Isomer Ratios Research Articles

Excitation functions and isomeric cross-section ratios of (d,xn) reactions on 86\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{86}$$\\end{document}Sr

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Volatile light hydrocarbons as thermal and alteration indicators in oil and gas fields

Volatile light hydrocarbons (VLH) are an essential component of reservoir petroleum fluids. Understanding of their origin and fate is crucial not only in exploration but increasingly also in petroleum engineering, as this greatly impacts fluid typing, proper mapping, recoverability and economic value. Due to their sensitivity to subsurface thermal stress and geological alteration processes, their proper characterisation holds promise to understanding the thermal conditions under which petroleum fluids were generated and subsequent fluid modifications during migration and within the reservoir. To study the behaviour of these hydrocarbons under different geological conditions we selected oil and gas fields from two giant conventional petroleum systems in the Arabian Peninsula collectively spanning the entire petroleum spectrum from heavy oil to dry and sour gas. In situ representative bottomhole or recombined pressure–volume–temperature (PVT) fluid composition data were constrained with molecular and stable carbon isotope geochemistry in key wells. Systematic covariance among the slope factor (SF) of propane to pentane and the isomer ratios of butane and pentane with reservoir engineering and geochemical variables in well-constrained black oil to gas condensate petroleum systems allowed the derivation of three formulas to calculate thermal maturity in terms of vitrinite reflectance equivalent from VLH fluid composition: (1) %VRe(SF) = 0.38 SF + 0.41, (2) %VRe(i4) = 1.70 (iC4/nC4) + 0.61, and (3) %VRe(i5) = 0.89 (iC5/nC5) + 0.56. The slope factor, iC4/nC4, and iC5/nC5 ratios all increase monotonically with the thermal evolution of unaltered fluids, allowing for effective application of their derived %VRe formulas across the entire unaltered fluid spectrum, from heavy oil to dry gas. Deviations from indigenous-fluid trends do occur for fluids altered by phase separation, biodegradation, thermal cracking, and thermochemical sulfate reduction (TSR), but corrections can be made to minimize uncertainty in assessing true thermal maturity of altered fluids while respecting other reservoir fluid properties such as gas-to-oil ratio (GOR) and saturation pressure relationships. For instance, although a single charge that has been phase fractionated yields fluids with variable GORs, saturation pressures and slope factors, their butane and pentane isomer ratios remain reflective of the original fluid maturity. In contrast, biodegradation-induced overestimation of maturity based on the isomer ratios of butane and pentane can be corrected by the less affected SF-derived maturity parameter. Reversal to lower apparent SF-derived maturity in thermally and TSR cracked fluids can, on the other hand, be corrected by considering the less affected butane and pentane isomer ratios. Overall, maturities calculated using VLH composition correspond well with fluid type defined based on phase behaviour and source-rock kinetics, thereby putting forward new tools to quantify thermal maturity of reservoir fluids that may be applicable in other petroleum systems.

Geographic variation in genetic composition, sexual communication and mating compatibility of the False Codling Moth, Thaumatotibia leucotreta for optimisation of area-wide control

Intraspecific variation in sex pheromones is a driver of reproductive isolation and speciation in insects. The False Codling Moth (FCM) Thaumatotibia leucotreta (Lepidoptera: Tortricidae) is a quarantine pest endemic to sub-Saharan Africa (SSA). The currently available precision control measures for FCM use female sex pheromone components to lure males into traps. However, the existing data on the composition of the female sex pheromone, especially the isomer ratios of the main pheromone component (E/Z)-8-dodecenyl acetate, are inconsistent for populations in SSA. This inconsistency led to speculation about possible reproductive isolation between geographically separated FCM populations and the potential need for local adjustment of pheromone-based FCM control tools. This, however, requires a comparative evaluation of geographic variation in FCM sexual communication and inter-population mating compatibility. We therefore investigated genetic isolation and mating compatibility between five geographically isolated FCM populations in South Africa and analysed the ratio of (E)- and (Z)-8-dodecenyl acetate in females from these populations. The five studied populations were found to form three genetically distinct groups with high genetic distances between each other. Mating compatibility tests showed that mating is possible across these groups, however, males preferred females of their own population when given choices; without a choice, males successfully mated with and transferred spermatophores to females from all other populations. The ratio of (E)- and (Z)-8-dodecenyl acetate was similar (c. 4:1) across the populations, indicating that this main female pheromone component does not cause the observed intra-population mating preferences. It remains to be investigated if qualitative/quantitative variation in other sex pheromone components influences intra-population recognition in South African FCM, providing a base for the development of regionally-specific lures for area-wide control programmes.

