  The recent application of electrosprays to characterize the air-water
interface, along with the reports on dramatically accelerated chemical
reactions in aqueous electrosprays, have sparked a broad interest. Herein, we
report on complementary laboratory and in silico experiments tracking the
oligomerization of isoprene, an important biogenic gas, in electrosprays and
isoprene-water emulsions to differentiate the contributions of interfacial
effects from those of high voltages leading to charge-separation and
concentration of reactants in the electrosprays. To this end, we employed
electrospray ionization mass spectrometry, proton nuclear magnetic resonance,
and quantum mechanical simulations. We found that the oligomerization of
isoprene in aqueous electrosprays involved minimally hydrated and highly
reactive hydronium ions. Those conditions, however, are non-existent at
pristine air-water interfaces and oil-water emulsions under normal temperature
and pressure. Thus, electrosprays should be complemented with surface-specific
platforms and theoretical methods to reliably investigate chemistries at the
pristine air-water interface.
