Gas phase studies of organic and biological species using mass spectrometry

This dissertation focuses on the study of gas phase properties of several organic and bioorganic species, using experimental (mass spectrometry) and computational (Gaussian) methods. Damaged nucleobases are from oxidation or methylation of normal nucleobases. These damaged bases are linked with diseases, aging, and cell death. They can be excised by enzymes such as DNA glycosylases. However the mechanism is still unknown. Tautomerism, proton affinity, and acidity of a damaged base xanthine have been studied to understand the mechanism of AlkA, the enzyme that excises xanthine. 1,2,3-triazoles are novel compounds that have various applications, especially in synthetic and catalytic chemistry. The fundamental properties of these triazoles could potentially be useful in understanding their binding to metals. Tautomerism, proton affinity, and acidity of several 1,2,3-triazoles have been studied by using computational and experimental methods. The results indicate that PA of the triazoles correlate with their binding ability to metals such as gold. N-Heterocyclic carbenes (NHCs) are good electron donors and are used as ligands in organometallic complexes. However, unlike the traditional carbenes (methylene), NHCs are not electrophilic. N,N’-Diamidocarbenes (DACs) display not only nucleophilic but also electrophilic properties. The proton affinity of several DACs were studied and found to be close to proton affinity of the NHCs. The electrophilic reactivities of DACs can be attributed to their low-lying LUMO orbitals. Nucleophilicity and electrophilicity in the gas phase are important reactivity parameters of organic species. Gas phase calculations and experiments can exclude the influence of solvents and reveal the intrinsic properties of nucleophiles and electrophiles. Classic physical organic approaches, including Hammett plots, kinetic isotope effect, and H/D exchange, have been employed to study the gas phase reactions between nucleophiles and electrophiles. RNA oligonucleotides (2-5nt) are found to play important roles in the transcription of DNA. However, the specific RNA species and their sequences are unknown. An LC-MS method has been developed for the separation and quantification of these oligonucleotides. Collision induced dissociation (CID) patterns of the oligonucleotides are found to be useful in the characterization of these biologically significant species.Ph. D.Includes bibliographical referencesby Mu Che