| Hydrolysis of fatty acid anhydrides in macromolecular crowded environment involves the formation of fatty acid vesicles,interfacial catalysis,self assembly and physiological crowding environment,which can be used as a model to understand the physicochemical mechanism of lipid hydrolysis catalyzed self-assembly vesicles in human intestine.Self-assembly of fatty acid vesicles Autocatalytic hydrolysis refers to the hydrolysis of fatty acid anhydride to produce a certain amount of fatty acids.When the critical concentration of fatty acids is reached,the protic and aprotic fatty acids are aggregated to form self-assembly within a certain pH range.When the fatty acid concentration reaches the critical vesicle concentration,the fatty acid vesicles will form.The resulting vesicle self-assembly,due to its hydrophobic region,is capable of solubilizing water-insoluble fatty acid anhydrides and allowing more anhydride to participate in the reaction,so that the rate of fatty acid production increases dramatically and more fatty acids in turn self-assemble into More vesicles,which is self-assembled fatty acid vesicles autocatalytic hydrolysis.In this paper,the nonionic hydroxyethyl cellulose polysaccharide of 2-HEC and ionic polysaccharides such as sodium alginate(SA)and sodium chondroitin sulfate A(CSA)as macromolecular crowding agents,and two kinds of fatty acid anhydrides(decanoicanhydride and oleic anhydride)were chosen to investigate the crowded effects of polysaccharides on the autocatalytic kinetics of fatty acids at the vesicle interface.(1)The kinetics of the autocatalytic formation of medium chain saturated fatty acid vesiclesThe kinetics of the autocatalytic formation of decanoicacid vesicles in polysaccharides was studied.It was found that in the 2-HEC crowding environment,the rate of the autocatalytic formation of decanoicacid vesicles was slower than that in dilute solutions,which increased with the increasement of both the concentration and molecular weight of 2-HEC.It indicates that the autocatalytic rate of the decanoic acid vesicles depends on the type of polysaccharides.Particle size experiments showed that the particle sizes of decanoicacid vesicles decreased with the increase of the concentration of polysaccharides,which facilitated the interfacial catalysis of vesicles and also accelerated the rate of autocatalytic formation of decanoic acid vesicles.In the initial stage of reaction,the vesicle diameter in CSA crowding environment was the smallest,followed by the dilute solution,which was the largest in 2-HEC crowding environment.This is one of the reason why reaction rate of decanoic anhydride hydrolysis was the fastest in CSA crowding environment,but the slowest in 2-HEC crowding environment.The rheological experiments showed that the viscosity of the 2-HEC crowding environment increased with the increasement of the molecular weight of 2-HEC.The viscosity of the crowding environment decreased with the increasement of polysaccharide concentration in the low concentration range(0.1 wt%?0.01 wt%)at molecular weight of both 90000 and 250000,which accompanied by the accelerated rate of the hydrolysis of decanoic anhydride.This phenomenon indicated that the viscosity of 2-HEC90000 and 2-HEC250000 crowding environment at low concentration was the main factor affecting the hydrolysis of decanoic anhydride.In the CSA and SA crowding environment,as the polysaccharide concentration increased,the viscosity of the crowding environment become higher and higher,and the hydrolysis rate of decanoicanhydride increased accordingly.Therefore,for the CSA and SA crowding environment,the viscosity is not the main factor affecting the hydrolysis of decanoic anhydride.Viscoelastic experiments on the polysaccharide macromolecule network revealed that their viscoelasticity mainly had elastic behaviors,which may promote the hydrolysis of decanoic anhydride at low concentration(0.1 wt%?0.01 wt%).In 2-HEC crowding environment,viscosity was the dominant factor that inhibited the hydrolysis of decanoic anhydride.Therefore,the polysaccharide macromolecular network structure is the main factor affecting the hydrolysis of decanoic anhydride.It was found that the vesicle membrane fluidity decreased with the increasement of 2-HEC concentration,and the degree of freedom of the decanoic acid molecule decreased,which was unfavorable for the hydrolysis of anhydride.Therefore,the hydrolysis of decanoic anhydride slowed down.In contrast,the hydrolysis rate of decanoic anhydride in the CSA and SA crowding environment accelerated with increasing their