Atomic Units Research Articles

Localized Boron Sites in Large Pore Borosilicate Zeolite EMM-59 Determined by Electron Crystallography.

The structure of novel large pore borosilicate zeolite EMM-59 (|C19H42N2|8[B5.2Si218.8O448]) with localized framework boron sites was determined by using three-dimensional electron diffraction (3D ED) and scanning transmission electron microscopy (STEM) imaging. EMM-59 was synthesized using 2,2-(cyclopentane-1,1-diyl)bis(N,N-diethyl-N-methylethan-1-aminium) as an organic structure-directing agent (OSDA). The framework has a three-dimensional intersecting channel system delimited by 12 × 10 × 10-ring openings and contains 28 T and 60 oxygen atoms in the asymmetric unit, making it the most complex monoclinic zeolite. The 3D ED data collected from as-made EMM-59 under cryogenic conditions revealed three symmetry-independent locations of the OSDAs, and STEM imaging showed that the OSDAs are flexible and adopt different molecular conformations in channels with identical structural environments. The framework boron atoms were exclusively found in T-sites of 4-rings, especially those shared by multiple 4-rings. The tetrahedral BO4 with the highest boron content (38.6%) was transformed into a trigonal BO3 after the OSDAs were removed upon calcination. Its location and boron content could also be identified by STEM imaging.

Unveiling the Anti-convulsant Potential of Novel Series of 1,2,4-Triazine- 6H-Indolo[2,3-b]quinoline Derivatives: In Silico Molecular Docking, ADMET, DFT, and Molecular Dynamics Exploration.

Epilepsy is a chronic neurological disorder caused by irregular electrical activity in the brain. To manage this disorder effectively, it is imperative to identify potential pharmacological targets and to understand the pathophysiology of epilepsy in depth. This research aimed to identify promising leads from a library of 1,2,4-triazine-6Hindolo[ 2,3-b]quinoline derivatives and optimize them using in silico and dynamic processes. We used computational studies to examine 1,2,4-Triazine-6H-indolo[2,3-b]quinoline derivatives. Some methods were used to strengthen the stability of binding sites, including Docking, ADMET, IFD, MMGBSA, Density Functional Theory (DFT), and Molecular Dynamics. HRSN24 and HRSN34 exhibited promising pharmacokinetic and pharmacodynamic characteristics compared to standard drugs (Carbamazepine and Phenytoin) and a co-crystal ligand (Diazepam). Both HRSN24 and HRSN34 presented notable Glide Xp docking scores (-4.528 and -4.633 Kcal/mol), IFD scores (-702.22 and -700.3 Kcal/mol), and MMGBSA scores (-45.71 and -14.46 Kcal/mol). HRSN24 was selected for molecular dynamics and DFT analysis. During MD, HRSN24 identified LYS21, GLY22, ASP24, ARG26, VAL53, MET55, and SER308 as the most important amino acid residues for hydrophobic interactions. A DFT computation was performed to determine the physicochemical properties of HRSN24, revealing a total energy of -1362.28 atomic units, a HOMO value of -0.20186, and a LUMO value of -0.01915. Based on computational modelling techniques, an array of 1,2,4-triazine-6H-indolo [2,3-b]quinoline derivatives were evaluated for their anti-convulsant properties. A stable compound within the GABAA receptor was identified by HRSN24, suggesting its affinity as an anti-convulsant.

