Amplification of chiral recognition and discrimination among amino-acid-based nanoscale ions during assembly induced by electrostatic interaction

该奖项支持实验研究和教育，旨在了解如何手性是保持和放大在形成超结构的带电大分子。大多数生物大分子如蛋白质和DNA是手性的，也就是说，同一分子具有两种不同的几何形状，不能叠加到其镜像上。虽然这两种形式在化学和物理性质上被认为是相同的，除了它们的手性，但在生物系统中只发现蛋白质中的L-氨基酸和D-糖-一种称为同手性的现象。人们发现了许多有趣的现象，如带电手性物种在形成大结构时只寻找自己的种类（手性识别），在一定条件下只有一种形式会组装，而另一种形式则作为分子留在溶液中（手性歧视，这导致了单手性）。这些都是从生命科学到催化分离科学的重要课题。PI将通过研究纳米级分子间的物理相互作用，特别是不同手性组分之间的长程静电相互作用，探索在溶液中实现这种现象所需的条件，这是可能的驱动力。该项目通过NSF-REU中心吸引研究生和本科生，以及阿克伦大学聚合物科学和聚合物工程学院新设立的聚合物学士学位课程，以及来自俄亥俄州东北部的高中生。PI的团队将专门从当地的学校招募学生，这些学校为传统上在STEM领域代表性不足的群体提供大量学生，鼓励学生学习科学课程并从事STEM相关的职业。来自阿克伦大学的PI Tianbo Liu将探索含有多种手性组分的稀释大离子溶液中的纳米级分子间相互作用，以含有不同手性氨基酸连接基的金属-有机笼为模型。这种相互作用负责实现手性识别（例如，形成对映体、手性超分子结构而不是外消旋混合结构）和手性鉴别和选择（例如，在少量手性抗衡离子或共离子存在下，手性大离子的仅一种对映体将组装）。PI计划设计实验，通过检查以下假设，探索远程静电相互作用的可能关键作用，以手性抗衡离子或共离子与中心手性大离子的相互作用为代表，在此类现象背后：（1）分子间的长程静电相互作用对于实现手性大离子之间的手性识别至关重要，在外消旋溶液中产生纯的对映体超分子结构而不是形成混合的组装体;（2）次要的手性环境（例如，低浓度的次要手性抗衡离子）足以实现手性选择（即，促进一种类型的对映体自组装而抑制另一种类型）;（3）当抗衡离子（氨基酸，例如，丙氨酸）和金属有机笼的配体是相同类型的（例如，丙氨酸）;（4）手性共离子（携带与大离子相同电荷的离子）本身也可以单独实现手性大离子的手性识别和手性选择;以及（5）少量手性组分可以导致形成具有可调手性的手性凝胶。PI的团队希望通过确定导致生物大分子手性识别和手性选择的关键力，从而进一步导致许多关键现象，例如生命的同手性特征，为我们对纳米级分子间相互作用的基本理解做出贡献。该项目通过NSF-REU中心吸引研究生和本科生，以及阿克伦大学聚合物科学和聚合物工程学院新设立的聚合物学士学位课程，以及来自俄亥俄州东北部的高中生。PI的团队将专门从当地学校招募学生，这些学校为传统上在STEM领域代表性不足的群体提供大量学生，鼓励学生学习科学课程并从事STEM相关职业。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 supports experimental research and education aimed at understanding how chirality is maintained and amplified during the formation of superstructures by charged macromolecules. Most biomacromolecules like proteins and DNA are chiral, that is, the same molecule has two different geometrical forms which cannot be superimposed onto its mirror image. Although both forms are considered identical in chemical and physical properties except their handedness, exclusively L-amino acids in proteins and D-sugars are found in biological systems – a phenomenon called homochirality. Many interesting phenomena have been discovered, such as that charged chiral species only seek their own kind when forming large structures (chiral recognition), and under certain conditions only one form will assemble while the other one stays as molecules in solution (chiral discrimination, which leads to homochirality). These are important topics in many fields from life sciences to catalysis and separation science. The PI will explore the conditions needed for achieving such phenomena in solution by studying nanoscale intermolecular physical interactions, especially the long-range electrostatic interaction between different chral components, which is the probable driving force. The project engages graduate and undergraduate students through the NSF-REU center, and the newly established BS program in Polymers, both at the School of Polymer Science and Polymer Eng. at the University of Akron, and high school students from northeast Ohio. The PI’s team will specifically recruit from local schools that serve large numbers of students from groups traditionally under-represented in STEM fields, encouraging students to take science courses and pursue STEM related careers.PI Tianbo Liu from the University of Akron will explore the nanoscale intermolecular interactions in dilute macroionic solutions containing multiple chiral components, by using metal-organic cages containing different chiral amino acid linkers as models . Such interactions are responsible for achieving chiral recognition (e.g., forming enantiomeric, chiral supramolecular structures instead of racemic mixed ones) and chiral discrimination and selection (e.g., only one enantiomer of chiral macroions will assemble, in the presence of small amount of chiral counterions or co-ions). The PI plans to design experiments to explore the probable key role of the long-range electrostatic interaction, represented by the interactions of chiral counterions or co-ions with the central chiral macroions, behind such phenomena, by examining the following hypotheses: (1) long-range electrostatic intermolecular interaction is critical for achieving chiral recognition between chiral macroions, resulting in pure enantiomeric supramolecular structures in racemic solutions instead of forming mixed assemblies; (2) a minor chiral environment (e.g., low concentrations of minor chiral counterions) is sufficient to achieve chiral selection (i.e., promoting one type of enantiomer to self-assemble while suppressing the other type) in chiral macroionic solution; (3) chiral selection of the metal organic cage macroions might become much more significant when the counterions (amino acids, e.g., Alanine) and the ligands of the metal organic cages are of the same type (e.g., Alanine); (4) chiral co-ions (ions carrying the same charge as the macroions) themselves alone might also be able to achieve chiral recognition and chiral selection of chiral macroions; and (5) minor chiral components can lead to the formation of chiral gels with tunable chirality. The PI’s team expects to contribute to our fundamental understanding of nanoscale intermolecular interactions by identifying the critical force leading to the chiral recognition and chiral selection of biomacromolecules, which further lead to many critical phenomena such as the homochirality feature of lives. The project engages graduate and undergraduate students through the NSF-REU center, and the newly established BS program in Polymers, both at the School of Polymer Science and Polymer Eng. at the University of Akron, and high school students from northeast Ohio. The PI’s team will specifically recruit from local schools that serve large numbers of students from groups traditionally under-represented in STEM fields, encouraging students to take science courses and pursue STEM related careers.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.