Analysis Of Density Distribution Research Articles

Investigation of nanoparticles shape that influence the thermal conductivity and viscosity in argon-based nanofluids: A molecular dynamics simulation

The shape of nanoparticles plays an essential role in the thermophysical properties of nanofluids, yet their mechanisms and characteristics remain lacking in comprehensive studies. Molecular dynamics simulations of non-equilibrium molecular dynamics (NEMD) and reversing perturbation non-equilibrium molecular dynamics (RNEMD) calculation methods were used to study thermal conductivity and viscosity of Cu/Au-Argon based nanofluids, taking into account a variety of influencing factors, as well as nanoparticles shape and volume fraction. Through the analysis of the number density distribution, radial distribution function (RDF) and mean square displacement (MSD), the influences of nanoparticles shape (represented by the surface-to-volume ratio) were described and investigated: the highest value was 0.182 WK−1m−1 containing columnar particles of Au at 2% volume fraction, while the thermal conductivity of Cu nanofluids was 0.162 WK−1m−1 under the same conditions; the average values of viscosity had very close values of 2.82 × 10−4 Pa·s (Cu-Ar) and 2.86 × 10−4 Pa·s (Au-Ar) at 1.5% particle volume fraction for nanofluids containing spherical particles, respectively. Simulations of argon-based nanofluids containing five different shapes of Au nanoparticles indicate that the thermal conductivity improves with the growth of the surface-to-volume ratio. And the enhancement of the interfacial nanolayer density turns out to be the main factor that nanoparticles with higher S/V value facilitated the enhancement of the thermal conductivity of argon-based nanofluids. This study enriches the molecular dynamics studies of nanofluids and provides important insights for understanding the effect of nanoparticle's shape on the thermal properties of nanofluids.

Significantly reduced lattice thermal conductivity with anharmonic lattice vibrations and band edge effect in electronic thermal conductivity in Ag2S1-xSex (0 ≤ x ≤ 0.6)

The composition dependence of the unusual behaviors in electronic and lattice thermal conductivity, κele and κlat, in Ag2S1-xSex (x = 0–0.6 in steps of 0.1, 300 K) is investigated in detail by means of precise electron and heat transport properties measurement, synchrotron X-ray crystal structure and electron density distribution analyses, and sound velocity measurement. We reveal that the κele of Ag2S1-xSex is strongly affected by the fine electronic structure of the conduction band edge near the chemical potential and the thermoelectric motive force; therefore, these effects make the κele of Ag2S1-xSe far different from that calculated by the Wiedemann–Franz law, κele = L0σT, with the Lorentz number L0 = π2kB2/(3e2). It is also clearly demonstrated that the κlat of Ag2S1-xSex is greatly reduced by anharmonic lattice vibrations and that the magnitude of κlat is quantitatively reproduced by an equation representing the thermal conductivity under the strongest scattering limit. The κlat decreases with increasing x and saturates at 0.4 W m−1 K−1 at x ≥ 0.4. This is caused by the increasing anharmonic lattice vibrations with x, and its saturating behavior is determined by the strongest scattering limit. On the other hand, a negligibly small κele at x = 0 turns out to be non-trivial at x ≥ 0.4 owing to the increasing carrier density with x, most likely contributed by the increasing interstitial Ag defects. Consequently, the total thermal conductivity of Ag2S1−xSex becomes minimum not at x = 0.5 (composition of the maximum structure entropy) but at x = 0.3.

Antitüberküloz Triptantrin analoglarının elektronik ve topolojik özelliklerinin ve enoil-ACP redüktaz ile etkileşimlerinin in silico yöntemlerle incelenmesi

