CAREER: Chirality and Polymer Thermodynamics: Frustration and Amplification

该奖项部分由2021年美国救援计划法案（公法117-2）资助。非技术性总结该职业奖支持理论和计算研究，以及导致聚合物材料手性结构的自组装综合教育。不把一只手翻过来，就不能把左手放在右手上。材料中的原子或分子可以定位自己，使它们具有相同的性质;材料中的原子与材料的镜像不重合。区分材料是右手还是左手的能力表明该材料具有手性。手性本身具有特定的相互作用和新颖的性质，其应用范围从选择性催化，负折射率材料到合成生命。在复杂的相互作用导致多个长度尺度的分级结构自组装的化学系统中，手性可能会或可能不会导致这些长度尺度中的每一个。许多例子存在于光谱的两侧，其中在较小尺度下的手性也在较大尺度下表现出来（放大），或者在较小尺度下的手性不转化为较大尺度下的手性（沮丧）。该项目的科学目标是通过研究基本的热力学，加强对手性何时以及如何从最小长度尺度转移到最大长度尺度的理解。原理和询问分子水平的细节。所考虑的系统是由聚合物制成的，聚合物是由重复的分子亚基组成的长链状分子。具体地说，它们是手性聚合物，可以单独研究，也可以混合研究，或者结合到具有手性部分和非手性部分的较长分子的一部分中。本计画发展了一种新颖的粒子模拟模型来量测多个热力学性质，包括能量与熵的各种成分。使用数千个分子还提供了对单个分子的构象和单个分子内的变化的见解。总之，该项目将确定热力学条件和分子机制，放大或挫败手性转移。这些发现可以应用于各种自组装聚合物，包括合成多肽和自组装折叠体。该项目的教育目标是开发活动和课程，提高K-12和本科生的空间思维能力。工具，如等距纸上的投影，触觉3D对象和可视化软件被用来支持学习。空间思维技能在手性结构的识别中尤其重要，在手性结构中，必须进行心理旋转以识别右手或左手。这些技能不仅可以提高学生在结构识别方面的表现，还可以提高STEM相关领域的整体表现。技术概述手性是材料不能叠加在其镜像上的属性。这种性质不仅可以在任何长度尺度上表现出来，而且还可以在几个长度尺度上同时表现出来。例如，在非手性-手性嵌段共聚物中，手性可以在原子尺度、在大分子的构象尺度和在介观尺度上表现出来。尽管手性从较低长度尺度转移到较高长度尺度的许多实例，但也存在手性仅限于较低长度尺度且不转移到较高长度尺度的各种实例。当这种转移被放大时，或当这种转移被阻碍时，对条件的热力学理解仍然是未知的。这些原理将对合成多肽和自组装折叠体等生物材料的组装产生影响，并可用于回答有关生命起源的基本问题。该项目的科学目标是理解热力学原理，并使用基于粒子的模拟建立模型聚合物系统中放大或阻碍手性转移的机制。具体来说，该项目开发了一个可调和参数化的模型，手性嵌段共聚物表现出的构象是与实验测量。在无序状态下的自由能计算解耦各种热力学贡献，即，内和分子间的能量，和熵所产生的构象变化。为了探究自组装过程中手性挫折的机制，该项目将层状（非手性）结构中聚合物的构象与理想情况下的构象进行了比较。为了促进自组装产生的手性放大，将采用诸如通过有目的地设计的混合物进行手性排序的策略。总体而言，该项目的见解将使人们更深入地了解分子和结构特征之间的关系。该项目的教育目标是加强学生的空间思维能力，以提高STEM的成绩和成就。活动是专为来自不同背景的学生在K-12水平，也将被纳入早期的本科课程。空间思维能力的提高预计将广泛提高学习收益。利用不同的模式来构建空间思维技能，包括等距纸上的绘图，使用触觉3D打印对象和可视化软件。通过该项目开发的课程将广泛地使学生受益，并将填补目前化学教育中手性结构鉴定的空白。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in part under the American Rescue Plan Act of 2021 (Public Law 117-2).NONTECHNICAL SUMMARYThis CAREER award supports theoretical and computational research, and integrated education on self-assembly that leads to chiral structures in polymeric materials. Without turning one hand over, one cannot superimpose one’s left-hand over their right one. Atoms or molecules in a material may position themselves so that they may have this same property; the atoms in the material are not in registry with those of the material’s mirror image. The ability to distinguish a material as being either right-handed or left-handed indicates that the material has chirality. Chirality lends itself to specific interactions and novel properties, with applications ranging from selective catalysis, negative refractive index materials, to synthetic life. In chemical systems where complex interactions lead to self-assembly of hierarchical structures at a multitude of length scales, chirality may or may not result in each of those length scales. Numerous examples exist on both sides of the spectrum where chirality at the smaller scale is also exhibited at the larger scale (amplification), or where chirality at the smaller scale does not translate to chirality at the larger scale (frustration).The scientific goal of the project is to enhance the understanding of when and how chirality is transferred from the smallest to the largest length scale by studying the underlying thermodynamic principles and interrogating the molecular-level detail. The systems under consideration are made from polymers, long chain-like molecules made of repeating molecular subunits. Specifically, they are chiral polymers, either studied in isolation, in mixtures, or incorporated into a portion of a longer molecule that has a chiral part and one that is not chiral. A novel particle-based simulation model is developed in this project to measure several thermodynamic properties, including various components of energy and entropy. The use of thousands of molecules also provides insights into the conformations of individual molecules and