油酸在氢氧化胆碱水溶液中的自组装及十二烷基硫酸钠对其囊泡化pH窗口的影响

Self-assembly of oleic acid in aqueous solution of choline hydroxide and effects of sodium dodecyl sulfate on the pH window thereof for vesicle formation

脂肪酸囊泡具有封闭双层膜结构,可包埋活性分子。以油酸(OA)为模型脂肪酸,依据pH滴定曲线和目视观察法划分胶束、囊泡、乳液或油水分相等相区,确定了OA在氢氧化胆碱(ChOH)中囊泡化的pH窗口为7.5~9.1,用动态光散射、相差显微镜结合透射电子显微镜技术进一步表征了OA/ChOH囊泡的尺寸和形貌,呈现尺度多分散性。为进一步改善OA/ChOH囊泡形成pH范围窄且远离人体生理条件的缺陷,加入阴离子表面活性剂十二烷基硫酸钠(SDS),结果表明SDS摩尔分数(x)为0.1时即可将囊泡化pH窗口向酸性迁移至生理pH条件附近;随x增加,复合囊泡pH窗口呈现向酸性拓宽的趋势,甚至可达到强酸性条件。复合囊泡形成的主要原因是SDS与OA分子间的氢键作用,在较低pH范围内可代替“酸-皂”二聚体间的氢键作用。复合囊泡作为包埋体时,具有较高的包封率和载药量以及良好的缓释效果。

Fatty acid vesicles have closed bilayer structure and can encapsulate active molecules.Taking oleic acid(OA)as model fatty acid,the phase regions including micelles,vesicles,emulsion and oil-water separation were designated using pH titration curve and visual observation method.The pH window of OA/hydroxide choline(ChOH)vesicles was determined to be 7.5-9.1.The size and morphology of OA/ChOH vesicles were characterized using dynamic light scattering,phase contrast microscopy and transmission electron microscopy,showing size polydispersity.An anionic surfactant,sodium dodecyl sulfate(SDS),was added to OA/ChOH system,aiming to shift and expand the pH window of OA/ChOH vesicles to a range from being acidic to slightly alkaline,depending on the molar ratio(x)of SDS.At x=0.1,the pH window could be shifted to lower pH which matched the pH range of body fluid.With increasing x,the pH window was significantly broadened towards acidity,even reaching a very low pH of 1.3.The hydrogen bonding between SDS and OA molecules played a key role in the vesicle formation in the lower pH range,which had replaced the hydrogen bonding between acid-soap dimers of fatty acids.The composite vesicles as capsules had higher encapsulation efficiency,drug-loading capacity,and sustained drug release properties.This research work could provide a theoretical guidance for potential application in drug delivery and cosmetics.