Tucker I M, Burley A, Petkova R E, Hosking S L, Penfold J, Thomas R K, Li P X, Webster J R P, Welbourn R, Doutch J
Unilever Research and Development, Port Sunlight Laboratory, Quarry Road East, Bebington, Wirral, UK.
Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford, UK; ISIS Facility, STFC, Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxon, UK.
J Colloid Interface Sci. 2021 Sep 15;598:444-454. doi: 10.1016/j.jcis.2021.03.101. Epub 2021 Mar 30.
There is an increased interest in the use of natural surfactant as replacements for synthetic surfactants due to their biosustainable and biocompatible properties. A category of natural surfactants which are attracting much current interest is the triterpenoid saponins; surface active components found extensively in a wide range of plant species. A wide range of different saponin structures exist, depending upon the plant species they are extracted from; but regardless of the variation in structural details they are all highly surface active glycosides. Greater exploitation and application requires a characterisation and understanding of their basic adsorption and self-assembly properties.
Glycyrrhizic acid, extracted from Licorice root, is a monodesmosidic triterpenoid saponin. It is widely used in cosmetic and pharmaceutical applications due to its anti-inflammatory properties, and is an ingredient in foods as a sweetener additive. It has an additional attraction due to its gel forming properties at relatively low concentrations. Although it has attracted much recent attention, many of its basic surface active characteristics, adsorption and self-assembly, remain relatively unexplored. How the structure of the Glycyrrhizic acid saponin affects its surface active properties and the impact of gelation on these properties are important considerations, and to investigate these are the focus of the study.
In this paper the adsorption properties at the air-water interface and the self-assembly in solution have been investigated using by neutron reflectivity and small angle neutron scattering; in non-gelling and gelling conditions.
The adsorption isotherm is determined in water and in the presence of gelling additives, and compared with the adsorption behaviour of other saponins. Gelation has minimal impact on the adsorption; apart from producing a rougher surface with a surface texture on a macroscopic length scale. Globular micelles are formed in aqueous solution with modest anisotropy, and are compared with the structure of other saponin micelles. The addition of gelling agents results in only minimal micelle growth, and the solutions remain isotropic under applied shear flow.
由于天然表面活性剂具有生物可持续性和生物相容性，人们对使用天然表面活性剂替代合成表面活性剂的兴趣日益增加。目前备受关注的一类天然表面活性剂是三萜皂苷；它们是在多种植物物种中广泛发现的表面活性成分。根据提取它们的植物物种不同，存在多种不同的皂苷结构；但无论结构细节如何变化，它们都是高度表面活性的糖苷。要进一步开发和应用，需要对其基本吸附和自组装特性进行表征和了解。
从甘草根中提取的甘草酸是一种单糖苷键三萜皂苷。由于其抗炎特性，它被广泛用于化妆品和制药应用中，并且作为甜味剂添加剂是食品中的一种成分。由于其在相对较低浓度下具有形成凝胶的特性，它还有额外的吸引力。尽管它最近受到了很多关注，但其许多基本的表面活性特征、吸附和自组装仍相对未被探索。甘草酸皂苷的结构如何影响其表面活性特性以及凝胶化对这些特性的影响是重要的考虑因素，而研究这些是本研究的重点。
在本文中，通过中子反射率和小角中子散射研究了在空气 - 水界面的吸附特性以及在溶液中的自组装；分别在非凝胶化和凝胶化条件下进行。
测定了在水中和存在凝胶添加剂时的吸附等温线，并与其他皂苷的吸附行为进行了比较。凝胶化对吸附的影响最小；除了在宏观长度尺度上产生具有表面纹理的更粗糙表面外。在水溶液中形成了具有适度各向异性的球状胶束，并与其他皂苷胶束的结构进行了比较。添加凝胶剂只会导致胶束生长最小，并且在施加剪切流时溶液保持各向同性。
