CAREER: Supramolecular Polycondensation of Polymer Brushes via DNA Hybridization

非技术总结生物体非常擅长利用纳米级物体，如蛋白质，作为构建块来创建它们所需的材料。事实上，蛋白质-蛋白质相互作用是所有细胞的基础，因为它们具有高度的方向性、特异性和可逆性;这些特征是合成化学家尚未完全模仿的。该项目的目标是通过提取这种组装的要求，并以现代聚合物和有机化学可访问的新形式重新创建它们，来模拟天然蛋白质所表现出的一些精确组装能力。为了实现这一目标，PI的团队将设计类似于瓶刷的合成聚合物（其中长聚合物分子有短的附属物，就像瓶刷中的刚毛一样），并将它们与短链DNA连接起来。由于互补链的DNA识别是明确定义的，因此原则上可以精确地设计刷状聚合物彼此的互连性。通过这种方法，有可能产生一类新的“超聚合物”，即其构建块是纳米级聚合物物体的聚合物。PI将探索可以形成的超级聚合物的种类，并确定其形成的规则。由于DNA识别的特异性，具有各种性质（如大小、电导率或生物相互作用）的聚合物结构单元可以以序列特异性和空间限定的方式连接在一起，以产生以前难以或不可能获得的功能材料。这种合成技术也有可能由细胞中的先天核酸介导，因此在医学上具有重要意义。这些研究活动将与教育计划相结合，为研究生/本科生（包括缺乏研究能力的机构的本科生）提供实验室培训，并促进高中生和STEM教师在科学相关职业中的学习和意识。技术概述纳米物体，如大分子和胶体纳米颗粒，当存在吸引力时，可以形成有序结构。由于球形颗粒在其表面均匀地相互作用，因此定向组装以形成1D或2D结构是一个重大挑战。在该项目中，由材料研究部的聚合物和生物材料项目共同资助，PI将利用DNA识别作为功能组等效物来编程按顺序制造的聚合物构建块的自下而上组装，这些聚合物构建块只能在定义的方向上相互作用。这些有限价的积木将被用来研究拓扑调控的超分子聚合。所提出的自组装策略涉及合成三嵌段刷状聚合物作为“大分子单体”，其将与核酸缀合。核酸链之间的杂交允许单体头对尾地自组装，将它们线性地或分支地连接，以形成更高级的组装体。通过系统地研究具有不同侧链长度、DNA双链体和反应性嵌段长度的刷状聚合物的库，将获得关于刷状构建块的线性组装的机械见解。此外，还将使用多单体体系（如AA+BB）研究超级聚合物序列控制，为创建多组分功能材料奠定基础。定义小分子聚合的缩聚反应的概念将被测试对超级聚合物合成，利用单价和多价大分子单体，这是预期提供控制架构，平均聚合度，和链端功能。从该项目中获得的能力将打开一个广泛的设计材料，其顺序和拓扑特征在纳米尺度上得到了很好的定义，并将带来聚合物科学的新知识，并创造研究未知特性的机会。

NON-TECHNICAL SUMMARYLiving organisms are very proficient at utilizing nanoscopic objects, such as proteins, as building blocks to create materials that they need. Indeed, protein-protein interactions are the foundation of all cells because they are highly directional, specific, and reversible; these are characteristics that synthetic chemists have yet to fully emulate. The goal of this project is to emulate some of the precision-assembly ability that natural proteins exhibit by extracting the requirements for such assembly, and recreating them in new forms accessible to modern polymer and organic chemistry. Towards this goal, the PI's team will design bottlebrush-like synthetic polymers (where long polymer molecules have short appendages across them like the bristles in a bottlebrush) and connect them with short strands of DNA. Because DNA recognition of a complementary strand is well defined, one can in principle design the interconnectivity of the brush polymers with one another accurately. With this approach, it is possible to create a new class of "superpolymers", i.e. polymers whose building blocks are nanoscale-sized polymeric objects. The PI will explore the kinds of superpolymers that can be formed, and identify rules governing their formation. Because of the specificity of DNA recognition, polymer building blocks with various properties, such as size, electrical conductivity, or biological interactions, can be linked together in a sequence-specific and spatially defined manner, to create functional materials previously difficult or impossible to access. This synthetic technique also has the potential to be mediated by innate nucleic acids in cells, and therefore has important implications in medicine. These research activities will intertwine with educational programs to provide laboratory training to graduate/undergraduate students (including undergraduates from institutions lacking research capabilities) and to promote learning and awareness in science-related careers among high school students and STEM teachers.TECHNICAL SUMMARYNanoscopic objects such as macromolecules and colloidal nanoparticles can form ordered structures when there exist attractive forces. Because sphere-like particles uniformly interact across their surfaces, directional assembly to form 1D or 2D structures represents a significant challenge. In this project, co-funded by the Polymers and Biomaterials Programs in the Division of Materials Research, the PI will utilize DNA recognition as a functional group-equivalent to program the bottom-up assembly of made-to-order polymeric building blocks that can interact with each other only in defined directions. These limited-valency building blocks will be used to study topologically regulated supramolecular polymerizations. The proposed self-assembly strategy involves the synthesis of triblock brush polymers as "macromonomers", which will be conjugated with nucleic acids. The hybridization between the nucleic acid strands allows the monomers to self-assemble head-to-tail, connecting them either linearly or with branching, to form higher order assemblies. By systematically studying a library of brush polymers with different side-chain length, DNA duplex, and reactive block length, mechanistic insights about linear assembly of the brush building blocks will be obtained. In addition, superpolymer sequence control will be studied using multiple monomer systems (e.g. AA+BB), paving the ground for creating multi-component functional materials. Concepts from polycondensation reactions that define small-molecule polymerization will be tested against superpolymer synthesis, utilizing mono- and multi-valency macromonomers, which are expected to provide control over architecture, average degree of polymerization, and chain-end functionality. The capabilities gained from this project will open a wide spectrum of designer materials whose sequential and topological characteristics are well-defined on the nanoscopic scale, and will bring about new knowledge in polymer science and create opportunities to study yet unknown properties.