Discrimination of Aspartic and Isoaspartic Acid Residues in Peptides by Tandem Mass Spectrometry with Hydrogen Attachment Dissociation.

Long-lived proteins undergo chemical modifications that can cause age-related diseases. Among these chemical modifications, isomerization is the most difficult to identify. Isomerization often occurs at the aspartic acid (Asp) residues. In this study, we used tandem mass spectrometry equipped with a newly developed ion activation method, hydrogen attachment dissociation (HAD), to analyze peptides containing Asp isomers. Although HAD preferentially produces [cn + 2H]+ and [zm + 2H]+ via N-Cα bond cleavage, [cn + 58 + 2H]+ and [zm - 58 + 2H]+ originate from the fragmentation of the isoAsp residue. Notably, [cn + 58 + 2H]+ and [zm - 58 + 2H]+ could be used as diagnostic fragment ions for the isoAsp residue because these fragment ions did not originate from the Asp residue. The detailed fragmentation mechanism was investigated by computational analysis using density functional theory. According to the results, hydrogen attachment to the carbonyl oxygen in the isoAsp residue results in the Cα-Cβ bond cleavage. The experimental and theoretical joint study indicates that the present method allows us to discriminate Asp and isoAsp residues, including site identification of the isoAsp residue. Moreover, we demonstrated that the molar ratio of peptide isomers in the mixture could be estimated from their fragment ion abundance. Therefore, tandem mass spectrometry with HAD is a useful method for the rapid discrimination and semiquantitative analysis of peptides containing isoAsp residues.

Stereoisomers of oxime ethers of 1,4-naphthoquinone: Synthesis, characterization, X-ray crystal structures, and DFT studies

In the present work, we use the C-3 substituted 2-hydroxy-1,4-naphthoquinones viz. 2-hydroxynaphthalene-1,4-dione (1), 2-hydroxy-3-methylnaphthalene-1,4-dione (2), and 2-chloro-3-hydroxynaphthalene-1,4-dione (3) as starting materials and obtained naphthoquinoneoxime ethers viz. 3-hydroxy-4-(methoxyimino)naphthalen-1(4H)-one (4), 3-hydroxy-4-(methoxyimino)-2-methylnaphthalen-1(4H)-one (5) and 2-chloro-3-hydroxy-4-(methoxyimino)naphthalen-1(4H)-one (6) via a facile and efficient synthesis involving condensation with methoxyamine hydrochloride. X-ray structure showed that 4 belongs to the orthorhombic (P212121) space group, whereas 5 and 6 (P21/c) crystalize in the monoclinic crystal system. The isomer ratios derived from NMR experiments elucidating stereoisomerism in compounds comprised of carbon-nitrogen double bonds have been analyzed; the naphthoquinone oxime ethers 4, 5, and 6 were also characterized employing the ωB97x-D/6–311++G (d, p) level of density functional theory. Theoretical studies reveal different conformational isomers with the ‘amphi’ and ‘syn’ isomers as low-lying structures along their energy hierarchy in accordance with the X-ray crystallography data. The spectral characterization of vibrational frequencies and 1H /13C NMR chemical shifts in unison with experiments and theory has been presented.

Spatial distribution of polycyclic aromatic hydrocarbons in water and sediment in the Ganga River: source diagnostics and health risk assessment on dietary exposure through a common carp fish Labeo rohita.

We evaluated spatial distribution and source apportionment of polycyclic aromatic hydrocarbons (PAHs) in water and sediments at four selected sites of the Ganga River. Also, we measured PAHs in muscle tissues of Rohu (Labeo rohita), the most common edible carp fish of the Ganga River and potential human health risk was addressed. Total concentration of PAHs (∑PAHs) in water was highest at Manika Site (1470.5ng/L) followed by Knuj (630.0ng/L) and lowest at Adpr (219.0ng/L). A similar trend was observed for sediments with highest concentration of ∑PAHs at Manika (461.8ng/g) and lowest at Adpr Site (94.59ng/g). Among PAHs, phenanthrene (Phe) showed highest concentration in both water and sediment. Of the eight major carcinogenic contributors (∑PAH8C), Indeno (1,2,3-C,D) pyrene (InP) did appear the most dominant component accounting for 42% to this group at Manika Site. Isomer ratios indicated vehicular emission and biomass combustion as major sources of PAHs. The ∑PAHs concentrations in fish tissue ranged from 117.8 to 758.0ng/g (fresh weight basis) where low molecular weight PAHs assumed predominance (above 80%). The risk level in fish tissues appeared highest at Manika Site and site-wise differences were statistically significant (p < 0.05). The ILCR (> 10-4) indicated carcinogenic risk in adults and children associated with BaP and DBahA at Manika Site and with BaP at Knuj Site. Overall, the concentrations exceeding permissible limit, carcinogenic potential and BaP equivalent all indicated carcinogenic risks associated with some individual PAHs. This merits attention because the Ganga River is a reservoir of fisheries.

