Reaction pathways leading to HPALD intermediates in the OH-initiated oxidation of isoprene.

In this study, we revisited the mechanism of isoprene oxidation by OH radicals, focusing on the formation of hydroperoxyaldehydes (HPALDs) in the reactions following O-addition at the α-position to ,'-OH-allyl radical products of the 1,6-H shift of the 1st-generation -δ-OH-isoprenylperoxy radicals. Utilizing high-level quantum chemical calculations and a master equation approach, we provide theoretical confirmation that the formation of δ-HPALDs dominates by far and show that production of β-HPALDs by the mechanism proposed by Wennberg (, 2018, , 3337-3390) is negligible. Besides the dominance of the δ-HPALD formation channel, our investigation also reveals a novel though minor reaction channel resulting in the formation of an allylic δ-hydroperoxy acid and OH radical.

Methanediol from cloud-processed formaldehyde is only a minor source of atmospheric formic acid.

Atmospheric formic acid is severely underpredicted by models. A recent study proposed that this discrepancy can be resolved by abundant formic acid production from the reaction (1) between hydroxyl radical and methanediol derived from in-cloud formaldehyde processing and provided a chamber-experiment-derived rate constant, = 7.5 × 10 cm s.

Contamination of tea leaves by anthraquinone: The atmosphere as a possible source.

The detection of anthraquinone in tea leaves has raised concerns due to a potential health risk associated with this species. This led the European Union to impose a maximum residue limit (MRL) of 0.02 mg/kg for anthraquinone in dried tea leaves.

Global Changes in Secondary Atmospheric Pollutants During the 2020 COVID-19 Pandemic.

We use the global Community Earth System Model to investigate the response of secondary pollutants (ozone O, secondary organic aerosols SOA) in different parts of the world in response to modified emissions of primary pollutants during the COVID-19 pandemic. We quantify the respective effects of the reductions in NOx and in volatile organic carbon (VOC) emissions, which, in most cases, affect oxidants in opposite ways. Using model simulations, we show that the level of NOx has been reduced by typically 40% in China during February 2020 and by similar amounts in many areas of Europe and North America in mid-March to mid-April 2020, in good agreement with space and surface observations.

The photolysis of α-hydroperoxycarbonyls.

In this work, we theoretically elucidated the mechanism and predicted the major products of the photolysis of α-hydroperoxycarbonyls, known to be products of the atmospheric oxidation of biogenic volatile organic compounds (BVOC) and components of secondary organic aerosol (SOA) in rural and remote areas. Using 2-hydroperoxypropanal OCHCH(OOH)CH as a model compound, we show that the likely major photolysis mechanism is a fast 1,5 H-shift in the initially excited singlet S state followed by spontaneous elimination of singlet oxygen to yield an enol HOCH[double bond, length as m-dash]CHCH, while intersystem crossing (ISC) to the triplet T state and C-C scission into HC˙O + HOOC˙HCH followed by expulsion of a hydroxyl radical from the unstable HOOC˙HCH is another product channel. The direct S reaction was found to occur at such a high rate that the quantum yield in atmospheric conditions is expected to approach unity.

Theoretically derived mechanisms of HPALD photolysis in isoprene oxidation.

In this work we identified and theoretically quantified two photolysis mechanisms of HPALDs (hydroperoxy aldehydes) that result from the isomerization of peroxy radicals in the atmospheric oxidation of isoprene at low/moderate NO. As a first photolysis mechanism, we show that a fraction of the initially excited S-state HPALDs isomerizes by a near-barrierless 1,5 H-shift at a rate approaching 10 s - competing with the ∼equally fast intersystem crossing to the T triplet state - forming an unstable biradical that spontaneously expels an OH (hydroxyl) radical. A second mechanism is shown to proceed through the activated T triplet biradical - formed from S - undergoing a concerted ring-closure and OH-expulsion, yielding an oxiranyl-type co-product radical that quickly ring-opens to enoxy radicals.

The reaction of methyl peroxy and hydroxyl radicals as a major source of atmospheric methanol.

Methyl peroxy, a key radical in tropospheric chemistry, was recently shown to react with the hydroxyl radical at an unexpectedly high rate. Here, the molecular reaction mechanisms are elucidated using high-level quantum chemical methodologies and statistical rate theory. Formation of activated methylhydrotrioxide, followed by dissociation into methoxy and hydroperoxy radicals, is found to be the main reaction pathway, whereas methylhydrotrioxide stabilization and methanol formation (from activated and stabilized methylhydrotrioxide) are viable minor channels.