Objective:
 This study aimed to investigate the structure-antitubercular activity relationships of a series of tryptanthrin analogues and the binding mechanisms of these analogues with InhA, Mycobacterium tuberculosis enoyl-acyl carrier protein (enoyl-ACP) reductase.
 Methods:
 Structure-activity relationships were investigated by using Electronic-Topological Method combined with Neural Networks (ETM-NN). Binding energies and non-covalent interactions stabilizing the ligand-InhA complex were obtained from the results of molecular docking. To assess these interactions, frontier molecular orbital analysis of the ligand-InhA complexes were also analysed. 
 Results: 
 The results of the ETM-NN application to the series of compounds in view are pharmacophoric and anti-pharmacophoric molecular fragments, which are characteristic of the class of compounds demonstrating activity against Mycobacterium tuberculosis strain H37Rv. The statistical characteristics of five pharmacophores (Phi) and five anti-pharmacophores (APhi) entering the forecasting system, are 0.90 and 0.86, correspondingly. Analysis of the electron density distribution has shown that the more effective binding with receptor was observed for active compounds.
 Conclusions: 
 A system of prognosis for the anti-tubercular activity of Mycobacterium tuberculosis H37Rv was developed on the base of the pharmacophores found, docking results, and electronic structure calculations. This prognosis system allows for designing of new potent antitubercular drugs.
 Keywords: Tryptanthrin analogues, mycobacterium tuberculosis H37Rv, InhA electronic-topological method, molecular docking, density functional theory

Ultra-high oxygen evolution potential of CuO5-Zn1 active sites on SnO2(1 1 0) surface and its origin: DFT theoretical study

SnO2 is an anode material with the potential to form a high oxygen evolution potential for organic wastewater treatment. Previous experiments found that CuZn, co-doped with SnO2 surfaces were suspected to form Cu-O-Zn sites with high catalytic activity. By utilising DFT calculations combined with previous experimental results, it was found that CuO5-Zn1 active sites were formed on the (110) surface of CuZn co-doped SnO2 with an oxygen evolution potential of 2.80 V (vs CHE). The electronic density of states, charge density distribution, Bader charge and charge density difference analysis indicated that the formation of ultra-high oxygen evolution potential was caused by the enhanced covalency of Cu-O-Zn. The indirect covalent enhancement between transition metal atoms found on the SnO2 surface means that atomically regulated and controlled catalytic activity can be achieved on the SnO2 surface.

Seismically-induced down-sagging structures in tephra layers (tephra-seismites) preserved in lakes since 17.5 cal ka, Hamilton lowlands, New Zealand

We analysed numerous soft-sediment deformation structures (SSDSs) identified in seven unconsolidated, up to 8-cm thick, siliceous tephra layers that had been deposited in ~35 riverine-phytogenic lakes within the Hamilton lowlands, northern North Island, New Zealand, since 17.5 calendar (cal) ka BP. Based on sediment/tephra descriptions and X-ray computed tomography scanning of cores taken from ten lakes, we classified these SSDSs into elongated load structures (i.e., down-sagging structures) of different dimensions, ranging from millimetre- to decimetre-scale, and centimetre-long dykes. Down-sagging structures were commonly manifested as intrusions of internal tephra beds of very fine to medium sand into underlying organic lake sediments. The tephra layers commonly exhibited an upper silt bed, which was not directly affected by deformation. Dry bulk density and grain size distribution analyses of both the organic lake sediment and the internal tephra beds provided evidence for the deformation mechanism of down-sagging structures and their driving force: the organic lake sediment and the upper silt bed are less liquefiable, whereas the very fine to medium sand internal tephra beds are liquefiable. The tephra layers and encapsulating organic lake sediments formed three-layer (a–b–a) density systems, where ‘a’ denotes the sediment unit of lower density. We infer that downward-directed deformation was favoured by the a–b–a density system with the upper, less-liquefiable, silt bed within the tephra layer preventing upward intrusion during the liquefaction process. The spatial distribution and ages of SSDSs within the lakes provided some evidence that liquefaction of the older tephra layers, i.e., Rerewhakaaitu, Rotorua, and Waiohau tephras, deposited 17.5, 15.6, and 14 cal ka BP, respectively, was triggered by a seismic source to the northeast of the Hamilton lowlands (i.e., Kerepehi and/or Te Puninga faults). In contrast, the liquefaction of the younger tephra layers, i.e., Opepe, Mamaku, and Tuhua tephras, deposited 10.0, 8.0, and 7.6 cal ka BP, respectively, may have been triggered by movement on local faults within the Hamilton lowlands, namely the Hamilton Basin faults, or by distant faulting at the Hikurangi subduction margin east of North Island.

