| Fatty acid vesicle is a colloidal suspension, composed of fatty acid/fatty acid salt, and has a closed bi-layer structure that similar to lipid. Compared with the traditional biomimic cell-liposome, fatty acid vesicle has a greater dynamic character. The molecules that form the vesicle exchange quicklier with those do not attend in the vesicle construction. Therefore, fatty acid vesicle can be better used to build chemical biomimic system. In the reported literatures, the fundamental properties of two static fatty acid vesicle reacting systems were studied, however, those systems were unstable, the reproducibility of the results was poor. Moreover, the reaction kinetic was seldom reported.In this paper, we employed fatty acid anhydride as substrate, systematically studied the formation conditions and self-replicating autocatalytic effect through the Fourier Transform Infrared spectroscopy (FTIR) and electron microscopy characterization. By the transition state energy calculation and mathematical model fitting, the relationship between the reaction kinetic and the vesicle shape parameters were revealed. Therefore, a stable and reliable dynamic vesicle reacting system was well build.The main research work and results are as follows:(1) Construction of self-replicating autocatalytic vesicle system. Three fatty acid anhydrides were selected to build a simple and stable vesicle system. Through the systematic study of various factors that would affect the result, the best reaction conditions were fixed. For octanoic anhydride, pH 6.80,0.5 M phosphate buffer solution,50 x (magnetic stirring,60 x corresponds to 2000 rpm) stirring speed, and 30℃,45℃,60℃reacting temperature were used; for decanoic anhydride, pH 8.25,0.3 M Tricine buffer,50 x stirring speed, and 35℃,45℃,60℃reacting temperature were employed; while for oleic anhydride, pH 8.50,0.2 M Bicine buffer,50 x stirring speed, and 20℃,30℃,40℃experiment temperature were the best condition.(2) Study of self-replicating effect. The vesicle morphology and quantity distribution were studied by electron microscopy. Particle size and quantity of fatty acid vesicle changed at different times. Took the decanoic acid vesicle reacted at 45 degrees for example, when time was short, there's no vesicle; more than 6 hours, vesicles formed; while it came to 6 h～12 h, vesicles increased dramatically. Took the 9 hours' sample (most notably vesicular catalysis and frequent reproduction) and sprayed gold for SEM observation, we saw a large number of full spherical vesicles and growth intermediates. Due to surface curvature and other factors, vesicles would experience a similar growth of bean budding and splitting instead of unlimitedly expansion. Combined the total interface area calculation with catalytic effect study, the vesicles' interface catalysis nature could be confirmed.(3) Kinetic study of autocatalysis. A quantitative analysis method based on FTIR was build and employed to monitor the hydrolysis of three anhydrides. Combined the Origin 8.0 Sigmoidal fitting results with the transition state energy calculation and Arrhenius equation, the physical meaning kinetic expressions were obtained. Based on the comprehensive experimental and mathematical fitting results, we listed the autocatalytic rate as follows:oleate vesicle> decanoate vesicle> octanoate vesicle, which was consistent with the critical aggregation concentration.Compared with the existing research, we expanded the experiment system, optimized the reaction conditions and build a stable and reliable dynamic vesicles system. It not only improved the accuracy of the experiment results, but also laid a good foundation to the later chemical biomimic system research in our lab.
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