Search Results (308)

Cross-reactions between peroxy radicals (RO₂) derived from different volatile organic compound (VOC) precursors have been proposed as an important pathway during atmospheric oxidation. However, direct molecular evidence has been limited. In this study, α-pinene and fully deuterated toluene (d8-toluene) were oxidized separately and as a mixture in a potential aerosol mass (PAM) flow reactor, and the resulting secondary organic aerosol (SOA) was characterized by a high-resolution mass spectrometer (ESI FT-ICR-MS). A constrained chemical mass balance (CMB) model attributed 82.9% of the mixed-SOA signal to single-precursor sources (66.5% α-pinene, 16.4% d8-toluene), leaving a 17.1% signal-based residual fraction unexplained by linear mixing. Among 2450 residual molecular formulas exclusive to the mixed-SOA, 1858 were identified as cross-reaction candidates, with carbon, oxygen, and double bond equivalents (DBE) distributions consistent with RO₂-RO₂ cross-reactions between toluene- and α-pinene-derived fragments. We also identified representative monomer-dimer pairs, where one monomer corresponded to a known α-pinene oxidation product, while the other matched a primary oxidation product of d8-toluene oxidation based on the Master Chemical Mechanism (MCM), providing strong molecular-level evidence for RO₂-RO₂ cross-reactions. Our findings demonstrate that the mixed VOCs generate unique SOA products that extend beyond simple additive chemistry, with implications for SOA yield parameterizations and chemical transport models. Full article

Photocatalytic reduction of carbon dioxide (CO₂) into high-value multicarbon products, such as ethylene (C₂H₄), remains a significant challenge due to the difficult C-C coupling process. Potassium poly(heptazine imide) (K-PHI) is a promising photocatalyst, yet efficiently exchanging its interlayer cations to tune catalytic selectivity without causing structural degradation is difficult. Herein, an efficient and green supercritical CO₂ (SC CO₂) assisted ion-exchange strategy was developed to successfully prepare a series of mono-/di-/trivalent cation-doped M-PHI photocatalysts (M = H⁺, Na⁺, Sr⁺, Ca²⁺, Co²⁺, Fe³⁺). Systematic characterizations confirmed that the SC-CO₂ treatment successfully achieved in-depth cation substitution without destroying the intrinsic heptazine framework, effectively regulating the interlayer structure and significantly optimizing the photoelectrochemical charge separation. Among the prepared samples, H-PHI exhibited the optimal photocatalytic CO₂ reduction performance with an outstanding selectivity toward C₂H₄ generation. Under simulated sunlight irradiation for 3 h, the yields of CO, CH₄, and C₂H₄ C₂H₄ C₂H₄ reached 3564.87, 807.32, and 40.00 μmol·g⁻¹, respectively, significantly outperforming pristine K-PHI and other metal-doped samples. Crucially, isotope-tracing experiments utilizing a SC CO₂-DCl treatment detected deuterated CH₄ and C₂H₄ products, providing direct evidence that the hydrogen in the carbon products originates from the introduced protons, thereby elucidating the precise reaction pathway for C-C coupling. This study provides a green and efficient supercritical CO₂ ion exchange strategy for the cation engineering of crystalline carbon nitride, and also offers new ideas and methods for designing high-activity photocatalysts for photocatalytic CO₂ reduction. Full article

Reductive deuteration of N-heterocycles provides an efficient route to deuterated scaffolds, yet achieving controlled deuterium incorporation in quinoline remains challenging. Herein, we report a high-temperature H₂-treated Rh/TiO₂ catalyst (Rh/TiO₂–H500) that enables efficient reductive deuteration of quinoline using D₂O as a deuterium source. Structural characterization reveals that reduction at 500 °C induces a pronounced strong metal–support interaction (SMSI), leading to partial TiO_x encapsulation of Rh nanoparticles and interfacial electron transfer that generates electron-rich Rh⁰ species. This optimized interfacial structure promotes cooperative C–H activation and effective H/D transfer across the reduced quinoline framework, affording high deuterium incorporation at multiple positions of 1,2,3,4-tetrahydroquinoline (THQ). These results highlight the importance of SMSI-driven electronic and interfacial modulation in regulating reductive H/D exchange over heterogeneous catalysts. Full article

