Structural insights into variation of intramolecular acid site using phase transition experiments and computation

Mass transfer from liquid to gas phase is a crucial process in chemical engineering. Due to the heterogeneity and dynamic nature of the phase transition process, monitoring the structural changes of compounds during this process is challenging. In this work, a combining of the mass spectrometry-based method and quantum chemistry calculations was used to study the structural changes during liquid-to-gas phase transitions. Electrospray is used to induce the transition of phenolic acid molecules from the liquid phase to the gas phase. The deprotonated structures were captured and separated using ion mobility mass spectrometry. Deprotonated structures helped to identify the most acidic functional group within the molecule. These deprotonated structures were confirmed by collision-induced dissociation and molecular collision cross-section measurements. Quantum chemistry calculations revealed the mechanisms about the variation of intramolecular acid site and “kinetic trapping.” Three liquid-to-gas phase transformation models were proposed, demonstrating that the variation in free energy among different deprotonated structures governs the thermodynamic/kinetic process of the liquid-to-gas phase conversion.