Reactivity studies of charged aryl monoradicals in the gas phase and solution using fourier transform ion cyclotron resonance (FT-ICR) and linear quadrupole ion trap (LQIT) mass spectrometry

The biological activity the enediyne antitumor agents was suggested to arise from formation of aromatic carbon-centered σ,σ-type biradicals, which cause irreversible damage to double stranded DNA. Knowledge on the reactivity of aromatic carbon-centered σ,σ-type biradical intermediates is needed to facilitate the rational design of a more selective synthetic antitumor drugs. In order to fully understand the reactivity of aromatic carbon-centered σ,σ-type biradical intermediates, one must also have a fundamental understanding on the factors that control the reactivity of their related σ-type monoradicals. Despite thorough investigations focused on hydrogen atom abstraction reactions in order to model and interpret trends in radical reactivity, the ability to predict the rates of such seemingly facile reactions has proven quite challenging due to the short lifetimes of these reactive intermediates in solution, the difficulty in their clean generation in both the gas phase and solution, as well as a rather poor understanding of the nature of the transition states for these reactions. Gas-phase experiments allow for studies of these monoradical intermediates in a solvent-free environment, eliminating unwanted reactions with reagents other than those of interest. By utilizing the distonic ion approach, gas-phase reactivity of a variety of charged aryl monoradicals toward simple hydrogen atom donors were examined in a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. This study demonstrates sheds new light on the factors that control the reactivity of charge aryl radicals toward simple hydrogen atom donors. While gas-phase experiments have been used to explore solution phenomena, correlation between the reactions observed in the gas phase and in solution needs to be studied thoroughly. Therefore, direct comparison of the reactivity of isomeric charged hydroxy-substituted pyridine-based radicals toward methanol and tetrahydrofuran in solution and in the gas phase were presented. Additionally, how temperature affects the reactivity of these radials toward methanol was also examined. In these studies, similar reactions were observed in solution and in the gas-phase and the insights obtained from gas phase study were found to be true in solution