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, k1 = 7.5 × 10-12 cm3 s-1. High-level accuracy coupled cluster calculations in combination with E,J-resolved two-dimensional master equation analyses yield k1 = (2.4 ± 0.5) × 10-12 cm3 s-1 for relevant atmospheric conditions (T = 260-310 K and P = 0-1 atm). We attribute this significant discrepancy to HCOOH formation from other molecules in the chamber experiments. More importantly, we show that reversible aqueous processes result indirectly in the equilibration on a 10 min. time scale of the gas-phase reaction [Formula: see text] (2) with a HOCH2OH to HCHO ratio of only ca. 2%. Although HOCH2OH outgassing upon cloud evaporation typically increases this ratio by a factor of 1.5-5, as determined by numerical simulations, its in-cloud reprocessing is shown using a global model to strongly limit the gas-phase sink and the resulting production of formic acid. Based on the combined findings in this work, we derive a range of 1.2-8.5 Tg/y for the global HCOOH production from cloud-derived HOCH2OH reacting with OH. The best estimate, 3.3 Tg/y, is about 30 times less than recently reported. The theoretical equilibrium constant Keq (2) determined in this work also allows us to estimate the Henry's law constant of methanediol (8.1 × 105 M atm-1 at 280 K).

Vegetation responses to climate extremes recorded by remotely sensed atmospheric formaldehyde.

Accurate monitoring of vegetation stress is required for better modelling and forecasting of primary production, in a world where heatwaves and droughts are expected to become increasingly prevalent. Variability in formaldehyde (HCHO) concentrations in the troposphere is dominated by local emissions of short-lived biogenic (BVOC) and pyrogenic volatile organic compounds. BVOCs are emitted by plants in a rapid protective response to abiotic stress, mediated by the energetic status of leaves (the excess of reducing power when photosynthetic light and dark reactions are decoupled, as occurs when stomata close in response to water stress). Emissions also increase exponentially with leaf temperature. New analytical methods for the detection of spatiotemporally contiguous extremes in remote-sensing data are applied here to satellite-derived atmospheric HCHO columns. BVOC emissions are shown to play a central role in the formation of the largest positive HCHO anomalies. Although vegetation stress can be captured by various remotely sensed quantities, spaceborne HCHO emerges as the most consistent recorder of vegetation responses to the largest climate extremes, especially in forested regions.

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)CH3 as a model compound, we show that the likely major photolysis mechanism is a fast 1,5 H-shift in the initially excited singlet S1 state followed by spontaneous elimination of singlet oxygen to yield an enol HOCH[double bond, length as m-dash]CHCH3, while intersystem crossing (ISC) to the triplet T1 state and C-C scission into HC˙O + HOOC˙HCH3 followed by expulsion of a hydroxyl radical from the unstable HOOC˙HCH3 is another product channel. The direct S1 reaction was found to occur at such a high rate that the quantum yield in atmospheric conditions is expected to approach unity. In the atmosphere, the enol should generally react with OH radicals or tautomerize into the more stable carbonyl O[double bond, length as m-dash]CH-CH2CH3. Vinylalcohol is shown to be a major end product of the photolysis of hydroperoxyacetaldehyde, an isoprene oxidation product. Taking into account also the important enhancement of the absorption cross sections over those of the constituent monofunctional compounds as observed for the analogous ß-ketohydroperoxides, (F. Jorand et al., J. Photochem. Photobiol. A: Chem., 2000, 134, 119-125) the atmospheric photolysis rate of α-hydroperoxycarbonyls was estimated to be in the range of (1 to 5) × 10-4 s-1, generally faster than the rate of their OH reactions.

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 NOx. As a first photolysis mechanism, we show that a fraction of the initially excited S1-state HPALDs isomerizes by a near-barrierless 1,5 H-shift at a rate approaching 1012 s-1 - competing with the ∼equally fast intersystem crossing to the T2 triplet state - forming an unstable biradical that spontaneously expels an OH (hydroxyl) radical. A second mechanism is shown to proceed through the activated T2 triplet biradical - formed from S1 - undergoing a concerted ring-closure and OH-expulsion, yielding an oxiranyl-type co-product radical that quickly ring-opens to enoxy radicals. In both mechanisms, subsequent chemistry of the co-product radicals yields additional first-generation OH. The combined HPALD-photolysis quantum yield by these two mechanisms - which may not be the only photolysis routes - is estimated at 0.55 and the quantum yield of OH generation at 0.9, in fair accordance with experimental data on an HPALD proxy (Wolfe et al., Phys. Chem. Chem. Phys., 2012, 14, 7276-7286).

