Boundary lines and linactants: Structure, function, and dynamics

非技术总结：本项目开发了设计有效吸附在“线”上的分子的一般原则：“溶解剂”，类似于“表面活性剂”（例如肥皂和脂质），可有效吸附在表面上。表面无处不在：细胞膜将细胞的内部和外部分开；油/水的混合物穿过岩石和沙子。任意两个面相交于一条直线。因此，有效的溶出剂具有提高原油采收率的潜力，了解溶出剂原理将有助于更深入地了解细胞膜的结构、动力学和功能。该项目和肯特州立大学（KSU）为培养高中生、本科生和研究生提供了丰富的跨学科环境，以应对当今经济中的各种机会。他们接受个人的专业指导，并与散射解决方案公司（一家初创公司）和KSU液晶研究所的工业合作伙伴密切互动。此外，首席研究员是一名女性，她在让女性参与研究方面有着悠久的历史：在她的实验室里，65%的研究生和50%的本科生是女性，远远高于物理学的标准。这个项目的各个方面都受到了主要研究者对初中、高中和社区大学学生及其老师的积极推广的推动。技术概述：本项目使用Langmuir薄膜作为模型系统，探索线张力（线的单位长度的能量）和线活性的结构起源。Langmuir薄膜是由分子/分子和分子/水的引力相互作用的微妙平衡而限制在空气/水界面的一层分子组成。分子结构与线活性之间的关系尚不清楚。与表面活性剂的类比表明，这是一种杂化分子：对两种表面相具有不同亲和力的两个部分。在实践中，这些分子形成第三相，与线边界具有中等亲和力。线和面边界结构之间的对比表明了一种截然不同的线活性模型，这将改变对线活性分子结构的研究。远离临界点的表面边界大约是一个分子的厚度。表面活性剂分子可以很容易地跨越相间的边界。相反，间接证据表明，线的边界是10个或更多分子的厚度：在这种情况下，活性剂应该比典型的表面活性剂大得多，或者它应该起非局部作用。为了研究分子尺度、介观尺度和宏观尺度之间的联系，本项目分为三个方面：(a)通过测量线能量和线熵间接测试边界的宽度，以及通过低温透射电镜和其他方法直接测试边界的宽度。这些测试集中在一个在表面形成液晶多层的模型系统上，简化了这些具有挑战性的实验，并提供了层数对比作为额外的控制变量。(b)在模型系统和生物相关的混合脂质层中，通过自发曲率和曲率弹性，测试作为溶剂的分子在非局部起作用。该项目最初专注于根据初步结果提出的线活性分子，随后是具有不同形状的液晶介质和具有相似但相反的有效自发曲率的脂质分子。(c)利用互补技术的独特组合，探讨线张力至关重要的一种情况，即脂质层内的成核动力学。有效的溶剂设计将使自组装膜的发展具有可控的规模以及化学和物理结构。这种薄膜适用于例如传感器。溶解剂也与细胞膜有关，被认为含有控制细胞内外通信的动态纳米级结构域：是什么控制这些结构域仍然是一个关键的悬而未决的问题。这个跨学科的项目培养了一群不同的高中生、本科生和研究生，并推动了主要研究者积极地向初中、高中和社区大学的学生和他们的老师伸出援手。

NON-TECHNICAL SUMMARY:This project develops general principles for the design of molecules that adsorb efficiently to a "line": "linactants", in analogy to "surfactants" (soaps and lipids, for example), which adsorb efficiently to surfaces. Surfaces are ubiquitous: cell membranes divide the inside from the outside of the cell; oil/water mixtures push through rock and sand. Any two surfaces meet at a line. Thus, effective linactants have potential for enhanced oil recovery and understanding linactant principles will enable a deeper understanding of the structure, dynamics and function of cell membranes. This project and Kent State University (KSU) provide a rich interdisciplinary environment for training high school, undergraduate and graduate students for a diversity of opportunities in today's economy. They receive personal, professional mentoring, and interact closely with Scattering Solutions Inc., a startup company, and with industrial partners of the KSU Liquid Crystal Institute. Further, the principle investigator, a woman, has a deep history of involving women in research: 65% of the graduate and 50% of the undergraduate students in her lab have been women, far above the norm in physics. All aspects of this project both fuel and are fueled by the principle investigator's active outreach to middle school, high school, and community college students and their teachers.TECHNICAL SUMMARY:This project uses Langmuir films, which consist of a layer of molecules confined at the air/water interface by a delicate balance of molecule/molecule and molecule/water attractive interactions, as a model system to explore the structural origin of line tension (the energy per unit length of a line) and line activity. The relationship between molecular structure and line activity is unclear. The analogy with surfactants suggests a hybrid molecule: two moieties with different affinities for the two surface phases. In practice, such molecules form a third phase, with moderate affinity to the line boundary. The contrasts between the structure of line and surface boundaries suggests a dramatically different model of line activity that would transform the search for line-active molecular structures. A surface boundary, away from a critical point, is about one molecule thick. A surfactant molecule can easily span the boundary between phases. In contrast, indirect evidence suggests that the line boundary is ten or more molecules thick: in that case, either a linactant should be much larger than a typical surfactant, or it should act nonlocally. This project is three-pronged, in order to develop the connection between molecular, mesoscopic, and macroscopic scales: (a) To test the width of the boundary both indirectly, through measurements not just of line energy but of line entropy, and directly, through cryoTEM and other methods. These tests concentrate on a model system that forms liquid crystalline multilayers on the surface, simplifying these challenging experiments and providing layer number contrast as an additional control variable. (b) To test as linactants molecules expected to act non-locally, through spontaneous curvature and curvature elasticities, both in the model system and in biologically-relevant mixed lipid layers. The project initially focuses on line-active molecules suggested by preliminary results, followed by liquid crystalline mesogens with different shapes and lipid molecules that have similar but opposite effective spontaneous curvatures. (c) To explore one case where line tension is critical, nucleation dynamics within lipid layers, with a unique combination of complementary techniques. Effective linactant design will enable the development of self-assembled films with domains of controllable scale as well as chemical and physical structure. Such films are applicable to e.g. sensors. Linactants are also relevant to cell membranes, thought to contain dynamic nano-scale domains that control communication between the inside and outside of the cell: what controls these domains remains a critical open question. This interdisciplinary project trains a diverse group of high school, undergraduate and graduate students and fuels the principle investigator's active outreach to middle school, high school, and community college students and their teachers.