Съвременен атомистичен модел на изкуството. Част трета

The Contemporary Atomistic Model of Art sought represents an ontogenetic process of creation, communication and perception of the artwork in the environment that surrounds us and that is within us. Instead of immutable wholes (holism), we have infinite sets of processes of connection and disconnection, merging and splitting of “nuclei” (atomism) where interactions are clearly visible. Through art, thought of as the porous structure of society with permeable sites of relation, each image and each material form of an artwork is only a connective element with values and other forms that are transferable in society. This is a principle of dynamic connection in which form is a kind of representation and a potential condition of exchange. The in-between zone has been distinguished, bearing its own traditions and recognizing both the connectedness as well as the separate items that are connected. Fluid culture atomism (fluid atomism) is where we observe the dynamics in interactions in an ever-changing structure that is itself made up of separated atomic units briefly grouped into more complex molecular formations, with all the connections between them being impermanent and temporary. Both the internal structures and the state of the whole change. The interactions of individual units are a key factor in the analysis of processes in art. These processes are embedded in perishable, dynamically transforming networks of ‘private’ art worlds, the sum of which is not the Universal World but a momentary state in an ever-changing system. The relationship between the individual artist and the overall system of organized artistic life passes through interactions of a socialpsychological type in organized temporary groups of artists. This article discusses the possible relations between the field of social psychology and art. Emphasis is placed on the aspects of innovative artistic inquiry, discussed as the singular and the unique in art as opposed to the established order. Innovation in art is juxtaposed with innovation in social bonding as a social psychological problem of creativity. Individual creativity is compared to the creativity of groups and the particularities of the creative processes inherent to individual artists. Such an interpretation develops further the idea of an art world seen as impermanent and dynamically changing networks of ‘private’ art worlds. Among the autonomous zones defined by the individual and the group are found shared zones through which polar differences are harmonized. Individual artistic innovation is juxtaposed with innovative practices that are formed through the action of the groups.

Te L-subshell x-ray emission induced by lower energy H2+ ions

The L-shell x-ray emission of tellurium induced by H2+ ions impact is investigated in an energy range of 150–300 keV. The blue shifts of various L-subshell x rays and the enhancement of the relative intensity ratios of Lι, Lβ to Lα x ray are observed and interpreted by the multiple ionization of outer-shell electrons. The new experimental x-ray production cross sections, which almost correspond to those of protons with half of the original energy, are extracted and compared with various theoretical estimations. The correction effects of the united atom approximation and the multiple ionization atomic parameters are compared, and the influence of atomic parameters from different databases on the simulations is discussed. Overall, the ECUSAR-MI calculations using theoretical atomic parameters present the best agreement with the experiment results.

Two-molecule theory of polyethylene liquids.

Two-molecule theory refers to a class of microscopic, self-consistent field theories for the radial distribution function in classical molecular liquids. The version examined here can be considered as one of the very few formally derived closures to the reference interaction site model (RISM) equation. The theory is applied to polyethylene liquids, computing their equilibrium structural and thermodynamic properties at melt densities. The equation for the radial distribution function, which is represented as an average over the accessible states of two molecules in an external field that mimics the effects of the other molecules in the liquid, is computed by Monte Carlo simulation along with the intramolecular structure function. An improved direct sampling algorithm is utilized to speed the equilibration. Polyethylene chains of 24 and 66 united atom CH2 units are studied. The results are compared to full, many-chain molecular dynamics (MD) simulations and self-consistent polymer-RISM (PRISM) theory with the atomic Percus-Yevick (PY) closure under the same conditions. It is shown that the two-molecule theory produces results that are close to those of MD and is thus able to overcome defects of PRISM-PY theory and predict more accurate liquid structure at both short and long ranges. Predictions for the equation of state are also discussed.

Investigation of the influence of the delivery tube position on liquid aluminum atomization

Gas atomization technology is one of the most essential technologies for preparing metal powders. With this process, the liquid metal flowing from the melt delivery tube is atomized through a high-velocity gas sprayed from a nozzle with an angled. In this work, the variation of the position of the melt delivery tube on the pressure at the tip of the delivery tube was investigated, and the effect of mass median diameter, particle size distribution, and yield was experimentally studied and analyzed. A melt atomization unit is used to produce aluminum powders. Three configurations were selected for this study, that is, sag, critical, and prominence positions concerning the outlet hole of the nozzle. Three pressure states (pressurization, atmospheric, and aspiration) were established by varying the relative distance between the delivery tube and the gas outlet orifice-based surface. Experimental studies showed that the yield gradually increased at critical and prominence positions at low pressure and decreased at sag positions, providing significantly lower yields. At higher pressure, yields at critical and prominence positions gradually reduced, with prominence positions at 3 MPa producing powders with smaller average particle sizes and higher yields. Therefore the 3 MPa in the prominence position is best suited for metal atomization using a free-fall configuration.

A comprehensive molecular dynamics simulation of plastic and liquid succinonitrile: Structural, dynamic, and dielectric properties.

