Vesicle-Catalyzed Production Of Fatty Acid In Macromolecular Crowding:Chain-Length-Dependence And Crowding-Degree-Dependence

Investigating the physicochemical nature involved in the formation of fatty acid catalyzed by the vesicles interfaces is of great importance to understand the digestion of lipid food.Hydrolysis of fatty acid anhydrides in macromolecular crowded environment may be a suitable model to explore the physical-chemical processes in gut,because vesicles forms in this reaction which further catalyze the hydrolysis.In this paper,an unusual chain-length-dependent vesicle-catalyzed production of fatty acid was disclosed by quantitatively exploring the effects of crowding degree,on the autocatalytic hydrolysis of three fatty acid anhydrides with different chain lengths,namely decanoic anhydride,lauric anhydride and oleic anhydride in different varied molecular weight and concentration of polyethylene glycol(PEG),Ficoll and Dextran.(1)Vesicle-catalyzed production of fatty acid in PEGThe results showed that vesicle-catalyzed production rate of fatty acid in PEG200,PEG2000 and PEG20000,decanoic acid is slower than that in diluting solution,but the rates of lauric acid and oleic acid are quicker than that in diluting solution.What's more,the higher concentrations or molecular weights of PEG led to the slower production rate of decanoic acid but faster rates of lauric acid and oleic acid.The presence of PEG increased the sizes of decanoic acid/decanoate vesicles,but decreased sizes of oleic acid/oleate vesicles.Meanwhile,when the concentration and molecular weight of PEG increase,the size of vesicles rangeability increases.Investigation on the viscosity of fatty acids vesicles of different chain length with or without crowding agents showed that increased crowding degree increased the viscosity of decanoic acid/decanoate vesicles,however it decreased that of oleic acid/oleate vesicles.The higher concentrations of PEG with decanoic acid/decanoate vesicles exhibited more viscous behavior,whereas PEG with oleic acid/oleate vesicles displayed more elastic behavior due to a stronger network formation.(2)Vesicle-catalyzed production of fatty acid in Ficoll and DextranThe results showed that the vesicle-catalyzed production rates of fatty acid,in Ficol170,Ficoll400 and Dextran20 are similar with that in PEG,where the rate of decanoic acid is slower than that in diluting solution,but the rate of oleic acid are quicker than that in diluting solution.What's more,the higher concentrations of polysaccharide led to the slower production rate of decanoic acid but faster rate of oleic acid.However,it showed that the influence of molecular weights of polysaccharide on the vesicle-catalyzed production rate of fatty acid was not obvious,and the macromolecular structure had certain influence on the production rate of fatty acid.The presence of polysaccharide increased the sizes of decanoic acid/decanoate vesicles,but decreased the sizes of oleic acid/oleate vesicles.Meanwhile,when both the concentration and molecular weight of polysaccharide increased,the size of vesicles rangeability increased.Investigation on the viscosity of fatty acids vesicles in different chain length with or without crowding agents disclosed that increased degree of crowding increased the viscosity of decanoic acid/decanoate vesicles but decreased that of oleic acid/oleate vesicles.The higher concentrations of Ficoll with decanoic acid/decanoate vesicles exhibited more viscous behavior,whereas Ficoll with oleic acid/oleate vesicles displayed more elastic behavior due to a stronger network formation.The above results show that in PEG and polysaccharide solution,the variation trend of vesicle-catalyzed production rate of decanoic acid is accordance with the variable trend of vesicle-catalyzed production rate of oleic acid.It showed that the abnormal effects of kinetic chain length on vesicle-catalyzed production rate of fatty acid in crowded environments constituted by different crowded agents is a universe phenomenon.When the crowding degree increases(including the increase of concentration and molecular weight),the vesicle-catalyzed production rate of decanoic acid decreases,and vesicle-catalyzed production rate of lauric acid and oleic acid.Three reasons may explain the above experimental results:1.The change of the size of fatty acid vesicles in crowding environment influences catalytic efficiency;2.The change of the viscocity of fatty acid vesicles in crowding environment influences the vesicle boundary material's diffusion rate;3.The change of macromolecule reticular structure's viscoelasticity influences the material transport.the above results also suggest that in the presence of crowed media,different hydrophobic interactions between fatty acids and macromolecules might exist in the complex catalytic reactions.In the autocatalytic process of producing fatty acid with medium hydrophobic chain,the diffusion might dominate the reaction;but for long-chain fatty acid,the promoting outcome of macromolecular crowding exhibited in the reaction.This research provides useful information for understanding the unusual autocatalyzed production of fatty acid in macromolecular crowding,which may also draw an attention to the physiologically relevant chain-length-dependence of fatty acid.