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. Chem. Phys . 2009 , 11 , 5935 ), is presented in an upgraded and extended version, LIM1. The kinetics of the crucial reactions in the proposed isoprene-peroxy radical interconversion and isomerization pathways are re-evaluated theoretically, on the basis of energy barriers computed at the much higher CCSD(T)/aug-cc-pVTZ//QCISD/6-311G(d,p) level of theory, and using multiconformer partition functions obtained at the M06-2X/6-311++G(3df,2p) level that, different from the B3LYP level used in our earlier work, accounts for the crucial London dispersion effects in the H-bonded systems involved. The steady-state fraction of the specific Z-δ-OH-peroxy radical isomers/conformers that can isomerize by a 1,6-H shift is shown to be largely governed by hydrogen-bond strengths, whereas their isomerization itself is found to occur quasi-exclusively by hydrogen atom tunneling. The isomer-specific Z-δ-OH-peroxy 1,6-H-shift rate coefficients are predicted to be of the order of 1 s(-1) at 298 K, but the experimentally accessible bulk rate coefficients, which have to be clearly distinguished from the former, are 2 orders of magnitude lower due to the very low Z-δ-OH-peroxy steady-state fractions that are only around or below 0.01 at low to moderate NO and depend on the peroxy lifetime. Two pathways subsequent to the peroxy radical 1,6-H shift are identified, the earlier predicted route yielding the photolabile hydroperoxy-methylbutenals (HPALDs), and a second, about equally important path, to dihydroperoxy-carbonyl peroxy radicals (di-HPCARP). Taking this into account, our predicted bulk peroxy isomerization rate coefficients are about a factor 1.8 higher than the available experimental results for HPALD production ( Crounse ; et al. Phys. Chem. Chem. Phys. 2011 , 13 , 13607 ), which is within the respective uncertainty margins. We also show that the experimental temperature dependence of the HPALD production rates as well as the observed kinetic isotope effect for per-deuterated isoprene support quantitatively our theoretical peroxy interconversion rates. Global modeling implementing LIM1 indicates that on average about 28% of the isoprene peroxys react via the 1,6-H-shift isomerization route, representing 100-150 Tg carbon per year. The fast photolysis of HPALDs we proposed earlier as primary OH regeneration mechanism ( Peeters and Muller . Phys. Chem. Chem. Phys . 2010 , 12 , 14227 ) found already experimental confirmation ( Wolfe ; et al. Phys. Chem. Chem. Phys. 2012 , 14 , 7276 ); based on further theoretical work in progress, reaction schemes are presented of the oxy coproduct radicals from HPALD photolysis and of the di-HPCARP radicals from the second pathway following peroxy isomerization that are both expected to initiate considerable additional OH recycling.

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. As atmospheric contamination has been identified as one of the possible sources of anthraquinone residue, this study investigates the contamination resulting from the deposition of atmospheric anthraquinone using a global chemical transport model that accounts for the emission, atmospheric transport, chemical transformation, and deposition of anthraquinone on the surface. The largest contribution to the global atmospheric budget of anthraquinone is from residential combustion followed by the secondary formation from oxidation of anthracene. Simulations suggest that atmospheric anthraquinone deposition could be a substantial source of the anthraquinone found on tea leaves in several tea-producing regions, especially near highly industrialized and populated areas of southern and eastern Asia. The high level of anthraquinone deposition in these areas may result in residues in tea products exceeding the EU MRL. Additional contamination could also result from local tea production operations.

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. In order to improve its reliability, a combined approach using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI-FTICRMS) was evaluated. The study was carried out on bovine serum albumin (BSA) digest. The influence of several important parameters (the matrix, the sample preparation method, the amount of the analyte) on the MOWSE score and the protein sequence coverage were evaluated to allow the identification of specific effects. A careful investigation of the sequence coverage obtained by each kind of experiment ensured the detection of specific peptides for each experimental condition. Results highlighted that DHB-FTICRMS and DHB- or CHCA-TOFMS are the most suited combinations of experimental conditions to achieve PMF analysis. The association (convolution) of the data obtained by each of these techniques ensured a significant increase in the MOWSE score and the protein sequence coverage.

