Thermo-mechanical properties of cubic titanium nitride

The equilibrium structure, elastic constants C_ij and thermodynamic functions of cubic titanium nitride (TiN) were calculated within the temperature range of 0–3100 K and under a pressure range 0–60 GPa. Properties were computed using the generalised gradient approximations (GGA) exchange-correlation functional. Calculated mechanical properties (Elastic constants, Young’s modulus and shear modulus) and phonon spectra of TiN obtained via robust DFT-QHA algorithm, were generally in a good agreement with available experimental and theoretical analogous values. In particular, a well-examined quasi-harmonic approximation method implemented in the Gibbs2 code is utilised herein to provide accurate estimation of thermal expansion coefficients, entropies, heat capacity values (at different combinations of temperature/volume/pressure) and Debye’s temperature. Parameters calculated herein shall be useful to elucidate the superior performance of TiN at harsh operational conditions encompassing elevated temperatures and pressures pertinent to cutting machineries and surface coatings.     

Lipophilic 1,4-naphthoquinone derivatives: synthesis and redox properties in solution and entrapped in the aqueous cubic liquid-crystalline phase of monoolein

1,4-Naphthoquinone derivatives (NQD) containing lipophilic alkyl chains, i.e. 2-((Z)-heptadec-8-enyl)-3-methyl 1,4-naphthoquinone (QMe), 2-((Z)-heptadec-8-enyl)-3-hydroxy-1,4-naphthoquinone (QOH) and (Z)-octadec-9-enyl 1,4-naphthoquinone-2-carboxylate (QE) were synthesized. The redox behavior of these NQD was studied in ethanol and entrapped in the reversed bicontinuous cubic phase of space group type Pn3m (Q²²⁴) of aqueous monoolein. In ethanol, cyclic voltammetry curves exhibit two pairs of oxidation-reduction peaks arising from the redox processes controlled by adsorption and molecular diffusion. The NQD molecules are also electrochemically active in the cubic phase, indicating the participation in the 2e⁻, 2H⁺-redox cycle at pH < 9. Therefore, it was concluded that the head group of the entrapped NQD reaches the lipid bilayer interface of cubic phase during the process.     

Physicochemical properties, binary and ternary phase diagrams of ketoprofen

Compared to simulated moving bed (SMB) chromatography, fractional crystallization is a simple and economical method for enantioseparation. Therefore, the coupling of SMB chromatography and fractional crystallization is suggested for enantioseparation of racemic compounds. In this work, a nonsteroidal antiinflammatory drug, ketoprofen (Kp), was chosen to be studied. Kp was verified as a racemic compound by FTIR, PXRD, and thermodynamic calculations. To derive the condition where pure (S)-Kp could be crystallized from a solution, which was previously enantiomerically enriched, the binary melting phase diagram and the ternary solubility phase diagram in the mixed solvent of ethanol and water over a temperature range of 15-30 degrees C were obtained. From these phase diagrams the eutectic point was determined as 91.6% mole percent (S)-Kp from the binary phase diagram and 91% from the ternary phase diagram. The results may provide valuable experiment data for the possibility of coupling fractional crystallization with SMB for Kp separation.     

Effect of phospholipids and a transmembrane peptide on the stability of the cubic phase of monoolein: implication for protein crystallization from a cubic phase

The cubic phase of monoolein has successfully been used for crystallization of a number of membrane proteins. However, the mechanism of protein crystallization in the cubic phase is still unknown. It was hypothesized, that crystallization occurs at locally formed patches of bilayers. To get insight into the stability of the cubic phase, we investigated the effect of different phospholipids and a model transmembrane peptide on the lipid organization in mixed monoolein systems. Deuterium-labeled 1-oleoyl-rac-[(2)H(5)]-glycerol was used as a selective probe for (2)H NMR. The phase behavior of the phospholipids was followed by (31)P NMR. Upon incorporation of phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, or phosphatidic acid, the cubic phase of monoolein transformed into the L(alpha) or H(II) phase depending on the phase preference of the phospholipid and its concentration. The ability of phospholipids to destabilize the cubic phase was found to be dependent on the phospholipid packing properties. Electrostatic repulsion facilitated the cubic-to-L(alpha) transition. Incorporation of the transmembrane peptide KALP31 induced formation of the L(alpha) phase with tightly packed lipid molecules. In all cases when phase separation occurs, monoolein and phospholipid participate in both phases. The implications of these findings for protein crystallization are discussed.     

