Isomer Distribution Research Articles

MS-based glycomics and glycoproteomics methods enabling isomeric characterization.

Glycosylation is one of the most significant and abundant posttranslational modifications in mammalian cells. It mediates a wide range of biofunctions, including cell adhesion, cell communication, immune cell trafficking, and protein stability. Also, aberrant glycosylation has been associated with various diseases such as diabetes, Alzheimer's disease, inflammation, immune deficiencies, congenital disorders, and cancers. The alterations in the distributions of glycan and glycopeptide isomers are involved in the development and progression of several human diseases. However, the microheterogeneity of glycosylation brings a great challenge to glycomic and glycoproteomic analysis, including the characterization of isomers. Over several decades, different methods and approaches have been developed to facilitate the characterization of glycan and glycopeptide isomers. Mass spectrometry (MS) has been a powerful tool utilized for glycomic and glycoproteomic isomeric analysis due to its high sensitivity and rich structural information using different fragmentation techniques. However, a comprehensive characterization of glycan and glycopeptide isomers remains a challenge when utilizing MS alone. Therefore, various separation methods, including liquid chromatography, capillary electrophoresis, and ion mobility, were developed to resolve glycan and glycopeptide isomers before MS. These separation techniques were coupled to MS for a better identification and quantitation of glycan and glycopeptide isomers. Additionally, bioinformatic tools are essential for the automated processing of glycan and glycopeptide isomeric data to facilitate isomeric studies in biological cohorts. Here in this review, we discuss commonly employed MS-based techniques, separation hyphenated MS methods, and software, facilitating the separation, identification, and quantitation of glycan and glycopeptide isomers.

Reaction kinetics study of ethylene oligomerization into linear olefins over carbon-supported cobalt catalysts

Ethylene oligomerization over carbon-supported cobalt catalysts at 200 °C selectively produces linear olefins (>80% linearity up to C12 olefins at < 48% conversion) and linear alpha olefins (LAOs) (>30% LAO isomer distribution up to C8 olefins at < 10% conversion). Increasing the catalyst pretreatment temperature from 230 to 560 °C in argon prior to a reaction reduces cobalt oxide to cobalt metal and increases the catalytic activity. Cobalt metal supported on carbon deactivates during the reaction, likely due to higher rate of polyethylene formation which decreases the catalytic activity. The product distribution follows a Schulz-Flory distribution. The reaction is first order with respect to ethylene partial pressure, suggesting a mechanism where ethylene reacts with adsorbed olefins on a surface that is highly covered with olefins.

Biomarker and Carbon Isotopic Evidence of Marine Incursions in the Himalayan Foreland Basin During Its Overfilled Stage

AbstractThe final stages of evolution of the Himalayan foreland basin (HFB) are preserved in the Siwalik Group of rocks deposited by meandering and/or braided rivers in the western and central regions of HFB. However, the time‐equivalent deposits in the eastern part of the foreland provide contradictory evidence of both terrestrial and marine environments. To address the ambiguity, molecular level characterization and stable isotopic composition of organic matter (OM) have been employed in the late Miocene‐Pliocene sequence of the eastern HFB. The n‐alkane distribution, carbon isotopic (δ13C) signature of n‐alkanes and distribution of hopane and sterane isomers suggest OM contributions from both marine and terrestrial sources during the late Miocene period. Increase in short‐chain n‐alkane abundance and gammacerane index, low pristane/phytane ratio, higher δ13C values, higher regular sterane/17α‐hopane, C31R/C30‐hopane and C27/C29 steranes ratios and presence of C30 sterane provides substantial evidence of stratified anoxic conditions and marine influences at specific stratigraphic intervals. During the late Miocene period, mixing of marine OM sources with terrestrial sources argue for marginal marine depositional conditions amid fluvial‐dominating environments. The entry of marine waters in the eastern HFB through the pre‐existing cratonic troughs possibly resulted from eustatic or relative sea‐level rise. No further evidence of marine incursions is observed in the younger Pliocene sediments. The higher detrital influx from the rising Himalayas, the onset of Northern Hemisphere Glaciation and evolution of physical barriers such as Shillong Massifs and Barind Tracts altogether led to the cessation of marine incursions into the HFB.

