Aicart Emilio, del Burgo Patricia, Llorca Oscar, Junquera Elena
Departamento de Química Física I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040-Madrid, Spain.
Langmuir. 2006 Apr 25;22(9):4027-36. doi: 10.1021/la053474q.
Several experimental techniques (conductivity, zeta potential, transmission electronic microscopy, and steady-state fluorescence spectroscopy) have been used to study the formation of mixed colloidal aggregates consisting of a cationic double-chain surfactant, di-dodecyldimethylammonium bromide (di-C12DMAB), and a single-chain alkyltrimethylammonium bromide with 10 and/or 14 carbon atoms (decyltrimethylammonium bromide, C10TAB, and/or tetradecyltrimethylammonium bromide, C14TAB). Special interest has been devoted to the prevesicle domain, within which the formation of aggregated nanostructures was first reported in our laboratory. For that purpose, studies have been carried out on the very dilute region by means of conductivity experiments, confirming the existence of two critical aggregation concentrations in that concentration domain: the so-called mixed critical aggregate concentration, CAC, and the mixed critical vesicle concentration, CVC. By carrying out TEM experiments on negatively stained samples, we were surprised to find a number of aggregates without a clear aggregation pattern and with a variety of sizes and shapes at concentrations below CAC, where only monomers were expected. However, the nanoaggregates found at concentrations between CAC and CVC, also by TEM microscopy, show a clear and ordered "fingerprint"-like aggregation pattern similar to the liquid-crystalline phases reported for DNA-liposome complexes and/or DNA packed with viral capsids. Finally, at total surfactant concentrations above CVC, the aggregates were confirmed, by means of cryo-TEM micrographs and zeta potential measurements, to be essentially unilamellar spherical vesicles with a medium polydispersity and a net-averaged surface density charge of around 12 x 10(-3) C m(-2). The fluorescence emission of two probes, TNS (anionic) and PRODAN (nonionic), allows for the analysis of the micropolarity and microviscosity of the different microenvironments present in aqueous surfactant solutions where the above-mentioned vesicle and prevesicle aggregates are present.
几种实验技术（电导率、zeta电位、透射电子显微镜和稳态荧光光谱）已被用于研究由阳离子双链表面活性剂二甲基二正十二烷基溴化铵（di-C12DMAB）与含10和/或14个碳原子的单链烷基三甲基溴化铵（癸基三甲基溴化铵，C10TAB，和/或十四烷基三甲基溴化铵，C14TAB）组成的混合胶体聚集体的形成。特别关注的是前囊泡区域，在我们实验室中首次报道了该区域内聚集纳米结构的形成。为此，通过电导率实验在极稀区域进行了研究，证实了在该浓度区域存在两个临界聚集浓度：所谓的混合临界聚集浓度（CAC）和混合临界囊泡浓度（CVC）。通过对负染色样品进行透射电子显微镜实验，我们惊讶地发现在低于CAC的浓度下，有许多聚集体没有清晰的聚集模式，且大小和形状各异，而在该浓度下预计只有单体存在。然而，同样通过透射电子显微镜观察，在CAC和CVC之间的浓度下发现的纳米聚集体呈现出清晰且有序的“指纹”状聚集模式，类似于报道的DNA-脂质体复合物和/或与病毒衣壳包装的DNA的液晶相。最后，在总表面活性剂浓度高于CVC时，通过冷冻透射电子显微镜照片和zeta电位测量证实，聚集体基本上是具有中等多分散性且净平均表面电荷密度约为12×10⁻³ C m⁻²的单层球形囊泡。两种探针TNS（阴离子型）和PRODAN（非离子型）的荧光发射，可用于分析存在上述囊泡和前囊泡聚集体的水性表面活性剂溶液中不同微环境的微极性和微粘度。
