Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, GuildfordGU2 7XH, U.K.
Groningen Research Institute of Pharmacy, University of Groningen, A. Deusinglaan 1, Groningen9713 AV, The Netherlands.
ACS Appl Mater Interfaces. 2022 Nov 30;14(47):53228-53240. doi: 10.1021/acsami.2c17558. Epub 2022 Nov 15.
A variety of two-dimensional (2D) nanomaterials, including graphene oxide and clays, are known to stabilize Pickering emulsions to fabricate structures for functions in sensors, catalysts, and encapsulation. We introduce here a novel Pickering emulsion using self-assembled amphiphilic triblock oligoglycine as the emulsifier. Peptide amphiphiles are more responsive to environmental changes (e.g., pH, temperature, and ionic strength) than inorganic 2D materials, which have a chemically rigid, in-plane structure. Noncovalent forces between the peptide molecules change with the environment, thereby imparting responsiveness. We provide new evidence that the biantennary oligoglycine, Gly-NH-CH-NH-Gly, self-assembles into 2D platelet structures, denoted as tectomers, in solution at a neutral buffered pH using small-angle X-ray scattering and molecular dynamics simulations. The molecules are stacked in the platelets with a linear conformation, rather than in a U-shape. We discovered that the lamellar oligoglycine platelets adsorbed at an oil/water interface and stabilized oil-in-water emulsions. This is the first report of 2D oligoglycine platelets being used as a Pickering stabilizer. The emulsions showed a strong pH response in an acidic environment. Thus, upon reducing the pH, the protonation of the terminal amino groups of the oligoglycine induced disassembly of the lamellar structure due to repulsive electrostatic forces, leading to emulsion destabilization. To demonstrate the application of the material, we show that a model active ingredient, β-carotene, in the oil is released upon decreasing the pH. Interestingly, in pH 9 buffer, the morphology of the oil droplets evolved over time, as the oligoglycine stabilizer created progressively a thicker interfacial layer. This demonstration opens a new route to use self-assembled synthetic peptide amphiphiles to stabilize Pickering emulsions, which can be significant for biomedical and pharmaceutical applications.
各种二维（2D）纳米材料，包括氧化石墨烯和粘土，已被证明可以稳定 Pickering 乳液，从而构建用于传感器、催化剂和封装的结构。我们在这里引入了一种使用自组装两亲性三嵌段寡聚甘氨酸作为乳化剂的新型 Pickering 乳液。与具有化学刚性、平面结构的无机 2D 材料相比，肽两亲物对环境变化（例如 pH 值、温度和离子强度）更敏感。肽分子之间的非共价相互作用随环境而变化，从而赋予其响应性。我们提供了新的证据表明，双触角寡甘氨酸 Gly-NH-CH-NH-Gly 在中性缓冲 pH 值下自组装成 2D 板状结构，称为 tectomers，使用小角 X 射线散射和分子动力学模拟。分子在板片中以线性构象堆叠，而不是 U 形。我们发现层状寡甘氨酸板在油/水界面上吸附并稳定水包油乳液。这是首次报道将 2D 寡甘氨酸板用作 Pickering 稳定剂。该乳液在酸性环境中表现出强烈的 pH 响应。因此，当降低 pH 值时，寡甘氨酸末端氨基的质子化由于排斥静电相互作用引起层状结构的解组装，导致乳液失稳。为了证明该材料的应用，我们展示了模型活性成分β-胡萝卜素在油相中释放。有趣的是，在 pH 值为 9 的缓冲液中，随着时间的推移，油滴的形态发生了演变，因为寡甘氨酸稳定剂逐渐在界面上形成更厚的层。这一演示为使用自组装合成肽两亲物稳定 Pickering 乳液开辟了新途径，这对于生物医学和制药应用具有重要意义。