concentration.Therefore,the vesicle membrane fluidity was also the major factor affecting the hydrolysis of decanoic anhydride.By studying the vesicle membrane fluidity during the hydrolysis,it was found that in the hydrolysis of decanoic anhydride,the changing trend of the decanoic acid vesicle fluidity first increased.It increased to a certain value at a certain time,then began to decrease,and finally tended to be stable.This phenomenon was common in both dilute solution and polysaccharide macromolecule solution.The controlled experiments showed that the size of decanoicacid capsules suddenly become smaller corresponding to the reaction time is the vesicular mobility of the moment.According to the hydrolysis rate of decanoic anhydride,one can speculate that at the moment when the particle size become smaller and the fluidity of the vesicle membrane increased,the decanoic anhydride hydrolysis reaction is abrupt.This may further prove that the vesicle size and membrane fluidity were both the main factors affecting the hydrolysis of decanoic anhydride.(2)The kinetics of autocatalytic growth of long-chain unsaturated fatty acid vesiclesThe kinetics of autocatalytic formation of long-chain unsaturated fatty acid vesicles in polysaccharides revealed that the hydrolysis rate of oleic anhydride increased in all three polysaccharide crowding environment.In the 2-HEC crowding environment,with the decrease of 2-HEC concentration,the rate of self-catalytic hydrolysis of acid vesicles increased gradually,but in CSA and SA crowding environment,the rate of autocatalytic hydrolysis of oleic acid vesicles increased with the increase of the polysaccharide concentration.Therefore,different polysaccharide crowding environment had different effects on the autocatalytic hydrolysis of oleic acid vesicles.The hydrolysis experiment of oleic acid vesicles showed that the particle size decreased with the increase of polysaccharide concentration,and the size of oleic acid vesicles in the 2-HEC crowding environment was smaller than that of CSA and SA crowding environment,which revealed the relationship between particle size and hydrolysis rate,that is,the size of oleic acid vesicles was the main factor affecting the hydrolysis of oleic anhydride.Viscosity experiments showed that the addition of low concentration of polysaccharide would reduce the overall viscosity of crowding environment,which may be attributed to reduced the size of oleic acid vesicles and lower viscosity of small size vesicles owing to the addition of polysaccharides.The high concentration of polysaccharides had a smaller particle size,which lead to the increased the viscosity of such crowding environment and the hydrolysis rate.Therefore,the low-concentration hydrolysis rate in the 2-HEC crowding environment is higher than that at high concentration.It demonstrated that the viscosity of 2-HEC crowding environment was the main factor affecting the hydrolysis of oleic anhydride.In the CSA and SA crowding environment,both the viscosity and hydrolysis rate of oleic anhydride increased with the increasement of polysaccharide concentration,which indicated that viscosity was not the main factor affecting the hydrolysis of oleic anhydride in the CSA and SA crowding environment.By studying the viscoelasticity of polysaccharide macromolecular network,it was found that in both the 2-HEC and SA crowding environment,the elastic behavior dominated their viscoelasticity,which may favor the promotion of oleic acid vesicles autocatalytic formation.Through the study of the vesicle membrane fluidity,it was found that increasing the polysaccharide concentration reduced the fluidity of the membrane and inhibited the movement of oleic acid molecules,which hindered the hydrolysis by vesicles.However,the hydrolysis of oleic anhydride are still accelerated.Therefore,the influence of the fluidity of oleic vesicle membrane on the hydrolysis rate of oleic anhydride was not the main factor.The effects of different crowding environments on the autocatalytic hydrolysis rate of fatty acid vesicles in different crowded environments were systematically illustrated by studying the autocatalytic hydrolysates induced by fatty acid vesicles of different saturations and chains with different polysaccharide macromolecule crowding conditions Revealing the law of fatty acid hydrolysis in a crowded environment,in order to understand the intestinal digestion and absorption of fat,build a reasonable diet,to prevent various diseases caused by excessive fat intake,provide a theoretical basis. |
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