Studying interfacial reactions of cholesterol sulfate in an unsaturated phosphatidylglycerol layer with ozone using field induced droplet ionization mass spectrometry

Jae Yoon Ko, Sun Mi Choi, Young Min Rhee, J. L. Beauchamp, Hugh I. Kim

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Field-induced droplet ionization (FIDI) is a recently developed ionization technique that can transfer ions from the surface of microliter droplets to the gas phase intact. The air-liquid interfacial reactions of cholesterol sulfate (CholSO4) in a 1-palmitoyl-2-oleoyl-sn-phosphatidylglycerol (POPG) surfactant layer with ozone (O3) are investigated using field-induced droplet ionization mass spectrometry (FIDI-MS). Time-resolved studies of interfacial ozonolysis of CholSO4 reveal that water plays an important role in forming oxygenated products. An epoxide derivative is observed as a major product of CholSO4 oxidation in the FIDI-MS spectrum after exposure of the droplet to O3 for 5 s. The abundance of the epoxide product then decreases with continued O3 exposure as the finite number of water molecules at the air-liquid interface becomes exhausted. Competitive oxidation of CholSO4 and POPG is observed when they are present together in a lipid surfactant layer at the air-liquid interface. Competitive reactions of CholSO4 and POPG with O3 suggest that CholSO4 is present with POPG as a well-mixed interfacial layer. Compared with CholSO4 and POPG alone, the overall ozonolysis rates of both CholSO4 and POPG are reduced in a mixed layer, suggesting the double bonds of both molecules are shielded by additional hydrocarbons from one another. Molecular dynamics simulations of a monolayer comprising POPG and CholSO4 correlate well with experimental observations and provide a detailed picture of the interactions between CholSO4, lipids, and water molecules in the interfacial region.

Original languageEnglish
Pages (from-to)141-152
Number of pages12
JournalJournal of the American Society for Mass Spectrometry
Volume23
Issue number1
DOIs
Publication statusPublished - 2012 Jan

Keywords

  • Cholesterol sulfate
  • Field induced droplet ionization
  • Interfacial chemistry
  • Ozonolysis
  • Reaction kinetics
  • Unsaturated phospholipid

ASJC Scopus subject areas

  • Structural Biology
  • Spectroscopy

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