Intensified bacterial productivity during the Paleocene–Eocene thermal maximum: Molecular evidence in the Tarim Basin in the eastern Tethyan realm

The investigation of bulk and molecular compositions in organic matter at the Bashibulake Section in the SW Tarim Basin, West China, across the Paleocene–Eocene boundary reveals a complex mixture of marine and terrigenous origins during the Paleocene–Eocene Thermal Maximum (PETM) in the eastern Tethys. Source-related biomarkers, such as n-alkanes, isoprenoid alkanes, steranes, hopanes and methylhopanes, exhibit diverse compositions influenced by both marine and terrigenous sources. Sterane and hopane isomer distributions, indicative of immature OM, are primarily controlled by biological configurations. Changes in compound class abundance and isomer ratios reflect variations in source inputs and depositional conditions. Elevated concentrations of n-alkanes from higher plants, along with ratios of C29-C32 moretanes/hopanes and C31/C32 homohopanes, suggest increased terrigenous OM supply during the PETM. However, the significant differences in concentration between n-alkanes from higher land plants and bacterial hopanes, coupled with the presence of 2α-methylhopanes, prevalence of C27 compounds in regular steranes, and absence of oleanane suggest a dominant aquatic bacterial contribution. The study highlights the role of enhanced continental flux and warming in stimulating microbial activity, enriching OM, a factor often overlooked by other analytical methods. The absence of carbonate carbon and low trisnorhopane isomerization provide supportive evidence of ocean acidification and carbonate dissolution during the PETM. Reduced pregnanes and tricyclic terpanes, along with low degree of hopane and sterane isomerization, indicate rising sea levels and low salinity. The findings emphasize the significance of the biomarker approach in identifying OM origin and characterizing the depositional environment in PETM-related sequences, suggesting a more substantial role of bacterial contributions than previously recognized.

First investigation on the isomeric ratio in multinucleon transfer reactions: Entrance channel effects on the spin distribution

The multinucleon transfer (MNT) reaction approach was successfully employed for the first time to measure the isomeric ratios (IRs) of 211Po isomer (25/2+) and its ground state (9/2+) at the IGISOL facility using a 945 MeV 136Xe beam impinged on 209Bi and natPb targets. The dominant production of isomers compared to the corresponding ground states was consistently revealed in the α-decay spectra. Deduced IR of 211Po populated through the 136Xe+natPb reaction was found to have an enhancement of ≈1.8-times than that observed for the 136Xe+209Bi. State-of-the-art Langevin-type model calculations have been utilized to estimate the spin distribution of an MNT residue. The computations qualitatively corroborate with the considerable increase in the IRs of 211Po produced from 136Xe+natPb compared to 136Xe+209Bi. Theoretical investigations indicate a weak dependence of target spin on the IRs. The enhancement of the 211Po isomer in the 136Xe+natPb over 136Xe+209Bi can be attributed to the different proton (p)-transfer production routes. Estimations demonstrate an increment in the angular momentum transfer, favorable for isomer production, with increasing projectile energy. Comparative analysis reveals the two entrance channel parameters, projectile mass and p-transfer channels, strongly influencing the population of the high-spin isomer of 211Po (25/2+). This letter reports the first experimental and theoretical study on the IRs of nuclei formed from two different p-transfer channels via two independent MNT reactions.

A computational and experimental study of cis-trans isomeric pesticides based on collision-induced dissociation of high-resolution mass spectrometry.