variations within an individual molecule. Altogether, the project will identify thermodynamic conditions and molecular mechanisms that amplify or frustrate chirality transfer. Such findings can be applied to a variety of self-assembling polymers including synthetic polypeptides and self-assembling foldamers. The education goal of the project is to develop activities and curricula that enhance spatial thinking skill among students at the K-12 and undergraduate levels. Tools such as projections on isometric paper, tactile 3D objects, and visualization software are utilized to support learning. Spatial thinking skills are especially important in the identification of chiral structures, where mental rotations must be performed to identify right-handedness or left-handedness. Such skills not only enhance student performance in structure identification, but also enhance overall performance in STEM-related fields.TECHNICAL SUMMARYChirality is the property where a material cannot be superimposed on its mirror image. This property can not only be exhibited at any length scale, but it can also be exhibited simultaneously at several length scales. For example, in achiral-chiral block copolymers, chirality can be exhibited at the atomic scale, at the conformational scale of a macromolecule, and at the mesoscale. Despite numerous examples of chirality transfer from lower to higher length scales, diverse examples also exist where chirality is limited to a lower length scale alone and does not transfer to a higher length scale. A thermodynamic understanding of conditions when such transfer is amplified, or conditions when such transfer is hindered, remain unknown. Such principles will have implications for the assembly of biomaterials such as synthetic polypeptides and self-assembling foldamers and can be used to answer fundamental questions regarding the origin of life.The scientific goal of the project is to understand the thermodynamic principles and to establish mechanisms that amplify or frustrate chirality transfer in model polymer systems, using particle-based simulations. Specifically, the project develops a tunable and parametrizable model for chiral block copolymers to exhibit conformations that are comparable to experimental measurements. Free energy calculations in the disordered state decouple various thermodynamic contributions, namely, intra- and inter-molecular energies, and entropy arising from conformational changes. To interrogate mechanisms of chiral frustration during self-assembly, the project compares the conformations of the polymers in a lamellar (achiral) structure to that of the ideal scenario. To promote chiral amplification arising from self-assembly, strategies such as nematic ordering through purposefully designed mixtures will be employed. Overall, insights from the project will enable a deeper understanding of the relationship between molecular and structural characteristics.The education goal of the project is to strengthen the spatial thinking skills of students for improved STEM achievement and attainment. Activities are designed for students from diverse backgrounds at the K-12 level and will also be incorporated in the early undergraduate curriculum. Enhancement of spatial thinking skills is anticipated to improve learning gains broadly. Diverse modes of building spatial thinking skills are utilized, including drawings on isometric paper, use of tactile 3-D printed objects, and visualization software. The curriculum developed through this project will benefit students broadly and will fill the current gap in chemical education for identification of chiral structures.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.