Mass spectrometric studies of ionic reactions in confined volumes

Despite the widespread use of mass spectrometry as an analytical method, this technique was recently used also for synthetic purposes performing reactions that are often more efficient than the same processes in bulk. This advancement was made possible by the introduction of the electrospray ionization (ESI) source by Fenn, who was awarded the Nobel Prize in 2002. It has been observed that, when reagents are confined within ESI-generated charged microdroplets, various fundamental reactions can be accelerated by several orders of magnitude compared to the same reactions in bulk. The main factors contributing to this acceleration include: i) rapid solvent evaporation, which increases reactant concentrations, ii) acidity or basicity enhancement within the microdroplets, and iii) confinement of reagents in small volumes with high surface-to-volume ratios. The studies reported in this thesis are all based on the acceleration of chemical processes in the confined volume of thin films produced by depositing charged microdroplets onto a solid surface. Thin films and microdroplets share similar properties, such as high surface-to-volume ratios and confinement of reagents, but, thin films allow also the recovery and analysis of the neutral product of the accelerated reactions. The properties of these confined systems were used to study the acceleration of known organic reactions such as: - the acid-catalyzed decomposition of D-fructose, leading to the formation of dehydration, polymerization, and methylation products. - the Maillard reaction, leading to the formation of the Amadori product with various types of amino acids. - Amino acids H2SO4 acid-catalyzed esterification. Moreover, using the synthesis of warfarin as a model, it was demonstrated for the first time that reaction stereoselectivity in microdroplets and thin film is comparable to bulk processes, despite the significant acceleration of the reaction in these confined volumes. Finally, the microdroplets accelerated reduction of Au3+ ions to gold nanoparticles without the use of reducing agent was exploited to the functionalization of graphite electrodes.