Polarity-extended 8 - Neff rule for semiconducting main-group compounds with the TiNiSi-type of crystal structure.

Application of chemical bonding analysis in position-space techniques based on combined topological analysis of the electron density and electron-localizability indicator distributions has recently led to the formulation of a polarity-extended 8 - Neff rule for consistent inclusion of quantum chemically obtained polar-covalent bonding data into the classical 8 - N scheme for main-group compounds. Previous application of this scheme to semiconducting main-group compounds of the cubic MgAgAs type of structure with 8 valence electrons per formula unit (8 ve per f.u.) has shown a covalent bonding tendency preferring one zinc blende type partial structure over the other one, which seems to corroborate the classical Lewis picture of maximally four covalent bonds per main-group element. In contrast to the MgAgAs type, the orthorhombic TiNiSi type of structure displays a much higher geometrical flexibility to incorporate different kinds of metal atoms. The analysis of polar-covalent bonding in semiconducting 8 ve per f.u. containing main-group compounds AA'E of this structure type reveals a transition to non-Lewis type bonding scenarios of species E with up to ten polar-covalently bonded metal atoms. This kind of situation is consistently included into the extended 8 - Neff type bonding scheme. A systematic increase of partially covalent bonding from chalcogenides E16 to the tetrelides E14 is found, summing up to as much as 2 covalent bonds E14-A and E14-A', and correspondingly remaining 4 lone pair type electrons on species E14. The familiar notion of this structure type consisting of a '[NiSi]'-type framework with 'Ti'-type atoms filling the voids cannot be supported for the compounds investigated.

Exploration of the structural, vibrational, electronic, mechanical and thermal properties of Ru4Al3B2 and Ru9Al3B8: a DFT study.

The structural, dynamical, electro-optical, mechanical, and thermal characteristics of the newly synthesized intermetallic compounds Ru4Al3B2 and Ru9Al3B8 have been studied under ambient and elevated pressure through density functional theory (DFT). The obtained lattice parameters of the compounds are consistent with the experimental values. The metallic character of these compounds is established by the band structure and density of states (DOS). The electronic charge density distribution and bond analysis imply that Ru4Al3B2 and Ru9Al3B8 have mainly both ionic and covalent bonding. The non-negative phonon dispersion frequency of the compounds reaffirms their dynamical stability. Both compounds are tough as well as have high melting points, and hence, can be applied in harsh conditions. Mechanical properties are significantly improved under pressure. Thermal barrier coating (TBC) is a possible field of application for both compounds. The different thermal properties such as the Debye temperature (ΘD), Grüneisen parameter (γ), melting temperature (Tm), minimum thermal conductivity (Kmin) and lattice thermal conductivity (κph) of these compounds have been studied to figure out the suitable application areas in thermally demanding situations. The pressure and temperature dependent bulk modulus (B) and other thermodynamic properties have also been analyzed, which suggested that the present compounds are strong candidates for device applications at high temperature and pressure. Owing to their high optical absorptivity and reflectivity in the UV region, they are also candidates for UV-based applications. Furthermore, they also have applicability in the fields of electronics, aviation, energy storage, and supercapacitor devices for their superior electronic, thermal and mechanical properties.

Investigation of Methyl-5-(pentan-3-yloxy)-7-oxabicyclo[4.1.0]hept-3-ene-3-carboxyhydrazide Derivatives as Potential Inhibitors of COVID-19 Main Protease: DFT and Molecular Docking Study.