The development of sustainable and environmentally benign N-methylation methodologies is essential for enhancing sustainable synthetic practice in pharmaceutical manufacturing. In this study, we demonstrate that microwave heating (MWH) markedly enhanced the efficiency of cobalt-catalyzed N-methylation using methanol or methanol-d₄ as green C1 sources. Compared with conventional heating (CH), MWH enabled highly efficient syntheses of key pharmaceutical intermediates—including 6-dimethylamino-1-hexanol, imipramine hydrochloride, and butenafine hydrochloride—under milder conditions and shorter reaction times and without generating hazardous halogen-containing waste. UV–vis spectroscopic analysis revealed that MWH accelerated the transformation of Co(acac)₂ into catalytically active Co species by approximately four-fold, providing a mechanistic basis for the enhanced reactivity. We hypothesized that this effect was caused by the selective microwave heating of the catalyst, which in turn promoted the rapid generation of catalytically active species. Notably, MWH also significantly improved the N-trideuteromethylation of amines using methanol-d₄, achieving a 95% yield for imipramine-d₃ hydrochloride versus 32% under CH. Molecular dynamics simulations indicated that methanol-d₄ exhibited slower dipole relaxation and enhanced cluster fragmentation under microwave fields, improving catalyst–substrate contact, while kinetic isotope effects stabilized reactive intermediates. These synergistic effects account for the pronounced microwave promotion observed in deuterated systems. Overall, the combination of MWH and cobalt catalysis offers an energy-efficient, waste-minimizing, and environmentally benign strategy for the scalable synthesis of both methylated and deuterated amines. Full article

Measurement of the turnover rate of proteins, different metabolites and lipids in living organisms is important for the understanding of biochemical pathways and physiology studies. Such experiments can be performed by administering isotopically labeled substances (food or water) to the organism and measuring the amount of the isotopes in the endogenous compounds. Here, we administered 20% heavy water (D₂O) to a guinea pig for 156 days and regularly measured the deuterium uptake in C-H groups in the different compounds of blood, urine and feces using high-resolution mass spectrometry. We successfully measured the time required for reaching the maximum deuteration level for several classes of compounds: 10 days for blood lipids (PC, PE, TAG); 60 days for sterol derivatives, heme B and hemoglobin; and 70 days for stercobilin. Also, for those compounds, we measured the deuterium elimination time from the organism when deuterium administration was stopped. The turnover of lipids was also studied by administering deuterated oat leaves grown at 10% D₂O to the guinea pig. The analysis of blood revealed that triglycerides demonstrate the inclusion of the deuterium after 5 h. All experiments were performed on a single guinea pig that remained alive and in good health after all experiments. The current research demonstrates the possibility of using long-term D₂O administration for the investigation of metabolism. Full article

Glucocorticoid (GC) residues present in aquatic products raise food safety concerns, as their chronic dietary intake may pose potential risks of endocrine and metabolic disruption. For the first time, a sensitive and reliable liquid chromatography–tandem mass spectrometry (LC-MS/MS) method was developed and validated herein for the simultaneous determination of 12 GCs residues, including critical isomeric pairs and acetate ester derivatives, in a variety of aquatic foods, employing deuterated isotopic internal standards. Key optimizations included using a pentafluorophenyl column for effective isomer separation, a synergistic extraction system for high recovery, and QuEChERS purification to mitigate matrix effects. The method exhibited excellent linearity (r² > 0.996) and high accuracy (recoveries 97.3–99.3%), and the intra- and inter-day precision values were below 3% in five representative aquatic matrices, with a limit of detection (LOD) and a limit of quantification (LOQ) of 0.5 μg/kg and 0.75 μg/kg, respectively. Animal experiments confirmed the in vivo retention of acetate derivatives, justifying their inclusion in monitoring. Real sample analysis of 18 market samples revealed the presence of cortisone and hydrocortisone in 17 samples. This represents the first reported LC-MS/MS method that provides a sensitive, reliable tool for regulatory monitoring of GC residues in diverse aquatic products, thereby supporting food safety assurance. Full article