Stable cubic phases in codispersions of glucocerebroside and palmitoyloleoylphosphatidylethanolamine

The effect of glucocerebroside (GlcCer) on the structure and thermotropic phase behavior of aqueous dispersions of palmitoyloleoylphosphatidylethanolamine (POPE) has been examined using simultaneous small-angle and wide-angle X-ray diffraction methods. Binary mixtures of GlcCer:POPE in molar ratios of 2:100, 5:100, 10:100, 20:100, 30:100, and 40:100 were examined in the temperature range 20-90 degrees C. Cubic phase has been observed in binary mixtures comprised of molar ratios greater than 5:100 in the temperature range of 60-90 degrees C upon heating at a rate of 2 degrees C/min. The cubic phase is relatively stable and coexists with inverted hexagonal or lamellar phases. It persists in the codispersions throughout subsequent cooling scans to 30 degrees C. The space group of the cubic phase is determined to be Pn3m or Pn3. The lattice constant of the Pn3m cubic phase was found to be almost constant when it coexists with lamellar liquid-crystal phase. Marked temperature-dependent changes were observed when cubic phase coexists with hexagonal phase or lamellar-gel phases. This is the first report of cubic phases formed by codispersions of glycosphingolipids and phospholipids. The mechanism of cubic phase formation and the interaction between GlcCer and POPE is discussed in terms of the putative biological functions of glycolipids.     

First-principles study of phase stability and elastic properties in metastable Ti-Mo alloys with cluster structure

This paper provided a novel approach for evaluating phase stability and elastic properties in metastable Ti–Mo alloys with low Mo content by first-principles combined with cluster structure. In 54-atom body-centered-cubic supercell by substituting Ti atoms with 2–7 Mo atoms (7.1–23.0?wt% Mo), individual cluster structure of β-phase was constructed by ‘-Mo-Ti-Mo-’ cluster unit having the lowest cohesive energy. The distorted supercell was more stable than undistorted one at a low Mo content. With increasing Mo content, the density of state at Fermi level decreased, and bonding electron number increased, indicating β-phase stability was gradually promoted. Tetragonal shear elastic constant (C′?=?(C₁₁?–?C₁₂)/2), shear modulus (G₁₁₁) and anisotropy factor (A?=?C₄₄/C′) exhibited a fluctuation with Mo addition, while the change trend of A was opposite to C′ and G₁₁₁. Calculated Young’s modulus exhibited similar changing trend to the C′, implying that the softening of C′ resulted in low Young’s modulus of β-phase. Measured Young’s modulus exhibited significant difference from calculated one, which was mainly caused by formation of α″-martensite and ω-phase. The values of C′, G₁₁₁ and A were considered to associate with not only elastic properties of β-phase itself but also transition from β-phase to α″-martensite and/or ω-phase.     

A unit-cell-based three-dimensional molecular mechanics analysis for buckling load,effective elasticity and Poisson's ratio determination of the nanosheets

By using a three-dimensional (3D) space-frame-like model, a molecular mechanics (MM) approach is proposed for determination of the buckling loads, effective Young's modulus and Poisson's ratio of the nanosheets, using a proper unit cell. The governing equations are derived based on the 3D kinematics of deformations and the principle of minimum total potential energy. The unit-cell-based results are employed for the space-frame-like finite element model of the nanosheet. The nonlinear MM equations are solved by representing bonds of the boron nitride nanosheet (BNNS) by beam elements to extract the local characteristics. These properties are employed in modelling of the nanosheet, as a space-frame-like finite element structure. The force field constants are chosen according to the Morse, AMBER, UFF and DREIDING models to determine the buckling strength, and effective Poisson's ratio and in-plane rigidity of the whole graphene and BNNSs. Silicon Carbide nanosheets are analysed based on different force constants. These results are concordant with the results available in the literature. The comparisons reveal that the DREIDING force field usually gives the most accurate predictions.     

A theoretical model for lipid mixtures, phase transitions, and phase diagrams.

We present a new model for the thermodynamic properties of lipid bilayers. The model consists of a system of hard cylinders of varying radii that correspond to the different molecular radii of lipids having different numbers of gauche rotations in their chains. Scaled particle theory is used to provide an accurate estimate of the entropy of packing of the cylinders. To apply the model to bilayers we introduce a semiempirical attractive potential energy. Once the form of this potential is chosen, we adjust one parameter, the interaction strength, so that the model fits the transition temperatures and entropies for various phospholipids. The model then agrees quite well with other published data for these systems. We also directly generalize our model to lipid mixtures, and we obtain phase diagrams that we compare to existing data for these systems. We use the model to describe lipid protein interactions in bilayers as well.     