Molecular dynamics simulations at constant temperature and pressure were carried out to investigate the structural, dynamical, and dielectric properties of succinonitrile in its plastic and liquid phases at several thermodynamic states. A six-site united atom model was employed with a force field incorporating an intramolecular torsional term that accurately describes gauche and trans conformers. Analysis of the radial distribution function showed that succinonitrile adopts a body-centered cubic arrangement below its melting point, transitioning to a less ordered state in the liquid phase. In addition, examination of alignments between methylene bonds and the diagonals of the simulating cubic box revealed pronounced directional preferences in the plastic phase. The study of conformational states suggested that succinonitrile molecules predominantly adopt gauche conformations, which exhibit longer lifetimes than trans conformers. Spectral density analysis highlighted distinct peaks for different molecular sites, revealing significant differences between gauche and trans conformers. The correlation functions of bending and torsional angles, as well as vectors joining different atoms, illustrated a sensitivity to internal motions, which were notably faster for trans conformers. Differences in decay rates between trans and gauche conformers underscored the influence of gauche-trans transitions. The static dielectric constant, which has been derived from the total dipole moment, was primarily influenced by the contribution of the gauche conformers. In addition, the distance-dependent Kirkwood factor was computed, revealing antiparallel alignment at short distances. Finally, the dielectric relaxation time and the static dielectric constant values were compared with experimental data.

Near‐Infrared‐Emitting Helically Twisted Conjugated Frameworks Consisting of Alternant Donor‐π‐Acceptor Units and Multiple Boron Atoms

AbstractA novel design strategy to construct bright and narrow near‐infrared (NIR) emission materials with suppressed shoulder peaks can significantly enhance their performance in various applications. Herein, we have successfully synthesized a series of helically twisted D‐π‐A conjugated systems bridged by boron atoms, achieving bright red to near‐infrared (NIR) emissions with notably narrow full‐width at half‐maximum (FWHM) values of 35 nm (0.08 eV) and photoluminescence quantum yields (PLQY) up to 80 %. These compounds display red‐shifted emissions up to 753 nm in higher concentrations. Cis/trans configurational isomers of multi‐boron‐bridged molecule BN3 exhibit similar photophysical properties. The unique combination of boron‐induced coordination‐enhanced charge transfer (CE‐CT) and the helically twisted conjugated framework is pivotal in achieving the red‐shifted, narrowband emission. X‐ray crystallographic analysis of BN2 and BN3‐a reveals that the extension of boron‐bridged D‐π‐A skeletons significantly increases the distortion of the skeleton. Systematic theoretical calculations show how the boron CE‐CT mechanism, in conjunction with the helical twist, leads to the narrowing of emission bands while simultaneously red‐shifting them into the NIR region. This work could open new avenues for the development of advanced materials with tailored optical properties, particularly in the challenging and highly sought‐after NIR spectrum.

Basicity-tuned graphitic carbon nitride supported MgO heterogeneous catalysts for efficient transesterification of groundnut oil to biodiesel

Quality and quantity of biodiesel derived from oil depend on the type of feedstock and the transesterification process. To maximize biodiesel production efficiency and ensure the desired fuel quality, it is crucial to develop and optimize feedstock-specific production processes. This study reports on the transesterification of groundnut oil using a heterogeneous catalyst. Magnesium oxide (MgO) and its composites with graphitic carbon nitride (g-C3N4) at 10, 30, and 50 wt% (MG10, MG30, MG50) were used. The composite catalyst combines basic sites from MgO and Lewis acid sites from the nitrogen atoms in the g-C3N4 triazine unit, giving rise to synergistic effects that enhances biodiesel production. MgO nanoparticles were synthesized via precipitation, followed by calcination at 500 °C, and MgO/g-C3N4 composites were prepared by grinding at different ratios. Morphological and structural studies confirmed material characteristics. BET analysis indicated an increased surface area of 71.39 m2/g, enhancing catalytic activity, while SEM revealed the agglomerated g-C3N4 and the cubic morphology of MgO. Response surface methodology was used to optimize catalyst loading, temperature, and reaction time parameters. The optimal conditions for biodiesel conversion using MG50 composite was determined to be methanol/oil ratio of 6:1, 2.5 wt% catalyst loading, 41.7 °C reaction temperature and spanning 52 min of reaction, yielding 94 % efficiency. GC–MS analysis confirmed successful transesterification, identifying key fatty acid esters such as ethyl oleate (34.72 %) and hexadecanoic acid methyl ester (7.69 %). This work supports further research into feedstock-specific catalysts for industrial biodiesel applications.