Polycyclic aromatic hydrocarbons (PAHs) can enter water bodies and bioaccumulate in fish, leading to biomagnification; therefore, their monitoring is necessary. Passive sampling is easy to handle and shows potential for this purpose. However, studies in vivo are scarce, and kinetic parameters governing analyte partitioning between tissue and samplers remain poorly characterized. In this study, the silicone rubber membranes (SRMs) were exposed to fish fillet from common carp (Cyprinus carpio) to determine bioaccumulation parameters based on dissipation modelling using performance reference compounds (PRCs). The SRM was implanted in vivo in fish, and the dissipated PRCs were measured and applied to a mono-compartmental model. The results in fish fillet showed a pseudo-first kinetic order, and the plateau was attained at a time > 30 h. However, the equilibrium may not be ensured because of the low lipid fraction (fl) in fish (4.5%), which could lead to a local saturation of the tissue in contact with the SRM. The ratio between elimination and uptake constants (K_e/K_u) showed faster PAHs–SRM sorption than PAHs-fish tissue sorption (200 times); thus, fish with low fl will lead to faster SRM sorption. By contrast, in fish with higher fl, the long-term exposures will be necessary. The percentage of released deuterated PAHs from SRM during in vivo fish exposure was 1.6 times higher than that observed in the fish fillet, indicating an active clearance process. Therefore, during implantation, the rate of clearance and the fl should be considered to ensure detectable levels for applying the integrative equation based on dissipation modelling. Full article

Although membrane proteins are of major importance in both physiology and disease, they remain less studied than soluble proteins due to the complex amphiphilic environments required to preserve their structure and function. As a consequence, membrane proteins are under-represented in structural databases. In this work, we present a robust structural characterization of lipid nanodiscs designed to facilitate membrane protein studies by small-angle neutron scattering. By combining small-angle X-ray and neutron scattering, we investigate nanodiscs of three different sizes and three lipid compositions to accommodate a broad range of systems. Specifically, nanodiscs with diameters of approximately 9 nm, 12 nm, and 15 nm were examined. Beyond the commonly used di-myristoyl-phosphatidylcholine lipid, we produced and characterized polar lipid extracts from a Gram-negative bacterium (Escherichia coli) and a Gram-positive bacterium (Bacillus subtilis) under both protonated and deuterated conditions. In conclusion, solubility-enhanced variants of the scaffold protein yield more stable nanodiscs and are therefore preferable for extended structural investigations. The co-fitting of small-angle scattering data provides robust geometrical models of these nanodiscs, which can be treated as well-defined reference systems for future studies of membrane proteins in native-like lipid environments. Full article

Iridium pyridine diimine (PDI) complexes provide a versatile platform for highly reactive Ir–nitrido species with pronounced multiple-bond character, capable of activating H–H, C–H, Si–H, and even C–C bonds. Building on this chemistry, we extended our studies to a system with a terminal Ir–S bond, starting from our recently reported PDI–Ir–SH complex, which exhibits partial multiple-bond character. Upon addition of the 2,4,6-tri-tert-butylphenoxy radical, the corresponding phenol and a tentative Ir–S• radical intermediate are formed at ambient temperature. DFT and LNO-CCSD(T) calculations consistently reveal a low barrier for this process, with the spin density localized primarily on sulfur, accounting for subsequent S–S coupling reactions. Instead of the anticipated dimeric disulfido Ir–S₂–Ir complex formed along a least-motion pathway, a trisulfido Ir–S₃–Ir species was obtained, and characterized by NMR spectroscopy, X-ray crystallography and mass spectrometry. The formation mechanism of the trisulfido complex was further elucidated by DFT calculations. Remarkably, the sulfur-bridge formation is thermally reversible, regenerating the monomeric sulfanido Ir–SH complex. The origin of the hydrogen atom was investigated using H₂, D₂, and deuterated solvents. Full article