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 O3, 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. We show that, relative to a situation in which the emission reductions are ignored and despite the calculated increase in hydroxyl and peroxy radicals, the ozone concentration increased only in a few NOx-saturated regions (northern China, northern Europe, and the US) during the winter months of the pandemic when the titration of this molecule by NOx was reduced. In other regions, where ozone is NOx-controlled, the concentration of ozone decreased. SOA concentrations decrease in response to the concurrent reduction in the NOx and VOC emissions. The model also shows that atmospheric meteorological anomalies produced substantial variations in the concentrations of chemical species during the pandemic. In Europe, for example, a large fraction of the ozone increase in February 2020 was associated with meteorological anomalies, while in the North China Plain, enhanced ozone concentrations resulted primarily from reduced emissions of primary pollutants.

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. Both 266 and 337 nm laser wavelengths were used but the 266 nm wavelength gave increased spatial resolution and better sensitivity for the detection of the targeted metabolites (resveratrol and linked stilbene compounds). Mass spectrometry imaging of grapevine Cabernet Sauvignon leaves revealed specific locations with respect to Plasmopara viticola pathogen infection or light illumination.

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. A similar photolysis mechanism of the resulting photolabile peroxy-acid-aldehydes (PACALDs) is shown to generate ample additional OH. Global modeling demonstrates the major importance of the new chemistry for the oxidizing capacity of the atmosphere over continents. The globally averaged yield of the HPALDs in the oxidation of isoprene by OH is estimated to be of the order of 0.6. The isomerisation reactions of isoprene peroxy radicals are found to result in modelled [OH] increases in the planetary boundary layer by up to a factor of 3, in agreement with the reported observations as in the Amazon basin.

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. Twenty-five subjects (5 free and 20 addicts from a heroin detoxification center) were included in a study to evaluate the potential application of a new device, the Cozart DDSV (drug detection system visual), to detect cannabis in oral fluid. The time cannabis was last smoked was recorded by the medical staff after interview with each subject. Samples were collected with the Cozart DDS Oral Swab and diluted with the Cozart DDS buffer as proposed by the manufacturer. The Cozart DDSV test was conducted on site at the time of collection, and the remainder of the sample retained for confirmation analysis by gas chromatography with mass spectrometry (GC/MS) after methylation of THC (limit of quantitation 0.5 ng/mL). All 25 samples were analyzed by GC/MS. On-site results were obtained within 10 minutes. The 5 drug-free subjects were negative for cannabis, irrespective of the method. From the 20 subjects declaring that they had smoked cannabis between 30 minutes and 24 hours previously, the DDSV device identified 8 positive subjects (with THC concentrations in the buffer in the range 15-219 ng/mL), whereas 18 subjects tested positive using GC/MS. THC concentrations in the Cozart buffer using GC/MS analysis ranged from 0.7 to 219 ng/mL. These concentrations represent about one third the authentic THC concentrations in oral fluid due to the dilution by the liquid of the device. Given the results, the DDSV device was considered as an acceptable tool to detect cannabis abuse in oral fluid within a period of 2-3 hours after smoking.

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. These processes are used to propose a set of pathways to rationalize the envelope of ionic clusters formed under photon bombardment.

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). We observed that KPF-SCoA, but not KPF-OG inhibited the conjugation of 1-chloro-2,4-dinitrobenzene and 4-nitroquinoline N-oxide catalyzed by both purified cytosolic rat liver GST and GST from FAO and H5-6 rat hepatoma cell lines. Photoaffinity labeling with KPF-SCoA suggested that the binding of this metabolite may overlap the binding site of 4-methylumbelliferone sulfate. Furthermore, high-performance liquid chromatography and mass spectrometry analysis showed that both hydrolysis and transacylation reactions were observed in the presence of GST and glutathione. The formation of ketoprofenyl-S-acyl-glutathione could be kinetically characterized (apparent K(m) = 196.0 +/- 70.6 microM). It is concluded that KPF-SCoA is both a GST inhibitor and a substrate of a GST-dependent transacylation reaction. The reactivity and inhibitory potency of thioester CoA derivatives toward GST may have potential implications on the reported in vivo toxicity of some carboxylic acid-containing drugs.

