Novel methods for the identification and counting of functional groups in oxygen-containing compounds and sequencing of peptides by ion -molecule reactions in a FT-ICR mass spectrometer

Jayalakshmi Somuramasami, Purdue University

Abstract

Mass spectrometry plays a major role in the identification of mixture components. This has been made possible by tandem mass spectrometric techniques, such as collision-activated dissociation, H/D exchange reactions and others. Though these techniques provide useful structural information, they rarely allow the unambiguous identification of unknown compounds. However, this may be achieved by ion-molecule reactions other than H/D exchange. Gas-phase ion-molecule reactions provide a powerful technique for obtaining molecular weight, structural, and chemical reactivity information for various species, such as small organic molecules, biomolecules, and polymers. The first five chapters in this thesis address the issue of identifying the functional groups present in protonated organic molecules. Boron reagents have been identified as the neutral reagent of choice for these studies due to their unique chemical properties. The first study involves the identification of functional groups present in protonated bifunctional oxygen-containing compounds by allowing them to react with trimethylborate (TMB). This approach also allows the counting of OH-groups in polyols. The method is shown to be specific for bifunctional oxygen-containing analytes based on the examination of reactions of nitrogen containing compounds and other analytes with TMB. However, this method cannot always differentiate hydroxyketones from hydroxyethers. The second study addresses this problem by solution derivatization of the analytes prior to mass spectrometric analysis. The third study extends the applicability of TMB for the differentiation of protonated regioisomers in the gas-phase. The fourth study involves the identification of functional groups present in negatively charged analytes. Examination of reactions of three different boron reagents, TMB, diethylmethoxyborane (DEMB) and triisopropylborate (TIPB), with deprotonated analytes, such as carboxylates, deprotonated carboxylate esters and alkoxides, suggests that TIPB and TMB can be used to differentiate these functional groups. The final study in this thesis presents a novel method for the sequencing of small neutral peptides, evaporated by laser-induced acoustic desorption (LIAD), by chemical ionization with +P(OCH3)2 ions followed by CAD. This approach has the potential to provide useful sequence information for peptides.

Degree

Ph.D.

Advisors

Kenttamaa, Purdue University.

Subject Area

Analytical chemistry

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