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

Abstract

PERSPECTIVEThe ozonolysis of an approximately one monolayer film of 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC) on NaCl was followed in real time using diffuse reflection infrared Fourier transform spectrometry (DRIFTS) at 23 1C. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry and Auger electron spectroscopy were used to confirm the identification of the products. Ozone concentrations ranged from 1.7 Â 10 12 to 7.0 Â 10 13 molecules cm À3 (70 ppb to 2.8 ppm). Upon exposure to O 3 , there was a loss of CQC accompanied by the formation of a strong band at B1110 cm À1 due to the formation of a stable secondary ozonide (1,2,4-trioxolane, SOZ). The yield of the SOZ was smaller when the reaction was carried out in the presence of water vapor at concentrations corresponding to relative humidities between 2 and 25%.

Hydroxyl radical oxidation of phospholipid-coated NaCl particles

“…A second set of masses at m/z 650 and 672 was also used as an internal standard in that region, based on the assumption that they are attributable to the proton and sodium adducts of the phospholipid aldehyde B (Scheme 2) observed previously in the ozone oxidation of POPC 28,41 and its isomer OPPC. 42,43 Table 1 lists the measured m/z of the proton adduct peaks, the formulae and exact masses of the closest matches to the measured m/z that are chemically and mechanistically reasonable, the relative error in ppm, and the assigned structures as shown in the schemes. For some of the peaks, potential additional formulae and structures are listed which may contribute to the peaks.…”

“…In previous studies, 43,47 the reaction of carboxylic acids with NH 3 converted -COOH to carboxylate (-COO À ) whose carbonyl absorption band shifts significantly, to B1580 cm…”

Acidity enhances the formation of a persistent ozonide at aqueous ascorbate/ozone gas interfaces

“…In Appendix 4 in SI Text, we show that the relatively slow (in the millisecond time scale) unimolecular decomposition of POZ into THR and AOZ accounts for nonvanishing ␥ AOZ (Figs. S7 and S8 Lower) and ␥ THR slopes, but the enhanced production of AOZ and THR at larger [O 3 (g)] implies that POZ decomposition is accelerated by O 3 (33). Neither pathway alone is able to account for both nonvanishing initial slopes ␥ AOZ and increased AOZ production at larger [O 3 (g)].…”

“…The thermal stability of secondary ozonides favors the former possibility (31-33). Ozonealkene reactions in dry polluted atmospheres produce stable secondary ozonides (33). Fig.…”

Reaction of gas phase OH with unsaturated self-assembled monolayers and relevance to atmospheric organic oxidations

“…29 Reaction mechanisms can also be different. For example, ozonolysis of alkenes on solid substrates forms secondary ozonides (SOZ) 30,31 because the Criegee intermediate and aldehyde or ketone precursors are stabilized and held in sufficiently close proximity to combine, whereas the SOZ yields are negligible under most conditions in the gas phase. Thus, understanding the kinetics and mechanisms of interaction of atmospheric oxidants with condensed phase organics and how they differ from gas phase chemistry is of fundamental chemical interest.…”