Laser-induced acoustic desorption mass spectrometry in studying the reactivity of aromatic σ,σ-biradicals toward trinucleoside diphosphates and in chemical ionization of nonpolar lipids
Abstract
Carbon-centered aromatic σ,σ-biradicals are the reactive intermediates that induce degradation of double-stranded DNA upon exposure to enediynes. Gas-phase experiments allow the reactivity of σ,σ-biradicals to be examined in a solvent-free environment. My first project involved the investigation of reactivity of σ,σ-biradicals and related monoradicals toward nucleosides and trinucleoside diphosphates in a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. Laser-induced acoustic desorption (LIAD) was used to evaporate oligonucleotides into the gas phase as intact neutral molecules. LIAD coupled with a novel chemical ionization reagent ion, ClMn(H 2O)+, was demonstrated to ionize saturated hydrocarbons without fragmentation of the analytes. The utility of LIAD/ClMn(H2O) + for the analysis of nonpolar lipids and selected steroids was tested. LIAD/ClMn(H2O)+ chemical ionization was found to be a better method than ESI and APCI for the mass spectrometric characterization of underivatized nonpolar lipids and steroids. The sensitivity of LIAD coupled with electron ionization (EI) was determined. LIAD was coupled to a standard APCI source in a linear quadrupole ion trap mass spectrometer. This allows LIAD experiment to be performed in the atmospheric pressure and gas-phase ion/molecule reactions to occur in the atmospheric pressure. Since APCI can be used to ionize compounds with low to medium polarity, this approach may be applicable to the analysis of nonvolatile and nonpolar compounds, such as petroleum. Gas-phase studies have predicted that the hydrogen atom abstraction ability of phenyl radicals may be tuned by controlling pH of the system in solution. Another project was to test this hypothesis by studying the effect of pH on the reactivity of three isomeric dehydropyridines toward methanol in solution. These results were compared to the gas-phase studies.
Degree
Ph.D.
Advisors
Kenttamaa, Purdue University.
Subject Area
Analytical chemistry|Biochemistry
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