Observations of speciated isoprene nitrates in Beijing: implications for isoprene chemistry

Abstract. Isoprene is the most important biogenic volatile organic compound in the atmosphere. Its calculated impact on ozone (O3) is critically dependent on the model isoprene oxidation chemical scheme, in particular the way the isoprene-derived organic nitrates (IN) are treated. By combining gas chromatography with mass spectrometry, we have developed a system capable of separating and unambiguously measuring individual IN isomers. In this paper we use measurements from its first field deployment, which took place in Beijing as part of the Atmospheric Pollution and Human Health in a Chinese Megacity programme, to test understanding of the isoprene chemistry as simulated in the Master Chemical Mechanism (MCM) (v.3.3.1). Seven individual isoprene nitrates were identified and quantified during the campaign: two β-hydroxy nitrates (IHN), four δ-carbonyl nitrates (ICN), and propanone nitrate. Our measurements show that in the summertime conditions experienced in Beijing the ratio of (1-OH, 2-ONO2)-IHN to (4-OH, 3-ONO2)-IHN (the numbers indicate the carbon atom in the isoprene chain to which the radical is added) increases at NO mixing ratios below 2 ppb. This provides observational field evidence of the redistribution of the peroxy radicals derived from OH oxidation of isoprene away from the kinetic ratio towards a new thermodynamic equilibrium consistent with box model calculations. The observed amounts of δ-ICN demonstrate the importance of daytime addition of NO3 to isoprene in Beijing but suggest that the predominant source of the δ-ICN in the model (reaction of NO with δ-nitrooxy peroxy radicals) may be too large. Our speciated measurements of the four δ-ICN exhibit a mean C1 : C4 isomer ratio of 1.4 and a mean trans : cis isomer ratio of 7 and provide insight into the isomeric distribution of the δ-nitrooxy peroxy radicals. Together our measurements and model results indicate that propanone nitrate was formed from the OH oxidation of δ-ICN both during the day and night, as well as from NO3 addition to propene at night. This study demonstrates the value of speciated IN measurements in testing understanding of the isoprene degradation chemistry and shows how more extensive measurements would provide greater constraints. It highlights areas of the isoprene chemistry that warrant further study, in particular the impact of NO on the formation of the IHN and the NO3-initiated isoprene degradation chemistry, as well as the need for further laboratory studies on the formation and the losses of IN, in particular via photolysis of δ-ICN and hydrolysis.

Exploring Complex Mixtures by Cyclic Ion Mobility High-Resolution Mass Spectrometry: Application Toward Petroleum.

The in-depth isomeric and isobaric description of ultra-complex organic mixtures remains one of the most challenging analytical tasks. In the last two decades, ion mobility coupled to high-performance mass spectrometry added an additional structural dimension. Despite tremendous instrumental improvements, commercial devices are still limited in ion mobility and mass spectrometric resolving power and struggle to resolve isobaric species and complex isomeric patterns. To overcome these limitations, we explored the capabilities of cyclic ion mobility high-resolution mass spectrometry with special emphasis on petrochemical applications. We could show that quadrupole-selected ion mobility mass spectrometry gives closer insights into the isomeric distribution. In combination with slicing the specific parts of the ion mobility dimension, isobaric interferences could be drastically removed. Collision-induced dissociation (CID) allowed separating structural groups of polycyclic aromatic hydrocarbons and heterocycles (PAH/PASH), deploying up to 10 passes in the cyclic ion mobility device. Finally, we introduce a data processing workflow to resolve the 3.4 mDa SH4/C3 mass split by combining ion mobility and mass spectrometric resolving power. Cyclic ion mobility with the intelligent design of experiments and processing routines will be a powerful approach addressing the isobaric and isomeric complexity of ultra-complex mixtures.

Dibenzothiophenes, phenyldibenzothiophenes, and benzo[b]naphthothiophenes in crude oils and source rock extracts from the Niger Delta Basin, Nigeria, and their applications as source facies, depositional environments, and thermal maturity indicators

