Search Results (1,235)

High-energy-density fuels (HEDFs) have garnered considerable interest in aerospace fields, primarily due to their superior density and volumetric net heat of combustion (NHOC) compared with traditional petroleum-based fuels. Strained polycyclic hydrocarbons are regarded as one of the most crucial categories of HEDF. As an isomer (C₁₀H₁₆) of JP-10, the target compound is composed of two cyclopropyl rings and one cyclobutyl ring connected in a linear manner. Notably, intramolecular H-migration reactions of peroxyl radicals derived from strained polycyclic hydrocarbons (C₁₀H₁₅OO•) are of great significance for establishing the reaction mechanism of high-energy-density fuels over a broad temperature range. In this work, the intramolecular H-migration kinetics of C₁₀H₁₅OO• with distinct cis and trans configurations are investigated by quantum chemical calculations. Geometry optimization and frequency calculations are carried out for all species using the M06-2X/6-311++G(d,p) level of theory, while single-point energy calculations are performed at the CBS-QB3 level. Our calculated results demonstrate that different types of intramolecular H-migration reactions exhibit significant differences in barrier heights. Based on the ring structures where the reaction centers are located, these reactions can be classified into three categories: the lowest barriers correspond to H-migration reactions occurring between the central cyclopropyl ring and the terminal cyclobutyl ring; the highest barriers correspond to H-migration reactions confined entirely within the terminal cyclobutyl ring; and the barriers for H-migration reactions occurring between the terminal cyclopropyl ring and the central cyclopropyl ring lie between the above two. High-pressure-limit rate constants for 33 elementary reactions are determined in the temperature range of 500 to 2500 K based on the conventional transition-state theory (TST) and expressed in the modified Arrhenius form. Full article

Accurate ionization energies are essential for understanding the electronic structures of atoms and molecules and benchmarking quantum-chemical methods. We report the calculated ionization energies of the H, C, N, O, F, P, and S atoms using several quantum-chemical approaches, aiming at reproducing the experimental values within chemical accuracy. The methods include the electron propagator approximations OVGF and P3+, the coupled-cluster methods CCSD(T), CCSDT, and IP-EOM-CCSD, and the composite methods G3 and CBS-QB3. The CCSD(T), CCSDT, G3, and CBS-QB3 methods, together with the DFT method with B2PLYP density functional and several post-Hartree–Fock methods, were used in conjunction with the energy-difference approach. The coupled-cluster calculations were combined with the aug-cc-pVXZ-DK, aug-cc-pVXZ, and ANO-RCC basis sets, all-electron correlation, DKH2 scalar relativistic corrections, atomic spin–orbit corrections, and extrapolation to the complete basis set (CBS) limit. The OVGF and P3+ methods do not achieve chemical accuracy on average, while CCSD(T) and CCSDT combined with the aug-cc-pVXZ-DK basis set and CBS extrapolation reach mean absolute errors of 0.0030 and 0.0026 eV, respectively, an order of magnitude below the chemical accuracy threshold. CCSD(T)/aug-cc-pVXZ-DK with CBS extrapolation provides the best compromise between accuracy and computational cost and can be used as a reference atomic benchmark for these ionization energies. Full article

The redox behavior of nickel complexes with sulfur-containing ligands remains of considerable interest due to their significant value in coordination chemistry, catalysis, and bioorganic modeling. In this context, it is important to investigate how aqueous media and acid–base equilibria influence the stability and transformation pathways of such complexes. In this work, the electrochemical behavior of nickel complexes with phosphorylated dithiocarbamate was studied using cyclic voltammetry at various scan rates and pH values. Compared to similar systems in organic solvents, the complexes exhibited additional oxidation and reduction signals, indicating coupled chemical steps. The pH dependence of these peaks confirmed the role of hydroxo groups in the oxidation processes. Varying the scan rate revealed competition between ligand exchange pathways. At low and moderate scan rates, tris-dithiocarbamate nickel(III/IV) complexes are formed, whereas at higher scan rates, hydroxo-containing compounds make a greater contribution. Based on the experimental results and standard redox potentials derived from quantum chemical calculation data, a general scheme for the resulting electrochemical processes was proposed. The results demonstrate the key role of aqueous media and pH in regulating the redox process of nickel complexes with phosphorylated dithiocarbamate. Full article

