Mass spectrometric studies on petroleum asphaltenes and organosulfur compounds, on functional-group selective ion-molecule reactions and on gas-phase reactivity of meta-benzynes toward amino acids
Abstract
Mass spectrometry has found a wide variety of applications in many fields of study, such as fundamental chemistry, biological science, food and fuels, advanced materials, etc. Due to its high sensitivity, selectivity and speed, mass spectrometry provides an invaluable tool for direct mixture analysis. When coupled with separation methods, such as gas chromatography or high performance liquid chromatography, analysis of minor components in complex mixtures is possible. In addition to the molecular weight information, mass spectrometers can provide structural information for the ionized analyte molecules. However, mass spectrometric analysis of complex mixtures is not without challenges, such as suitable evaporation/ionization methods are not readily available for different types of samples. For example, because of such limitations, little is known about the molecular weight or structural information of asphaltenes, which are the heaviest components of crude oil and one of the most complex mixtures in nature. Characterization of asphaltenes at the molecular level can alleviate some of the problems they cause to petroleum industry and facilitate the discovery of beneficial uses for asphaltenes. Multiple-stage tandem mass spectrometry (MSn) based on collision-activated dissociation (CAD) is usually a method of choice for structural elucidation of unknown compounds. However, this method alone does not always unambiguously identify the functional groups in an unknown analyte. Therefore, tandem mass spectrometry (MS/MS) based on ion-molecule reactions was developed and implemented in a linear quadrupole ion trap (LQIT) mass spectrometer for functional group identification. This method has great potential for rapid identification of unknown drug metabolites in the pharmaceutical industry. Gas-phase ion-molecule reactions are also very useful in study of reaction kinetics and mechanisms. The intrinsic chemical properties of such highly reactive molecules as radicals can be studied in the gas phase, which are otherwise difficult to access by other experimental approaches. Knowledge on the reactivity of aromatic carbon centered σ,σ-type biradical intermediates is desirable as they are associated with the biological activity of a naturally occurring enediyne antitumor agents. Of particular interest is the reactivity of 1,3-biradical species (meta-benzynes) because of its therapeutic importance. In this thesis, the reactivity of four meta-benzyne analogues towards eight amino acids was examined by using “distonic ion approach” in a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. The experiments described in this thesis were aimed to provide more detailed structural information of mixture components by using different mass spectrometry based methods. Chapter 2 briefly describes the theory, instrumentation, and experimental aspects of the two instruments used for these studies. Chapter 3 focuses on structural comparisons of asphaltenes of different origins by using multiple-stage tandem mass spectrometry. Chapter 4 describes structural characterization of organosulfur model compounds related to fossil fuels by using high-resolution tandem mass spectrometry. Chapter 5 focuses on development of gas-phase ion-molecule reactions for the identification of the sulfone functionality in drug metabolites. Chapter 6 is devoted to the study of gas-phase reactivity of pyridine, quinoline, and isoquinoline based meta-benzynes towards various amino acids.
Degree
Ph.D.
Advisors
Kenttamaa, Purdue University.
Subject Area
Analytical chemistry|Organic chemistry
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.