Detection of lunar water, hydroxyl ion and their diurnal changes from CHACE-2 orbiter observation

This work reports the spatial and diurnal variations of the number densities of lunar molecular water (H2O), atomic mass unit (amu) 18 and hydroxyl (OH), amu 17 over low (0° to 30°), middle (31° to 60°) and high (61° to 80°) latitudinal regions of the lunar exosphere during the pre-sunrise, noon, sunset and midnight periods using the mass spectrometric data of CHandra's Atmospheric Composition Explorer-2 (CHACE-2) on board Chandrayaan-2, the second lunar mission developed in India. Both H2O and OH exhibit, particularly in the low latitude regions, a trend of increasing number density after the sunrise and up to noon, followed by a decrease till sunset. An overall higher density of H2O is obtained compared to the previous reports. The findings are justified in terms of the polar orbital height of the instrument and the duration of data procurement. The maximum number density for the low, middle and high latitudes reaches 5225 cm−3, 5135 cm−3 and 3747 cm−3, respectively. The corresponding OH abundances are found to be 5079 cm−3, 5565 cm−3 and 5720 cm−3. The diurnal variations of H2O and OH and their comparisons, similar to those of the present report may provide suitable means for tracing the lunar water cycle. The CHACE-2 observations imply that the influence of magnetotail passage on volatiles like water is to be further quantified in future missions with other sensors.

Near-Infrared-Emitting Helically Twisted Conjugated Frameworks Consisting of Alternant Donor-π-Acceptor Units and Multiple Boron Atoms.

A novel design strategy to construct bright and narrow near-infrared (NIR) emission materials with suppressed shoulder peaks can significantly enhance their performance in various applications. Herein, we have successfully synthesized a series of helically twisted D-π-A conjugated systems bridged by boron atoms, achieving bright red to near-infrared (NIR) emissions with notably narrow full-width at half-maximum (FWHM) values of 35 nm (0.08 eV) and photoluminescence quantum yields (PLQY) up to 80 %. These compounds display red-shifted emissions up to 753 nm in higher concentrations. Cis/trans configurational isomers of multi-boron-bridged molecule BN3 exhibit similar photophysical properties. The unique combination of boron-induced coordination-enhanced charge transfer (CE-CT) and the helically twisted conjugated framework is pivotal in achieving the red-shifted, narrowband emission. X-ray crystallographic analysis of BN2 and BN3-a reveals that the extension of boron-bridged D-π-A skeletons significantly increases the distortion of the skeleton. Systematic theoretical calculations show how the boron CE-CT mechanism, in conjunction with the helical twist, leads to the narrowing of emission bands while simultaneously red-shifting them into the NIR region. This work could open new avenues for the development of advanced materials with tailored optical properties, particularly in the challenging and highly sought-after NIR spectrum.

Boosting photocatalytic nitrogen fixation performance by adjusting the intramolecular D-A structure and band gap of thiophene-based COFs

Herein, we successfully synthesized two photoactive donor–acceptor (D-A) covalent organic frameworks by incorporating electric-deficient triazine and electric-rich benzotrithiophene moieties into the framework. The introduction of sulfur atom and triazine unit significantly change the intrinsic band gap of JLNU-COFs, this leads to an expanded range of light absorption, encompassing wavelengths from ultraviolet to visible. The narrow band gap of JLNU-311 allows for efficient utilization of visible light while maintaining the thermodynamic activity required for nitrogen reduction within appropriate energy bands. JLNU-311 modified with strong electron absorbing groups has higher activity to NH3 production without co-catalyst or sacrificial agent, and yield can reach 325.6 µmol/g/h. Theoretical calculation further confirm that acceptor structure can effectively regulate the band gap width, promote the adsorption, dissociation and protonation of N2 molecules on JLNU-COFs, and thus reduce the energy barrier of photocatalytic nitrogen reduction reaction (PNRR). Therefore, this study provides an effective strategy for design of active nitrogen fixing photocatalysts.

