Study On Autocatalytic Reaction Kinetic Of Fatty Acid Vesicles In Crowding

Fatty acid vesicles are researched widely as biomimic membrane, food and drug delivery carrier around home and abroad, which also have been studied at the initial stage in our lab. When the drug is released in the target cell, the carrier will be affected by the cellular intracellular environment—the crowding, but there were no reports about the influence of crowding on the behavior of vesicles. So, it has directive significance to deeply explore the biomimic membrane and the drug delivery systems by the behavioral changes of fatty acid vesicles.This paper is to explore the variation and the law of autocatalytic reaction of fatty acid vesicles in crowding, then the types, molecular weight and concentration of crowding agents which is suitable to this system were screened; then used the conductivity, transmission electron microscopy (TEM), dynamic light scattering (DLS) and low-field NMR (LF-NMR) technology to investigate the influence of the crowded environment on the fatty acid vesicles in the CMC value, morphology, size distribution, and water distribution in this system and so on; Finally, a reaction model was proposed through the mechanism assumptions of the hydrolysis of fatty acid anhydride process and derived a kinetic equation which then was verified and from which the reaction rate constant and the activation energy were calculated. The autocatalytic reaction characteristics and laws of fatty acid vesicles in crowding and buffer were obtained by deeply analysing the results above.(1) Construction of the crowding system.The macromolecular polymers of PEG and Dextran were used to create the crowding, then the PEG-2000(molecular weight) which is the main crowding agent and Dextran-20000which is to compare with PEG were chosen through taking account of the melting point and solubility of polymers in the moderate temperature. The10wt.%concentration of crowing agents was selected as the concentration of crowed environment from the results of autocatalytic curve and size distribution of fatty acid vesicles. Besides, the stable and reliable dynamic vesicle reaction systems in different solutions were builded by choosing five types of fatty acid anhydride and using the experimental condition at the initial stage in our lab.(2) Study on the effect of the crowding on fatty acid vesicles. Conductance method was used to investigat the CMC of fatty acid salts in different solutions, from the results we found the value of CMC changed little in crowding and aqueous which indicated the crowding don't influence the formation of micelle. By electron microscopy and DLS technology to study the fatty acid vesicles morphology and sizes, we found that the crowding affect the aggregation of vesicles in solutions that results in the vesicles becaome crowded, while the cross-linking between polymer and vesicles makes the vesicle deformation, or even rupture, which was also showed in the size distribution of vesicles that is much larger in crowding than in buffer. The results of water distribution in different systems from LF-NMR also illustrate the analysis above. The influence of crowding on vesicles is similar to the low concentration of polymer solutions, so it provide a reference to further explore the crowded environment of higher concentration.(3) Study on the autocatalytic reaction kinetic of fatty acid vesicles.The reaction mechanism model was assumed, then the kinetic equation was derived, finally the kinetic equation was validated and the activation energy was obtained by the autocatalytic reaction curves in different temperature and different solutions.The results of data validation to the kinetic equation indicat that the assumed model of the reaction mechanism meet the experimental results, the mechanism in this model is second-order reaction; it also shows that when to derive this type of kinetic equations some of reactions can be omitted to simplify. From the calculation of the catalytic reaction rate we found that the k become larger as temperature increases and the length of carbon chain, the autocatalytic reaction of octanoic anhydride, nonanoic anhydride and decanoic anhydride are inhibited in the crowded environment compared to in the buffer, but promote the hydrolysis reaction of lauric anhydride and oleic anhydride. From the activation energy obtained by the reaction rate constant data at different temperatures, we found the activation energy reduce with the increase of the carbon chain of fatty acid anhydride, short carbon-chain systems (≦10) from the catalytic reaction required more energy in crowding than in the buffer and long carbon-chain system (>10) and vice versa. It can be found the analysis results of the data was consistent with experimental observations, which also verified the assumption that the reaction mechanism and the derivation of the kinetic equation are correct.It provides reference to study the variety regular of other systems in crowding through this reasearch and resolves the problem that didn't find in the above experiment by deeply study the autocatalytic reaction mechism and kinetic of fatty acid vesicles, which offer the theory evidence to the further research on fatty acid vesicles.