The search for effective therapeutics to combat COVID-19 has led to the exploration of the biological activity of numerous compounds. In this study, hydrazones derived from oseltamivir intermediate, methyl 5-(pentan-3-yloxy)-7-oxabicyclo[4.1.0]hept-3-ene-3-carboxylate have been investigated for their potential as drug candidates against the COVID-19 virus using computational methods, including density functional theory (DFT) studies, molecular docking, and absorption, distribution, metabolism, excretion and toxicity (ADMET) analysis. The DFT studies provide information on the electronic properties of the compounds while the molecular docking results using AutoDock reported the binding energies between the main protease of COVID-19 and the compounds. The DFT results revealed that the energy gap of the compounds ranged from 4.32 to 5.82 eV while compound HC had the highest energy gap (5.82 eV) and chemical potential (2.90 eV). The electrophilicity index values of the 11 compounds ranged from 2.49 to 3.86, thus they were classified as strong electrophiles. The molecular electrostatic potential (MESP) revealed electron-rich and electron-deficient regions of the compounds. The docking results reveal that all the compounds had better docking scores than remdesivir and chloroquine, frontline drugs employed in combating COVID-19, with HC having the best docking score of -6.5. The results were visualized using Discovery studio, which revealed hydrogen bonding, pi-alkyl interaction, alkyl interaction, salt bridge interaction, halogen interaction as being responsible for the docking scores. The drug-likeness results showed that the compounds qualify as oral drug candidates as none of them violated Vebers and Lipinski's rule. Thus, they could serve as potential inhibitors of COVID-19.

CO2 hydrogenation to formic acid on Pd-Cu nanoclusters: a DFT study.

Carbon dioxide (CO2) hydrogenation to formic acid is a promising method for the conversion of CO2 to useful organic products. The interaction of CO2 with hydrogen (H2) on PdmCun (m + n = 4, 8 and 13) clusters to form formic acid (HCOOH) has been explored using density functional theoretical (DFT) calculations. Pd2Cu2, Pd4Cu4 and 13-atom Pd12Cu clusters are found to be the most stable among all of the PdmCun (m + n = 4, 8 and 13) clusters with binding energies of -1.75, -2.16 and -2.40 eV per atom, respectively. CO2 molecules get adsorbed on the Pd2Cu2, Pd4Cu4 and Pd12Cu clusters in an inverted V-shaped way with adsorption energies of -0.91, -0.96 and -0.44 eV, respectively. The hydrogenation of CO2 to form formate goes through a unidentate structure that rapidly transforms into the bidentate structure. To determine the transition state structures and minimum energy paths (MEPs) for CO2 hydrogenation to formic acid, the climbing image nudge elastic band (CI-NEB) method has been adopted. The activation barriers for the formation of formic acid from formate on Pd2Cu2 and Pd4Cu4 are calculated to be 0.79 and 0.68 eV, respectively whereas that on the Pd12Cu cluster is 1.77 eV. The enthalpy for the overall process of CO2 hydrogenation to formic acid on the Pd2Cu2, Pd4Cu4 and Pd12Cu clusters are found to be 0.83, 0.48 and 0.63 eV, respectively. Analysis of the density of states (DOS) spectra show that the 4d orbital of Pd, the 3d orbital of Cu, and the 2p orbitals of C and O atoms are involved in the bonding between CO2 molecules and the Pd2Cu2 clusters. The CO2 adsorption on the PdmCun (m + n = 4 and 8) clusters has also been explained in terms of the charge density distribution analysis.

Synthesis of (μ2,η3-allyl-η5-oxapentadienyl)diiron pentacarbonyl complexes, an unusual reaction product from η4-(vinylketene)Fe(CO)3 complexes: structure and electron density distribution analysis.

The synthesis of a series of ferrocenylvinylketenes as stable η4-[Fe(CO)3] complexes (3a-f) was successfully accomplished through the reaction of η2-[Fe(CO)4] complexes under mild carbonylation conditions. The reactivity of 3a-f under thermal conditions afforded the unexpected formation of a novel family of (μ2,η3-allyl-η5-oxapentadienyl)diiron pentacarbonyl complexes 5a-f proposed to be formed by a sequence metathesis-haptotropic rearrangement between the starting η4-vinylketene iron(0) complex 3 and a η4-vinylcarbene iron(0) complex trapped in situ after a reversible carbonylation process favored by the thermal conditions. An electron density distribution analysis (EDD) of 5e using high-resolution X-ray diffraction data in combination with the DFT framework was performed to understand the electronic communication between the two iron fragments.

