Energy Calibration in the Interface of Tandem Trapped Ion Mobility Mass Spectrometry

Proteins and their complexes take on central roles in biological processes and disease mechanisms. More recently, significant efforts are being devoted into revealing the molecular mechanisms by which differentially modified variants of the same protein (proteoforms) can exhibit different biological activities. These efforts are hampered by the lack of a method that determines the structure of a protein and simultaneously its sequence and post-translational modifications. Tandem-trapped ion mobility spectrometry (tandem-TIMS) has the potential to fill this gap. A central aspect here is the ability to characterize the unfolding pathways of the protein in the gas-phase. To this end, ions are accelerated by an electric field in the presence of a buffer gas and the gained kinetic energy is converted into internal energy of the ions through collisions with the buffer gas. What remains unknown, however, is how analytes are collisionally-activated in a tandem-TIMS instrument. In this thesis, I show using reference molecules that it is possible to relate the dissociation barrier of ions to the activation voltage applied in tandem-TIMS. I construct a strong linear model that predicts either the activation energy and the Gibbs energy of activation as a function of the activation voltage needed for dissociation and other parameters that account for the identity of the different analytes. Since the reaction rates and the activation energies can be related by different equations, it is possible to predict the dissociation reaction rate with the model constructed in this thesis. Therefore, the stability of different analytes in the gas phase can be studied by performing simple dissociation experiments in Tandem TIMS. The findings discussed in this thesis are intended to illustrate the different tendencies on reaction dynamics and is wished to be extrapolated to much larger and complex systems in future studies.