Atmospheric Vinyl Alcohol to Acetaldehyde Tautomerization Revisited.

The atmospheric oxidation of vinyl alcohol (VA) produced by photoisomerization of acetaldehyde (AA) is thought to be a source of formic acid (FA). Nevertheless, a recent theoretical study predicted a high rate coefficient k1(298 K) of ≈10(-14) cm(3) molecule(-1) s(-1) for the FA-catalyzed tautomerization reaction 1 of VA back into AA, which suggests that FA buffers its own production from VA. However, the unusually high frequency factor implied by that study prompted us to reinvestigate reaction 1 .

Hydroxyl radical recycling in isoprene oxidation driven by hydrogen bonding and hydrogen tunneling: the upgraded LIM1 mechanism.

The Leuven isoprene mechanism, proposed earlier to aid in rationalizing the unexpectedly high hydroxyl radical (OH) concentrations in isoprene-rich, low-nitric-oxide (NO) regions ( Peeters ; et al. Phys. Chem.

Metabolic study of grapevine leaves infected by downy mildew using negative ion electrospray--Fourier transform ion cyclotron resonance mass spectrometry.

Grapevine is of worldwide economic importance due to wine production. However, this culture is often affected by pathogens causing severe harvest losses. Understanding host-pathogen relationships may be a key to solve this problem.

Evaluation of combined matrix-assisted laser desorption/ionization time-of-flight and matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry experiments for peptide mass fingerprinting analysis.

Peptide Mass Fingerprinting (PMF) is still of significant interest in proteomics because it allows a large number of complex samples to be rapidly screened and characterized. The main part of post-translational modifications is generally preserved. In some specific cases, PMF suffers from ambiguous or unsuccessful identification.

A new method to analyze copolymer based superplasticizer traces in cement leachates.

Enhancing the flowing properties of fresh concrete is a crucial step for cement based materials users. This is done by adding polymeric admixtures. Such additives have enabled to improve final mechanicals properties and the development of new materials like high performance or self compacting concrete.

HO(x) radical regeneration in isoprene oxidation via peroxy radical isomerisations. II: experimental evidence and global impact.

A consistent body of experimental evidence from work of other groups is presented in support of the novel, theoretically based, isoprene oxidation mechanism we recently proposed to rationalize the unexpectedly high OH concentrations observed over areas with high isoprene emissions. Some explicit or implicit criticisms on the new mechanism are addressed. A particular photochemical mechanism is newly proposed for the OH-regenerating photolysis of the crucial hydroperoxy-methyl-butenals (HPALDs), formed by isomerisation of the initial isoprene hydroxy-peroxy radicals, that rationalizes a quantum yield close to 1.

Heroin markers in hair of a narcotic police officer: active or passive exposure?

On March 2007, a police officer (46-year-old man) and a clerk (37-year-old woman) were arrested and subjected to investigation on the charges of drugs of abuse trafficking. The loving couple was exploiting their administrative positions to make money with the resale of seized drugs. The laboratory was requested to analyse their hair for drugs of abuse.

Determination and imaging of metabolites from Vitis vinifera leaves by laser desorption/ionisation time-of-flight mass spectrometry.

Analysis of grapevine phytoalexins at the surface of Vitis vinifera leaves has been achieved by laser desorption/ionisation time-of-flight mass spectrometry (LDI-ToFMS) without matrix deposition. This simple and rapid sampling method was successfully applied to map small organic compounds at the surface of grapevine leaves. It was also demonstrated that the laser wavelength is a highly critical parameter.

Study of active naphtodianthrone St John's Wort compounds by electrospray ionization Fourier transform ion cyclotron resonance and multi-stage mass spectrometry in sustained off-resonance irradiation collision-induced dissociation and infrared multiphoton dissociation modes.

Five well-known active naphtodianthrone constituents of Hypericum perforatum (St John's Wort) extracts have been investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) and ESI-FTICRMSn. The studied compounds were hypericin, pseudohypericin, protohypericin, protopseudohypericin (biosynthetic precursors of the two former compounds, respectively) and isopseudohypericin (alkaline degradation product of pseudohypericin). Dissociation mass spectrometry measurements performed on the [M-H]- ion presented a variable efficiency as a function of the used activation mode.

Evaluation of the Cozart DDSV test for cannabis in oral fluid.