Electron Density Analysis of Metal–Metal Bonding in a Ni4 Cluster Featuring Ferromagnetic Exchange

We present a combined experimental and theoretical study of the nature of the proposed metal-metal bonding in the tetranuclear cluster Ni4(NPtBu3)4, which features four nickel(I) centers engaged in strong ferromagnetic coupling. High-resolution single-crystal synchrotron X-ray diffraction data collected at 25 K provide an accurate geometrical structure and a multipole model electron density description. Topological analysis of the electron density in the Ni4N4 core using the quantum theory of atoms in molecules clearly identifies the bonding as an eight-membered ring of type [Ni-N-]4 without direct Ni-Ni bonding, and this result is generally corroborated by an analysis of the energy density distribution. In contrast, the calculated bond delocalization index of ∼0.6 between neighboring Ni atoms is larger than what has been found for other bridged metal-metal bonds and implies direct Ni-Ni bonding. Similar support for the presence of direct Ni-Ni bonding is found in the interacting quantum atom approach, an energy decomposition scheme, which suggests the presence of stabilizing Ni-Ni bonding interactions with an exchange-correlation energy contribution approximately 50% of that of the Ni-N interactions. Altogether, while the direct interactions between neighboring Ni centers are too weak and sterically constrained to bear the signature of a topological bond critical point, other continuous measures clearly indicate significant Ni-Ni bonding. These metal-metal bonding interactions likely mediate direct ferromagnetic exchange, giving rise to the high-spin ground state of the molecule.

Theoretical Study of Complexes of Tetravalent Actinides with DOTA

1,4,7,10-Tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid (H4DOTA) is a prominent chelating ligand with potential applications in various fields, from radiotherapy to the separation of fission products. The present study explores the stability, structure, and bonding properties of its complexes with tetravalent actinides (An = Th, U, Np, Pu) using density functional theory and relativistic multireference calculations. Neutral complexes prefer to form symmetric (C4) structures with DOTA. The first coordination sphere of the actinide ions is readily saturated by a weakly bonded H2O ligand. The latter ligand reduces the molecular symmetry while exerting only marginal effects on the properties of the parent complex. An-ligand bonding is mainly electrostatic, but there are also significant charge-transfer contributions from DOTA to the An 6d/5f orbitals. The charge-transfer interactions and the covalent character of bonding increase gradually in the order of Th < U < Np < Pu, as indicated by analysis of the electron density distribution using the Quantum Theory of Atoms in Molecules.

Radical scavenging capacity, UV activity, and molecular docking studies of 2ʹ, 5ʹ, 3, 4-Tetrahydroxychalcone: An insight into the photoprotection

A theoretical evaluation of radical scavenging activity and UV absorbing ability of chalcone named 2ʹ, 5ʹ, 3, 4-Tetrahydroxychalcone has been performed in the gas phase and aqueous media. The DFT-B3LYP/6–311+G (d, p) level of theory was utilized for geometry optimization and the calculation of reaction enthalpies, while the CAM-B3LYP/6–311+G (d, p) level of theory was employed for TDDFT analysis. Three potential working mechanisms of radical scavenging activity, hydrogen atom transfer mechanisms (HAT), stepwise electron transfer proton transfer (SET-PT), and sequential proton loss electron transfer mechanisms (SPLET) were investigated within the gas phase and aqueous phase. The results obtained demonstrate that the HAT will be the probable mechanism in the gas phase whereas SPLET will be in the water medium. Using the same level of theory, explicit surface analysis of the title compound was performed. The compound wave function analysis and molecular docking investigations were also performed in the optimized structure. The theoretical UV spectra were recorded in both the solvents and the compound's electronic absorption spectrum was analyzed using the TD-DFT method. The distribution of hole and electrons in the peaks of maximal oscillator strength corresponds to local excitation within the molecule. The Quantum Theory of Atoms in Molecule (QTAIM) was used to compute the strength of intramolecular hydrogen bonds and non-covalent interactions. The global reactivity parameters and electrostatic potential (ESP) were also included to define the reactivity of the whole molecule. The spin density distribution analysis was come upon to be complementary to the radical scavenging activity. Besides the radical scavenging activity of the compound, it can also be used as a potential UVA filter.

