Transient Intermediates in Electron and Proton Transfer

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With the support of an award from the Organic and Macromolecular Chemistry Program, Professor Franticek Turecek will address highly reactive molecules, radicals, and cation-radical intermediates that are produced by electron transfer to and deprotonation of cations derived from polar molecules such as peptides, nucleosides, and transition metal complexes. The knowledge gained from the proposed studies will be used to explain the reactivity of transient species relevant to electron-ion and ion-ion recombination processes in biomolecules of current interest and to formulate specific and general mechanisms governing the stability and unimolecular dissociations of a variety of highly reactive and elusive species. The proposed studies of reactive intermediates will employ experimental methods allowing for femtosecond collisional electron transfer in beam experiments, as well as electron capture in isolated ions trapped in electrostatic and magnetic fields. Special model compounds will be synthesized to separate intramolecular interactions by restricting the peptide ion conformational space. Fixed-charge groups will be used to control the energetics of electron attachment and transfer and thus to affect the electronic state(s) that are accessed by ion-electron recombination and collisional electron transfer. Ab initio computational methods will be employed to provide relative, dissociation, and transition state energies to be used for RRKM calculations of unimolecular dissociation and isomerization rate constants. Intellectual meritThe proposed research addresses fundamental and hitherto unresolved questions regarding the dissociations of peptide radicals and cation-radicals. Experiments are proposed that will permit the study of unimolecular dissociations of these transient species on a range of short time scales and under conditions of electron attachment and femtosecond collisional transfer. Electron structure theory calculations are an integral part of the proposed research in both experiment planning and data interpretation.Broader impactsPeptide radicals and cation-radicals have been of considerable interest due to their role as intermediates in mass spectrometric analytical methods for peptide sequencing and detection of protein post-translational modifications. Applications of these methods extend to biology, medicine, and other life sciences, and have been fueled by the availability of commercial instruments for electron capture dissociation and electron transfer dissociation. However, fundamental understanding of the chemistry of transient peptide cation-radicals is essential for the rational use of electron-based methods for peptide and protein sequencing. Studies of ion discharge and immobilization on metal-oxide surfaces have already brought practical results in procedures for the manufacturing of special surfaces for medical implants and selective mass spectrometric detection of phosphopeptides. The proposed research in this area is aimed at gaining insight into the processes leading to biomolecule discharge and immobilization on surfaces.