Fundamental studies of collision-activated dissociation (CAD) of deprotonated model compounds relevant to lignin degradation products
Abstract
Lignin is an extremely complex polyphenolic biopolymer found in plants. Since lignin makes up a large portion of the biomass, it is an attractive target for the production of renewable fuels and high value chemicals. Because of lignin’s complexity, it cannot be removed from the plant intact and is instead degraded in various ways. This degradation can produce very complex mixtures which pose a unique analytical challenge. Mass spectrometry is an extremely powerful analytical tool that can be utilized to study complex mixtures and identify unknown molecules due to its high selectivity, sensitivity, and versatility. Tandem mass spectrometry (MS n) experiments play a critical role in the analysis of complex mixtures and the identification of unknown molecules. A common type of tandem mass spectrometry is collisionally activated dissociation, where ions are subjected to high energy collisions with a non-reactive gas in order to induce fragmentation. The resulting fragment ions, as well as the neutral molecules lost from the initial ion, can provide a wealth of information regarding the ion’s structure. However, the fragmentation observed is often not understood or cannot unambiguously identify a molecule without direct comparisons to known compounds. This thesis focuses on the fundamental study of the collisionally activated dissociation of various lignin degradation product model compounds. A large selection of model compounds with various functionalities found in lignin degradation products was examined via CAD until no further fragmentation was observed. The types of fragmentations were examined and mechanisms were drawn in order to gain a better understanding of how these deprotonated ions behaved upon CAD. One of these model compound, vanillin, exhibited a difficult to understand loss of CO2 upon CAD. This fragmentation was examined in greater detail using carbon labelling studies and molecular orbital calculations to determine the mechanism by which the CO2 loss occurs. Lignin degradation products can also contain compounds which contain a lignin-carbohydrate linkage. A selection of model compounds that contained this linkage type were also examined via CAD. The types of fragmentation observed for these compounds were very different than that observed for the other model compounds studied, which would make these compounds easily distinguishable in a complex mixture. Finally, the CAD of several lignin model compounds was compared to the fragmentation observed upon higher energy collisionally activated dissociation (HCD). Since HCD occurs with a single isolation and fragmentation step, as opposed to the multiple steps necessary for CAD,+ this method could prove to be faster for this type of analysis.
Degree
Ph.D.
Advisors
Kenttamaa, Purdue University.
Subject Area
Analytical chemistry|Organic chemistry
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