Nanometric Surface-Selective Regulation of Au/In2O3 Nanofibers as an Exhaled H2S Chemiresistor for Periodontitis Diagnosis.

As one of the most prevalent diseases in the world, timely early intervention for periodontitis is a great challenge because the indicator is imperceptible. The exhaled H2S is considered to be a promising biomarker for fast and invasive periodontitis screening; however, the high-performance H2S gas sensor with excellent selectivity and sensitivity which is applicable to the oral cavity remains technically challenging. Herein, a self-assembled monolayer (SAM)-functionalized Au/In2O3 nanofiber (NF) sensor for H2S exhalation analysis was developed to flexibly and effectively modulate the selectivity of the sensor. Through optimizing the specific binding capacity to H2S by systematic adjustment with terminal groups and alkyl chains of SAMs, the sensing performance of the SAM-functionalized Au/In2O3 NF sensor is greatly enhanced. In the optimal (Au/In2O3-MPTES) sensor, the functionalization of the MPTES molecule could achieve significant response enhancement because of the stronger interaction between the sulfhydryl group at the end of the MPTES and H2S. Density functional theory simulation supports the proposed selective sensing mechanism via the analysis of adsorption energy and charge density distribution. The sensor exhibited a high response to H2S (1505.3-10 ppm) at an operating temperature of 100 °C with a low practical detection limit of 10 ppb and 13-145 fold enhanced selectivity. Furthermore, the Au/In2O3-MPTES sensor was successfully applied to distinguish the breath of healthy individuals and patients with severe periodontitis. This study provides novel design insights for the development of highly selective gas sensors for clinical aids in the diagnosis and detection of oral diseases such as periodontitis.

Novel Organotin(IV) Complexes of 2-[4-Hydroxy-3-((2-hydroxyethylimino)methyl)phenylazo]benzoic Acid: Synthesis, Structure, Noncovalent Interactions and In Vitro Antibacterial Activity

Three new organotin(IV) complexes, [Me3Sn(H2L)]2 (1), Bu3Sn(H2L) (2), and [(Bu2Sn(H2L))2O]2 (3) were synthesized by the reaction of 2-[4-hydroxy-3-((2-hydroxyethylimino)methyl)phenylazo]benzoic acid (H3L) with appropriate alkyltin(IV) precursors. The complexes were characterized by elemental analysis, IR, and multinuclear (1H, 13C and 119Sn) NMR spectroscopy. Further, the complex 1 was analyzed by single-crystal X-ray analysis. It displays a 24-membered cyclic dimeric Me3SnIV(H2L) unit where the ligand act as a bridging framework using its carboxylate-O and phenoxy-O atoms. The Sn(IV) adopts distorted trigonal-bipyramidal geometry. In the solution state, the structures were determined by 119Sn-NMR spectroscopy, and the complexes 1 and 2 have distorted tetrahedral geometry, whereas complex 3 shows distorted trigonal-bipyramidal geometry around the tin centres. The Hirshfeld surface analysis and DFT calculations, together with a topological analysis of the electron density distribution in the crystal structure of complex 1, indicate that its molecular packing determined by various noncovalent interactions, including stacking and hydrogen bonding. The antibacterial studies of the ligand and the complexes (1–3) against gram-negative bacteria viz. Klebsiella pneumoniae (A),Vibrio cholerae (M) and Shigella boydii (Q) and gram-positive bacteria viz.Staphylococcus aureus (J), Streptococcus pneumonia (K) are promising and the compounds can be treated as potential common antibacterial materials.

