Thermochemistry of Metal-Ligand Bonds and the Dynamics of Collision-Induced Dissociation

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AbstractProposal: CHE-0135517PI: Armentrout, Peter B.This project consists of continuing research in the fields of chemical dynamics and gas-phase organometallic ion chemistry using a combined techniques of flow tube ion production and guided ion beam tandem mass spectrometry (GIBMS). With this apparatus, thermalized atomic and polyatomic ions will be produced. Detailed kinetic and thermodynamic data on single mass-selected species will be obtained by accurately measuring the absolute reaction probabilities at thermal and hyperthermal energies. Two new experimental facilities will be developed: 1) An electrospray ion (ESI) source that should enable more routine generation of nonvolatile and thermally fragile ions in the gas phase and provide easier access to multiply charged species. 2) A source to study state-specific chemistry of heavier transition elements that utilizes "electronic state chromatography". A range of chemical systems will be studied and will emphasize three related areas: 1) the dynamics of collision-induced dissociation; 2) the chemistry of the heavier third-row transition metals; and 3) metal ion binding to biologically relevant molecules. Implicit in all three areas will be theoretical calculations needed to augment the experiments. One motivation for this program is the obvious interest in making better correlations between the detailed information available from gas-phase ion studies with the "real world" of condensed-phase organometallic chemistry, homogeneous catalysis, and biological systems. We make the conscious choice to study simple systems that progress in complexity in order to quantitatively assess trends in metal chemistry. By comprehensively studying the thermochemistry of many metals and many ligands, the trends (periodic, changes with number of ligands, variations in electronic states) in the thermodynamic data allow us to transcend the gas-phase venue where the data are obtained. Students and post doctoral research associates will participate in this research.As chemical reagents, metals are important components of biological systems, acting as active sites in enzymes and helping to regulate cell function and to control structure. Technologically, metals are used extensively as catalysts to produce a wide range of important fine chemicals and fuels. In addition, molecules specifically designed to interact selectively with certain metals are needed for nuclear waste cleanup and decontamination. The research done in this project is designed to provide fundamental information about the strength of the interactions of metals with chemical components relevant to biological systems and the chemical industry. This is most readily accomplished by examining model systems that progress in complexity. This permits the trends in this information to be quantitatively assessed, which allows the development of predictive capabilities for more complex chemical environments. In this work, specialized devices known as guided ion beam tandem mass spectrometers are utilized to examine metal ion interactions with a variety of chemical species. This can be accomplished on single molecules such that interfering interactions from the environment can be eliminated. This allows the study to focus on elucidating the specific factors that control the interaction. A close collaboration with theory provides additional insight and provides essential predictive capabilities. The research will be done with students and post doctoral research associates who thereby receive training in preparation for advanced studies or entering the scientific/technical workforce.