Development of Air–Ti Gas-Surface Reaction Mechanisms and Rate Calculations

Gas-surface reaction mechanisms and rates were developed for an air–titanium surface to support finite-rate catalytic surface reaction models used in computational fluid dynamics. For the surface dissociation/recombination reactions, a two-step reaction method was applied based on the assumption that two atoms must be positioned in adjacent cells to recombine. Transition state theory was used to calculate the surface reactions for adsorbed diatomic molecules to dissociate to the adjacent unit cell or atoms located in the adjacent cells to recombine into diatomic molecules. For the second step, atoms located in the adjacent cells are allowed to further dissociate to another cell (total separation), or totally separated atoms recombine into the adjacent cells. A stochastic gas-surface kinetics simulation code, STOKIN, was developed to simulate gas-surface reactions and to calculate the equilibrium constants of second molecular dissociation ⇌ recombination processes. Thermodynamic properties of the adsorbates (enthalpies, entropies, and heat capacities) were calculated using density functional theory along with statistical mechanics assuming no rotational and translational contributions to the entropies and heat capacities due to the adsorbates’ inability to freely move or rotate on the surface.

Trp-cage-1,1,1,3,3,3-Hexafluoro-2-propanol-Water Interactions in a Nanosphere at 298 K.

MD simulations of the peptide Trp-cage dissolved in a solvent composed of 28% 1,1,1,3,3,3-hexafluoroisopropanol-water and contained within a nanosphere of 4.2 nm radius are described. To provide a thermal buffer, the nanosphere is submerged in a collection of liquid neopentane molecules, modeled as united atoms. It was found that the HFIP-water mixture demixes when confined under these conditions, with most of the fluoroalcohol becoming strongly associated with the walls of the nanosphere. The remaining HFIP interacts with the peptide and itself in the interior of the nanoshell. Diffusion of HFIP molecules near the surface of the nanoshell is limited, taking place over a small volume, while diffusion of the fluoroalcohol in the center of the nanoshell is more wide-ranging. By contrast, diffusion of the water in the solvent mixture appears to take place equivalently throughout the shell. The conformation of the peptide, distribution of solvent components around it, and the number and duration of the contacts with solvent molecules are calculated and contrasted to results previously reported for the bulk (non-nanocontained) system.

Unraveling the Mechanical Response of Short-Chain Branched Amorphous Polyethylene: Insights from Molecular Dynamics Simulations

The deformation behavior of short-chain branched, amorphous polyethylene (PE) was investigated using united atom molecular dynamics (MD) simulations under uniaxial stretching. Our research reported in this paper examined the internal mechanisms underlying the mechanical response of the PE by analyzing potential energies, dihedral angle distributions, chain orientation and entanglements. The findings indicated that the short-chain branching generally enhanced Young’s modulus, except for sample B60 with a critical ethyl branch content of 60/1000 (60 ethyl branches per 1000 backbone carbons). The Young’s modulus of B60 was the local minimum value in the various samples. Analysis of the evolution of dihedral angles shows that the short-chain branching hinders the transition from gauche to trans configurations, leading to a decrease in the trans population as the branch content increases. Regarding the sample B60 with critical branch content 60/1000, the orientation parameter and entanglement parameter of the molecular chains along the backbone were lowest in the initial structure, and the efficiency of chain disentanglement was at its lowest during deformation. The simulation results elucidated the deformation mechanism related to the conformational evolution of the molecular chains, which can provide atomic-scale insights into the mechanical properties and processability of branched polyethylene, thereby allowing for optimization in its design and application.

Ultrasonic atomization technique for enhancing humidification process in thermal desalination

The need for desalination is expected to evolve, and interests in novel techniques to enhance thermal desalination are developing. Research studies on ultrasonic atomization for desalination application has been observed in the last few years. Hence, this study aims to examine humidification process enhancement using ultrasonic atomization and interaction of atomized droplets with hot air in the humidifier. In the Humidification and Dehumidification (HDH) desalination system examined, the humidifier is equipped with a single ultrasonic atomizer unit which operates continuously with preheated hot air entering the humidifier chamber. The system is investigated for different air flowrates (40 – 100 LPM) and hot air temperatures (40, 50, and 60 °C). The average relative humidity at the humidifier outlet was maximum reaching 94 % for the highest flowrate. The results indicate that increasing hot air temperatures have significant improvement in droplet evaporation which causes higher relative humidity at the outlet, and increasing hot air flowrates have significant impact on the faster response of the humidification process to reach equilibrium.