Pesticide isomers are widely available in agricultural production and may vary widely in biological activity, potency, and toxicity. Chromatographic and mass spectrometric analysis of pesticide isomers is challenging due to structural similarities. Based on liquid chromatography time-of-flight mass spectrometry, identification of cis-trans isomeric pesticides was achieved through retention time, characteristic fragment ions, and relative abundance ratio. Furthermore, theoretical and basic research has been conducted on the differences in characteristic fragment ions and their relative abundance ratios of cis-trans isomers. On the one hand, the cleavage pathways of six cis-trans isomers were elucidated through collision-induced dissociation to explain different fragment ions of the isomers. On the other hand, for those with the same fragment ions but different abundance ratios, energy-resolved mass spectrometry combined with computational chemical density functional theory in terms of kinetics, thermodynamics, and bond lengths was employed to explain the reasons for the differences in characteristic fragment ions and their abundance ratios. A high-resolution mass spectrometry method was developed for the separation and analysis of cis-trans isomers of pesticides in traditional Chinese medicine Radix Codonopsis, and six pesticide isomers were distinguished by retention time, product ions, and relative abundance ratios. The limits of quantification of the six pesticides were up to 10μg/kg, and the linear ranges of them were 10-200 μg/kg, with coefficients of determination (R2) > 0.99, which demonstrated the good linearity of the six pesticides. The recoveries of the pesticides at spiked concentrations of 10, 20, and 100 μg/kg reached 70-120% with relative standard deviations ≤20%. It was demonstrated that the application of the method was well suited for accurate qualitative and quantitative analysis for isomers with different structures, which could avoid false-negative results caused by ignoring other isomers effectively.

Characterization of polycyclic aromatic hydrocarbons in mangrove sediments from Ifiekporo Creek, Warri, Nigeria

The occurrence and level of polycyclic aromatic hydrocarbons (PAHs) in mangrove sediment from Ifiekporo Creek in Warri, Delta State, Nigeria, were assessed in this study. The extraction of PAHs from the sediment samples was achieved using the PAH analytical test method (USEPA 8270). This method measures the individual concentrations of extractable PAHs in samples. The PAHs were quantified within the C11-C22 subgroup. The basic GC parameters for the analysis of polyaromatic hydrocarbons were analysed using a gas chromatography‒mass selective detector (GC‒MSD). The individual PAH concentrations in the mangrove sediment samples ranged from 850 µg/kg−1 to 3470 µg/kg−1. PAH source apportionment employing isomeric ratios and multivariate statistics indicated both pyrogenic and petrogenic source inputs in the sediment samples. The order of PAH homology in the sediment was 3-ring > 2-ring > 4-ring. The sediment samples were mostly dominated by LMW PAHs. The results of the ecological risk assessment in the study area indicate that there is low ecological risk associated with PAH exposure in sediment. These results provide data on the concentrations and compositional patterns of PAHs, which is useful for understanding the effects, sources, fates, and transport of PAHs in sediment in the study area, as well as for providing relevant information for environmental quality management and forensic studies.

Independent isomeric yield ratios of fission products in the epi-cadmium neutron induced fission of 233U

The independent isomeric yield ratios (IR) of 128,130,132Sb, 131,133Te, 132,134,136I, 135Xe and 138Cs have been measured in the epi-cadmium neutron induced fission of 233U by using an off-line gamma-ray spectrometric technique. The average neutron energy of the epi-cadmium reactor neutron spectrum is 1.9 MeV. The root mean square fragment angular momenta (JRMS) were deduced from the IR values by using spin dependent statistical model analysis. The IR and JRMS values of considered fission products in the epi-cadmium neutron induced fission of 233U were compared with the literature data in the thermal neutron induced fission of 233U to examine the influence of excitation energy on nuclear structure effect.

Electropolymerization and characterization of a new ambipolar perimidine polymer with a perylene core

We successfully synthesized a stable electroactive perinone polymer by electropolymerization from the mixture of syn- and anti- isomers (ratio 1:1) of 3,4:9,10-bis(1,8-naphthapyrimidine)-1,6,7,12-tetrakis(1,1,3,3-tetramethylobutylphenoxy)perylene (NPP). The polymer p(NPP) exhibited distinct redox process, with reduction at -1.20 V and oxidation at 0.60 V (vs. ferrocene/ferrocenium couple). Spectroscopic and computational analyses confirmed structural similarity of the polymer to its monomeric form, revealing a perimidine unit involved in electrocoupling. Our thorough investigations elucidated the redox reactions electrochemical mechanism within the polymer film, identifying predominantly deprotonated bis-perimidine segments contributing to oxidation peaks at 0.60 V and 0.68 V. Additionally, the perylenediamide core exhibits the reversible, multi-stage reduction process. Impedance analysis highlighted efficient n-doping-induced conductivity, suggesting application in organic optoelectronic devices. This work positions p(NPP) as a versatile ambipolar multiredox p- and n-type conductor, indicating a potential for expanding perinone-based perylene-diperimidine polymers for innovative electronics.

