The effect of macromolecular crowding degree on the self-assembly of fatty acid and lipid hydrolysis.

Investigation on the physiochemical nature involved in the production of fatty acid catalyzed by the vesicles is of importance to understand the digestion of lipid. In this paper, the effects of crowding degree, which was constructed by polyethylene glycol (PEG), on the autocatalytic production of fatty acid with different chain lengths was studied. The results showed that the higher crowding degree led to the slower production rate of decanoic acid but the faster rate of oleic acid. The reason lies in that the presence of macromolecules resulted in the increased sizes of decanoic acid vesicles, but decreased sizes of oleic acid vesicles. Meanwhile, decanoic acid vesicles in more crowded medium exhibited viscous behavior, whereas oleic acid displayed elastic behavior. This research provides useful information for understanding the unusual autocatalyzed production of fatty acid in macromolecular crowding and may also draw an attention to the physiologically relevant lipid digestion.

Thermodynamics and Structural Evolution during a Reversible Vesicle-Micelle Transition of a Vitamin-Derived Bolaamphiphile Induced by Sodium Cholate.

Interaction of endogenous sodium cholate (SC) with dietary amphiphiles would induce structural evolution of the self-assembled aggregates, which inevitably affects the hydrolysis of fat in the gut. Current work mainly focused on the interaction of bile salts with classical double-layered phospholipid vesicles. In this paper, the thermodynamics and structural evolution during the interaction of SC with novel unilamellar vesicles formed from vitamin-derived zwitterionic bolaamphiphile (DDO) were characterized. It was revealed that an increased temperature and the presence of NaCl resulted in narrowed micelle-vesicle coexistence and enlarged the vesicle region. The coexistence of micelles and vesicles mainly came from the interaction of monomeric SC with DDO vesicles, whereas micellar SC contributed to the total solubilization of DDO vesicles. This research may enrich the thermodynamic mechanism behind the structure transition of the microaggregates formed by amphiphiles in the gut. It will also contribute to the design of food formulation and drug delivery system.

Chain-length-dependent autocatalytic hydrolysis of fatty acid anhydrides in polyethylene glycol.

Autocatalytic hydrolysis of fatty acid anhydrides induced by the spontaneously formed vesicles has been studied for years. However, whether the reaction autocatalyzed by vesicles formed in diluted solutions applies also to macromolecular crowded conditions remains unknown. The aim of this study is to characterize hydrolysis behavior of fatty acid anhydrides and formation of vesicles in crowded media. Inert macromolecular crowding agents such as polyethylene glycol (PEG) and Dextran were used to probe the impact of external crowding on the autocatalytic hydrolysis of fatty acid anhydrides with varied hydrophobic chain length. Under stringent conditions of crowding, hydrolysis rates of octanoic anhydride, nonanoic anhydride, and decanoic anhydride were found to decrease, but the rates of lauric anhydride and oleic anhydride increased. These results suggest that the effect of the crowding agent on the hydrolysis of fatty acid anhydrides was chain-length-dependent. Characterization of the size and polydispersity of vesicles formed from hydrolyzed fatty acid anhydrides in crowding revealed that long-chain fatty acids formed monodisperse vesicles easier at lower concentrations of PEG. Measurement of the critical aggregation concentration of ionized fatty acid in the presence of PEG showed that crowding media promoted vesicle formation from long-chain fatty acids but inhibited those from fatty acids with fewer carbon atoms. Further investigation of the diffusion property of ionized fatty acids in crowding agents suggested that PEG might create more hydrophobic areas for long-chain fatty acids anhydrides, which subsequently promoted the unreacted anhydride in the aqueous phase to be solubilized in the formed vesicles. This research provides information for understanding the autocatalytic reaction accompanied by self-producing aggregates and the behavior of fatty acids in crowding media.