Thermochemistry of Metal-Ligand Bonds (Singly and Multiply Charged) and Protonated Peptides

在这个由化学部门化学结构、动力学和机制A （CSDM-A）项目资助的项目中，犹他大学的Peter B. Armentrout教授和他的学生正在探索气相中各种分子的结构和反应性，包括金属阳离子（“阳离子”意味着带正电）和由金属阳离子和其他分子（如水（H2O）、一氧化碳（CO）和生物相关的氨基酸和肽）组成的复合物。这些研究是在气相进行的，因为了解这些分子系统的固有结构和性质很重要，换句话说，在没有无数水分子的情况下，他们会在水溶液中遇到。亚美尼亚特劳特研究小组实际上正在开发一种新技术，将带电分子和复合物送入气相，要么不含水，要么与选定数量的水分子或其他有机溶剂分子结合。这项研究包括四个主要重点：溶剂分子与双带电金属的结合有多强？当一个分子离子的电子被激光或碰撞激发时，它的反应性是如何变化的？电离肽是如何分解的？分解产物的分子结构是什么？这些信息对于开发新的催化系统、了解生物功能（包括对健康的影响）和环境补救工作都很有价值。在所有情况下，这些实验研究都得到对同一现象的理论检验的补充。参与该研究项目的学生在最先进的物理和分析方法方面获得了宝贵的经验，包括一种称为引导离子束质谱（GIBMS）的技术，以及量子力学计算。该研究使用两种类型的仪器进行。热力学实验是通过使用引导离子束串联质谱仪实现的，该质谱仪可以测量绝对反应截面作为动能的函数。这使得可以直接测量阳离子化肽分解或金属指示物或金属氢氧化物阳离子脱溶所需的能量。该装置还配备了离子迁移源，允许分离不同电子状态的金属阳离子或阳离子化肽的不同构象。这种仪器组合使自旋轨道耦合效应的定量研究和不同构象之间能量差异的直接测量成为可能，这两者都是潜在的变革性研究。结构研究包括使用在荷兰FELIX设施进行的红外多光子解离光谱，其中包括关于阳离子化肽和金属阳离子激活烷烃的实验。这些研究的广泛影响包括更好地理解如何在蛋白质中引出序列信息，为理论提供热力学基准，阐明过渡金属催化的机制信息，以及涉及本科生和研究生的全方位实验和理论工作的教育方面。用于从实验中获取热化学信息的软件包（CRUNCH）正在不断更新和改进，并继续提供给对基于质谱的热力学测量感兴趣的其他团体。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。

In this project funded by the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program of the Chemistry Division, Professor Peter B. Armentrout and his students at the University of Utah are exploring the structure and reactivity of various molecules in the gas-phase, including metal cations (“cation” means positively charged) and complexes composed of metal cations and other molecules such as water (H2O), carbon monoxide (CO) and biologically relevant amino acids and peptides. These studies are being conducted in the gas phase because it is important to understand the inherent structure and properties of these molecular systems, in other words in the absence of the countless water molecules they would encounter in an aqueous solution. The Armentrout research group is actually developing new techniques to deliver charged molecules and complexes into the gas phase, either free of water or with a selected number of water molecules or other organic solvent molecules. The research includes four main thrusts: how strongly bound are solvent molecules to doubly charged metals? How does the reactivity of a molecular ion change when its electrons are excited by laser light or collisions? How do ionized peptides decompose, and what are the molecular structures of decomposition products? Such information is valuable in developing new catalytic systems, in understanding biological function (including effects on health), and in environmental remediation efforts. In all cases, these experimental studies are complemented by theoretical examinations of the same phenomena. Students engaged in this research project are gaining valuable experience in state-of-the-art physical and analytical methods, including a technique called guided ion beam mass spectrometry (GIBMS), and quantum mechanical calculations.The research is conducted using two types of instrumentation. Thermodynamic experiments are enabled by using a guided ion beam tandem mass spectrometer that permits measurement of absolute reaction cross sections as a function of kinetic energy. This enables the direct measurement of the energies required for cationized peptides to decompose or for desolvation of metal dications or metal hydroxide cations. This apparatus is also being fitted with an ion mobility source that allows separation of metal cations in different electronic states or of different conformers of cationized peptides. This instrumental combination enables quantitative studies of spin-orbit coupling effects and direct measurements of the energetic differences between different conformers, both of which are potentially transformative studies. Structural studies involve the use of infrared multiple photon dissociation spectroscopy conducted at the FELIX facility in the Netherlands, which include experiments concerning cationized peptides and alkane activation by metal cations. Broader impacts of these studies include a better understanding of how to elicit sequence information in proteins, providing thermodynamic benchmarks for theory, and elucidating mechanistic information regarding transition metal catalysis, in addition to the educational aspects of involving both undergraduate and graduate students in a full range of experimental and theoretical work. A software package (CRUNCH) developed to obtain thermochemical information from the experiments is undergoing continuous updates and refinement and continues to be made available to other groups interested in mass spectrometry based thermodynamic measurements.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.