The pyrolysis of polypropylene (PP) microplastics offers a potential route to convert plastic waste into fuel-range hydrocarbon mixtures and chemical feedstocks. However, the elementary radical pathways underlying the formation of medium-chain hydrocarbon fragments remain insufficiently resolved. In this study, a representative isotactic PP oligomer model (C₄₅H₉₂) was evaluated using a comparative density functional theory (DFT) framework. The main mechanistic analysis was based on M06-2X, ωB97X-D, and M11 calculations combined with the def2-TZVP basis set, whereas LANL2DZ was retained only as a lower-cost comparative level during reaction-pathway exploration. Thermochemical profiles were evaluated over a temperature range of 298–923 K. Three selected pathways involving mid-chain homolytic cleavage, intramolecular hydrogen transfer (backbiting), radical rearrangement, and β-scission were examined. Within the selected reaction set, Route 1 exhibited a comparatively more favorable thermochemical profile than Routes 2 and 3 and provided a mechanistically plausible sequence toward medium-chain hydrocarbon fragments. The −TΔS contribution strongly influenced the calculated Gibbs free-energy profiles because fragmentation increases the number of molecular species under the ideal-gas thermochemical approximation. Accordingly, the ΔG values were interpreted comparatively and were not treated as direct evidence of spontaneous fragmentation under condensed-phase pyrolysis conditions or as quantitative predictions of experimental product selectivity. Differences among the evaluated functionals further indicate that the relative description of radical intermediates and transition-state regions is method-dependent. These results provide a molecular-level framework for future studies integrating quantum-chemical calculations, microkinetic modeling, and experimental product characterization. Full article

The potency of urate, an abundant human plasma antioxidant, in preventing oxidative damage caused by the carbonate radical anion CO₃^•−, was studied using quantum chemical calculations. The influence of microhydration of CO₃^•−/CO₃²⁻ and urate⁻/urate^• couples on the thermodynamic and kinetics of the one-electron oxidation process was investigated. Depending on the degree of microhydration, the estimated rate constant for one-electron transfer is in the range of 2.0–7.3 × 10⁹ M⁻¹ s⁻¹, in good agreement with the experimental value of 1.3 × 10⁹ M⁻¹ s⁻¹. Modeling using vertical detachment energy and electron affinity, the driving forces of single electron transfer revealed urate(H₂O)₆⁻ and CO₃(H₂O)₉^•− clusters as the most likely existing species in water. Molecular docking revealed a favorable interaction of urate with the catalytic pocket of SOD1. Urate binds more strongly to the anionic active center of SOD1 than the reference inhibitor LSC-1, indicating its potency to prevent HCO₃⁻-supported CO₃^•− formation. In contrast, the known OGG1 inhibitor TH13264 shows substantially stronger binding than urate, indicating urate’s weaker affinity toward the DNA repair enzyme catalytic pocket. The molecular dynamics data indicate that urate binding does not destabilize either SOD1 or OGG1. In light of increasing evidence that the major source of oxidative stress could be CO₃^•−, rather than the commonly assumed hydroxyl radical HO^•, the obtained results indicate the inherent ability of plasma to combat oxidative stress induced by this selective, milder oxidant. Such an ability with respect to the non-selective, highly reactive HO^• does not exist in vivo. Full article

The ATP-binding cassette transport protein Pdr5p is known to play a role in multidrug resistance in Saccharomyces cerevisiae by effluxing structurally diverse xenobiotics; yet the physicochemical determinants of substrate recognition remain poorly defined. To address this, density functional theory (DFT) calculations at the B3LYP-D3BJ/def2-SVP level were combined with machine learning to derive a predictive model of substrate recognition using a curated dataset of 66 compounds spanning 9 functional categories. A hybrid support vector machine (SVM) classifier achieved 96.3% accuracy (95% CI: 81.0–99.9%, Clopper–Pearson exact) in discriminating substrates from non-substrates under leave-one-out cross-validation. Feature importance analysis identified lipophilicity (LogP, F-score = 37.5) as the dominant descriptor, suggesting that membrane partitioning constitutes the initial recognition step. The HOMO–LUMO gap contributed secondarily (F-score = 12.4). Substrates were further distinguished by high frontier orbital focalization, with frontier orbital spread of 1.8–2.6%, compared to 4.18–7.22% for non-substrates. Notably, a model trained exclusively on Pdr5p data achieved 87% prediction accuracy when applied without retraining to the human P-glycoprotein (ABCB1) dataset, suggesting conserved physicochemical principles of substrate recognition across evolutionarily distant ABC transporters. These findings provide a quantum chemical framework for understanding and potentially predicting MDR transporter substrate specificity. Full article

