Unusual Oxidation of Organics at Interfaces from the Bottom Up and Atmospheric Implications

Abstract

Photolysis of a mixture of NaNO2 with NaCl with an adsorbed coating of 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC) is shown to lead to oxidation of the OPPC. This oxidation "from the bottom up" is due to the generation of the OH free radical from nitrite ion photochemistry in the presence of water and its addition to the OPPC double bond. Such chemistry may be important in the lower atmosphere.

Atmospheric chemistry of bioaerosols: heterogeneous and multiphase reactions with atmospheric oxidants and other trace gases

“…In the absence of water vapor, carboxylate ions are also formed. 84,86 These two different oxidation mechanisms of unsaturated phospholipids have important implications on the lifetime of the lipids. Freshly emitted SSA particles with phospholipid coating will experience top down oxidation.…”

Reactions at surfaces in the atmosphere: integration of experiments and theory as necessary (but not necessarily sufficient) for predicting the physical chemistry of aerosols

“…186,187 Because photolysis of nitrite ions generates OH radicals, reaction (11) above, similar oxidation of adsorbed organics would be expected during irradiation of particles containing NO 2 À , and this has indeed been observed. 188,189 In this case, a phosopholipid, 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC), was adsorbed on a dilute (0.4 wt%) NaNO 2 /NaCl salt solid mixture and the loss of nitrite and OPPC and the formation of organic products followed with time using diffuse reflection infrared Fourier transform spectrometry (DRIFTS). 190 In the absence of added water vapor (but some strongly adsorbed water remains on the salt and zwitterionic end of OPPC), products due to O À attack on the OPPC were observed, particularly carboxylates, RC(O)O À , to which the 1580 cm À1 peak was assigned (Fig.…”

Hydroxyl radical oxidation of phospholipid-coated NaCl particles

“…Even if every OH produced this way reacted with an organic molecule, oxidation from the bottom up would not be competitive with top-down oxidation. The products in both these top-down and the previous bottom-up studies 23,24 include organic nitrates. These species can serve as reservoirs for oxides of nitrogen that can decompose to release NO x back into the atmosphere 59,60 far from where they were formed.…”

“…The results of the present studies can be compared to previous work on OH oxidation of OPPC from the bottom up, in which OH was generated at the salt surface by photolysis of NaNO 2 -NaCl mixtures. 23,24 We only consider NaNO 2 experiments carried out in the presence of water, where the O À generated on photolysis is converted to OH radicals. Bottom-up oxidation was slower than top-down oxidation.…”