The distribution of dibenzothiophenes, phenyldibenzothiophenes, and benzo[b]naphthothiophenes and their geochemical significance in the crude oils and source rocks from Niger Delta Basin have been investigated by gas chromatography-mass spectrometry. The dimethyldibenzothiophenes, 4-phenyldibenzothiophene, and benzo[b]naphtho[2,1-d]thiophene were the most abundant among the dibenzothiophene and its derivatives in the crude oils and rock samples. The phenyldibenzothiophene ratio-1 and phenyldibenzothiophene ratio-2 values in the rock samples were in the ranges of 0.08 to 0.67 and 0.20 to 2.53, respectively, while the 4-/1-methyldibenzothiophene, 4,6-/(1,4 + 1,6)-dimethyldibenzothiophene, 2,4,6-/(2,4,7 + 2,4,8)-trimethyldibenzothiophene, phenyldibenzothiophene ratio-1, and phenyldibenzothiophene ratio-2 values in the crude oils ranged from 1.52 to 5.82, 0.76 to 1.98, 0.77 to 1.22, 0.11 to 0.42, and 0.30 to 0.75, respectively. These values indicate source rocks and crude oils with mixed input of terrestrial and marine organic matter and deposited in lacustrine-fluvial/deltaic environments within immature to early mature stages. Four isomers of MDBT were also present in appreciable amounts in all the samples studied. The distribution patterns of MDBTs were generally observed in the order 4-MDBT > 2+3-MDBT > 1-MDBT in the crude oils and rock samples. The (1 + 4)-/(2+3)-methyldibenzothiophene ratio in the oils and rock samples ranged from 0.03 to 0.13 and 1.31 to 2.54, respectively. These values suggested source rocks with shale lithologies. A cross plot of (1+4)-/(2+3)-methyldibenzothiophene versus pristane/phytane measured on rock samples and crude oils from Niger Delta was used to study the influence of depositional environment and lithology on the distribution of the MDBT isomers. This cross plot clearly showed that the source rocks and crude oils studied have shale lithologies and were distinguished into lacustrine and fluvial/deltaic/freshwater environments and thus proposed in this study as a potential lithology and paleoenvironment indicator. This study showed that dibenzothiophenes, phenyldibenzothiophenes, and benzo[b]naphthothiophenes were effective in determining the origin, depositional environments, and thermal maturity status of crude oils and source rocks in the Niger Delta Basin, Nigeria.

Evaluation of post synthesis treatments over commercial ZSM-5 zeolite in the reaction route of oleic acid esterification with methyl acetate

The objective of this work was to evaluate the influence of post-synthesis treatments applied on high ratio Si/Al commercial ZSM-5 zeolite on its properties and catalytic activity in oleic acid esterification with methyl acetate. Treatments as acidification, desilication, ion exchange and mechanical and ultrasound-assisted impregnation tungsten oxide were applied. The catalysts were properly characterized and the esterification reactions were performed at 240 °C, 1:10 oleic acid:methyl acetate molar ratio and 10% (m/m) catalyst concentration. Properties of the catalysts were significantly changed by the applied treatments, resulting in different yields and isomers distribution of cis and trans esters. The highest ester yield, equal to 66.71%, was obtained with zeolite subjected to ion exchange. This catalyst also provided an equal distribution between the two isomers. It was proposed, based on kinetic experiments, a mechanism for the reaction consisting of isomerization of oleic acid to elaidic acid followed by esterification of both fatty acids.

Wax Hydrocracking over Pt/SiO2–Al2O3 at 2 MPa: Product Characterization and Its Implications for Catalysis

Hydrocracking of Fischer–Tropsch wax can be used to produce kerosene-range products that can be blended in jet fuel. Performing the hydrocracking at pressures near that of Fischer–Tropsch synthesis could be beneficial for some refinery scenarios, as unconverted H₂ from Fischer–Tropsch synthesis can be used for hydrocracking without further compression. At lower pressure, the equilibrium alkene content during hydrocracking is increased and this could affect the product distribution. In particular, the degree of isomerization of the kerosene-range products affects the properties of hydrocracked kerosene to be used for jet fuel. The purpose of this study was to gain a better understanding of the isomer distribution obtained by wax hydrocracking. Hydrocracking of paraffin wax was carried out over a 0.5 wt % Pt/SiO₂–Al₂O₃ catalyst at a pressure of 2 MPa. Detailed chromatographic analysis of narrow distillation cuts of the obtained kerosene-range product was used to obtain isomer distributions for the C₈, C₉, and C₁₁ alkanes formed during hydrocracking. While the observed carbon number and isomer distributions were generally what would be expected from the hydrocracking and hydroisomerization mechanism, there were two observations that could not be explained in this way. (i) The isomer distributions were not equilibrated and were dominated by 2- and 3-methylalkanes. (ii) There were also percentage levels of cyclic compounds. An increased contribution of Pt catalysis under the chosen low-pressure conditions contributed to the observed deviations. The formation of cyclic compounds could be attributed to the increased contribution of Pt catalysis at 2 MPa. Although some speculation was offered about what could have affected the isomer distribution, the prevalence of 2- and 3-methylalkanes in the product remained unexplained.

