Computer-Chemie-Centrum, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91052 Erlangen, Germany.
Langmuir. 2010 Jul 6;26(13):10460-6. doi: 10.1021/la9038123.
A combined study using cryo-TEM experiments and molecular dynamics simulations reveals remarkable details of the factors that affect the self-organization of specifically designed T-shaped amphiphilic dendrimers upon treatment of an aqueous solution with ultrasound under a layer of hexane. This treatment leads to dodecameric, structured micelles rather than the heptameric ones observed without hexane. Three-dimensional reconstruction of the cryo-TEM images provides very detailed structures of the micelles, and molecular dynamics simulations suggest that approximately 36 hexane molecules are needed to stabilize the dodecameric micelles. Sodium counterions are found to exert a significant stabilizing effect that results in an apparent attraction between the highly negatively charged polycarboxylate headgroups. DFT calculations support the observation that the formation of ion multiplets is especially crucial for this stabilizing counterion effect, which reduces headgroup repulsion. This and the increased hydrophobic stabilization that results from the hexane-enlarged core of the micelle lead to stable dodecameric micelles. The specific effects found for sodium counterions are largely absent for potassium.
一项结合了低温透射电子显微镜实验和分子动力学模拟的研究揭示了在超声处理下，特定设计的 T 型两亲性树状大分子在正己烷层存在的水溶液中自组装的影响因素的显著细节。这种处理导致形成十二聚体结构的胶束，而不是在没有正己烷的情况下观察到的七聚体胶束。低温透射电子显微镜图像的三维重构提供了胶束非常详细的结构，分子动力学模拟表明，大约需要 36 个正己烷分子来稳定十二聚体胶束。钠离子被发现具有显著的稳定作用，导致带高度负电荷的多羧酸根基团之间明显的吸引力。DFT 计算支持这样的观察结果，即形成离子聚集体对于这种稳定的抗衡离子效应至关重要，它可以减少头基排斥。这种由于胶束核心增大的疏水性稳定作用以及正己烷的存在，导致了稳定的十二聚体胶束。对于钠离子的具体影响在很大程度上不存在于钾离子中。
