Search Results (139)

Fulgides are a class of organic compounds that exhibit photochromic behavior in both the solid state and in solution. These compounds have attracted considerable research interest due to their wide range of potential applications, including photochromic eyewear, smart windows, optical switches, data storage, and chemical and biological sensors. Here, we report the synthesis and crystal structures of fulgides bearing four different para-substituents on the phenyl moiety. All four molecules crystallize in space groups containing an inversion center. The distances between the two carbon atoms that would form the single C–C bond in the cyclized products fall within the range of 3.301–3.475 Å. The observed structural variations are attributed to intermolecular interactions based on Hirshfeld surface analysis. The fulgides exhibit photochromism, but they are not expected to display ferroelectric behavior due to their crystallization in centrosymmetric space groups. Full article

The fast settling rate of solid particles in the CO₂ fracturing fluid is a serious obstacle to ensuring the smooth progress of reservoir stimulation during conventional energy extraction, exerting a critical influence on enhancing both transformation efficiency and crude oil recovery. In this study, a fluid–solid coupling numerical model was developed, incorporating reservoir conditions and fluid properties, to simulate the settling behavior of solid particles in geological reservoir fluids. In addition, the effects of various geological factors and fluid parameters on particle settling were systematically examined. Furthermore, molecular dynamics theory, together with the analysis of intermolecular bonding interactions, was employed to elucidate the underlying mechanisms governing particle settling under different conditions. The findings of this study have the potential conclusion that the numerical model constructed in this study showed a high degree of fit (98.7%) with the experimental data, demonstrating the high applicability and good match of the numerical model. Furthermore, CO₂ viscosity is a significant factor influencing the differential settling of particles in reservoir fluids, and CO₂ fracturing fluid at 8 mPa·s can reduce the settling distance and velocity of solid particles to 3.2 m and 0.21 m/s, respectively. Simultaneously, both high reservoir pressure and a rough surface can effectively suppress the settling behavior of solid particles in CO₂ fracturing fluid, reducing the settling distance to 3.4 cm and 3.8 cm, respectively. However, the utilisation of high-temperature reservoirs at 383 K has been demonstrated to reduce the particle settling distance to 3.5 cm, a phenomenon that is evidently not conducive to the stimulation of deep, high-temperature reservoirs. The findings of this research endeavour have the potential to provide fundamental data for the utilisation of CO₂ fracturing fluids in reservoir stimulation and EOR. Full article

The miscible process of virgin and aged asphalt in rejuvenated asphalt was studied by molecular dynamics (MD) simulation. In this paper, we used MD software to establish a molecular model of asphalt, and the model of aged asphalt was established by adding ketone and sulfoxide functional groups to the original asphalt. Wood tar rejuvenator (WTR) was selected for rejuvenation of aged asphalt, and parameters such as density, surface free energy, cohesion energy density, and Young’s modulus were used to verify the molecular model. The density, relative concentration, interaction energy, mean square displacement of molecules, diffusion coefficient, mixing free energy, and radial distribution function were used to analyze the action mechanism of the rejuvenator in the rejuvenation process and the suitable service temperature and optimal amount of WTR. The results demonstrated that the WTR with 373 K and 15% mass ratio has the best rejuvenation effect on aged asphalt. The addition of WTR can increase the interaction energy between original and aged asphalt by 12.9%, reduce the Van der Waals potential energy of aged asphalt by 13.85%, and thus ensure the uniform distribution of internal molecules in rejuvenated asphalt. A 15 wt% WTR can reduce the intermolecular distance of asphaltenes from 9.4 Å to 5.2 Å, thereby alleviating the displacement effect during the asphalt aging process. The diffusion coefficients of WT-rejuvenated asphalt at 298 K and 373 K are 28.6% and 44.6% higher than those of extracted oil-rejuvenated asphalt, respectively; thus, WT-rejuvenated asphalt has better crack resistance. Full article