Differentiation of bisphenol F diglycidyl ether isomers and their derivatives by HPLC-MS and GC-MS\u2014comment on the published data

Positional isomers of bisphenol F diglycidyl ether (BFDGE) have been analyzed by high-pressure liquid chromatography-mass spectrometry and by gas chromatography-mass spectrometry (HPLC-MS, GC-MS). Positional isomers of BFDGE derivatives (BFDGEx2H2O, BFDGExH2OxHCl) have been analyzed by HPLC-MS. On the basis of the obtained fragmentation patterns, the elution order of the isomers has been unequivocally determined, in standard solutions and in the sample of liquid obtained after rinsing an empty mackerel fish can with acetonitrile. Under HPLC condition, para,para isomers are eluted first, then ortho,para isomers’ elution follows, and ortho,ortho isomers are eluted last. Under GC condition, the reverse elution order has been obtained. For the first time, two ortho,para isomers of BFDGExH2OxHCl have been detected and their elution order has been determined. The obtained results are of key importance for determination of the isomer distribution of BFDGE and its derivatives in food samples.

Self-Assembly of Metallo-Supramolecules with Dissymmetrical Ligands and Characterization by Scanning Tunneling Microscopy.

Asymmetrical and dissymmetrical structures are widespread and play a critical role in nature and life systems. In the field of metallo-supramolecular assemblies, it is still in its infancy for constructing artificial architectures using dissymmetrical building blocks. Herein, we report the self-assembly of supramolecular systems based on two dissymmetrical double-layered ligands. With the aid of ultra-high-vacuum, low-temperature scanning tunneling microscopy (UHV-LT-STM), we were able to investigate four isomeric structures corresponding to four types of binding modes of ligand LA with two major conformations complexes A. The distribution of isomers measured by STM and total binding energy of each isomer obtained by density functional theory (DFT) calculations suggested that the most abundant isomer could be the most stable one with highest total binding energy. Finally, through shortening the linker between inner and outer layers and the length of arms, the arrangement of dissymmetrical ligand LB could be controlled within one binding mode corresponding to the single conformation for complexes B.

Mapping the distribution of double bond location isomers in lipids across mouse tissues.

Lipids are highly diverse and essential biomolecules in all living systems. As lipid homeostasis is often perturbed in metabolic diseases, these molecules can serve as both biomarkers and drug targets. The development of modern mass spectrometry (MS) provided the platform for large-scale lipidomic studies at the level of molecular species. Traditionally, more detailed structural information, such as the C[double bond, length as m-dash]C location, was mostly assumed instead of properly measured, though the specific isomers were indicated as potential biomarkers of cancers or cardiovascular diseases. Recent C[double bond, length as m-dash]C localization methods, including the Paternò-Büchi (PB) reaction, have shown the prevalent and heterogeneous distribution of C[double bond, length as m-dash]C location in lipids across tissues. Mapping the lipidome of model animals at the level of C[double bond, length as m-dash]C position would increase the understanding of the metabolism and function of lipid isomers, facilitating clinical research. In this study, we employed an online PB reaction on a liquid chromatography-high resolution MS platform to map C[double bond, length as m-dash]C location isomers in five different murine tissues. We analyzed phosphatidylcholines, phosphatidylethanolamines, and sphingomyelins; we relatively quantified and mapped the distribution of ∼30 groups of co-existing isomers, characterized by different chain lengths and degrees of unsaturation. More specifically, we performed relative quantitation of four isomers of the C16:1 fatty acyl, which included rarely reported n-10 and n-5 species besides n-9 and n-7 isomers. We showed a small variation of the isomers' relative composition among individual animals (<20%) but significant differences across different lipid species and mouse tissues. Our results provided an initial database to map alternative lipid metabolic pathways at the tissue level.

