Molecular rotors for studying transition state stabilization by non-covalent interactions

南卡罗来纳大学清水健教授在化学系大分子、超分子和纳米化学项目的支持下，研究了非键相互作用在稳定反应物和产物之间过渡态中的作用。催化剂经常被用来加速化学反应，并使它们对所需产品更具选择性。催化开发中的一个关键挑战是提高催化剂将分子聚集成拥挤的反应结构的能力，这种结构被称为过渡态。清水教授和他的学生正在构建分子机器(转子)，帮助从根本上理解和优化催化剂的反应性。分子旋转器的设计是为了评估通过改变旋转速度来简化这些拥挤的反应结构形成的因素。因此，分子旋转器为研究和改进催化剂设计提供了一种简单而系统的方法。新的和改进的催化剂的开发使新的化学品、聚合物、燃料和药品的生产变得高效。通过与当地一所女子学院的教职员工和学生合作，对研究生和本科生进行研究方法方面的培训，特别是女化学家。研究生课程旨在为学生提供基本技能，如如何介绍研讨会、时间和研究管理策略，以及如何撰写研究出版物和提案。用一系列分子旋转体测量了非共价相互作用稳定过渡态的能力。转子在平面过渡态中形成非共价相互作用。非共价相互作用的稳定效应可以通过分子转子的速度增加来测量。转子骨架的多功能性和模块化使得能够研究广泛的非共价相互作用，包括氢键、阳离子-pi、阴离子-pi、n-pi*、硫系-硫族、CH-pi、芳烃-芳烃、OH-pi和金属-pi相互作用。通过使用动态核磁共振光谱测量转动势垒，可以方便而准确地评估过渡态效应。最后，刚性框架限制了基本态和过渡态的自由度，从而能够使用标准的DFT方法进行精确的建模和仿真，这些方法提供了对实验测量的势垒、过渡态结构的计算证实，并深入了解了稳定效应的起源。该项目广泛影响了改进合成催化剂的新策略的开发，并为酶系统中的大速率加速提供了见解。此外，使用分子旋转器研究和询问过渡态能量的新策略的开发为化学家提供了基础动力学研究的新工具。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。

Professor Ken D. Shimizu of the University of South Carolina is supported by the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry to investigate the role of non-bonding interactions in the stabilization of the transition state between reactants and products. Catalysts are frequently used to speed up chemical reactions and make them more selective for the desired product. A key challenge in catalysis development is enhancing the ability of catalysts to bring together molecules into crowded reactive structures know as transitions states. Professor Shimizu and his students are constructing molecular machines (rotors) that assist in the fundamental understanding and optimization of catalyst reactivity. The molecular rotors are designed to assess factors that simplify the formation of these crowded reactive structures via changes in the speed of their rotation. Thus, the molecular rotors provide a simple and systemic way to study and improve catalyst design. The development of new and improved catalysts enables the efficient production of new chemicals, polymers, fuels, and pharmaceuticals. Graduate and undergraduate students are trained in research methods, in particular women chemists through a collaboration with faculty and students at a local women’s college. A graduate course is developed to provide students with fundamental skills, such as how to present seminars, time and research management strategies, and how to write research publications and proposals. The ability of non-covalent interactions to stabilize transition states is measured using a series of molecular rotors. The rotors form non-covalent interactions in their planar transition states. The stabilizing effects of the non-covalent interactions can be measured from the increase in speed of the molecular rotors. The versatility and modularity of the rotor framework enables the study of a wide range of non-covalent interactions including hydrogen bonds, cation-pi, anion-pi, n-pi*, chalcogen-chalcogen, CH-pi, arene-arene, OH-pi, and metal-pi interactions. The transition state effects are easily and accurately assessed by measuring the rotational barriers using dynamic NMR spectroscopy. Finally, the rigid framework limits the degrees of freedom in the ground and transition states enabling accurate modeling and simulation using standard DFT methods, which provide computational-corroboration of the experimentally measured barriers, transition state structures, and insights into the origins of the stabilizing effects. The project broadly impacts the development of new strategies to improve synthetic catalysts and provides insights into the large rate accelerations in enzymatic systems. In addition, the development of a new strategy for studying and interrogating transition state energies using molecular rotors provides chemists with new tools for fundamental kinetic studies.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.