Paleovegetation and environment during deposition of the Late Oligocene sub-bituminous coal in the Bobov Dol Basin (SW Bulgaria) as deduced from petrographic and geochemical characteristics

Coal and carbonaceous shale samples were taken from the Late Oligocene Bobov Dol Basin, SW Bulgaria. Seams Ia, I, IIa+b, III, IV and V from the coal-bearing Bobov Dol Fm. were sampled to provide insights into the peat forming vegetation and depositional environment based on detailed organic petrological and geochemical study.The petrographic composition indicates that both coals and carbonaceous shales contain predominantly terrestrial organic matter with abundant huminite macerals and locally enriched liptinite macerals. Inertinite is rare or absent. Good tissue preservation in seams I, IV and V indicates deposition under wet sedimentary environment, whereas predominance of detrohuminite and lower Tissue Preservation Index (TPI) in seams Ia, IIa+b and III are linked to enhanced humification of the plant remains due to changes in the hydrological regime. The low percent of inertinite and the overall high Gelification Index (GI), however, argue for peat formation under wetter climatic settings, whereas low to moderate ash yields of coal samples indicate organic matter deposition in oligo- to mesotrophic topogenous mires. Reconstructed evolution of the environmental settings during peat formation denotes differences which might be caused by changes in the hydrological regime and tectonic activity.The biomarker composition shows prevalence of gymnosperm-derived sesqui- and diterpenoids, followed by lower concentration of n-alkanes (apart from the carbonaceous shale samples from seam Ia), whereas angiosperm-derived non-hopanoid triterpenoids, acyclic isoprenoids, steroids and hopanoids, are generally present in minor amounts. Diterpenoid composition indicates dominant contribution from Cupressaceae and Pinaceae conifers. Minor amounts of predominantly lupane-type non-hopanoid triterpenoids denote limited development of angiosperm vegetation, presumably mostly related to Betulaceae family. Relative abundance of mid-chain (n-C21–25) n-alkanes, associated with elevated proxy ratio (Paq) furthermore, suggest possible contribution from aquatic macrophytes to peat formation. Very low hopane concentrations and low/moderate ββ/(ββ + αβ) hopane ratios imply minor aerobic bacterial activity under mild acidic conditions. The presence of inorganic carbon suggests that environmental acidity might be controlled by the occasional input of neutral to slightly alkaline ground waters. Moderate sulfur contents and the occurrence of hopenes denote anaerobic bacterial activity after organic matter burial.Low maturity of the organic matter and limited hydrocarbon generation potential is indicated by the low huminite reflectance, hopane (C31 22S/(22S + 22R)) and sterane (αααC29 20S/(20S + 20R)) isomerization ratios, as well as Rock-Eval parameters, Tmax and Production Index (PI).

Evaluation of 180mTa formation cross-sections in photoneutron reactions

Determining the relative production cross-sections of the short-lived (ground) and long- lived (metastable) states of 180Ta is integral in nuclear physics research. However, direct measurement of these cross-sections is challenging. In this study, we proposed a method for estimating the total flux-weighted average formation cross-section of 180m+gTa based on GEANT4 modeling to evaluate the short-lived (ground) and long-lived (metastable) states of 180Ta. A Ta target was irradiated by a bremsstrahlung photon beam (maximum electron energy: 20 MeV) obtained from the linear electron accelerator LUE-75 at the A.I. Alikhanyan National Science Laboratory (AANL), Armenia. The experiment was performed using the activation technique, and the proposed GEANT4 simulation-based method was employed to evaluate the flux-weighted average formation cross-section of 180mTa. In addition, the isomeric cross-section ratio for the 180m,gTa isomeric pair was calculated. The theoretical results obtained using the TALYS 1.96 and EMPIRE 3.2 codes were consistent with the experimental ones. To the best of the authors’ knowledge, this paper reports the estimated flux-weighted average formation cross-section of 180mTa and isomer ratio for the 180m,gTa isomeric pair, induced by the irradiation of a bremsstrahlung beam with an end-point energy of 20 MeV, for the first time. This study opens new avenues for determining the relative production cross-sections of the ground and metastable states of 180Ta, which is widely studied as a natural isomeric target in various fields, including nuclear transformation reactions, fission dynamics, etc.