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. This screening protocol involves matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) detection of target-bound compounds. Firstly, a screening protocol is developed and proves to be a simple, fast, and specific method to characterize the binding capability of a compound. Secondly, the possibility of determining the relative affinities of DHFR-binding compounds by comparing MALDI-TOFMS data is discussed. A ratio is calculated for a compound X such as R(X) = A.I.(denaturation)(X)/A.I.(direct)(X) (where AI(direct) and AI(denaturation) are the average absolute intensities of a binding compound X before and after denaturation of DHFR). It is shown that by using this protocol, one can characterize the strength of the binding of different compounds. These two strategies are then applied to screen green tea (Camellia sinensis) extracts for DHFR-binding compounds, and epigallocatechin gallate is shown to be an active compound with a relative affinity between those of pyrimethamine and methotrexate.

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. strain 6PY1 [S. Krivobok et al., Identification of pyrene-induced proteins in Mycobacterium sp. strain 6PY1: evidence for two ring-hydroxylating dioxygenases, J. Bacteriol. 185(13) (2003) 3828-3841], was used to isolate a 14kb DNA fragment from strain SNP11. Twelve putative open reading frames (ORFs), divided into two groups by a promoter intergenic region, were detected in this DNA sequence. The first gene cluster, located upstream of the promoter region, showed low but significant deduced amino acid sequence homologies with enzymes involved in aromatic degradation. The second gene cluster, under control of the promoter, contained pdoA2 (designated phdA in this study) and several other ORFs with deduced amino acid sequences closely related to enzymes involved in the phenanthrene-degrading pathway of Nocardioides sp. strain KP7. Gene expression analysis in Mycobacterium smegmatis mc(2)155 revealed broad substrate specificity of the ring-hydroxylating dioxygenase, since transformant cells containing phdAB strongly oxidized fluoranthene, phenanthrene, anthracene, fluorine and dibenzofuran. Laser desorption/ionization time-of-flight mass spectrometry (LDI-ToF MS) analyses of culture media after PAH degradation by M. smegmatis transformants also revealed that the second gene cluster, located downstream of the promoter, takes an active share in initial phenanthrene and anthracene degradation by allowing transformation of these two PAHs in aromatic ring-cleaved metabolites.

Activation processes and polyethylene formation on a phillips model catalyst studied by laser ablation, laser desorption, and static secondary ion mass spectrometry.

Since the discovery of the Phillips catalysts, there still is much uncertainty concerning their activation, their molecular structure, the nature of the active chromium sites, and the polymerization mechanisms. Surface techniques are not easy to be used for such study according to the nonconductive behavior of the support. Therefore, model Phillips catalyst is elaborated by spin coating a trivalent chromium precursor on a silicon wafer. The surface characterization of this model catalyst is conducted by laser ablation mass spectrometry (LA-MS), laser desorption/ionization mass spectrometry (LDI-MS), and static secondary ion mass spectrometry (s-SIMS), at different steps of its preparation. To validate our approach, a comparison is also made between the model and the real Philips catalyst. Moreover, the model catalyst efficiency for polyethylene synthesis is evaluated and allows us to discuss the validity of the mechanisms previously proposed to explain the catalytic process. The characterization of Phillips model catalyst by mass spectrometry allows us to better understand the activation processes of such catalyst. Depending on the activation temperature, chromium oxide species are formed and anchored at the support surface. They consist mainly in mono-chromium sites at high temperature. The chromium valence is hexavalent. This model catalyst is active for the polymerization of ethylene. A pseudo-oligomer molecular weight distribution is observed by LA-MS, whereas s-SIMS allows us to elucidate the anchorage of the polymer at activate chromium surface sites.

Laser ablation and secondary ion mass spectrometry of inorganic transition-metal compounds. Part I: comparison between static ToF-SIMS and LA-FTICRMS.

