Dipartimento di Chimica, Università di Roma "La Sapienza" , P. le A. Moro 5, 00185 Roma, Italy.
Langmuir. 2013 Oct 8;29(40):12342-51. doi: 10.1021/la402602d. Epub 2013 Sep 24.
In this paper, the preparation and characterization of an anionic and a cationic surfactant obtained by chemical modifications of a natural bile acid (cholic acid) are reported. The bile acid was modified by introducing a diamine or a dicarboxylic aromatic residue on the lateral chain. The pure cationic surfactant self-assembles in a network of fibers with a cross-section gyration radius of about 15.1 Å, providing hydrogels with a pH-dependent compactness. On the other hand, the anionic molecule gives rise to prolate ellipsoid micelles. Homogeneous catanionic mixtures have also been obtained, with molar fraction of each surfactant ranging from 0.125 to 0.875. At total surfactant concentration of 0.05% (w/v), the mixtures form gels of fibrils partially arranged in secondary twisted superstructures. Comparison of this concentration with the minimum gelation concentration of the pure cationic derivative (0.16% w/v) suggests that, in the mixtures, the presence of the electrostatic component in self-assembly of the molecules allows the formation of gels starting from more dilute samples. In view of these achievements, this work suggests that catanionic mixtures can be exploited to enhance the efficiency of gelators.
本文报道了通过化学修饰天然胆酸（胆酸）得到的阴离子和阳离子表面活性剂的制备和表征。胆酸通过在侧链上引入二胺或二羧酸芳基残基进行修饰。纯阳离子表面活性剂在纤维网络中自组装，其横截面回转半径约为 15.1 Å，提供了具有 pH 依赖性致密性的水凝胶。另一方面，阴离子分子产生了扁长椭球胶束。还获得了均匀的混合胶束，每种表面活性剂的摩尔分数范围为 0.125 至 0.875。在总表面活性剂浓度为 0.05%（w/v）时，混合物形成部分排列在二级扭曲超结构中的纤维凝胶。与纯阳离子衍生物的最小凝胶化浓度（0.16%w/v）相比，该浓度表明在混合物中，分子自组装中静电分量的存在允许从更稀的样品开始形成凝胶。鉴于这些成就，这项工作表明混合胶束可以用于提高凝胶剂的效率。