Thiourea and structurally related urea derivatives are widely recognised for their ability to transport anions through hydrogen bonding interactions. The strength of these interactions correlates with the electronegativity of the ligand and the acidity of the NH hydrogens involved. Thiourea, being more acidic than urea, exhibits partial deprotonation in the presence of certain anions such as organic carboxylates, fluoride, and bromide, while remaining resistant to deprotonation by chloride. This behaviour suggests a degree of selectivity toward chloride ions. Additionally, while carbamide-containing molecules tend to aggregate—potentially reducing their ion-binding efficiency—thiourea derivatives show reduced aggregation, preserving their binding capabilities. In this study, we report the synthesis and characterisation of 21 novel thiourea derivatives obtained by reacting 2-aminobenzoylamino acid esters with various substituted phenyl isothiocyanates. Seven similar thiourea-containing molecules were made as a comparison—without the amino acids—by reacting aniline with the different phenyl isothiocyanates. The reaction kinetics were found to be influenced primarily by the electronic nature of the substituents on the phenyl ring. Electron-withdrawing groups (EWGs), such as para-nitro, 3,5-bis(trifluoromethyl), and fluorine, accelerated the reaction, while electron-donating groups (EDGs), such as para-methoxy, slowed it down. Interestingly, the nature of the amino acid precursors had no significant impact on reaction time; however, reactions with aniline proceeded the fastest. Solvent choice also played a role: reactions in N,N-dimethylformamide (DMF) proceeded faster than in acetone, although with reduced yields. Consequently, reaction conditions were optimised to balance time efficiency and product yield. To evaluate the chloride ion-binding properties of the synthesised compounds, ¹H NMR titration experiments were conducted in deuterated dimethyl sulfoxide (DMSO-d₆). The association constants (K_a) derived from these studies revealed a clear correlation with the electronic nature of the substituents. Compounds bearing EWGs exhibited enhanced chloride binding, while those with EDGs showed diminished binding affinity. Surprisingly, the presence of amino acid moieties led to a decrease in K_a values, despite the electron-withdrawing nature of the amide groups. This suggests that steric or conformational factors may play a role in modulating binding strength. Overall, the synthesised thiourea derivatives demonstrate mild, reversible chloride ion-binding behaviour, making them promising candidates for further development as selective anion receptors. The insights gained from this study contribute to a deeper understanding of structure–activity relationships in anion-binding systems and may inform the design of future supramolecular architectures with tailored ion recognition properties. Full article

The liquid crystal (LC) poly-γ-benzyl-L-glutamate (PBLG) is known to possess a narrow biphasic range at the phase transition from an isotropic liquid to an anisotropic liquid crystal. We have characterized the biphasic region via deuterium nuclear magnetic resonance (NMR) of the deuterated solvent CDCl₃, with which isotropic and anisotropic populations can unambiguously be identified and quantified due to the quadrupolar coupling induced by partial alignment. In addition to a dilution series, we measured the kinetics of the alignment inside the magnet for each dilution step and were able to follow the kinetic buildup of partial alignment. Beginning with the dynamic line broadening indicative of slow fluctuations, to microheterogeneous patches of isotropic and anisotropic islands, with increasing island size being consistent with sharpened spectra, ending in fully separated isotropic and anisotropic phases on top of each other after two weeks. In addition, we studied the influence of the two example guest molecules borneol and camphor—which essentially differ in their capability to act as hydrogen bond donors or acceptors—on the biphasic region of PBLG. Full article

