Ghosh Arjun, Dey Joykrishna
Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India.
J Phys Chem B. 2008 May 29;112(21):6629-35. doi: 10.1021/jp712111d. Epub 2008 May 1.
Surface activity and aggregation behavior of an amino acid-based zwitterionic amphiphile N-(2-hydroxydodecyl)-L-valine were studied in aqueous solutions (pH 13). The self-assembly formation was investigated by use of a number of techniques including surface tension, conductivity, viscosity, fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The amphiphile exhibits two breaks in the surface tension vs concentration plot indicating stepwise aggregate formation and thus results in two values of critical aggregation concentration. The amphiphile was found to be very surface active compared to fatty acid soaps. The average hydrodynamic diameter and size distribution of the aggregates were obtained from DLS measurements. Conductivity measurements suggested formation of vesicles or closed tubules. TEM pictures revealed the existence of spherical vesicles, separated tubules, and tubules with multiple Y-type junctions in going from dilute to moderately concentrated solution. However, in concentrated solution, the junctions break to form separate tubular structures which upon further increase of concentration are converted to rod-like micelles. The mechanism of branched tubule formation is discussed in light of the experimental observations.
在pH为13的水溶液中研究了基于氨基酸的两性离子两亲物N-(2-羟基十二烷基)-L-缬氨酸的表面活性和聚集行为。通过多种技术研究自组装形成，包括表面张力、电导率、粘度、荧光光谱、动态光散射和透射电子显微镜。两亲物在表面张力对浓度的图中呈现两个断点，表明逐步形成聚集体，因此产生两个临界聚集浓度值。与脂肪酸皂相比，发现该两亲物具有非常高的表面活性。通过动态光散射测量获得聚集体的平均流体动力学直径和尺寸分布。电导率测量表明形成了囊泡或封闭小管。透射电子显微镜图片显示，从稀溶液到中等浓度溶液，存在球形囊泡、分离的小管以及具有多个Y型连接的小管。然而，在浓溶液中，连接处断裂形成单独的管状结构，随着浓度进一步增加，这些管状结构转变为棒状胶束。根据实验观察结果讨论了分支小管形成的机制。
