Interactions of monolayers of unsaturated phosphocholines with ozone at the air-water interface

Lai, Chia-Yun; Yang, Su–Hua; Finlayson-Pitts, Barbara J.

doi:10.1021/la00024a041

Cited by 70 publications

(126 citation statements)

References 4 publications

(5 reference statements)

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“…An enhanced reaction probability for the surface reaction is consistent with the fact that the terminal double bond should be the part of the SAM that OH first encounters in the structured monolayer, as also proposed for the NO 3 reaction, 57 and with previous studies showing enhanced reactivity at interfaces compared to the gas phase. [19][20][21][22][23][24][25][26][27][28] Reaction on every collision has also been observed for the reaction of Cl atoms with a C3Q SAM. 22 Although there are a number of studies of the OH oxidation of organics on surfaces and in or on particles, there are 25 measured g = 0.29 for the same surface, indicating that even for saturated alkyl chains, the surface reaction is fast.…”

Section: Kineticsmentioning

confidence: 79%

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

Moussa

Finlayson-Pitts

2010

Phys. Chem. Chem. Phys.

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The kinetics and mechanisms of the reaction of gas phase OH radicals with organics on surfaces are of fundamental chemical interest, as well as relevant to understanding the degradation of organics on tropospheric surfaces or when they are components of airborne particles. We report here studies of the oxidation of a terminal alkene self-assembled monolayer (7-octenyltrichlorosilane, C8Q SAM) on a germanium attenuated total reflectance crystal by OH radicals at a concentration of 2.1 Â 10 5 cm À3 at 1 atm total pressure and 298 K in air. Loss of the reactant SAM and the formation of surface products were followed in real time using infrared spectroscopy. From the rate of loss of the CQC bond, a reaction probability within experimental error of unity was derived. The products formed on the surface include organic nitrates and carbonyl compounds, with yields of 10 AE 4% and r7 AE 4%, respectively, and there is evidence for the formation of organic products with C-O bonds such as alcohols, ethers and/or alkyl peroxides and possibly peroxynitrates. The yield of organic nitrates relative to carbonyl compounds is higher than expected based on analogous gas phase mechanisms, suggesting that the branching ratio for the RO 2 + NO reaction is shifted to favor the formation of organic nitrates when the reaction occurs on a surface. Water uptake onto the surface was only slightly enhanced upon oxidation, suggesting that oxidation per se cannot be taken as a predictor of increased hydrophilicity of atmospheric organics. These experiments indicate that the mechanisms for the surface reactions are different from gas phase reactions, but the OH oxidation of surface species will still be a significant contributor to determining their lifetimes in air.

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Section: Kineticsmentioning

confidence: 79%

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

Moussa

Finlayson-Pitts

2010

Phys. Chem. Chem. Phys.

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“…This discrepancy increases with decreasing ozone concentrations; other studies on the heterogeneous oxidation of unsaturated alkenes by ozone have indicated similar trends. 13,15,16,22,25,27 Unlike the case of very Figure 9. Calculated reaction probabilities for the oxidation of C3d at the time when half of the SAM has been oxidized (f ) 0.5) as a function of the gas-phase ozone concentration.…”

Section: Resultsmentioning

confidence: 94%

Interaction of Gas-Phase Ozone at 296 K with Unsaturated Self-Assembled Monolayers: A New Look at an Old System

et al. 2004

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The oxidation of organics adsorbed on surfaces by ozone is of fundamental chemical interest and potentially important in the lower atmosphere. Studies of the oxidation of the three-carbon and eight-carbon vinylterminated self-assembled monolayers (SAMs, C3d and C8d) on a silicon ATR (attenuated total reflectance) crystal by gas-phase O 3 at 296 K are reported. Oxidation of the SAMs was followed in real time by ATR-FTIR using ozone concentrations that spanned 5 orders of magnitude, from ∼10 11 to 10 16 molecules cm -3 . For comparison, some studies of the saturated C8 SAM were also carried out. The films were also characterized by atomic force microscopy and water contact angle measurements. The loss of CdC and the formation of CdO were measured in real time and shown to be consistent with a Langmuir-Hinshelwood mechanism in which O 3 is rapidly adsorbed on the surface and then reacts more slowly with the alkene moiety. This is supported by molecular dynamics (MD) calculations which show that O 3 does not simply undergo elastic collisions but has a significant residence time on the surface. However, the kinetics measurements indicate a much longer residence time than the MD calculations, suggesting a chemisorption of O 3 . Formaldehyde was observed as a gas-phase product by infrared cavity ring down spectroscopy. Possible mechanisms of the ozonolysis and its atmospheric implications are discussed.

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“…The exact masses of the proton and sodium adducts of POPC were used as internal standards to obtain more accurate mass measurements of the peaks in the mass spectra. 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.…”

Section: Resultsmentioning

confidence: 99%

“…27 This amount of POPC would coat 2 mm cubic particles with approximately one monolayer of POPC, assuming a surface concentration of 1.6 Â 10 14 molecules cm À2 obtained from previous studies of surface pressure-area isotherms of OPPC films on water. 28,29 To examine the effect of varying the amount of POPC in the sample, some experiments were performed with 0.10 mL of POPC solution added to 0.35 g NaCl to give approximately 1 4 of a monolayer of coverage. Experiments were also performed using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC, 0.37 mL DPPC solution mixed with 0.35 g NaCl) to elucidate the reactions with a saturated phospholipid that has the same number of -CH 2 -groups, but no double bond.…”

Section: Sample Preparationmentioning

confidence: 99%

Hydroxyl radical oxidation of phospholipid-coated NaCl particles

Dilbeck

Finlayson-Pitts

2013

Phys. Chem. Chem. Phys.

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Interactions of monolayers of unsaturated phosphocholines with ozone at the air-water interface

Cited by 70 publications

References 4 publications

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

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

Interaction of Gas-Phase Ozone at 296 K with Unsaturated Self-Assembled Monolayers: A New Look at an Old System

Hydroxyl radical oxidation of phospholipid-coated NaCl particles

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