Applications of desorption chemical ionization tandem mass spectrometry

Steven Hamilton Hoke, Purdue University

Abstract

Four different chemical investigations are undertaken by implementing desorption chemical ionization tandem mass spectrometry (DCI-MS/MS) with a Finnigan TSQ 700 mass spectrometer. A method was developed for the rapid quantitation of the anticancer drug taxol and the analogs cephalomannine and baccatin III using d$\sb3$-internal standards. With this method, crude plant extracts can be screened for these three target taxanes at the femtomole level with a 12% relative standard deviation in less than five minutes per sample. Various MS/MS scans are also described for the identification of novel analogs of taxol. Derivatization of buckminsterfullerene is studied in the condensed phase by various mechanisms of carbon-carbon bond formation including photochemical, nucleophilic, (2+2) cyclo- and diradical addition. Products are characterized by DCI-MS and DCI-MS/MS. Fullerene reactivity is also studied in the gas phase, including Diels-Alder (4+2) cycloaddition and adduct formation with carbocations, halides and hydrogen in the chemical ionization source. Application of the kinetic method to the determination of free radical proton affinities is demonstrated. The proton affinity of phenoxyl was determined to be 205.6 $\pm$ 0.3 kcal/mol which is in agreement with a thermochemical cycle value of 204.8 $\pm$ 2.0 kcal/mol. The proton affinities of various substituted phenoxyl radicals were measured and compared with thermochemical cycle values and the results of ab initio calculations. In addition, DCI-MS/MS is used for structure differentiation of isobaric ions by proton affinity measurement. The microstructure of alkyl isocyanate copolymers comprised of (R)- and (S)-monomers is determined by incorporation of a mirror image selective label, deuterium, into the (S)-enantiomer. The mass spectrometric analysis of the copolymers produced by polymerization of these enantiomers reveals that the monomers units are randomly distributed. These results, along with empirical force field calculations and optical analyses, lead to the conclusion that the handedness of the poly(alkyl isocyanate) helical coil is determined by the majority isomer and that the minority isomer is inserted, randomly, into this coil.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Analytical chemistry

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