Ozonation of methyl oleate in hexane, in a thin film, in SDS micelles, and in distearoylphosphatidylcholine liposomes: yields and properties of the Criegee ozonide.
We here explore the use of Criegee ozonides as markers of ozone damage to lipids in systems that model pulmonary surfactant, lung lining fluids, and/or pulmonary membranes. Ozonation of methyl oleate in hexane gives an 89% yield of the Criegee ozonide. The presence of water should reduce the yield of this ozonide, and as expected, small but significant yields of Criegee ozonides are formed when the ozonation of methyl oleate is carried out as a film over phosphate buffer, in aqueous micelles of sodium dodecyl sulfate (SDS), or in distearoyl-L-alpha-phosphatidylcholine (DSPC) liposomes spiked with methyl oleate. Analysis utilizes reversed-phase HPLC and 1H NMR. The total yield of ozonides in 0.02 M SDS micelles exposed to 26 ppm ozone for 3 h at pH 7.4 and 22 degrees C is 11%; 7.5% is the normal ozonide, methyl 5-octyl-1,2,4-trioxolane-3-octanoate (MOO2) (ca. 4.2% trans and ca. 3.3% cis), and 3.5% is accounted for by the two cross ozonides, 3,5-dioctyl-1,2,4-trioxolane (MOO1) and dimethyl 1,2,4-trioxolane-3,5-dioctanoate (MOO3). No significant difference of ozonide yields is observed for ozonations with 26 ppm and 1.2% (12,000 ppm) ozone. The conversion of methyl oleate increaes with increasing SDS concentration. Approximately comparable yields of ozonides also are found in the ozonation of methyl oleate in DSPC liposomes although yields are not quantified. The ozonides slowly hydrolyze at pH 7.4 and 37 degrees C with half-lives for trans-MOO2 and cis-MOO2 in 0.10 M SDS micelles of 23 and 6 days, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)