The Effects of Additives on the Physicochemical Properties of Catanionic Vesicles Formed by Dihexdecyl-Chained Ion Pair Amphiphile

Autor: Wei-FenChang, 張維芬
Rok vydání: 2012
Druh dokumentu: 學位論文 ; thesis
Popis: 100
In this study, the surfactant solubility in water was increased by rasimg the temperature and the ion pair amphiphile (IPA) hexadecyltrimethylammonium-hexadecylsulfate (HTMA-HS) was prepared by a precipitation approach. Then the catanionic vesicles were fabricated from HTMA-HS with the addition of different molar fractions of cholesterol and dihexadecyl phosphate (DHDP) by a force formation process, and the effects of additives on the physicochemical properties of the catanionic vesicles composed of HTMA-HS were investigated. In addition, the effects of alkyl chain length and symmetry of IPA on the physicochemical properties of catanionic vesicles were analyzed by comparing the catanionic vesicles composed of HTMA-HS with those composed of two other IPAs with different chain lengths. The experimental results indicated that catanionic vesicles which were stable up to 50 days could be prepared from HTMA-HS. However, significant aggregation between the vesicles was detected. The addition of a proper amount of cholesterol or DHDP could slow down the aggregation or fusion rates of the vesicles, but defects in the vesicular bilayer structures might be induced, resulting in limited enhancement effect on the physical stability of the catanionic vesicles. By adding both cholesterol and DHDP, the mechanical strength of the vesicular bilayers and the electrostatic repulsion between the vesicles were increased, and the physical stability of the catanionic vesicles could be significantly improved. The arrangement of molecular alkyl chains in the vesicular bilayers was analyzed by the infrared spectroscopy, and it was found that the molecular alkyl chains became less ordered when cholesterol was added below the phase transition temperature of the HTMA-HS bilayers. The addition of DHDP only slightly lowered the order of the molecular alkyl chains. By analyzing the physicochemical characteristics of the catanionic vesicles composed of different IPAs with the addition of cholesterol, one could find that the longer the alkyl chain length of IPA, the more positive the zeta potential of catanionic vesicles. This might be the reason for the vesicles composed of HTMA-HS possessing better physical stability than the vesicles composed of two other IPAs. However, the IPA (DTMA-DS) with shorter and symmetric alkyl chains could better interact and match well in structure with cholesterol. As a result, adding a small amount of cholesterol could significantly enhance the physical stability of the vesicles composed of DTMA-DS.
Databáze: Networked Digital Library of Theses & Dissertations
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