Characterizing the Energy Surfaces of Competing Pathways in Gas-Phase Charge Inversion Ion/Ion Reactions Involving
Yingchan Guo1, Jonathan T Specker1, Pratiksha B Gaikwad1,2
1Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States.
Journal of the American Society for Mass Spectrometry
|September 20, 2025
Summary
Gas-phase charge inversion ion/ion reactions improve lipid identification by altering ion types. Understanding reaction mechanisms, influenced by ion type and cation coordination, is key to enhancing lipid structural elucidation in lipidomics.
Area of Science:
- Analytical Chemistry
- Physical Chemistry
- Biochemistry
Background:
- Accurate lipid structural identification is crucial for lipidomics and understanding cellular systems.
- Gas-phase charge inversion ion/ion reactions offer improved lipid identification by modifying ion types before dissociation.
- Limited studies have characterized the mechanisms of these complex ion-ion reactions.
Purpose of the Study:
- To characterize the mechanisms of competing pathways in charge inversion ion/ion reactions involving 1,4-phenylenedipropionic acid (PDPA) and phosphatidylcholines (PCs).
- To provide structural information on fatty acyl sn-positions and enable separation of isobaric and isomeric lipids.
- To elucidate the factors influencing product ion partitioning in these reactions using computational methods.
Main Methods:
- Utilized charge inversion ion/ion reactions between PDPA and various phosphatidylcholine (PC) analyte ion types ([PC+H]+, [PC+Na]+, [PC+K]+).
- Employed density functional theory (DFT) calculations to characterize potential energy barriers for competing reaction pathways.
- Analyzed structural dynamics and competing interactions, including proton transfer and methyl group migration.
Main Results:
- Observed differential partitioning of PC analyte ions between charge inversion and single-particle transfer pathways.
- DFT calculations revealed significant differences in transition states based on ion type and cation coordination.
- Identified that cation size and coordination state influence the energetic landscape of ion-ion reactions.
Conclusions:
- Understanding energy barriers in ion-ion reaction complexes is vital for increasing reaction efficiency and designing better reagents for lipid structural elucidation.
- The ion type and structure significantly impact product ion partitioning in gas-phase reactions.
- This research provides fundamental insights into ion/ion reaction mechanisms, highlighting the interplay of thermodynamics and kinetics for controlling reaction products.
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