Quantum chemical mass spectromery: detailed insight into the fragmentation behaviour of small organic molecules, peptides and lipids
16 April 2019
Campus Middelheim, A.143 - Middelheimlaan 1 - 2020 Antwerpen (route: UAntwerpen, Campus Middelheim
Organization / co-organization:
Department of Chemistry
PhD defence Julie Cautereels - Faculty of Science, Department of Chemistry
Spectroscopic and spectrometric techniques, like MS, IR and NMR spectroscopy, have been an important tool for the physicochemical characterisation of compounds for many decades. While quantum chemical calculations are routinely used to reproduce, predict and assign IR and NMR spectra, MS is one of the few remaining techniques for which no quantum chemical methods are available for the systematic reproduction or prediction of spectra. The current methods to predict mass spectra all display some disadvantages and, therefore, we developed a new quantum-chemical based method to predict mass spectrometric fragmentation pathways, named Quantum Chemical Mass Spectrometry for Materials Science (QCMS2).
QCMS2 takes no energy supply into account in the prediction resulting in the energetics of the fragmentations to be positive: QCMS2, therefore, follows the fragmentation pathway(s) with the least resistance from precursor ion to fragments through all fragment generations. The method is based on DFT/B3LYP/6-311+G* calculations of bond orders, reaction energies for bond cleavages and activation energies for rearrangements.
During this doctoral thesis, QCMS2 was applied to predict the electron ionisation fragmentation pathways of four small organic molecules and the electrospray collision-induced dissociation fragmentation pathways of melphalan and benzocaine analogues, sphingosylphosphorylcholine and 38 X-His-Z tripeptides whereby X and Z were chosen based on their ability to form strong hydrogen bonds. In all cases, QCMS2 was able to reproduce the main features in the mass spectra of these compounds and, more importantly, QCMS2 predicts new fragmentation pathways. The final chapter of this thesis presents an evaluation of the achievements, points of improvements and future perspectives of QCMS2.