Control of Intermediates and Products by Combining Droplet Reactions and Ion Soft‐Landing

Abstract

Despite being recognized primarily as an analytical technique, mass spectrometry also has a large potential as a synthetic tool, enabling access to advanced synthetic routes by reactions in charged microdroplets or ionic thin layers. Such reactions are special and proceed primarily at surfaces of droplets and thin layers. Partial solvation of the reactants is usually considered to play an important role for reducing the activation barrier, but many mechanistic details still need to be clarified. In our study, we showcase the synergy between two sequentially applied "preparative mass spectrometry" methods: initiating accelerated reactions within microdroplets during electrospray ionization to generate gaseous ionic intermediates in high abundance, which are subsequently mass‐selected and soft‐landed to react with a provided reagent on a substrate. This allows the generation of products at a nanomolar scale, amenable to further characterization. In this proof‐of‐concept study, the contrasting reaction pathways between intrinsically neutral and pre‐charged reagents, respectively, both in microdroplets and in layers generated by ion soft‐landing are investigated. This provides new insights into the role of partially solvated reagents at microdroplet surfaces for increased reaction rates. Additionally, further insights into reactions of ions of the same polarity under various conditions is obtained.

Visualizing partial solvation at the air–water interface

“…This reaction enhancement has been observed in hydrophobic-water emulsions, [1][2][3][4] small water droplets (<100 mm), [5][6][7] and thin aqueous lms. 8,9 Reaction acceleration in these systems is oen accompanied by improved product selectivity, 6,[10][11][12][13][14] and some reactions which do not proceed in bulk water such as spontaneous hydrogen peroxide generation have been found to occur in these aqueous droplets. 7 These interface-rich systems have been proposed as the ideal environments for the origin of biogenic molecules [15][16][17] and reactions relevant to the origin of life have recently been reported in microdroplets.…”