 3.23.(2)A preliminary study on the antioxidant activities of ACSP and SACSP in vitroThe antioxidant activities of ACSP and SACSP were investigated by measuring the reducing capacity,chelating ability of Fe2+ and the scavenging ability on superoxide anion radical,DPPH radical,and hydroxyl radicals of ACSP and SACSP with different DS.The semi-inhibitory concentrations(IC50s)of ACSP,SACSPL-DS,SACSPM-DS,and SACSPH-DS when clearing O2-· were 0.485 mg/m L,0.017 mg/m L,0.022 mg/m L and 0.015 mg/m L respectively.And in the range of 0.02-0.1 mg/m L,the ability of all modified samples to eliminate O2-· was better than that of Vc control.The semi-inhibitory concentrations(IC50s)in the ability to scavenge DPPH free radicals of ACSP,SACSPL-DS,SACSPM-DS,and SACSPH-DS were 3.807 mg/m L,2.202 mg/m L,2.95 mg/m L and 1.133 mg/m L respectively.ACSP,SACSPL-DS,SACSPM-DS,and SACSPH-DS all had certain ability to remove ·OH radical,and their semi-inhibitory concentrations(IC50)were 37.376 mg/m L,15.445 mg/m L,16.981 mg/m L and 5.321 mg/m L respectively.Both ACSP and SACSP had a certain degree of total reduction capacity and were positively correlated with the degree of substitution of the samples.The samples had a certain ability to chelate Fe2+,but the chelation ability of the sample to Fe2+ didn’t show a significant dependence on the degree of substitution.In addition,the ability of SACSP to scavenge DPPH radical,·OH radical,O2-· radical,and reducing power as well as chelating capacity on Fe2+ were concentration-dependent.In summary,it can be concluded that moderately sulfation modification of ACSP is an effective way to increase its antioxidant activity. |
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