Description of non-covalent interactions in benzyl chalcocyanate crystals from smoothed Cromer–Mann electron density distribution functions

A well-known method to characterize non-covalent interactions consists in the topological analysis of electron density distribution (EDD) functions, complemented by the search for minima in the reduced density gradient (RDG) distributions. Here, we characterize intermolecular interactions occurring in crystals of benzyl chalcocyanate compounds through bond critical points (BCP) of the promolecular electron density (ED) built from the crystallographic Cromer–Mann parameters, at several smoothing levels t. The trajectories formed by the t-dependent BCP locations are interpreted in terms of the intermolecular interactions occurring within the crystal arrangements. Chalcogen…nitro BCPs are clearly present in the unsmoothed EDDs but are annihilated as t increases, while chalcogen…chalcogen BCPs appear and are among the only BCPs left at the highest smoothing level. The chalcogen bonds are differentiated from the other chalcogen interactions through the linear chalcogen…BCP…nitro geometry at low smoothing level and their more negative Laplacian values. The annihilation of CPs can be followed by the apparition of a RDG minimum, associated with a very weak interaction. Along the BCP trajectories, the Laplacian shows a progressive concentration of the ED in the intermolecular space within the crystals and adopts the most negative values at the shortest atom…atom separations. At the termination point of a BCP trajectory, the drastic increase of the ellipticity value illustrates the flattening of the EDD.

Quantitative analysis of intermolecular interactions in crystalline substituted triazoles

This manuscript comprehensively examines four triazole derivatives using Hirshfeld surface and fingerprint analysis, PIXEL energy for molecular pairs, lattice energies for crystal packing, atoms-in-molecules (AIM) topological analysis, and noncovalent interaction (NCI) plots for intermolecular interactions. The fingerprint plots of the Hirshfeld surface analysis provide a quantitative picture of various substituent effects on the noncovalent interactions that contribute to the crystal packing stabilization of these four structures (TN1–TN4). The PIXEL method provides the intermolecular interaction energies for the molecular dimers observed in these structures. The nature and strength of intermolecular interactions at the (3, -1) bond critical point have been studied using the approach of atoms-in-molecules (AIM) via a topological analysis of the electron density distribution. The topology parameters suggested that the intermolecular interactions are classified as closed-shell interactions, and NCI plots were employed to identify the nature of the involved noncovalent interactions. Therefore, a detailed computational analysis renders insights into the electronic characteristics of different noncovalent interactions in the solid state of the structures in the current investigation.

Molecular Dynamics Study of Adsorption Phenomenon of Aromatic Hydrocarbon Ionomer in Catalytic Layer of Polymer Electrolyte Fuel Cell

In response to the current global energy crisis and environmental problems, fuel cells are an optional solution. Among them, polymer electrolyte fuel cell (PEFC) has high expectations because of its low operating temperature and suitability for applications in households and mobility devices. Since PEFC requires the use of proton exchange membranes, the transmission efficiency and durability of the exchange membrane is a major concern. To improve the proton transport efficiency, which is generally required, a catalytic layer is integrated into the PEFC. The catalyst layer of PEFC generally contains platinum catalyst covered with the ionomer membrane. Proton conductivity increases with ionomer thickness, while oxygen permeability decreases with ionomer thickness. Therefore, in order to improve the power generation efficiency of PEFC, it is important to design the catalyst layer. In addition, the fluorinated ionomer membrane material (such as Nafion) used for PEFC has good proton conductivity and chemical stability, but the synthesis cost is relatively high. As a consequence, new materials such as composite materials and non-fluorine-based materials have received a lot of attention in recent years. In this study, we focus on a new ionomer material of aromatic hydrocarbon (named SPP-BP) and elucidate the adsorption state of the ionomer on the platinum surface on a nanoscale using molecular dynamics (MD) simulations. Then, the structural properties and water diffusion characteristics of the ionomers of new material (SPP-BP) and conventional Nafion were analyzed based on the MD simulation results.The degree of polymerization (m, p, s) of the monomers were given as 20, 5, and 23 (molecular weight 7.38 kDa), respectively, based on the reported experimental values of SPP-BP. For the polymer composition, molecular models of a random type (r-type), which shows a randomness of monomers, were used. A molecular model of Nafion was also created as the conventional fluorinated membrane materials for comparison with the SPP-BP. The platinum surface was built with a three layers of platinum atoms in a face-centered cubic lattice structure. Regarding the calculation potentials, the DREIDING forcefield was used for the interactions with the molecules. While for the intermolecular potential, the Spohr potential was used for Pt-H2O and Pt-H3O+ interactions, and the others were applied with the Lennard Jones (LJ). The parameters of those potentials were based on the previous studies.In the ionomer membrane, water content is an important indicator that affects the transfer of protons and substances. Based on the water absorption results obtained in the experiment, the water content of SPP-BP was calculated to be between 1.8 and 7.2. Therefore, the water content during the MD simulation was used 3, 5, and 7. The computational size was 55.5 Å × 52.9 Å in the transverse direction of the ionomer membrane (X and Y directions), and the thickness of the membrane adsorbed on the platinum surface was about 50-60 Å. A vacuum region of about 40 Å was set at the top of the system. To calculate the diffusion coefficient and the cluster character of water, multiple simulations with different initial structure were considered. Furthermore, in order to compare to the Nafion, the number of polymers and the computational size was adjusted for containing the same water content.Based on the simulation results, the density distribution of water, hydrophilic sulfo groups, and main body of polymer was analyzed. By the analysis of density distribution, the structure of the ionomer at the interface-vacuum, near the Pt surface and inside was studied. In addition, the orientation of the sulfo group of SPP-BP and Nafion near the Pt surface was analyzed. Besides, the water cluster characteristics and water diffusion properties of the ionomers of SPP-BP and Nafion were also investigated.Acknowledgements: This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan through the fund for ECCEED'30 Projects (No. JPNP20003). Numerical simulations were performed on the Supercomputer system "AFI-NITY" at the Advanced Fluid Information Research Center, Institute of Fluid Science, Tohoku University.