We have theoretically examined the intermolecular interactions in the cationic states of π-stacked dimers of 4nπ antiaromatic molecules. The ground state of face-to-face π-dimer models, consisting of cyclobutadienes (CBDs), was analyzed as a function of the stacking distance (d) for their monocationic and dicationic states using multi-reference second-order perturbation theory. Multi-configurational wavefunction analysis in a diabatic representation was employed to understand the electronic structures of the dimer models in terms of the monomer electron configurations. It is found that the monocationic dimer exhibits a local minimum at about d = 2.4 Å in the ground state, where each monomer is represented by a superposition between neutral triplet and cationic doublet electron configurations. Crossing of the ground and excited states occurs through changing d, which is due to the small energy gap between the highest occupied and lowest unoccupied molecular orbitals of antiaromatic molecules. Full article

The aging of SBS-modified asphalt (SBSMA) is a kinetic process that significantly deteriorates pavement performance and shortens service life. Although previous studies have explored the evolution of SBSMA during aging, the underlying kinetic mechanisms remain unclear. In this study, SBSMA samples were subjected to varying degrees of aging to simulate the kinetic aging process. Changes in four components and chemical functional groups were characterized, supporting the construction of molecular models at different aging stages. Molecular dynamics simulations indicate that the oxidation rate of SBSMA and degradation rate of SBS molecular chains are significantly higher in the initial aging stage than later, leading to a pronounced increase in cohesive energy density and solubility parameters, along with a decrease in surface free energy, fractional free volume, and binding energies, predominantly occurring during the first aging stage. Aging also shortens intermolecular distance between asphaltene molecules while increasing the distances between asphaltene–resin and asphaltene–SBS. The adsorption competition between asphaltene and SBS for lightweight components intensifies initially, whereas asphaltene exhibits stronger adsorption in the later aging stage. Furthermore, the diffusion coefficients of asphaltene and SBS increase rapidly initially then slow, causing a corresponding rapid initial decline followed by decrease in resin, aromatic, and saturate components. Full article

The control of crystal form in chiral active pharmaceutical ingredients (APIs) is a critical challenge in pharmaceutical development, as differences in solid-state structure can significantly influence physical properties and manufacturing performance. Troglitazone, a molecule with two chiral centers, exists as four stereoisomers (RR, SS, RS, SR) that crystallize as two enantiomeric pairs: RR/SS and RS/SR. This study aims to elucidate the relationship between solution-state molecular interactions and crystallization behavior of these diastereomeric pairs. Antisolvent crystallization experiments were conducted for both mixed solutions containing all four isomers and solutions of individual pairs. Crystallization kinetics were monitored by HPLC, and the resulting solids were characterized by PXRD, DSC, TG, and microscopic observation. Nucleation induction times were determined over a range of supersaturation levels. To probe intermolecular interactions in solution, NOESY and targeted NOE NMR experiments were performed, and the results were compared with crystallographic data. The RS/SR crystals(H-form) consistently exhibited shorter induction times and faster crystallization rates than the RR/SS crystals (L-form), even under conditions where RR/SS solutions were more supersaturated. In mixed solutions, H-form crystallized preferentially, with L-form either remaining in solution or being incorporated into H-form crystals as a solid solution. NOESY and NOE analyses revealed intermolecular proximities between protons that are distant in the molecular structure, indicating the presence of ordered aggregates in solution. These aggregates were more structurally compatible with the H-form than with the L-form crystal lattice, as supported by crystallographic distance analysis. The results demonstrate that differences in nucleation kinetics between troglitazone diastereomers are closely linked to solution-state molecular arrangements. Understanding these relationships provides a molecular-level basis for the rational design of selective crystallization processes for chiral APIs. Full article