Effect of an additional donor on decene formation in ethylene oligomerization catalyzed by a Cr/PCCP system: a combined experimental and DFT study

Cr catalyst based on a PCCP ligand shows high activity in ethylene oligomerization, giving 1-hexene and considerable C10 fraction. DFT calculation results are consistent with the experimental observations on the distribution of C10 isomers.

Exploration of Free Energy Surface and Thermal Effects on Relative Population and Infrared Spectrum of the Be6B11- Flux-Ional Cluster.

The starting point to understanding cluster properties is the putative global minimum and all the nearby local energy minima; however, locating them is computationally expensive and difficult. The relative populations and spectroscopic properties that are a function of temperature can be approximately computed by employing statistical thermodynamics. Here, we investigate entropy-driven isomers distribution on Be6B11− clusters and the effect of temperature on their infrared spectroscopy and relative populations. We identify the vibration modes possessed by the cluster that significantly contribute to the zero-point energy. A couple of steps are considered for computing the temperature-dependent relative population: First, using a genetic algorithm coupled to density functional theory, we performed an extensive and systematic exploration of the potential/free energy surface of Be6B11− clusters to locate the putative global minimum and elucidate the low-energy structures. Second, the relative populations’ temperature effects are determined by considering the thermodynamic properties and Boltzmann factors. The temperature-dependent relative populations show that the entropies and temperature are essential for determining the global minimum. We compute the temperature-dependent total infrared spectra employing the Boltzmann factor weighted sums of each isomer’s infrared spectrum and find that at finite temperature, the total infrared spectrum is composed of an admixture of infrared spectra that corresponds to the spectra of the lowest-energy structure and its isomers located at higher energies. The methodology and results describe the thermal effects in the relative population and the infrared spectra.

Different temperature dependence of marine-derived brGDGT isomers in a sediment core from the Chukchi Sea shelf

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are thought to be produced by as yet unknown bacteria on land, and their distribution in soils, peats, and lake sediments has been shown to correlate with mean annual air temperature (MAAT). Recently, an increasing number of studies have shown that in situ production of brGDGT in marine environments is likely. However, the influence of environmental factors on marine-derived brGDGT distributions is still unknown. In this study, we assessed the sources of brGDGTs preserved in a sediment core from the Chukchi Sea shelf using multiple brGDGT-based indices, including the branched and isoprenoid tetraethers (BIT) index, the ratio of IIIa/IIa, cyclization degree of branched tetraethers (CBT), and #rings indices, and discuss the influence of seawater temperature changes over the last 70 years on the distribution of brGDGT isomers. The low BIT and CBT values, high IIIa/IIa ratios, and significant correlations between different #rings indices suggest that these brGDGTs primarily have a marine source. With increasing sea surface temperatures (SSTs), the fractional abundances of 5-Me IIIa (IIIa5) showed an increased trend, while there was no obvious trend in 6-methyl IIIa (IIIa6). This finding indicates different behaviors of 5-Me and 6-Me isomers in marine-derived brGDGTs, similar to what has been observed in soils, peats and lakes. In addition, we found a significant correlation between IIIa5 and IIIa7 (a novel isomer of IIIa), indicating that they might share the same bacterial source and/or are controlled by the same environmental factors (e.g., temperature). Finally, the fractional abundances of IIIa5 and IIIa7 are significantly correlated with SST (r2 = 0.64 and 0.49, respectively), which suggests that marine-derived brGDGTs have the potential to reconstruct seawater temperature.

Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NOx from the atmosphere

The formation of a suite of isoprene-derived hydroxy nitrate (IHN) isomers during the OH-initiated oxidation of isoprene affects both the concentration and distribution of nitrogen oxide free radicals (NOx). Experiments performed in an atmospheric simulation chamber suggest that the lifetime of the most abundant isomer, 1,2-IHN, is shortened significantly by a water-mediated process (leading to nitric acid formation), while the lifetime of a similar isomer, 4,3-IHN, is not. Consistent with these chamber studies, NMR kinetic experiments constrain the 1,2-IHN hydrolysis lifetime to less than 10 s in deuterium oxide (D2O) at 298 K, whereas the 4,3-IHN isomer has been observed to hydrolyze much less efficiently. These laboratory findings are used to interpret observations of the IHN isomer distribution in ambient air. The IHN isomer ratio (1,2-IHN to 4,3-IHN) in a high NOx environment decreases rapidly in the afternoon, which is not explained using known gas-phase chemistry. When simulated with an observationally constrained model, we find that an additional loss process for the 1,2-IHN isomer with a time constant of about 6 h best explains our atmospheric measurements. Using estimates for 1,2-IHN Henry's law constant and atmospheric liquid water volume, we show that condensed-phase hydrolysis of 1,2-IHN can account for this loss process. Simulations from a global chemistry transport model show that the hydrolysis of 1,2-IHN accounts for a substantial fraction of NOx lost (and HNO3 produced), resulting in large impacts on oxidant formation, especially over forested regions.

