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.