Solid solutions of the metallocenes ferrocene (Cp₂Fe), nickelocene (Cp₂Ni), and cobaltocene (Cp₂Co) have been prepared by manually grinding the components together, or by co-crystallizing them from solution. In the solid solutions Cp₂Fe/Cp₂Ni and Cp₂Co/Cp₂Ni, the cyclopentadienyl (Cp) protons relax via dipolar electron–proton interactions, which represent the dominant relaxation mechanism. The ¹H T₁ relaxation times of the molecules Cp₂Ni and Cp₂Co, dissolved in CDCl₃, and in the solid solutions, show that the relaxation takes place intramolecularly. The relaxation of the protons is propagated exclusively via the unpaired electrons of the metal centers to which their Cp rings are coordinated, due to the large intermolecular distances that are greater than 3.91 Å. In contrast, the intramolecular distances between the electrons of the metal atoms and the protons of their coordinated Cp rings are merely 2.70 Å. Using these intramolecular distances and the ¹H T₁ relaxation times, the electron relaxation times T_1e have been determined as 17 × 10⁻¹³ s in CDCl₃ solutions and 45 × 10⁻¹³ s in the solid state for Cp₂Ni. The corresponding T_1e times for Cp₂Co are calculated as ca. 5 × 10⁻¹³ s and 20 × 10⁻¹³ s. Grinding Cp₂Fe and Cp₂Ni together leads to two different ¹H T₁ relaxation times for the protons of Cp₂Fe. The longer T₁ relaxation time indicates domains that consist mostly of Cp₂Fe molecules. The short T₁ times show a close contact of Cp₂Fe and Cp₂Ni molecules. An analysis of the short ¹H T₁ times reveals the presence of at least two to three short distances of 3.91 Å between Cp₂Fe and Cp₂Ni molecules. These results support the hypothesis that dry grinding of the metallocenes Cp₂Fe and Cp₂Ni in ratios that were changed in 10% increments from 90%/10% to 30%/70% leads to domains that mostly consist of Cp₂Fe molecules, and additionally to domains that contain a mixture of the components on the molecular level. Full article

A centrosymmetric dinuclear complex, [Dy₂(H₂dapp)₂(μ-OH)₂(H₂O)₂]·4TCNQ·2CH₃OH, was synthesized using the TCNQ^·− radical anion (TCNQ = 7,7,8,8-tetracyanoquino-dimethane) and pentadentate nitrogen-containing Schiff base ligand (H₂dapp = 2,6-diacetylpyridine)-bis(2-pyridylhydrazone). In the Dy₂ dimer, the two Dy^III ions adopt eight-coordinated geometries intermediate between D_4d and D_2d symmetries, linked by two OH⁻ groups, with ferromagnetic Dy-Dy interactions. The TCNQ^·− radical anions are uncoordinated, and they pack tightly into antiparamagnetic dimers to balance the system charge. Under zero field, weak magnetic relaxation was observed, with an approximate Δ_eff = 2.82 K and τ₀ = 6.88 × 10⁻⁶ s. This might be attributed to the short intermolecular Dy···Dy distance of 7.97 Å, which could enhance intermolecular dipolar interactions and quantum tunneling of magnetization (QTM). Full article

N′-Phenylbenzohydrazides are valuable precursors for air- and moisture-stable Blatter radicals, with applications in magnetism and spintronics. This study presents the single-crystal X-ray structures of N′-(4-methyl-2-nitrophenyl)benzohydrazide (I) and N′-(2-nitro-(4-trifluoromethyl)phenyl)benzohydrazide (II), highlighting the influence of substituents on supramolecular arrangement. Compounds I and II are found to crystallize within the monoclinic crystal system, with the space groups I2/a and P2₁/n, respectively, with centrosymmetric, one-dimensional columnar packing driven by π-π stacking. In I, π-π dimers form between benzoyl rings (3.018 Å), with additional stacking between aryls (3.408 Å) of neighboring dimers. In II, alternating benzoyl and aryl rings stack with interplanar distances of 2.681 and 2.713 Å. Bifurcated intra- and intermolecular hydrogen bonds (1.938–2.478 Å) further stabilize the packing. Compound II exhibits inter-stack F···F contacts (2.924 Å), attributed to steric effects. The trifluoromethyl group enhances N′NCO-NO₂ conjugation, resulting in a near-parallel arrangement of aromatic rings and planar geometry at the N′ nitrogen. In contrast, compound I shows reduced conjugation, leading to pyramidalization at the N′ nitrogen and increased hydrazide bond flexibility, as seen in the 56° angle between aromatic rings. Full article

