CAREER: Supramolecular Polycondensation of Polymer Brushes via DNA Hybridization

非技术人员生物非常擅长利用纳米物体，如蛋白质，作为构建块来创造它们所需的材料。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以获得的新形式重新创造，来模拟天然蛋白质所展示的一些精密组装能力。为了实现这一目标，PI的团队将设计瓶刷式合成聚合物(长聚合物分子上有短小的附属物，就像瓶刷中的刷毛一样)，并将它们与短链DNA连接起来。因为DNA对互补链的识别是明确的，所以原则上可以准确地设计刷子聚合物之间的互连。有了这种方法，就有可能创造出一类新的“超级聚合物”，即以纳米级聚合物为构件的聚合物。PI将探索可以形成的超级聚合物的种类，并确定它们的形成规则。由于DNA识别的特殊性，具有各种性质的聚合物构建块，如大小、电导率或生物相互作用，可以以特定序列和空间定义的方式连接在一起，创建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内的天然核酸介导，因此在医学上具有重要的意义。这些研究活动将与教育项目交织在一起，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教师对与科学相关的职业的学习和意识。技术和技术摘要当存在吸引力时，大分子和胶体纳米颗粒等纳米物体可以形成有序结构。由于球状粒子在其表面上均匀地相互作用，定向组装形成一维或二维结构是一个巨大的挑战。在这个由材料研究部聚合物和生物材料计划共同资助的项目中，PI将利用DNA识别作为功能基团-相当于对定做的聚合物构建块的自下而上组装进行编程，这些构建块只能在指定的方向上相互作用。这些限价构建块将被用于研究拓扑调控的超分子聚合。所提出的自组装策略包括合成三嵌段刷状聚合物作为大单体，这些大单体将与核酸结合。核酸链之间的杂交使单体能够头到尾地自组装，以线性或分支的方式将它们连接起来，形成更高顺序的组装。通过系统地研究具有不同侧链长度、DNA双链和反应性嵌段长度的刷子聚合物文库，将获得关于刷子构建块的线性组装的机理见解。此外，还将研究使用多单体体系(例如AA+BB)的超级聚合物顺序控制，为创造多组分功能材料铺平基础。来自缩聚反应的定义小分子聚合的概念将与使用单价和多价大单体的超聚合物合成进行对比测试，这些大单体有望提供对体系结构、平均聚合度和链端官能度的控制。从该项目中获得的能力将开启一系列设计材料，这些材料的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，并为研究未知的性质创造机会。

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.