Study On Controlled Transition Of A Vitamin-Derived Bolaamphiphile Vesicles By Self-Assembly

Bolaamphiphile-based vesicles have many unique properties both in air-water surface and in aqueous solution. We can control a reversible transition between vesicles and micelles by changing external environment factors. The self-assembly characteristics of bolaamphiphiles also have a great effect on the assembling behavior of food protein, which influence the microstructure of the food system. To date, the controlled transition of vesicles formed by self-assembly of bolaamphiphiles has been rarely reported. Therefore, study on the controllable transformation of this novel green vitamin-derived bolaamphiphile vesicles offers great promise for drug delivery system, biological membrane simulation, food microstructure control and related fields.The single-chain bolaamphiphile1,12-diorotate diaminododecane (DDO) was synthesized for the present research. This novel green surfactant can form vesicles spontaneously in aqueous solution. Isothermal titration calorimetry (ITC) technology, dynamic light scattering (DLS) technology, transmission electron microscopy (TEM) technology and fluorescence spectrum technology were used to investigate the effect of classical surfactants and temperature on the controlled transition process of DDO vesicles, and the effect of the self-assembly properties of bolaamphiphiles on the assembling behavior of sodium caseinate (SC). By tracking the heat change mechanism of the self-assembly and disassembly process of DDO vesicles, we succeed in obtaining the real-time information of structural transformation process of vesicles, sequentially realizing the controllable change of the structure of DDO vesicles.(1) Study on vesicle-micelle transition of DDO induced by surfactants.This paper studied the transition of DDO vesicles induced by three classic surfactants of CTAB, SDS and TX100respectively. The results showed that all the three kinds of surfactants were able to induce DDO vesicles turned into micelles. Cationic surfactant CTAB and anionic surfactant SDS induced DDO vesicles to micelles transition through the hydrophobic interaction and electrostatic repulsion force, and the ITC curve of titration surfactants to DDO vesicles contains dynamic process of the disassembly of vesicles. By utilizing the methods of DLS and TEM, we proved that the inflection points of energetics on the ITC curve always correspond to the structure change of DDO vesicles. Nonionic surfactant TX100can change the surface tension of DDO vesicles that disrupt its structure through hydrogen bonding interaction, and induce the vesicles to micelles transition.(2) Study on a temperature-dependent reversible vesicle-micelle transition of DDO vesicles.Using ITC to investigate the effect of temperature on thermodynamic process of the interaction between CTAB and DDO vesicles, and connecting with DLS and TEM, we caught vesicles undergoing the dynamic process of disaggregation, growth, vesicles transformed into micelles, and micelles to vesicles transition. The inflection points of thermogram on the ITC always correspond to the structure of molecules self-assembly in aqueous solution. The results showed that the DDO vesicles formed by bolaamphiphiles were controllable by addition of CTAB and heat change. Addition of SDS combined with heating can also induce a reversible transition between DDO vesicles and micelles. However, a reversible transition of micelles to vesicles by heating can not be realized in the case of TX100. Moreover, we selected pyrene as a fluorescent probe molecule mixed it with DDO vesicles. The results showed that the embedding and release of pyrene fluorescent molecule can be realized by controlling the reversible transition of DDO vesicles and micelles.(3) Effect of DDO self-assembly characteristics on the aggregation behavior of sodium caseinate. We study the effect of DDO self-assembly characteristics on the aggregation behavior of sodium caseinate by using DLS and pyrene fluorescent probe methods. The results showed that when the DDO concentration was low, electrostatic repulsion was the driving force between DDO and SC. Adding DDO will destroy the aggregates of SC, therefore arousing the decrease of average size. With more DDO added, the hydrophobic force turned into the main force, causeing the SC gathered together and increased the average size of mixed system. As temperature can affect the self-assembly behavior of DDO, it could also control the interaction between DDO and SC. The Ⅰ·/Ⅰ3ratio of pyrene dissolved in mixed system decreased upon heating, which indicated the hydrophobic environment of solution was enhanced and induced the aggregation of SC through hydrophobic interaction, resulting in the increase of average size of mixed system. The color of the solution also changed from clear into light blue until milky white. Moreover, temperature effect on the aggregation behavior of mixed system was reversible.Based on analysis of energy effect of the molecular self-assembly process, we succeed in achieving a reversible transition between DDO vesicles and micelles by adding CTAB combined with heat change, and we also studied the effect of DDO self-assembly features on the aggregation behavior of sodium caseinate, which provide a reference for investigating more controllable process of self-assembly of novel green bolaamphiphiles, and also offered theoretical basis on the study of bolaamphiphiles in drug-delievery, food microstructure control and biological membrane simulation and related fileds.