Effect of deformation ratio of flow-induced crystallization on polyethylene in crystalline behavior, thermal stability, and tensile loading: A molecular dynamics simulation

Since the physical and mechanical properties of semicrystalline polymers strongly depend on crystalline morphology, understanding the correlation between the crystallization kinetics and crystalline structure of polythene is beneficial for their rational processing and applications. In this study, united-atom (UA) molecular dynamics (MD) simulations were employed to elucidate the variations in crystalline structure, phase transition temperatures, and uniaxial tensile deformation among polyethylene (PE) with randomly oriented and flow-induced crystallization (FIC). The results showed that crystallization occurs in areas with low potential energy. For the FIC process, the entanglement parameter and interplanar spacing was less than for randomly oriented crystallization, and the crystallinity was higher. The relationship between the deformation and the crystallinity of PE with randomly oriented crystallization was expressed, which indicates that the crystalline structure promoted elongation at break of PE in tensile deformation. As PE was oriented to crystallize during the FIC process, the polymer stiffness is positively correlated with the deformation ratio of the PE model, so crystal conformation systems with higher deformation ratios produce higher ultimate stresses in tensile loading. From the visualization results, the crystalline phase was stable and does not easily transform into an amorphous phase during tensile loading. Additional results show that the fracture region of PE at tensile fracture tends to develop in the amorphous phase under tensile loading. Energy analysis showed that the elastic and yield regions were mainly dominated by intra-chain bonds, angles, and dihedral motion of PE, whereas interchain nonbonded interactions mainly dominated strain-hardening regions.

(Invited) Thermally Selective Skeletal Rearrangements at Interfaces

Thermal rearrangements, in which an atom, ion or chemical unit of a molecule is rearranged to obtain a structural isomer of the original molecule under a thermal stimulus, represents an excellent alternative to induce the formation of novel antiaromatic PCHs and conjugated polymers not accessible otherwise. Only recently, a few strain-induced rearrangement reactions of precursors that are composed of rigid and strained three dimensional (3D) structures have shown skeletal rearrangements in their backbone after planarization on metal surfaces. In this respect, the selectivity of on-surface chemical reaction pathways is a promising approach to increase synthetic versatility, though remains largely underexplored. In this talk I will review our recent discoveries regarding the exploitation of thermal rearrangements to form 0D, 1D and 2D unique molecular nanocarbons.

Long-Range Configuration Interaction with an Ab Initio Short-Range Correction and an Asymptotic Lower Bound†.

Short-range corrections to long-range selected configuration interaction calculations are derived from perturbation theory considerations and applied to harmonium (with two to six electrons for some low-lying states). No fitting to reference data is used, and the method is applicable to ground and excited states. The formulas derived are rigorous when the physical interaction is approached. In this regime, the second-order expression provides a lower bound to the long-range full configuration interaction energy. A long-range/short-range separation of the interaction between electrons at a distance of the order of one atomic unit provides total energies within chemical accuracy, and, for the systems studied, provide better results than short-range density functional approximations.

Molecular structure refinement based on residual dipolar couplings using magnetic-field rotational sampling.

A method for structure refinement of molecules based on residual dipolar coupling (RDC) data is proposed. It calculates RDC values using magnetic-field rotational sampling of the rotational degrees of freedom of a molecule in conjunction with molecule-internal configurational sampling. By applying rotational sampling, as is occurring in the experiment, leading to observable RDCs, the method stays close to the experiment. It avoids the use of an alignment tensor and, therefore, the assumptions that the overall rotation of the molecule is decoupled from its internal motions and that the molecule is rigid. Two simple molecules, a relatively rigid and a very flexible cyclo-octane molecule with eight aliphatic side chains containing 24 united atoms, serve as so-called "toy model" test systems. The method demonstrates the influence of molecular flexibility, force-field dominance, and the number of RDC restraints available on the outcome of structure refinement based on RDCs. Magnetic-field rotational sampling is basically equivalent but more efficient than explicitly sampling the rotational degrees of freedom of the molecule. In addition, the performance of the method is less dependent on the number NRDC of measured RDC-values available. The restraining forces bias the overall orientation distribution of the molecule correctly. This study suggests that the information content of RDCs with respect to molecular structure is limited.