The practical aspects of the full regioselective preparation of 2-(tert-butyl)-3-hydroxy-7-2,3-dihydro-1H-pyrrolo[3,4-c]pyridine-1-ones and their derivatives were described. Created in our laboratory, the reaction protocol is simple and occurs under mild conditions. It is important that all obtained products are stable, pure, crystalline and can be easily identified based on spectral data and X-ray analysis results. Key aspects of the reaction course were explained based on the DFT quantum chemical calculations. Full article

Total cross-sections for the single electron impact ionization of deoxyribose (C₅H₁₀O₄), Uridine (C₉H₁₂N₂O₆), Thymidine (C₁₀H₁₄N₂O₅), Cytidine (C₉H₁₃N₃O₅), Adenosine (C₁₀H₁₃N₄O₄), and Guanosine (C₁₀H₁₃N₅O₅) have been calculated using the binary-encounter-Bethe model from the first ionization threshold up to 4 keV. Electronic structure calculations of the studied targets have been performed at the Hartree–Fock (H-F) level using quantum chemical methods, including the outer valence Green function (OVGF) method, in order to obtain all the necessary physical input parameters for the BEB method. The possibility and feasibility of estimating the ionization cross-sections of larger DNA building blocks, such as nucleosides, based on the sum of the ionization cross-sections of DNA bases and simple sugar analogs, such as $\alpha$-tetrahydrofurfuryl alcohol or deoxyribose, are also discussed. Full article

This study presents a quantum chemical investigation of halogen–π interactions involving halogen molecules (F₂, Cl₂, Br₂, and I₂) and a series of π-systems, including benzene, alkenes, and alkynes. Special emphasis is placed on the role of the position of the unsaturated bond (terminal vs. internal) in determining the strength and nature of these interactions. Geometry optimizations and interaction energies were calculated at the wB97X-D3/def2-TZVPP level of theory, with additional validation against CCSD(T)/CBS data. Energy decomposition analysis using SAPT0 and QTAIM analysis were also performed. The results show a clear increase in interaction strength from F₂ to I₂, with interaction energies ranging from −0.47 to −5.61 kcal/mol. The position of the double or triple bond and the local symmetry of the π-system significantly influence interaction energies, with internal and more substituted alkenes and alkynes forming stronger interactions than terminal analogs. SAPT analysis shows that halogen–π interactions are governed by a balance of electrostatic and dispersion contributions, with electrostatics representing the largest attractive term in most cases, whereas dispersion becomes increasingly important for heavier halogens and more extended π-systems and benzene. QTAIM analysis confirms the noncovalent nature of these interactions, with increasing electron density at bond critical points correlating with stronger binding. Full article

Nitrogen-containing molecules are fundamental components of astrobiology and play a key role in planetary environments. These species are particularly important because they may serve as key precursors to prebiotic molecules and contribute to chemical complexity. Reactions involving the highly reactive species methylidyne (CH) play a key role in complex organic formation in astrochemical environments, yet their interactions with nitriles such as acetonitrile (CH₃CN) remain relatively unexplored. In this work, we investigate the reaction network of CH + CH₃CN using high-level quantum-chemical calculations with RRKM and microcanonical transition-state theories to characterize the relative energies of reactants, intermediates, transition states, and products to identify the most favorable reaction pathways. Our results reveal that the most energetically favorable reaction channels proceed via barrierless CH addition to the triple CN bond and three-membered ring opening or CH insertion into a C-H bond, followed by a hydrogen elimination to form acrylonitrile (C₂H₃CN). This route highlights an efficient pathway toward a molecule of astrobiological interest. Acrylonitrile is particularly significant due to its stability and dual functional groups, which enable molecular growth complexity, both in planetary atmospheres and on surfaces, under astrochemical conditions. In addition to acrylonitrile, we identified a few other competing channels leading to an isonitrile species, which emphasizes a previously unexplored aspect of isomerization chemistry in the atmospheric planetary science. These isonitrile products, while less abundant, provide insight to the diversity of nitrogen-containing molecules that may form in environments such as Titan’s atmosphere or the interstellar medium. In these environments, acrylonitrile may serve as a reactive precursor that facilitates cyclization and molecular growth, which enables the formation of nitrogen-containing polycyclic aromatic molecules and N-heterocycles. This, in turn, contributes to the emergence of larger, more complex organic species relevant to prebiotic chemistry and potential origin of life in our solar system. Full article

