Institute of Food, Nutrition and Health, ETH Zurich, 8092 Zurich, Switzerland.
Laboratory of Neutron Scattering and Imaging, Paul Scherrer Institut PSI, 5232 Villigen, Switzerland.
Phys Chem Chem Phys. 2024 Jan 24;26(4):2806-2814. doi: 10.1039/d3cp04835g.
Bio- or plant-based surfactants are a sustainable and renewable alternative to replace synthetic chemicals for environmental, drugs and food applications. However, these "green" surfactants have unique molecular structures, and their self-assembly in water might lead to complex morphologies and unexpected properties. The micellization of saponin molecules, such as glycyrrhizic acid (GA), differs significantly from those of conventional synthetic surfactants, yet these differences are often overlooked. Saponins self-assemble in complex hierarchical helical morphologies similar to bile salts, rather than the expected globular, ellipsoidal and wormlike micelles. Here, we review two potential routes for molecular self-assembly of GA, namely kinetics of crystallization and thermodynamic equilibrium, focusing on their structure as a function of concentration. Some uncertainty remains to define which route is followed by GA self-assembly, as well as the first type of aggregate formed at low concentrations, thus we review the state-of-the-art information about GA assembly. We compare the self-assembly of GA with conventional linear surfactants, and identify their key similarities and differences, from molecular and chemical perspectives, based on the critical packing parameter (CPP) theory. We expect that this work will provide perspectives for the unclear process of GA assembly, and highlight its differences from conventional micellization.
生物或植物基表面活性剂是一种可持续且可再生的替代品，可以替代用于环境、药物和食品应用的合成化学品。然而，这些“绿色”表面活性剂具有独特的分子结构，它们在水中的自组装可能导致复杂的形态和意想不到的性质。与常规合成表面活性剂相比，甘草酸（GA）等皂苷分子的胶束化有很大的不同，但这些差异往往被忽视。皂苷自组装成复杂的螺旋状层次结构，类似于胆汁盐，而不是预期的球状、椭圆形和蠕虫状胶束。在这里，我们综述了 GA 分子自组装的两种潜在途径，即结晶动力学和热力学平衡，重点关注其结构随浓度的变化。目前仍存在一些不确定性，无法确定 GA 自组装遵循哪种途径，以及在低浓度下形成的第一种聚集体，因此我们综述了有关 GA 组装的最新信息。我们将 GA 的自组装与传统的线性表面活性剂进行了比较，并从分子和化学的角度，根据临界堆积参数（CPP）理论，确定了它们的关键相似点和不同点。我们希望这项工作将为 GA 组装过程的不明确性提供一些视角，并突出其与传统胶束化的不同之处。
