Functional Nanotubes from Self-Assembled Bis-Urea Macrocycles

自然界使用自组装方法来控制生物结构的大小和形状，以实现特定的功能。例子包括蛋白质通道和酶。蛋白质通道是由折叠成中空管状结构并跨越膜的蛋白质形成的，以允许小分子或离子从膜的一侧通过通道到达另一侧。酶是一种蛋白质，它折叠成一个三维结构，形成一个特定大小和形状的口袋，用于结合目标分子并将其转化为所需的化学产品。受自然的启发，南卡罗来纳大学的Linda Shimizu教授制造了小的甜甜圈形状的分子，这些分子高保真地组装成被称为纳米管的稻草状结构。这些纳米管具有直径不到一纳米(大约一缕头发宽度的1/1000倍)的微小一维通道。清水团队进行研究，以了解气体和小分子是如何组织起来的，并通过这些微小的通道进行移动。她的研究小组还使用这些纳米管来限制这些通道中的分子相互之间的取向，这改变了这些被困客人的反应方式。从这项研究中获得的基础知识可能对分离技术、流动反应器和新合成方法的开发具有重要意义。广泛的研究方法为培养不同的研究生群体提供了一个具有挑战性的跨学科环境，并为本科生和高中生提供了初步的研究经验。此外，该奖项还支持一项化学推广计划，该计划通过将化学家带到南卡罗来纳州少数族裔入学率较高的初中和高中的K-12教室，广泛促进公众对科学的兴趣。这些学校访问旨在展示科学方法，突出尖端研究，并培养人们对化学和自然科学的兴趣。清水教授的实验室在国家科学基金会高分子、超分子和纳米化学计划的支持下，利用双尿素大环的受控组装来提供功能管状组件来探索基本问题。这项研究调查了含有三苯胺、二苯甲酮和其他有机三重态增敏剂的大环和线性类似物的结构-性质关系。紫外光照射后，这些组件在纳米管壁内形成自由基。这些自由基的数量、持久性和性质与它们的结构和组织有关。在本项目中，清水团队1)研究组装以了解自由基稳定性的起源；2)研究探针在纳米通道内的扩散；3)评估通道壁中的自由基与通道内包裹的客体如何相互作用；4)评估三重态敏化剂在含氧溶液中的组装情况，以确定它们形成活性氧物种的效率；以及5)研究纳米反应器促进溶液中的光氧化、光环加成和光聚合反应的能力。所获得的知识应该会导致新的预测工具，以确定何时会形成持久的自由基，并提供更好的了解限制对反应性的影响。这些结果应该会导致有机自由基结构多样性的增加，有机自由基作为分子磁铁、生物系统中的探针、极化试剂和聚合的自由基引发剂具有重要意义。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nature employs self-assembly approaches to control the size and shape of biological structures for performing specific functions. Examples include protein channels and enzymes. A protein channel is formed by a protein that folds into a hollow tubular structure and spans across a membrane to allow passage of small molecules or ions from one side of a membrane to the other side through the channel. An enzyme is a protein that folds into a 3-dimensional structure to create a pocket of specific size and shape for binding and converting target molecules into desired chemical products. Inspired by Nature, Professor Linda Shimizu of the University of South Carolina makes small donut-shaped molecules that assemble in high fidelity into straw like structures called nanotubes. These nanotubes have tiny 1-dimensional channels of less than a nanometer (about 1/1000 times of the width of a strand of hair) in diameter. The Shimizu group conducts research to understand how gases and small molecules are organized and move through these tiny channels. Her research group also uses these nanotubes to restrict how molecules in these channels are oriented with respect to one another, which alters how these trapped guests can react. Fundamental knowledge to be gained from this research could have important implications in separation technologies, flow reactors and the development of new synthetic methods. The broad research approach provides a challenging and interdisciplinary environment to train a diverse group of graduate students as well as provides first research experiences for undergraduates and high school students. In addition, this award supports a chemistry outreach program that broadly promotes public interest in science by bringing chemists into South Carolina K-12 classrooms of high minority enrollment middle schools and high schools. These school visits are intended to showcase the scientific method, highlight cutting edge research, and foster interest in chemistry and in the natural sciences.Work in Professor Linda Shimizu's laboratory, supported by the Macromolecular, Supramolecular and Nanochemistry Program at the National Science Foundation, utilizes the controlled assembly of bis-urea macrocycles to afford functional tubular assemblies to probe fundamental questions. This research investigates structure-property relationship of macrocycles and linear analogues that contain triphenylamines, benzophenones, and other organic triplet sensitizers. After UV-irradiation, these assemblies form radicals within the walls of the nanotubes. The quantity, persistence and properties of these radicals are related to their structure and organization. In this project, the Shimizu group 1) studies the assemblies to understand the origin of the radical stability; 2) probes diffusion within the nanochannels; 3) evaluates how radicals in the channel walls interact with guests encapsulated within the channels; 4) evaluates the assemblies of triplet sensitizers in oxygenated solutions to determine their efficiency at forming reactive oxygen species; and 5) studies the ability of the nanoreactors to facilitate photooxidations, photocycloadditions and photopolymerization reactions in solution. The knowledge acquired should lead to new predictive tools to determine when persistent radicals will form as well as afford a better understanding of the effects of confinement on reactivity. These results should lead to an increase in structural diversity of organic radicals, which are of interest as molecular magnets, as probes in biological systems, for polarizing agents and as radical initiators for polymerization.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.