Saliva or "oral fluid" has been presented as an alternative matrix to establish drug exposure. The noninvasive collection of an oral fluid sample, which is relatively easy to perform and can be achieved under close supervision, is one of the most important benefits when testing for driving under the influence of drugs. Moreover, the detection of Delta9-tetrahydrocannabinol (THC) in oral fluid is a better indication of recent use than a positive urine test, so there is a higher probability that the subject is experiencing pharmacological effects at the time of sampling.

Screening of DHFR-binding drugs by MALDI-TOFMS.

The class of antimetabolite chemotherapeutical agents has been used to treat cancers in humans for almost 50 years and gives significant results by binding dihydrofolate reductase (DHFR), a key enzyme in DNA synthesis. Therefore, finding new active compounds inhibiting DNA synthesis through their binding to DHFR is of prime interest. The aim of this work is to describe a protocol designed to study the binding of compounds to DHFR.

Laser ablation mass spectrometry of inorganic transition metal compounds. Additional knowledge for the understanding of ion formation.

Laser ablation of transition-metal oxides have been investigated to better understand the formation processes of inorganic cluster ions. The study of binary oxide mixtures and the relative distribution of the ions produced suggest three salient mechanisms that occur after laser/matter interaction, that function to produce the observed ensemble of ionic species. Molecular recombination reactions, unimolecular dissociation processes, emission of small neutrals, including molecular oxygen from transition-metal oxide samples, or from species expelled in gas phase appear to be a significant mechanism, especially under high laser irradiance conditions.

Interaction of the electrophilic ketoprofenyl-glucuronide and ketoprofenyl-coenzyme A conjugates with cytosolic glutathione S-transferases.

Carboxylic acid-containing drugs are metabolized mainly through the formation of glucuronide and coenzyme A esters. These conjugates have been suspected to be responsible for the toxicity of several nonsteroidal anti-inflammatory drugs because of the reactivity of the electrophilic ester bond. In the present study we investigated the reactivity of ketoprofenyl-acylglucuronide (KPF-OG) and ketoprofenyl-acyl-coenzyme A (KPF-SCoA) toward cytosolic rat liver glutathione S-transferases (GST).

Post-source decay of alkylated and functionalized polycyclic aromatic compounds.

Post-source decay (PSD) is a valuable tool for providing structural information from large molecules by time-of-flight mass spectrometry (TOFMS). We used PSD to obtain this type of data from small molecules in the laser desorption/ionization (LDI) study of diesel engine exhaust particles. As the original nitrogen laser (lambda = 337 nm, E = 3.

Isolation and characterization of a gene cluster involved in PAH degradation in Mycobacterium sp. strain SNP11: expression in Mycobacterium smegmatis mc(2)155.

Mycobacterium sp. strain SNP11 is able to grow with pyrene, fluoranthene, phenanthrene and fluorene the sole carbon and energy sources. A probe based on the previously described gene pdoA2, which encodes the alpha subunit of a PAH ring-hydroxylating dioxygenase in Mycobacterium sp.

Kinetics of alpha-hydroxy-alkylperoxyl radicals in oxidation processes. HO2*-initiated oxidation of ketones/aldehydes near the tropopause.

A comparative theoretical study is presented on the formation and decomposition of alpha-hydroxy-alkylperoxyl radicals, Q(OH)OO* (Q = RR'C:), important intermediates in the oxidation of several classes of oxygenated organic compounds in atmospheric chemistry, combustion, and liquid-phase autoxidation of hydrocarbons. Detailed potential energy surfaces (PESs) were computed for the HOCH2O2* <==>HO2* + CH2O reaction and its analogues for the alkyl-substituted RCH(OH)OO* and R2C(OH)OO* and the cyclic cyclo-C6H10(OH)OO*. The state-of-the-art ab initio methods G3 and CBS-QB3 and a nearly converged G2M//B3LYP-DFT variant were found to give quasi-identical results.

Tubulin-binding drug screening by MALDI-TOFMS.

Despite a large amount of drugs available to treat cancer, none is totally satisfactory with respect to its tolerance or side effects. It is very important to discover new compounds that exhibit specific features such as binding to proteic targets. Given the clinical successes of the poisons of the mitotic spindle chemotherapeutic agent class, it is often considered that tubulin represents one of the best cancer targets identified so far, and it seems likely that discovering new drugs of this class will significantly improve the range of active chemotherapeutic agents.