The contamination of drinking water by per- and polyfluoroalkyl substances (PFASs) presents a global concern due to their extreme persistence, driven by strong C–F bonds. This study investigated the potential of graphene as a filtration material for PFAS removal, focusing on six key compounds regulated by the U.S. EPA: PFOA, PFNA, GenX, PFBS, PFOS, and PFHxS. Using molecular simulations, adsorption energy, diffusion coefficients, and PFAS-to-graphene distances were analyzed. The results showed that adsorption strength increased with molecular weight; PFOS (500 g/mol) exhibited the strongest adsorption (−171 kcal/mol). Compounds with sulfonic acid head groups (e.g., PFOS) had stronger interactions than those with carboxylate groups (e.g., PFNA), highlighting the importance of head group chemistry. Shorter graphene-to-PFAS distances also aligned with higher adsorption energies. PFOS, for example, had the shortest distance at 8.23 Å (head) and 6.15 Å (tail) from graphene. Diffusion coefficients decreased with increasing molecular weight and carbon chain length, with lower molecules like PFBS (four carbon atoms) diffusing more rapidly than heavier ones like PFOS and PFNA. Interestingly, graphene enhanced PFAS mobility in water, likely by disrupting the water structure and lowering intermolecular resistance. These results highlight graphene’s promise as a high-performance material for PFAS removal and future water purification technologies. Full article

A tetradentate Pt(II) complex with a 5/6/6 structural backbone, Pt(PhPiPy-O-PytmCz), was synthesized by incorporating two distinct cycloalkyl groups. These structural modifications significantly enhanced the photoluminescence quantum yield and effectively increased the distance between molecules, thereby mitigating undesirable intermolecular interactions and triplet-state quenching. This strategic molecular design resulted in an external quantum efficiency of 11.5% at a wavelength of 539 nm and significantly enhanced operational lifetimes in green phosphorescent organic light-emitting diodes (OLEDs). These findings are expected to inspire the development of new green luminescent materials and innovative strategies in OLED technology. Full article

n-Octanol and related ether alcohols are studied via molecular dynamics (MD) simulations using the two classical all-atom force fields OPLS-AA and CHARMM. The ether alcohols studied possess one ether functionality separated by varying n carbon atoms from the hydroxy group to elucidate how the positioning of the ether functionality affects intra- and intermolecular hydrogen bonding and, in turn, the physical properties of the studied alcohols. Important general trends observed from simulations with both force fields include the following: Intramolecular hydrogen bonding is majorly present in 3-butoxypropanol and 4-propoxybutanol (n = 3 and 4) while being only marginally present for 5-ethoxypentanol and 6-methoxyhexanol (n = 5 and 6) and absent in 1-hexyloxymethanol and 2-pentyloxyethanol (n = 1 and 2). The intramolecular hydrogen bonds formed by 3-butoxypropanol and 4-propoxybutanol are among the most stable ones of all present hydrogen bonds. Intermolecular hydrogen bonding is stronger between hydroxy groups (OH-OH) than between hydroxy and ether groups (OH-OE). An increased temperature causes a reduction in intermolecular OH-OH and OH-OE hydrogen bonding but a slight increase in intramolecular hydrogen bonding. A reduction in end-to-end distances at a higher temperature is also observed for all studied alcohols, which is likely a reflection of increased dihedral bond rotations. Hydrogen bonding extends mostly between just two molecules while hydrogen bonding networks are rare but do exist, involving, in some instances, up to 30 hydrogen bonds. Regardless of force field and temperature, the obtained radial distribution functions (RDFs) mostly show the same features at same distances that only vary in their intensity. 1-hexyloxymethanol forms a very specific and stable intermolecular double OH-OE hydrogen-bonded dimer. Similar double-hydrogen-bonded dimers can be found for the ether alcohols but are only significantly present for 2-pentyloxyethanol. Overall, the main difference between OPLS-AA and CHARMM is their quantitative prediction of the present hydrogen bonding speciation largely due to the stiffer dihedral potentials in OPLS-AA compared to the CHARMM force field. The simulations indicate that (a) the variations in densities are correlated to the reduced packing efficiency caused by intramolecular hydrogen bonding, (b) self-diffusion correlates with the stability of the intermolecular hydrogen bonds, and (c) the presence of hydrogen-bonded networks, although small in numbers, affect the viscosity. Full article

