The factors controlling radicals' *reactivity toward molecules of biological importance in the gas phase
Abstract
Several ion-molecule reactions have been examined in order to gain more knowledge on the factors controlling mono- and biradicals' reactivity toward molecules of biological importance. These gas-phase reactions were examined in a dual-cell Fourier-transform ion cyclotron resonance mass spectrometer by using the "distonic ion approach" of introducing an inert charge site on the radicals for manipulation in the mass spectrometer. The first study involved examination of the effects of the charge to radical site distance on the reactivity of isomeric monoradicals. The observed reaction efficiency ordering correlates with ordering of the monoradical's electron affinities. Radicals with larger electron affinities generally react faster than ones with smaller electron affinities. An unprecedented aromatic hydrogen atom abstraction was observed for 4-dehydropyridinium. The reaction likely occurs via nonradical addition to the aromatic neutral reagent. The results of a second study involving several substituted phenyl monoradicals suggest that stabilizing hydrogen bond formation in the transition state for hydrogen atom abstraction by some radicals can significantly enhance reactivity. The third study focused on singlet biradicals' reactivity towards sugars and nucleobases. The observed reactions suggest that the radical-reactivity hindering effect of a large singlet-triplet gap may be counterbalanced by a large EA. The fourth study revealed that the presence of a σ-lone pair of electrons (e.g, from a heteroaromatic N-atom) in the aromatic ring appears to cause some biradicals to undergo ring-opening when they react with some neutral organic reagents.
Degree
Ph.D.
Advisors
Kenttamaa, Purdue University.
Subject Area
Analytical chemistry|Organic chemistry
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