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

在这项由化学系化学结构、动力学和机理A(CSDM-A)计划资助的项目中，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活性，包括金属阳离子(“阳离子”是指带正电荷的)以及由金属阳离子和其他分子组成的络合物，如水(H2O)、一氧化碳(CO)和生物相关的氨基酸和多肽。这些研究是在气相中进行的，因为了解这些分子体系的内在结构和性质是很重要的，换句话说，在没有水分子的情况下，它们将在水溶液中遇到无数的水分子。Armentrout研究小组实际上正在开发新的技术，将带电分子和络合物输送到气相中，要么不含水，要么带有选定数量的水分子或其他有机溶剂分子。这项研究包括四个主要方面：溶剂分子与双电荷金属的结合强度有多大？当分子离子的电子被激光或碰撞激发时，其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了对相同现象的理论检验的补充。参与这一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，包括一种名为引导离子束质谱仪(GIBMS)的技术和量子力学计算。这项研究使用了两种类型的仪器。热力学实验是通过使用引导离子束串联质谱计实现的，该质谱仪允许测量作为动能函数的绝对反应截面。这使得能够直接测量阳离子多肽分解或去溶金属离子或金属氢氧化物阳离子所需的能量。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不同构象的阳离子多肽。这种仪器组合使得能够定量研究自旋-轨道耦合效应，并直接测量不同构象之间的能量差异，这两者都是潜在的变革性研究。结构研究涉及使用在荷兰Felix设施进行的红外多光子解离光谱，其中包括关于阳离子多肽和金属阳离子激活烷烃的实验。这些研究的更广泛的影响包括更好地理解如何获得蛋白质中的序列信息，为理论提供热力学基准，以及阐明关于过渡金属催化的机理信息，此外，还包括让本科生和研究生参与全面的实验和理论工作的教育方面。为从实验中获取热化学信息而开发的软件包(CRUCK)正在不断更新和完善，并继续提供给对基于质谱学的热力学测量感兴趣的其他小组。该奖项反映了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。

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.