研究目的
The purpose of our study is to estimate the thermodynamic parameters with respect to lamellar-vesicular transition and to understand the transition mechanism forming the vesicles from the lamellar-bilayer structure from a molecular viewpoint.
研究成果
We estimated the Gibbs free energy of vesicle formation, and its calculated value was approximately ?2.7 kJ/mol at 303 K. The change in Gibbs free energy for the transition from lamellar LCs into vesicles on the addition of a chemical additive was negative; that is, the vesicles are more stable than the initial lamellar LCs. In the transition process from lamellar LCs to vesicles, an excited state was formed due to the solubilization of organic substances in the bilayer structures.
研究不足
The thermodynamic parameters of vesicle formation have never been estimated because the amount of added external energy cannot be known exactly. Furthermore, no studies have been reported concerning the energetics of vesicle formation for cationic amphipathic substances; furthermore, vesicle stabilization has not been clarified experimentally.
The vesicles were prepared by our previously reported chemical additive method. In this procedure, a lipophilic compound is added to the lamellar LCs first, followed by addition of a neutral salt. Here, we used limonene as the lipophile and calcium chloride as a neutral salt, and we attempted to estimate the thermodynamic parameters of vesicle formation of DEAE in accordance with following concepts. First, we defined three DEAE conditions: (1) 20 wt% DEAE dispersion with no additives (state 0), (2) limonene was added to state 0 (forming state 1), and (3) calcium chloride was added to state 1 (forming state 2). Models of the bilayers under these conditions are shown in Scheme 1. When both limonene whose molar fraction for DEAE reached ≥ 0.1 and the calcium chloride whose concentration for water reached ≥ 500 mmol kg?1 were added to DEAE lamellar LCs, SEM and AFM images of the DEAE dispersion revealed spherical structures, such as the vesicles12. Therefore, the minimal concentrations were used to estimate the thermodynamic parameters of lamellar-vesicular transition.
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