Nitrosation and Nitration Reactions of the Radical Cations of Guanine, 8-Oxoguanine and their Derivatives by NOx: Radical-radical Interactions at Multiple Electron Configurations

With support from the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program in the Division of Chemistry, Professor Jianbo Liu of Queens College is investigating the reactions of the radical cations of guanine and its oxidized derivative 8-oxoguanine with nitric oxide (NO) and nitrogen dioxide (NO2) using electrospray ionization and mass spectrometry. Guanine has the lowest oxidation and ionization potential among DNA nucleobases, leading to the preferential formation of the radical cations of guanine and 8-oxoguanine upon the oxidation and ionization of DNA. Reactions of these radical cations are difficult to study in solution due to their rapid deprotonation and the inability to separate, detect, and characterize products. Professor Liu and his students will study the reactions of these radical cations with NO and NO2 in a rarefied gas-phase environment where individual products can be measured. These studies are expected to provide a better understanding of DNA damage upon oxidative, nitrosative, and nitrative stress. The students working on this project will gain experience in reaction dynamics, instrumentation development, and computational modeling. Queens College is a Minority Serving Institution, with 40% of students from traditionally underserved groups. This project have direct implications for diversity and broadening participation, including collaboration with LaGuardia Community College to transfer qualified students from an associate degree to the Chemistry B.S. program. Many of the instruments developed for research will also used in undergraduate laboratory courses. The project will utilize electrospray ionization and guided-ion beam tandem mass spectrometry to conduct ion-molecule reactions wherein the radical cations of guanine and 8-oxoguanine are produced by electron-transfer induced-dissociation of Cu(II)-nucleobase complexes. Reactions of mass-selected radical cations with NO and NO2 will be carried out under gas-phase single-collision conditions provided in the guided-ion beam scattering experiment where structures and cross sections of individual product ions will be measured as a function of collision energy. Experiments will be complemented by electronic structure calculations, dynamics simulations, and kinetic analysis. The in-house, synergetic experiments and computations should allow for interpretation of various aspects of reaction mechanism and non-adiabatic kinetics. A major thrust of this research is to benchmark experiment and theory for tackling multireferential characters and non-adiabatic transitions in doublet-doublet electronic-state reactions. 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.