Understanding the atomic-scale mechanisms of coal pyrolysis is essential for efficient coal utilization and carbon-neutral energy strategies, yet conventional computational approaches often struggle to balance between the high accuracy of quantum-chemical calculations and the efficiency of reactive force fields. To overcome this limitation, we proposed a multiscale computational framework integrating high-throughput density functional theory (DFT) calculations, ReaxFF-based configuration sampling, YARP reaction enumeration, and DPA3-based machine learning potentials (MLPs). Two coal-specific MLPs, DPA3-coal and DPA3-coal@dftb, were constructed and systematically benchmarked on both small molecular systems and larger C20–30 coal fragments extracted from MD simulations. DPA3-coal@dftb model demonstrated significantly improved accuracy over ReaxFF in predicting energies and atomic forces while maintaining good transferability. To balance computational efficiency and accuracy in large-scale simulations, the DPA3-coal model was employed to perform accelerated reactive molecular dynamics simulations of a Solomon-type bituminous coal molecule from 1600 to 2600 K. The simulations revealed temperature-dependent evolution of coke, tar, and gas products, including secondary condensation and deep-cracking processes at elevated temperatures. Higher-level DFT calculations further confirmed the thermodynamic consistency of key reaction pathways involving radical formation, H-transfer, recombination, and CO generation, indicating that coal-specific MLPs provide an effective atomistic tool for investigating mechanistic trends in coal pyrolysis. Full article

Waste vegetable oil-based regenerants (WVO-Rs) are essential for sustainable asphalt pavements; however, their formulation optimization frameworks remain insufficient, and both the component synergy and the multi-component regeneration mechanism remain unclear. In this study, Response Surface Methodology was employed to optimize the WVO-R formulation by jointly considering the multi-temperature performance and interfacial water stability of the regenerated bitumen. Multi-scale performance tests and quantum chemical calculations were conducted to comprehensively evaluate its regeneration effectiveness and thermal behavior and to elucidate the underlying molecular mechanisms. The results indicate that the formulation optimization framework dominated by multi-temperature rheological properties and interfacial water stability exhibits superior engineering applicability compared with traditional methods, and the optimal WVO-R formulation corresponds to a mass ratio of WVO:DBP:CPR:SCA:ATO = 100:23.6:14.4:1.7:1. The WVO-R achieves optimal comprehensive regeneration at a dosage of 6–8%, exhibiting excellent thermal and storage stability along with uniform mixing. At the molecular level, the WVO-R forms a dynamic and stable molecular aggregate structure by integrating inherently stable components, leveraging the bipolar silane coupling agent to regulate critical polarity mismatches of dibutyl phthalate (DBP), and establishing a synergistic interaction network dominated by dispersion forces, supplemented by localized stacking and hydrogen-bonding interactions. On this basis, Oleic acid further depolymerizes aged asphaltene (AAS) aggregates through hydrogen bonding interactions, DBP enhances the reversible deformation capacity of AAS via π–π stacking effects, and the overall WVO-R components reshape the electronic structural characteristics of AAS to levels comparable to virgin asphaltene by smoothing the surface electrostatic potential gradient and suppressing electronic reactivity. Overall, this study establishes a systematic framework for WVO-Rs that integrates formulation optimization, regeneration performance evaluation, thermal behavior analysis, and molecular-level mechanism elucidation, thereby providing solid theoretical support for the efficient design and engineering application of bio-based bitumen regenerants. Full article

