Products and mechanism of the reaction of ozone with phospholipids in unilamellar phospholipid vesicles

Abstract

While considerable effort has been expended on determining the health effects of exposure to typical urban concentrations of O3, little is known about the chemical events responsible for toxicity. Phospholipids containing unsaturated fatty acids in the cell membranes of lung cells are likely reaction sites for inhaled ozone (O3). In this study, we examined the reaction of O3 with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in unilamellar phospholipid vesicles. Reaction of ozone with the carbon-carbon double bond of POPC yielded an aldehyde and a hydroxy hydroperoxide. The hydroxy hydroperoxide eliminated H2O2 to yield a second aldehyde. Upon further ozonolysis, the aldehydes were oxidized to the corresponding carboxylic acids. A material balance showed that no other reaction consumed POPC and O3 or produced these products. As a mechanistic probe, we measured incorporation of oxygen-18 from 18O3 into aldehyde, carboxylic acid, and H2O2. Approximately 50% of the aldehyde oxygen atoms were derived from O3. Oxygen in H2O2 was derived solely from O3, where both oxygen atoms in a molecule of H2O2 were from the same molecule of O3. One of the carboxylic acid oxygen atoms was derived from the precursor aldehyde, while the other was derived from O3. These results support the following mechanism. Cleavage of the carbon-carbon double bond of POPC by O3 yields a carbonyl oxide and an aldehyde. Reaction of H2O with the carbonyl oxide yields a hydroxy hydroperoxide, preventing formation ozonide by reaction of the carbonyl oxide and aldehyde. Elimination of H2O2 from the hydroxy hydroperoxide yields a second aldehyde. Oxidation of the aldehydes by O3 yields carboxylic acids.

A new mechanism for ozonolysis of unsaturated organics on solids: phosphocholines on NaCl as a model for sea salt particles

“…Additional reaction paths are available for CI's, including isomerization to the acid or reaction with water vapor, if present. 14,43,[46][47][48][49][50][51][52][53] The spectrum in Fig. 3 shows that even in the absence of added water vapor, adsorbed water is present on the surface of the OPPC/NaCl.…”

“…43, [46][47][48][49][50][51][52][53] However, the spectra in Fig. 4 also show that -CH 2 -groups are lost during the reaction.…”

Hazardous air pollutants and asthma.

“…Interestingly, once inhaled, ozone is likely to react with unsaturated fatty acids in the airway lining fluid or the cell membranes to form aldehydes, hydroxyhydroperoxides, and hydrogen peroxide (116,117). These intermediates are HAPs and can activate mediator release from human airway epithelial cells, thereby linking the biochemical outcomes of ozone with these compounds (118,119).…”

Studying Interfacial Reactions of Cholesterol Sulfate in an Unsaturated Phosphatidylglycerol Layer with Ozone Using Field Induced Droplet Ionization Mass Spectrometry

“…In order to yield HHP, a primary ozonide (POZ) reacts with a water molecule (Scheme 2) [32,33]. However, this unstable product converts to an aldehyde product through a proton transfer with a water molecule in the bulk phase [33]. Abundant hydroperoxide products in the FIDI-MS spectra have been reported in our previous study of heterogeneous POPG ozonolysis [15].…”

“…After 30 s exposure of O 3 to the droplet, only a small amount of product III is observed along with highly abundant product IV and product V. The air-liquid interfacial ozonolysis of CholSO 4 yields HHP (product IV) and MHP (product V) products as the most abundant products. In order to yield HHP, a primary ozonide (POZ) reacts with a water molecule (Scheme 2) [32,33]. However, this unstable product converts to an aldehyde product through a proton transfer with a water molecule in the bulk phase [33].…”