MALDI-TOF/TOF tandem mass spectrometry imaging reveals non-uniform distribution of disaccharide isomers in plant tissues

Mass spectrometry imaging (MSI) is a powerful technique for investigating the biomolecular locations within tissues. However, the isomeric compounds are rarely distinguished due to inability of MSI to differentiate isomers in the probing area. Coupling tandem mass spectrometry with MSI can facilitate differentiating isomeric compounds. Here MALDI-TOF/TOF tandem mass spectrometry imaging approach was applied to probing the spatial distributions of isomeric disaccharides in plant tissues. First, MS/MS imaging analysis of disaccharide-matrix droplet spots demonstrated the feasibility of distinguishing isomeric species in tissues, by measuring the relative intensity of specific fragments. Then, tandem MS imaging of disaccharides in onion bulb tissues indicated that sucrose and other unknown non-sucrose disaccharides exhibit heterogeneous locations throughout the tissues. This method enables us to image disaccharide isomers differentially in biological tissues, and to discover new saccharide species in plant. This work also emphasizes the necessity of considering isobaric compounds when interpreting MSI results.

Combinatorial Selection Among Geometrical Isomers of Discrete Long-Carbon-Chain Naphthalenediimides Induces Local Order at the Liquid/Solid Interface.

We report two families of naphthalenediimides (NDIs) symmetrically functionalized with discrete carbon chains comprising up to 55 carbon atoms (Cn-NDI-Cn, n = 39, 44, 50, and 55) and their self-assembly at the 1-phenyloctane/highly oriented pyrolytic graphite interface (1-PO/HOPG interface). The compounds differ by the presence or absence of two or three internal double bonds in the carbon chains (unsaturated and saturated Cn-NDI-Cn, respectively). Combinatorial distributions of geometrical isomers displaying either the E- or Z-configuration at each double bond are obtained for the unsaturated compounds. Analysis of the self-assembled monolayers of equally long unsaturated and saturated Cn-NDI-Cn by scanning tunneling microscopy (STM) reveal that all Cn-NDI-Cn tend to form lamellar systems featuring alternating areas of aromatic cores and carbon chains. Extended chain lengths are found to significantly increase disorder in the self-assembled monolayers due to misalignments and enhanced strength of interchain interactions. This phenomenon is antagonized by the local order-inducing effect of the internal double bonds: unsaturated Cn-NDI-Cn give qualitatively more ordered self-assembled monolayers compared to their saturated counterparts. The use of combinatorial distributions of unsaturated Cn-NDI-Cn geometrical isomers does not represent a limitation to achieve local order in the self-assembled monolayers. The self-assembly process operates a combinatorial search and selects the geometrical isomer(s) affording the most thermodynamically stable pattern, highlighting the adaptive character of the system. Finally, the antagonistic interplay between the extended carbon chain lengths and the presence of internal double bonds brings to the discovery of the lamellar “phase C” morphology for unsaturated Cn-NDI-Cn with n ≥ 50.

Temporal trends, sources, and relationships between sediment characteristics and polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in sediment cores from the major Seine estuary tributary, France