Rosa roxburghii is a distinctive medicinal and edible plant resource. In an effort to uncover structurally novel secondary metabolites from this plant and explore their pharmacological potential, a phytochemical investigation of the fresh fruits of R. roxburghii led to the isolation of two new dihydroavicine alkaloids, roxburghcids D (1) and E (2), and a new triterpenoid glycoside, roxburghcid C (6), together with five known compounds (3–5, 7–8). The structures of the new compounds were unambiguously elucidated through extensive spectroscopic analyses (including 1D and 2D NMR and HRESIMS), quantum chemical calculations, and single-crystal X-ray diffraction. In bioassay evaluations, compounds 2 and 3 exhibited significant ABTS radical scavenging activities, with IC₅₀ values of 39.59 and 17.38 μM, respectively. Additionally, compounds 2, 6, and 8 exhibited modest α-glucosidase inhibitory activities, with inhibition rates of 33.13%, 38.61%, and 36.85%, respectively, at a concentration of 100 μM. Furthermore, compounds 2 and 4 showed significant cytotoxicity against the A549 human cancer cell lines, with IC₅₀ values of 7.23 and 8.36 μM, respectively. This study represents the first report of alkaloids isolated from R. roxburghii, enriching its phytochemical profile and providing valuable chemotaxonomic insights for this species. Full article

Background/Objectives: Cardiovascular diseases (CVDs) and cancer remain major global health challenges and are among the leading causes of mortality worldwide, including in Kuwait. Medicinal plants are important sources of bioactive compounds with therapeutic potential. This study aimed to identify the phytochemical constituents of Curcuma longa L. root extract and evaluate their potential cardioprotective and anticancer activities using integrated computational approaches. Methods: Phytochemical profiling of Curcuma longa root extract was performed using gas chromatography–mass spectrometry (GC–MS). The identified compounds were evaluated through molecular docking against selected cardiovascular- and cancer-related targets, including HMG-CoA reductase, phosphoinositide 3-kinase (PI3K), cyclin-dependent kinase 6 (CDK6), and HER2 kinase receptors. Protein–ligand interactions were analyzed to determine binding stability. Biological activity prediction and pharmacokinetic properties were assessed using PASS prediction and SwissADME tools, while density functional theory (DFT) calculations were conducted to investigate electronic and quantum chemical characteristics associated with ligand reactivity. Results: GC–MS analysis identified seventeen phytochemical constituents with retention times ranging from 7.57 to 32.70 min. The major compounds detected were 2-oxo-cyclooctaneacetic acid (30.88%), curlone (20.99%), and tumerone (13.85%). Molecular docking revealed favorable binding affinities for α-curcumene, caryophyllene, bergamotene, cyclohexene derivatives, tumerone, curlone, and (6R,7R)-bisabolone against the selected targets, with interaction profiles comparable to reference drugs. PASS and SwissADME analyses indicated promising biological activities, acceptable drug-likeness, and favorable pharmacokinetic properties. DFT analysis demonstrated that curlone and tumerone possessed stable electronic configurations and favorable reactivity profiles. Conclusions: The findings suggest that bioactive compounds from Curcuma longa may serve as promising lead candidates for the development of cardioprotective and anticancer agents. However, further experimental validation through in vitro and in vivo studies is required to confirm these computational predictions. Full article

Aromatic compounds are abundant in urban and industrial environments and potentially serve as one of the primary precursors for new particle formation (NPF). Pi-pi stacking is a distinctive weak interaction observed between aromatic compounds. Aromatic oxygenated organic molecules (AOOM) are key products of atmospheric oxidation of aromatic compounds; however, the role of pi-pi stacking in their involvement in atmospheric new particle formation (NPF) remains unclear. This study used quantum chemical calculations to reveal the nucleation mechanism of AOOM through pi-pi stacking and hydrogen bonding. The results indicate that the contribution of pi-pi stacking to nucleation in aromatic compounds is primarily determined by the stacking area. For aromatic hydrocarbons with 1–2 phenyl groups, the Gibbs free energy (ΔG) of dimolecular clusters formed solely by pi-pi stacking is positive. In contrast, for polycyclic aromatic hydrocarbons with three or more phenyl groups, the ΔG of these clusters decreases significantly and becomes negative. Single-phenyl AOOM primarily participates in the NPF process through hydrogen bonding with sulfuric acid molecules. In this work, an explanation is provided for observations and laboratory findings of the appearance of aromatic-ring-retaining species in nanoparticles. The discovery of pi-pi stacking also completes the variety of atmospheric nucleation weak interactions. The oxidation and nucleation mechanisms of aromatic compounds should be reassessed, considering the effects of pi-pi stacking, especially polycyclic aromatic hydrocarbons. These findings have important implications for sustainable urban air-quality management. By clarifying the role of pi-pi stacking, particularly in polycyclic aromatic hydrocarbons, this study may improve predictions of new particle formation, refine secondary organic aerosol modeling, and inform targeted emission-control policies to protect public health and mitigate climate impacts. Full article