Preparation Of Low Molecular Weight Acidic Oligosaccharides By Ultrasound-Fenton Treatment

Acid polysaccharides are a class of macromolecule matters widely existing in nature with multi-activities.They have been reported to possess various biological benefits,such as anticoagulant activities,antioxidation,antiviral activities,bacteriostasis,anticancer activities and neuroprotection.The present studies show that the molecular weight?Mw?and structure of polysaccharides are in direct contact with their biological activities and low molecular weight polysaccharides could exhibit stronger activities.However,the degrading rate of acid polysaccharides is low due to the presence of acidic groups.Therefore,it is a new research hotspot in the field of carbohydrate chemistry to find a mild and efficient way to reduce the molecular weight of polysaccharides and improve their biological activities.At present,the most common degradation methods of polysaccharides include ultrasound,acid hydrolysis and free radical depolymerization.However,the ultrasonic degradation capacity is limited,acid degradaion is considered as a harsh process and can cause structural damage of suger chains and a large amount of chemical reagents are needed for free radical degradation.Researchers hope to find a more green and effective way to degrade the polysaccharides.In this thesis,the ultrasound combined with Fenton system?US-Fenton?was applied to degrade heparin and pectin.The influencing factors of US-Fenton,structure and activites changes of degraded products were systematically investigated to optimize and predict the mechanism of degradation.The main methodologies and their corresponding results of this paper are as follows:1.Ultrasonic intensity,temperature,Fe²⁺ concentration,H₂O₂ concentration and pH all had a direct influence on the efficiency to degrade heparin.Ultrasound could catalyze Fenton process,but its intensity had little effect on the degradation rate.The comparable higher temperature,more concentred Fenton reagent and lower pH were beneficial to increase the degradation rate of heparin.According to the results of single factor experiments,the degradation parameters were obtained:ultrasonic intensity,3.8 W/mL,temperature,30 ?,Fe²⁺ concentration,1.5 mmol/L,H₂O₂ concentration,6 g/L and pH,3.FT-IR,NMR and HILIC-MS analysis showed that there was no significant change in the structure of heparin during US-Fenton process and-OH produced by US-Fenton was more susceptible to attack the uronic acid in heperin.The results showed that the anticoagulant activities of degraded product LWMH-2 were close to that of enoxaparin,parnaparin and nadroparin.Besides,low-molecular-weight heparin was effective for both intrinsic and common pathway of coagulation and there was a dose-dependent relationship.2.US-Fenton system had more efficient degradation of pectin than US,Fenton and US-H₂O₂ and the Mw of citrus pectin decreased with the prolongation of US-Fenton treatment time.Ultrasound catalyzed Fenton reaction to improve the degradation efficiency of pectin,but the ultrasonic intensity had little effect on the degradation efficiency.Higher temperature and Fe²⁺ concentration promoted the degradation rate and the optimum parameters were as follows:ultrasonic intensity,3.8 W/mL,temperature,30 ?,Fe²⁺ concentration,1.0 mmol/L,H₂O₂ concentration,6 g/L and pH,3.Under these conditions,the low molecular weight pectin?UFP-1 and UFP-2?was prepared.Compared with the natural pectin,US-Fenton process reduced the degree of esterification and the content of uronic acid of UPF-1 and UFP-2.Combined with FT-IR and NMR analysis,it was concluded that the oxidative degradation induced by US-Fenton system focused on galacturonic acid attacking the HG domain and retained the RG-I domain to a greater extent.In addition,antioxidant experiments showed that UPF-1 and UFP-2 possessed a stronger antioxidant activity.