In this study, we report the preparation of platinum nanoparticles (Pt NPs) deposited on HTiNbO₅ and the application of the resultant material in the catalytic decomposition of sodium borohydride (NaBH₄) to generate hydrogen. The starting material, KTiNbO₅, was prepared through a solid-state process involving Nb₂O₅, K₂CO₃, and TiO₂. The subsequent treatment with HNO₃ resulted in the exchange of potassium by protons, rendering HTiNbO₅. This material served as support for Pt nanoparticles (3.6 ± 0.7 nm), producing Pt NPs/HTiNbO₅. All compounds were characterized using TGA, FTIR, XRD, Raman, SEM-EDS, and HRTEM. The influence of different factors on the reaction kinetics was evaluated, resulting in a hydrogen generation rate (HGR) of 22,790.18 $\mathrm{m}\mathrm{L} {\mathrm{m}\mathrm{i}\mathrm{n}}^{-1}{\mathrm{g}}_{\mathrm{c}\mathrm{a}\mathrm{t}}^{-1}$ at 50 °C. The activation energy (41.83 kJ mol⁻¹) was also determined. A mechanistic study with deuterated water revealed a kinetic isotopic effect (KIE) value of 1.27, indicating the dissociation of B-H from BH₄⁻ as the rate-determining step of the process. Furthermore, the reuse and durability of the material were evaluated, revealing a catalyst performance close to 100% over the 10 tested cycles. Therefore, it can be concluded that the synthesized material, Pt-nanoparticles dispersed on HTiNbO₅, exhibits excellent performance and is suitable for hydrogen evolution from NaBH₄. Full article

A topological analysis was performed by taking ESEEM measurements of site-specifically labeled E protein from SARS-CoV-2. The intensity of deuterium modulation arising from either deuterated solvent or deuterated lipid acyl chains revealed exposure to solvent or the bilayer hydrophobic region. Spin-labeled lipids and soluble spin labels were used as points of comparison. The data indicate that spin labels placed along the transmembrane helix of the E protein showed close contact with lipid acyl chains, but also substantial contact with solvent, while those placed on the C-terminal domain showed substantial but lower exposure to lipid acyl chains, with comparable solvent exposure. The results support the view that the C-terminal domain is in contact with the bilayer surface. Full article

This study presents new findings on the conformational mobility of the nonsteroidal antiandrogen blocker, bicalutamide, in deuterated chloroform. Based on NOE NMR spectral analysis, quantitative information was obtained regarding the distribution of «open» and «closed» conformer groups in four systems: one with a solid phase (16.7%/83.3%), one without the solid phase (19.7%/80.3%), and two diluted solutions at different concentrations (16.1%/83.9% and 85.3%/14.7%). It was shown that the preparation of molecules for nucleation and the transition to the «closed» conformation occurs at low concentrations and is maintained as the concentration increases until the solid phase is formed. This behavior of conformational evolution contrasts previous understandings of the solid phase’s influence on molecular conformation in solution. The results obtained will offer deeper insights into the conformational evolution of small molecules during nucleation, using bicalutamide as a model. Full article

An experimental and theoretical investigation of the reaction between chlorine atoms and propane/deuterated propane (C₃H₈/C₃D₈) was performed. The experimental work aimed to determine absolute and site-specific rate constants for hydrogen and deuterium abstraction in the Cl + C₃H₈/C₃D₈ system. Measurements were conducted using the relative rate method at three temperatures between 298 and 387 K. Total rate constants for H/D abstraction by chlorine, as well as individual rate constants for abstraction from primary and secondary carbon sites, were obtained. The kinetic data for H abstraction agree well with previously reported literature values, confirming the reliability of the experimental approach. Notably, rate constants for the C₃D₈ + Cl reaction were determined for the first time, and the consistency of these results supports the reliability of the newly derived kinetic parameters. In the theoretical part of the study, hydrogen/deuterium abstraction from propane by atomic chlorine was analyzed within an atmospheric-chemistry context to clarify temperature dependence and site selectivity. Stationary points (SC, TS, PC, reactants, products) were optimized at MP2/aug-cc-pVDZ and verified by harmonic frequencies and intrinsic reaction-coordinate analyses. Eyring transition-state theory yielded 298–550 K rate constants with activation free energies referenced to SC. Our calculations indicate entrance-channel complex formation and effectively barrierless progress for most pathways; a small barrier appears only for RD1′. L-parameter evaluation classifies TS2 as reactant-like, and branching ratios identify –CH₂– abstraction (RX2) as dominant. These findings align with the experimental data. Full article