| The low-dispersion xylan preparation and functionalization reactions are very important for realizing the high value utilization of hemicellulose.In this study,corncob was used as the raw material for xylan extraction,separation and purification.By selecting suitable reaction conditions,a series of low-dispersion xylan was extracted.The sulphur trioxide pyridine complex was used for sulphation reaction.The sulphated derivative of xylan was synthesized,and its functionalization test was conducted to study its role in biomedicine.The research progress has opened up the application of hemicellulose and established the basis for its application in biomedicine.(1)The method of extracting hemicellulose from corncob was studied.Alkaline hydrogen peroxide solution was selected as the extract in this study.The Na OH concentration,reaction temperature,time,and the ratio of solid to liquid are very important to affect the extraction efficiency of corncob hemicellulose.The reaction temperature of 50 °C,time of 16 h,and liquid to solid ratio of 20:1 were the best extraction conditions.At this time,the yield of corn cob hemicellulose was 83.15 %.(2)A graded ethanol precipitation technique was employed to obtain xylan from the alkaline hydrogen peroxide-extracted corncob liquid.And the effects of vacuum freezing and drying methods on the properties of xylan were investigated.The structure of the products were characterized by FT-IR,GPC,1H NMR and 13 C NMR.Results showed that the fractions of xylan prepared by this method consisted of xylose,glucose,arabinose and etc.And the degree of branching of xylan is from 0.17 to 0.52,which increased with the increase of ethanol concentration.The drying method has a great influence on the molecular weight of the product.The weight-average molecular weight of the vacuum-freeze dried xylan was from 108 533 to197 752.The weight-average molecular weight of vacuum drying and drying was from 42 311 to 47 242.Among the 12 products obtained by the two drying methods,the dispersion coefficients ranged from 1.17 to 1.52,and 11 of them had a dispersion coefficient of less than1.5,which was a low dispersion uniform polymer.Different fractions of xylan had different thermal stability.It was found for the first time that below 200°C,except for the H30 fraction,the thermogravimetric curves of Y10-30 fractions showed the degradation characteristics of a single polymeric segment,which could be used not only as the raw material for pharmaceuticals,but also for the synthesis of degradable polymers.(3)A new anticoagulant xylan sulfate sodium was synthesized by introducing sulfate groups into corncob xylan with the assistance of Li Cl.The structures and properties of sulfated polysaccharides were investigated by GPC,FT-IR and 13 C NMR spectroscopy.The effects of different solvents,material ratios,reaction temperatures,and time were studied,and the in vitro anticoagulant activity was investigated.The results indicated that the optimal conditions for sulfation were obtained when SO3·Py complex was added to DMF/Li Cl with –SO3/-OH ratio of1.5:1 and maintained at 55 ? for 3 h,and the degree of substitution(DS)was 1.53 and the yield was 78.2 %.A preliminary study of vitro anticoagulant activity was conducted and the results showed that the xylan sulfate sodium had anticoagulant activity. |
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