Distribution, sources and health risk assessment of polycyclic aromatic hydrocarbons in urban soils under different landform conditions of Taiyuan, China

Public concern about polycyclic aromatic hydrocarbons (PAHs) is rising due to their potential carcinogenic, teratogenic, and mutagenic effects. This study assessed PAHs in Taiyuan City’s plain and mountain soil, investigating concentrations, distribution, sources, and carcinogenic risk. Σ21PAHs concentrations in plain topsoil ranged from 133.2 to 6,410.6 ng/g (mean 1,444.7 ng/g), and in mountain soil from 66.5 to 2,250.2 ng/g (mean 585.5 ng/g). Approximately 55.1% of plain and 19.0% of mountain soil samples had contamination levels exceeding 600 ng/g. In plain soil, 4-ring and 5-ring PAHs dominated, while 2-ring and 3-ring PAHs were prevalent in mountain soil. Polluted areas in Taiyuan were primarily centered in the central-north, with higher content closer to industrial or business districts. PAH isomer ratios and principal component analysis/multiple linear regression (PCA/MLR) indicated coal combustion as the main PAH source, followed by coke production, vehicle emissions, and biomass combustion. Incremental lifetime cancer risks (ILCRs) showed Taiyuan’s PAH-related cancer risks were generally low, though heavily contaminated areas exhibited moderate risks. Plain regions had three times higher cancer risk than mountains, with children facing higher risk than adults. These findings highlight the need to consider PAH pollution while enhancing urban environmental quality.

Measurement of isomeric yield ratios of 119m,gTe in the 60 and 70 MeV bremsstrahlung induced reaction of natTe

The isomeric yield ratio i.e. the yield ratio of high to low spin state (IR=Yh/Yl) of 119m,gTe in the natTe(γ,xn) reaction at the bremsstrahlung end-point energies (Ee) of 60-, and 70-MeV were measured for the first time by using an off-line gamma-ray spectrometric technique. The bremsstrahlung energies were generated by impinging pulsed electron energies of 60-, and 70-MeV on a thin W-target at the Pohang Accelerator Laboratory. The present data at 60 and 70-MeV and similar literature data at other energies shows that the IR values of 119m,gTe increases sharply from 10 MeV to 18 MeV, which indicates the role of excitation energy. Thereafter it increases marginally due the opening of other reaction channels, which indicates the partition of excitation energy in different reaction channels.

Distribution, sources, partition behavior and risk assessment of polycyclic aromatic hydrocarbons (PAHs) in the waters and sediments of Lake Ulansuhai, China

This study represents the first comprehensive investigation of 16 polycyclic aromatic hydrocarbons (PAHs) in the waters and sediments of Lake Ulansuhai. It explores their occurrence, sources, transport behavior, and associated risks to human health and ecosystems. The results revealed that concentrations of ∑PAHs in dissolved phase and sediment with no significant seasonal differences. In contrast, ∑PAHs concentrations in suspended particulate matter were significantly higher during the ice-free period compared to the ice period. Spatially, the northern part of Lake Ulansuhai displayed higher PAHs content. Diagnostic isomeric ratios and PMF models indicated that the PAHs were primarily derived from combustion sources. The distribution of PAHs within water-sediment demonstrated that non-equilibrium status. Fugacity calculations indicated that 2–4 rings PAHs acted as secondary sources of sediment emissions. Toxicity assessment, indicated that PAHs posed no significant carcinogenic risk to humans. Risk quotient values showed that PAHs as low to high ecological risk.

Lipid Isobaric Mass Tagging for Enhanced Relative Quantification of Unsaturated sn-Positional Isomers.