Most of the first-row transition-metal oxides, M(A)O(B) (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) were examined by static secondary ion mass spectrometry (s-SIMS) and laser ablation/ionization Fourier transform ion cyclotron resonance mass spectrometry (LA-FTICRMS). Positive and negative ions show strong correlation between the studied oxide and the detected cluster ions. Specific M(x)O(y) (+/-) species were systematically observed with both MS techniques for each investigated M(A)O(B) transition-metal oxide. Moreover, the ion composition and ion distribution are greatly dependent on the ionization technique. Laser ablation (LA)/ionization leads to larger cluster ions (ionic species with nearly hundred atoms were in particular detected for Sc2O3 and Y2O3 oxides), whereas hydrogenated, dihydrogenated, and sometimes trihydrogenated species were observed in s-SIMS. However, the ion distribution for a given M(x)O(y) (+/-) ion series (i.e. ions including the same number of metal atoms M) generally presented important similarities in both techniques.Finally, it was demonstrated that the chemical state of metal atoms in the observed ionic species is closely dependent on the metal electronic valence shell. High valence states (+III, +IV, +V, and +VI) are favored for metals with a less-than-half full valence shell configuration, whereas for other first-row transition metals (manganese, iron, cobalt, nickel, copper and zinc) lower metal valence states (0, +I or, +II) are involved.

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. Criegee intermediate formation is found to be negligible. Given the theoretical uncertainties, useful constraints on the yields are provided by atmospheric methanol measurements. Using a global chemistry-transport model, we show that the only explanation for the high observed methanol abundances over remote oceans is the title reaction with an overall methanol yield of ∼30%, consistent with the theoretical estimates given their uncertainties. This makes the title reaction a major methanol source (115 Tg per year), comparable to global terrestrial emissions.

MALDI-TOF mass spectrometric analysis for the characterization of the 5,10,15,20-tetrakis- (m-hydroxyphenyl)bacteriochlorin (m-THPBC) photoproducts in biological environment.

Photoproducts formation upon irradiation (739 nm) of 5,10,15,20-tetrakis(m-hydroxyphenyl)bacteriochlorin (m-THPBC) in phosphate buffer saline (PBS) supplemented with human serum albumin (HSA) were studied by means of absorption spectroscopy and MALDI-TOF mass spectrometry. The experiments were performed with a freshly prepared PBS-HSA solution of m-THPBC and with a PBS-HSA m-THPBC solution incubated for 6 h at 37 degrees C. The incubation of m-THPBC solution leads to the dye monomerisation, whereas in the freshly prepared solution, m-THPBC is under an aggregated form. Regardless of the incubation condition, photobleaching experiments carried out by absorption spectroscopy demonstrate the degradation of the photosensitizer and its phototransformation in m-THPC. Moreover, m-THPC was the sole photoproduct detected using absorption spectroscopy. Together with a degradation of m-THPBC and formation of m-THPC, MALDI-TOF mass spectrometry evidenced several other photoinduced modifications. Photoproducts such as dihydroxy m-THPBC and dihydroxy m-THPC were detected in both conditions; however, the formation of hydroxylated photoproducts was significantly greater in incubated solution. In addition, small molecules arising from the degradation of the photosensitizer and identified as dipyrin derivatives and dipyrrolic synthon were observed.

Characterization of photoproducts of m-THPP in aqueous solution.

This study examined the nature of photoproducts after pulse laser irradiation (647.5 nm) of 5,10,15,20-tetrakis(meso-hydroxyphenyl)porphyrin (m-THPP) (10 micromol/L) in ethanol-water (1/99, vol/vol) solution. Spectroscopic measurements (UV-visible absorption and fluorescence) and mass spectrometry techniques (matrix-assisted laser desorption-ionization [MALDI] coupled with time-of-flight mass spectrometer [TOF-MS] or tandem time of flight mass spectrometer [TOF/TOF-MS]) were used to follow photomodifications. Spectroscopic measurements evidenced photomodification as the main process after m-THPP irradiation. Three oxidized photoproducts at m/z 693.25, 695.24 and 713.25 were characterized by MS. After prolonged irradiation new isotopic distributions were registered at m/z 1355.41, 2031.57, 2707.80 and 3383.98 with MALDI-TOF-MS and TOF/TOF-MS. These new photoproducts were attributed to covalent oligomeric structures as dimer, trimer, tetramer and pentamer of m-THPP.