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King Abdullah University of Science and Technology

1. Junior, Adair Gallo. An Investigation of Chemical Landscapes in Aqueous Electrosprays by Tracking Oligomerization of Isoprene.

Degree: 2017, King Abdullah University of Science and Technology

Electrospray ionization mass spectrometry (ESIMS) is widely used to characterize neutral and ionic species in solvents. Typically, electrical, thermal, and pneumatic potentials are applied to create electrosprays from which charged ionic species are ejected for downstream analysis by mass spectrometry. Most recently, ESIMS has been exploited to investigate ambient proton transfer reactions at air-water interfaces in real time. We assessed the validity of these experiments via complementary laboratory experiments. Specifically, we characterized the products of two reaction scenarios via ESIMS and proton nuclear magnetic resonance (1H-NMR): (i) emulsions of pH-adjusted water and isoprene (C5H8) that were mechanically agitated, and (ii) electrosprays of pH-adjusted water that were collided with gas-phase isoprene. Our experiments unambiguously demonstrate that, while isoprene does not oligomerize in emulsions, it does undergo protonation and oligomerization in electrosprays, both with and without pH-adjusted water, confirming that C-C bonds form along myriad high-energy pathways during electrospray ionization. We also compared our experimental results with some quantum mechanics simulations of isoprene molecules interacting with hydronium at different hydration levels (gas versus liquid phase). In agreement with our experiments, the kinetic barriers to protonation and oligomerization of isoprene were inaccessible under ambient conditions. Rather, the gas-phase chemistries during electrospray ionization drove the oligomerization of isoprene. Therefore, we consider that ESIMS could induce artifacts in interfacial reactions. These findings warrant a reassessment of previous reports on tracking chemistries under ambient conditions at liquid-vapor interfaces via ESIMS. Further, we took some high-speed images of electrosprays where it was possible to observe the main characteristics of the phenomena, i.e. Taylor cone, charge separation, and Coulomb fission. Finally, we took the freedom to speculate on possible mechanisms that take place during electrospray ionization that affected our system and possibly may influence other common analytical techniques on ESIMS.

Subjects/Keywords: electrospray ionization; air-water interfaces; electrospray droplets; isoprene oligomerization; reactions in electrospray; proton transfer reaction

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Junior, A. G. (2017). An Investigation of Chemical Landscapes in Aqueous Electrosprays by Tracking Oligomerization of Isoprene. (Thesis). King Abdullah University of Science and Technology. Retrieved from http://hdl.handle.net/10754/626292

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Junior, Adair Gallo. “An Investigation of Chemical Landscapes in Aqueous Electrosprays by Tracking Oligomerization of Isoprene.” 2017. Thesis, King Abdullah University of Science and Technology. Accessed July 23, 2019. http://hdl.handle.net/10754/626292.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Junior, Adair Gallo. “An Investigation of Chemical Landscapes in Aqueous Electrosprays by Tracking Oligomerization of Isoprene.” 2017. Web. 23 Jul 2019.

Vancouver:

Junior AG. An Investigation of Chemical Landscapes in Aqueous Electrosprays by Tracking Oligomerization of Isoprene. [Internet] [Thesis]. King Abdullah University of Science and Technology; 2017. [cited 2019 Jul 23]. Available from: http://hdl.handle.net/10754/626292.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Junior AG. An Investigation of Chemical Landscapes in Aqueous Electrosprays by Tracking Oligomerization of Isoprene. [Thesis]. King Abdullah University of Science and Technology; 2017. Available from: http://hdl.handle.net/10754/626292

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

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