title: Studying interfacial reactions of cholesterol sulfate in an unsaturated phosphatidylglycerol layer with ozone using field induced droplet ionization mass spectrometry.
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 (CholSO(4)) in a 1-palmitoyl-2-oleoyl-sn-phosphatidylglycerol (POPG) surfactant layer with ozone (O(3)) are investigated using field-induced droplet ionization mass spectrometry (FIDI-MS). Time-resolved studies of interfacial ozonolysis of CholSO(4) reveal that water plays an important role in forming oxygenated products. An epoxide derivative is observed as a major product of CholSO(4) oxidation in the FIDI-MS spectrum after exposure of the droplet to O(3) for 5 s. The abundance of the epoxide product then decreases with continued O(3) exposure as the finite number of water molecules at the air-liquid interface becomes exhausted. Competitive oxidation of CholSO(4) and POPG is observed when they are present together in a lipid surfactant layer at the air-liquid interface. Competitive reactions of CholSO(4) and POPG with O(3) suggest that CholSO(4) is present with POPG as a well-mixed interfacial layer. Compared with CholSO(4) and POPG alone, the overall ozonolysis rates of both CholSO(4) 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 CholSO(4) correlate well with experimental observations and provide a detailed picture of the interactions between CholSO(4), lipids, and water molecules in the interfacial region.
authors: Department of Chemistry, Pohang University of Science and Technology (POSTECH), 790-784, Pohang, Republic of Korea.
authors: Jae Yoon
authors: JY
authors: Ko
authors: Sun Mi
authors: SM
authors: Choi
authors: Young Min
authors: YM
authors: Rhee
authors: J L
authors: JL
authors: Beauchamp
authors: Hugh I
authors: HI
authors: Kim
mesh_terms: D000388:Air; D002788:Cholesterol Esters / Q000737:chemistry*; D007700:Kinetics; D056004:Molecular Dynamics Simulation; D010126:Ozone / Q000737:chemistry*; D010715:Phosphatidylglycerols / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D014867:Water
chemical_list: D002788:Cholesterol Esters; D010715:Phosphatidylglycerols; D014867:Water; D010126:Ozone; C060037:1-palmitoyl-2-oleoylglycero-3-phosphoglycerol; C007045:cholesteryl sulfate