Temporal trends in polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were reconstructed from sediment cores collected in the Martot and Les Damps ponds, downstream of the Eure River watershed. PAHs exhibited a positive correlation with fine fractions, but mainly with the refractory organic carbon measured in the sediments, which suggests PAH inputs from materials largely composed of refractory carbon (e.g. soot). Since around the 1940s, PAH concentrations ranged between 2.93–38.20 and 2.27–28.20 mg kg−1 in sediment cores from the Martot and Les Damps ponds, respectively. Based on the temporal distribution of isomers and diagnostic ratios, the PAHs in the sediments were found to be predominantly of pyrogenic origin, particularly in the 1940s–1960s, when PAH levels were particularly high. PCBs also showed an affinity with the fine fraction and with refractory organic carbon, albeit less so than PAHs. Since around the 1940s, PCB concentrations ranged between 0.02–1.57 in Martot Pond and 0.09–1.60 mg kg−1 in Les Damps Pond. The recorded PCB temporal trends were mainly associated with the production, consumption, and banning of these chemicals in France. According to the temporal distribution of PCB congeners, high levels in the 1950s–1970s were linked to “technical mixture” discharges into waterways, which were mainly composed of “low chlorinated congeners”, whereas PCB levels after the 1970s were of atmospheric origin.

Design, synthesis, DNA binding, modeling, anticancer studies and DFT calculations of Schiff bases tethering benzothiazole-1,2,3-triazole conjugates

In an attempt to design and prepare a new library of anticancer candidates, focused thiopropargylated benzothiazole was reacted with ethyl azidoacetate and/or ethyl azidobenzoate to yield newer 1,2,3-triazole-benzothiazole conjugates bearing ester functionality through click chemistry approach. The hydrazinolysis of the obtained ester-based triazoles was also carried out to give the corresponding 1,2,3-triazole acid hydrazide derivatives as precursors for the synthesis of the focused Schiff bases by their condensation with various benzaldehyde derivatives. Spectroscopic study was investigated on the establishment of the structures of all newly synthesized Schiff bases bearing benzothiazole-1,2,3-triazole molecular conjugate. The newly designed hydrazones showed two isomers (cis-E and trans-E) with different isomeric distribution as confirmed by NMR spectral data and supported by DFT carried out in gas phase at B3LYP 6‒311G (d,p) basis set. The DFT results showed that the cis-E isomer is the lower energy structure and this finding was illustrated in terms of the intermolecular H-bonding. These molecules were screened for anticancer activities with A549 and H1299 lung cancer cell lines. The anticancer activities ranged from 55 to 90%. DNA binding study was also carried out to see the mechanism of action and the DNA binding constants were of good value ranging from of 2.0 × 105 and 14.7 × 105 M−1; indicating good interactions of the reported molecules with DNA. Finally, the modeling was confirmed and it was found that the results of modeling were in good agreement with the results of anticancer and DNA binding studies. All these finding confirmed that the reported molecules work as anticancer agents by interacting with DNA.

Chemistry deriving from OOQOOH radicals in alkane low-temperature oxidation: A first combined theoretical and electron-ion coincidence mass spectrometry study

While there is consensus on the fact that OOQOOH radicals, produced by two oxygen additions from alkyl radicals, are the heart of the low-temperature oxidation of alkanes, the determination of the isomeric distribution and the quantification of their derived products (ketohydroperoxides and diones) are still a challenge. For the first time, heavy oxygenated products produced during alkane oxidation have been investigated using electron/ion coincidence mass spectrometry. The investigated prototype reaction is n-pentane oxidation carried out in a jet-stirred reactor (temperatures from 585 to 665 K, pressure of 1.1 bar, lean mixture). Identification attempts were made for m/z 100 and 118 species using coincident mass-tagged Slow PhotoElectron Spectra obtained by electron-ion coincidence mass spectrometry combined with first principle computations, consisting in the determination of their adiabatic ionization energies and the Franck-Condon envelope of the photoionization spectra. 4-hydroperoxypentan-2-one has been confirmed as the dominant obtained ketohydroperoxide, as predicted by up-to-date kinetic models. However, difficulties due to fragmentation has made impossible the identification of the ketohydroperoxides present in lower amounts. In parallel, C5H8O2 isomers were identified, showing the possible formation, in addition to diones, of species with a ketone and an enol function. In addition, we provide new information on the first steps of the fragmentation pathways of C5 ketohydroperoxides. From the shape of their corresponding peaks on mass spectra and the energy and temperature dependence of their signal, ions at m/z 43, 57 and 85 have been identified as fragments from ketohydroperoxides. Taking into account these fragmentations lowers, by more than a factor of 10, the previously observed deviation between experiments and modeling for ketohydroperoxide mole fractions. The formation of the C1-C2 carboxylic acids, predicted from Korcek decomposition, was also observed, but with a favored formation of acetic acid versus formic acid that what was predicted for propane.