The London dispersive and polar surface properties of solid materials are very important in many chemical processes, such as adsorption, coatings, catalysis, colloids, and mechanical engineering. One of the materials, a styrene–divinylbenzene copolymer modified with 5-hydroxy-6-methyluracil at different percentages, has not been deeply characterized in the literature, and it isparticularly crucial to determine its London dispersive and polar properties. Recent research in the inverse gas chromatography (IGC) technique allowed a full determination of the surface properties of a styrene–divinylbenzene copolymer modified with 5-hydroxy-6-methyluracil by using well-known polar and non-polar organic solvents and varying the temperature. Applying the IGC technique at infinite dilution resulted in the retention volume of adsorbed molecules on styrene–divinylbenzene copolymer modified with 5-hydroxy-6-methyluracil at different percentages, using the Hamieh thermal model and our recent results on the separation of the two polar and dispersive contributions to the free energy of interaction. The surface properties of these materials, such as the surface free energy of adsorption, the polar acid and base surface energy, and the Lewis acid–base parameters, were obtained as a function of temperature and for different percentages of 5-hydroxy-6-methyluracil. The obtained results proved that the polar free energy of adsorption on styrene–divinylbenzene copolymer increased when the percentage of 5-hydroxy-6-methyluracil (HMU) increased. However, a decrease in the London dispersive surface energy of the copolymer was observed for higher percentages of 5-hydroxy-6-methyluracil. A Lewis amphoteric character was shown for the copolymer with the highest acidity, while the basicity linearly increased when the percentage of HMU increased. Full article

This work reports the quasi-atomic orbital analysis of the XC(NO₂)₃ (X=F, Cl, Br, and I) compounds and shows that the interactions between the C-N σ bonds and the lone electron pairs on the halogen atom and oxygen atoms of the nitro groups may contribute to the unusually short C-X distances observed. While the presence of a σ-hole on the halogen atom of the XC(NO₂)₃ compound may not be obvious from the electron density distribution, an analysis of the intermolecular forces of the NH₃--XC(NO₂)₃ complexes suggests a σ -hole interaction between the nitrogen lone pair and halogen atom X (X=Cl, Br, and I) in the linear N--X-C configuration, where electrostatics and exchange forces dominate. The linear N--X-C bond in these systems is shown to have a noticeable covalent character, which is captured in the polarization energy term. Complexation with the ammonia nucleophile is shown to affect the electronic structure of the entire compounds, notably the oxygen/halogen lone electron pairs interactions with the C-N σ bonds. Full article

Bio-hybrid fuels, chemically derived from sustainable raw materials and green energies, offer significant potential to reduce carbon dioxide emissions in the transport sector. However, when these fuels are used as drop-in replacements in internal combustion engines, material compatibility with common sealing materials is not always given. Within the cluster of excellence, “The Fuel Science Center (FSC)” at RWTH Aachen, experimental immersion tests were conducted on a limited set of fuel and sealing material combinations. Given the extensive range of possible fuel and sealing combinations, a data-based machine learning prediction framework was developed and validated to pre-select promising fuel candidates. Due to the limited number of samples, preliminary results indicate a need to expand the database. Since experimental investigations are time-consuming and costly, this work explores faster physics-motivated data generation approaches by modeling molecular interactions between fuel and sealing materials. Two modeling scales are employed. One calculates the intermolecular distance using density functional theory. The other uses Hansen solubility parameters, representing an abstract modeling of intermolecular forces. Both approaches are compared, and their limitations are assessed. Including the generated data in the prediction framework improves its accuracy. Full article