Ligand Exchange Equilibrium at Quantum Dot Surfaces in Polar and Aqueous Solvent Environments

在化学学部大分子、超分子和纳米化学项目的支持下，南卡罗来纳大学的Andrew Greytak博士将研究极性溶剂（如水）中量子点（QDs）表面的化学性质，以增加其在生物应用中的效用。量子点是由半导体化合物组成的纳米级粒子，通常在溶液中通过附着在其表面的有机分子层来稳定。量子点通常表现出明亮和大小可调的荧光，这导致了它们在成像应用中的应用，但它们的效用受到未知控制原理的限制。格雷塔克博士和他的团队正在将新兴的分析方法和物理模型与产生水溶性量子点的化学反应联系起来，以更好地理解这些局限性。更广泛的影响包括研究生和本科生的指导；在物理化学实验课程中引入新的实验模块与南卡罗来纳大学可持续发展办公室协调研究和实践展示，为讨论量子点和其他先进材料在照明、显示和太阳能应用中的作用提供机会；并通过为初中和高中学生举办的当地科学和工程博览会进行推广。该研究采用等温滴定量热法（ITC）结合核磁共振技术来研究极性溶剂环境中，表面配位和配体间相互作用在控制配体在量子点（QDs）上的结合强度和交换速率中的相对重要性。在过去的几年里，Greytak团队已经证明了等温滴定量热法（ITC）可以成为表征量子点配体相互作用的重要技术，并成功地测量了配体结合、配体交换以及硫系量子点表面的顺序交换和结合过程。本提案将扩展并超越这些成果，将ITC应用于极性溶剂中的新型纳米晶体反应，特别是那些探测适合生物成像应用的水溶性量子点的形成和行为的纳米晶体反应。由于ITC可以根据结合焓的差异区分不同位点的顺序结合，这种方法有望提高对胶体量子点表面化学的理解。比较是在代表性的小分子阴离子配体在水缓冲液。进一步的研究试图澄清基于咪唑和类似杂环的新兴嵌段共聚物配体的结合性质。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Dr. Andrew Greytak of the University of South Carolina will investigate the chemistry at the surface of quantum dots (QDs) in polar solvents such as water to increase their utility in biological applications. QDs are nanometer-scale particles composed of semiconducting compounds, that are typically stabilized in solution by layers of organic molecules attached to their surfaces. QDs often exhibit bright and size-tunable fluorescence that has led to their use in imaging applications, but their utility is limited by unknown governing principles. Dr. Greytak and his group are connecting emerging analytical methods and physical models to chemical reactions that yield water-soluble QDs to better understand these limitations. Broader impacts involve mentorship of graduate and undergraduate students; introduction of new experimental modules into a physical chemistry lab course; coordination of a research and practice showcase with the University of South Carolina Office of Sustainability that provides an opportunity to discuss the role of QDs and other advanced materials in lighting, display, and solar energy applications; and outreach through a local science and engineering fair for junior and senior high school students.The research employs isothermal titration calorimetry (ITC) in combination with NMR techniques to investigate the relative importance of surface coordination and inter-ligand interactions in governing the binding strength and exchange rate of ligands on quantum dots (QDs) in polar solvent environments. In the last few years, the Greytak group has demonstrated that isothermal titration calorimetry (ITC) can be an important technique for characterizing QD-ligand interactions, with success in measuring ligand association, ligand exchange, and sequential exchange and binding processes at chalcogenide QD surfaces. This proposal will extend and go beyond these achievements by applying ITC to new classes of nanocrystal reactions in polar solvents, especially those that probe the formation and behavior of water-soluble QDs suitable for bio-imaging applications. Because ITC can distinguish sequential binding to various sites based on differences in their enthalpy of binding, this approach is expected to lead to improved understanding of colloidal QD surface chemistry. Comparisons are to be made among representative small molecule anionic ligands in aqueous buffers. Additional investigations seek to clarify the nature of binding in emerging block copolymer ligands based on imidazoles and analogous heterocyclic.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.