Cigarette Smoke Extract Produces Superoxide in Aqueous Media by Reacting with Bicarbonate

The toxicity of cigarette smoke (CS) is largely attributed to its ability to generate reactive oxygen species (ROS). Reportedly, CS generates superoxide in cell culture systems by stimulating the cells to produce superoxide and through direct chemical reactions with components of the culture media. In this study, we investigated CS-induced superoxide formation in biocompatible aqueous media and its characteristics. Cigarette smoke extract (CSE) and total particulate matter (TPM) were prepared from the mainstream smoke of 3R4F reference cigarettes. CSE and TPM generated superoxide in Hank’s balanced salt solution (HBSS), Dulbecco’s modified Eagle media (DMEM), and blood plasma, but not in distilled water and phosphate-buffered saline. Each constituent of HBSS in solution was tested, and bicarbonate was found to be responsible for the superoxide generation. More than half of the superoxide formation was abolished by pretreating CSE or TPM with peroxidase, indicating that the substrates of peroxidase, presumably peroxides and peroxy acids, mainly contributed to the superoxide production. In conclusion, the presence of bicarbonate in experimental conditions should be considered carefully in studies of the biological activity of CS. Furthermore, the local amount of bicarbonate in exposed tissues may be a determinant of tissue sensitivity to oxidative damage by CS.

Reaction between CH₃C(O)OOH (peracetic acid) and OH in the gas-phase: A combined experimental and theoretical study of the kinetics and mechanism

Peracetic acid (CH3C(O)OOH) is one of the most abundant organic peroxides in the atmosphere, yet the kinetics of its reaction with OH, believed to be the major sink, have been studied only once experimentally. In this work we combine a pulsed-laser photolysis kinetic study of the title reaction with theoretical calculations of the rate coefficient and mechanism. We demonstrate that the rate coefficient is orders of magnitude lower than previously determined, with an experimentally derived upper limit of ≤ 4 × 10−14 cm3 molecule−1 s−1. The relatively low rate coefficient is in good agreement with the theoretical result of 3 × 10−14 cm3 molecule−1 s−1 at 298 K, increasing to ~ 6 × 10−14 in the cold upper troposphere, but with associated uncertainty of a factor-two. The reaction proceeds mainly via abstraction of the peroxidic-hydrogen via a relatively weakly bonded and short-lived pre-reaction complex, in which H-abstraction occurs only slowly due to a high barrier and low tunneling probabilities. Our results imply that the lifetime of CH3C(O)OOH with respect to OH-initiated degradation in the atmosphere is of the order of one year (and not days as previously believed) and that its major sink in the free and upper troposphere is likely to be photolysis, with dry-deposition important in the boundary layer. Similar conclusions can be made for other, saturated peroxy-acids.

Formation of Criegee intermediates and peroxy acids: a computational study of gas-phase 1,3-cycloaddition of ozone with catechol

A novel pathway leading to peroxy acids from ozonolysis of catechol.

Synthesis and characterisation of peroxypinic acids as proxies for highly oxygenated molecules (HOMs) in secondary organic aerosol

Peroxy acids were recently found to be involved in new particle formation in the atmosphere and could also substantially contribute towards particle toxicity. However, a lack of suitable analytical methods for the detection and characterisation of peroxy acids in the particle phase is currently hindering the quantitative investigation of their contribution to these important atmospheric processes. Further development of appropriate techniques and relevant standards is therefore urgently needed. In this study, we synthesised three peroxypinic acids, developed a liquid chromatography separation method and characterised them with tandem mass spectrometry. The observed fragmentation patterns clearly distinguish the different peroxypinic acids from both the acid and each other, showing several neutral losses previously already observed for other peroxy acids. Both monoperoxypinic acids were found to be present in secondary organic aerosol generated from ozonolysis of α-pinene in laboratory experiments. The yield of monoperoxypinic acid formation was not influenced by humidity. Monoperoxypinic acid quickly degrades on the filter, with about 60 % lost within the first 5 h. This fast degradation shows that time delays in traditional off-line analysis will likely lead to severe underestimates of peroxy compound concentrations in ambient particles.

Identification of organic hydroperoxides and peroxy acids using atmospheric pressure chemical ionization–tandem mass spectrometry (APCI-MS/MS): application to secondary organic aerosol

Molecules with hydroperoxide functional groups are of extreme importance to both the atmospheric and biological chemistry fields. In this work, an analytical method is presented for the identification of organic hydroperoxides and peroxy acids (ROOH) by direct infusion of liquid samples into a positive-ion atmospheric pressure chemical ionization–tandem mass spectrometer ((+)-APCI-MS/MS). Under collisional dissociation conditions, a characteristic neutral loss of 51 Da (arising from loss of H2O2+NH3) from ammonium adducts of the molecular ions ([M + NH4]+) is observed for ROOH standards (i.e. cumene hydroperoxide, isoprene-4-hydroxy-3-hydroperoxide (ISOPOOH), tert-butyl hydroperoxide, 2-butanone peroxide and peracetic acid), as well as the ROOH formed from the reactions of H2O2 with aldehydes (i.e. acetaldehyde, hexanal, glyoxal and methylglyoxal). This new ROOH detection method was applied to methanol extracts of secondary organic aerosol (SOA) material generated from ozonolysis of α-pinene, indicating a number of ROOH molecules in the SOA material. While the full-scan mass spectrum of SOA demonstrates the presence of monomers (m∕z = 80–250), dimers (m∕z = 250–450) and trimers (m∕z = 450–600), the neutral loss scan shows that the ROOH products all have masses less than 300 Da, indicating that ROOH molecules may not contribute significantly to the SOA oligomeric content. We anticipate this method could also be applied to biological systems with considerable value.