On the impact of nanoscale γ’’ precipitates on the Bauschinger effect in single- and polycrystal Ni-base superalloy 718

Tension compression experiments were performed on Ni-base superalloy 718 single and polycrystals to investigate the effects of nanoscale γ’’ precipitates on cyclic deformation behavior and in particular the Bauschinger effect. γ’’ precipitates led to a more pronounced Bauschinger effect in the single crystal, but to a less pronounced one in the polycrystal. A potential mechanism is suggested to explain variations in the Bauschinger effect based on the analysis of slip traces and dislocation density distribution during cyclic deformation. It was found that an increasing amount of γ’’ precipitates promotes the activation of additional slip systems. In the single crystal, this leads to latent kinematic hardening and the formation of a substructure with local deformation gradients. The resulting increase in long-range and slip system-related back stresses is believed to be responsible for the increase in Bauschinger effect. In polycrystals, by contrast, the activation of additional slip systems leads to a more homogeneous deformation behavior and a reduction of back stresses at grain boundaries. Macroscopically, this results in a reduction of Bauschinger effect with increasing γ’’ precipitation amount.

Binuclear metal ruthenium complexes bridged by isomeric bis(ethynyl)pyridine: Syntheses, characterization and electronic coupling properties

Isomeric diruthenium complexes with bis(ethynyl)pyridine as bridge core [2,6-bis(ethynyl)pyridine (1), 3,5-bis(ethynyl)pyridine (2), 2,5-bis(ethynyl)pyridine (3)] were successfully prepared and characterized by 1H NMR, 13C NMR and elemental analysis. The electrochemical properties of complexes 1–3 were investigated by cyclic voltammetry (CV) and square-wave voltammetry (SWV), and different potential difference values were revealed and affected by N atom position and distance between redox metal centers. Electron absorption spectra showed that the absorption of the linear molecule 3 displayed a red shift relative to that of complexes 1 and 2. The broad near-infrared absorption characteristic of the singly-oxidized complex 3+ revealed the existence of a mixed-valence state, which can be classified as a class II mixed-valence system according to the intervalence charge transfer (IVCT) absorption parameter Hab and Г. These results indicated that 3 has higher conjugation and charge delocalization ability than isomers 1 and 2. Density functional theory (DFT) calculations spin density distribution analysis further confirmed the above results, and time-dependent DFT showed the NIR multi-absorption of complex 3+, and effectively attributed to Ru–CC→Ru IVCT absorption characteristics.