Changes in the levels of lipid sn-positional isomers are associated with perturbation of the physiological environment within the biological system. Consequently, knowing the concentrations of these lipids holds significant importance for unraveling their involvement in disease diagnosis and pathological mechanisms. However, existing methods for lipid quantification often fall short in accuracy due to the structural diversity and isomeric forms of lipids. To address this challenge, we have developed an aziridine-based isobaric tag labeling strategy that allows (i) differentiation and (ii) enhanced relative quantification of lipid sn-positional isomers from distinct samples in a single run. The methodology enabled by aziridination, isobaric tag labeling, and lithiation has been applied to various phospholipids, enabling the determination of the sn-positions of fatty acyl chains and enhanced relative quantification. The analysis of Escherichia coli lipid extracts demonstrated the enhanced determination of the concentration ratios of lipid isomers by measuring the intensity ratios of mass reporters released from sn-positional diagnostic ions. Moreover, we applied the method to the analysis of human colon cancer plasma. Intriguingly, 17 PC lipid sn-positional isomers were identified and quantified simultaneously, and among them, 7 showed significant abundance changes in the colon cancer plasma, which can be used as potential plasma markers for diagnosis of human colon cancer.

Intrinsic and environmental modulation of stereoselective aldol organocatalyzed reactions by proline-containing lipopeptides.

Proline, along with its derivatives, has been employed as an efficient organocatalyst for aldol reactions, with the ability to promote the creation of stereoselective C-C bonds. Even though the Houk-List transition state model is able to explain the stereoselectivity observed when proline is used as a catalyst, few studies investigate the role of microheterogeneous media in modulating the reaction outcome. In this work, molecular dynamics and electronic structure calculations were used to investigate the aldol reaction in the condensed phase. Our research focused on a lipopeptide compound incorporating the proline residue within the sequence PRWG-(C18H37), where P represents l-proline, R stands for l-arginine, W for l-tryptophan, and G for l-glycine. This sequence is covalently bonded to a hydrophobic segment formed by a long aliphatic chain, acting as an organocatalyst in an aqueous solution. This catalytic phase utilizes the complex chemical environment of the solution to achieve high selectivity. Our findings indicate a Houk-List-like mechanism, in which the amide acts as an H-bond donor, complemented by a mechanism in which the counter ion, trifluoracetic acid (TFA), acts as a proton shuttle. Both mechanisms demonstrated low energy barriers-12.23 and 1.42 kcal mol-1 for the (S,R) stereoisomer formation, computed using DLPNO-CCSD with def2-TZVPP basis set. Further, to explore the catalytic effect of the PRWG-(C18H37) lipopeptide in water, molecular dynamics simulations were conducted. It was observed that the micellar phase significantly enhances stereospecific encounters, favouring the experimentally observed ratio of (SR/SS) isomers, in contrast to reactions in a pure cyclohexanone medium. By quantifying the effects enabled by the supramolecular assembly, we were able to shed light on the factors that modify and enhance the stereoslectivity of the reaction.

Structure-property relationships in renewable composites of poly(lactic acid) reinforced by low amounts of micro- and nano-kraft-lignin.

We investigate the direct and indirect effects of micro- and nano-kraft lignin, kL and NkL, respectively, at a quite low amount of 0.5 wt%, in poly(lactic acid) (PLA)-based composites. These renewable composites were prepared via two routes, either simple melt compounding or in situ reactive extrusion. The materials are selected and prepared using targeted methods in order to vary two variables, i.e., the size of kL and the synthetic method, while maintaining constant polymer chain lengths, L-/D-lactide isomer ratio and filler amounts. The direct/indirect effects were respectively investigated in the amorphous/semicrystalline state, as crystallinity plays in general a dominant role in polymers. The investigation involves structural, thermal and molecular mobility aspects. Non-extensive polymer-lignin interactions were recorded here, whereas the presence of the fillers led to both enhancements and suppressions of properties, e.g., glass transition, crystallization, melting temperatures, etc. The local and segmental molecular dynamics map of the said systems was constructed and is shown here for the first time, demonstrating both expected and unexpected trends. An interesting discrepancy between the trends in the calorimetric measurement against the dielectric Tg is revealed, providing indications for 'dynamical heterogeneities' in the composites as compared to neat PLA. The reactive extrusion as compared to compounding-based systems was found to exhibit stronger effects on crystallizability and mobility, most, probably due to the severe enhancement of the chains' diffusion. In general, the effects are more pronounced when employing nano-lignin compared to micro-lignin, which is the expected beneficial behaviour of nanocomposites vs. conventional composites. Interestingly, the variety of these effects can be easily manipulated by the proper selection of the preparation method and/or the thermal treatment under relatively mild conditions. The latter capability is actually desirable for processing and targeted applications and is proved here, once again, as an advantage of biobased polyesters such as PLA.