Functionalized Boron Nitride Nanosheets/Graphene Interlayer for Fast and Long‐Life Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have a much higher energy density than Li ion batteries and thus are considered as next generation batteries for electric vehicle applications. However, the problem of rapid capacity fading due to the shuttling of soluble polysulfides between electrodes remains the main obstacle for practical applications. Here, a thin and selective interlayer structure has been designed and produced to decrease the charge transfer resistance and mitigate the shuttling problem, simply by coating the surface of cathode with a thin film of functionalized boron nitride nanosheets/graphene. Due to this thin and ultralight interlayer, the specific capacity and cycling stability of the Li–S batteries with a cathode of sulfur‐containing porous carbon nanotubes (≈60 wt% sulfur content) have been improved significantly with a life of over 1000 cycles, an initial specific capacity of 1100 mA h g^?1 at 3 C, and a cycle decay as low as 0.0037% per cycle. This new interlayer provides a promising approach to significantly enhance the performance of Li–S batteries.     

Influence of the lamellar phase unbinding energy on the relative stability of lamellar and inverted cubic phases

Based on curvature energy considerations, nonbilayer phase-forming phospholipids in excess water should form stable bicontinuous inverted cubic (Q_II) phases at temperatures between the lamellar (L_α) and inverted hexagonal (H_II) phase regions. However, the phosphatidylethanolamines (PEs), which are a common class of biomembrane phospholipids, typically display direct L_α/H_II phase transitions and may form intermediate Q_II phases only after the temperature is cycled repeatedly across the L_α/H_II phase transition temperature, T_H, or when the H_II phases are cooled from T > T_H. This raises the question of whether models of inverted phase stability, which are based on curvature energy alone, accurately predict the relative free energy of these phases. Here we demonstrate the important role of a noncurvature energy contribution, the unbinding energy of the L_α phase bilayers, g_u, that serves to stabilize the L_α phase relative to the nonlamellar phases. The planar L_α phase bilayers must separate for a Q_II phase to form and it turns out that the work of their unbinding can be larger than the curvature energy reduction on formation of Q_II phase from L_α at temperatures near the L_α/Q_II transition temperature (T_Q). Using g_u and elastic constant values typical of unsaturated PEs, we show that g_u is sufficient to make T_Q > T_H for the latter lipids. Such systems would display direct L_α → H_II transitions, and a Q_II phase might only form as a metastable phase upon cooling of the H_II phase. The g_u values for methylated PEs and PE/phosphatidylcholine mixtures are significantly smaller than those for PEs and increase T_Q by only a few degrees, consistent with observations of these systems. This influence of g_u also rationalizes the effect of some aqueous solutes to increase the rate of Q_II formation during temperature cycling of lipid dispersions. Finally, the results are relevant to protocols for determining the Gaussian curvature modulus, which substantially affects the energy of intermediates in membrane fusion and fission. Recently, two such methods were proposed based on measuring T_Q and on measuring Q_II phase unit cell dimensions, respectively. In view of the effect of g_u on T_Q that we describe here, the latter method, which does not depend on the value of g_u, is preferable.     

Synthesis and mesogenic properties of glycosyl diacylglycerols

We synthesised glycosyl diacylglycerols bearing unsaturated or chiral methyl branched fatty acid chains. The thermotropism was measured with polarising microscopy and additionally the lyotropism with the contact preparation method. The synthesised compounds displayed thermotropic S(A) (lamellar), cubic and columnar phases and investigation of the lyotropic phase behaviour led to the observation of inverted bicontinuous cubic V(II) phases, lamellar L(alpha) phases and normal bicontinuous cubic V(I) phases. The phases are discussed with respect to the chemical structures that have been varied systematically to derive structure--property relationships.     

Conductive Boron Nitride as Promising Catalyst Support for the Oxygen Evolution Reaction

Catalyst support with good conductivity and stability is an eternal pursuit in the search for a high‐performance electrocatalyst. Here, an unusual catalyst support, laser‐modified boron nitride with C, O dopants (L‐BN), for the oxygen evolution reaction is reported. L‐BN exhibits unique advantages for electrocatalysis, namely, high corrosion resistance under oxidizing conditions, enhanced electrical conductivity arising from interlayer B–B dipolar interaction, and strong interaction with IrO_x catalyst caused by N? C?N bonds. As an excellent substrate, L‐BN helps to achieve higher activity and stability than its carbon black counterpart.     

Cytocompatibility, interactions, and uptake of polyethyleneimine-coated boron nitride nanotubes by living cells: confirmation of their potential for biomedical applications

Boron nitride nanotubes (BNNTs) have unique physical properties, which can be exploited in the biomedical field. Hence, the surprising lack of reported studies on their biocompatibility and interactions with living cells, addressed by the present paper which deals the results of such an investigation based on 72 h culture of human neuroblastoma cell line (SH-SY5Y) in the presence of an aqueous suspension of polyethyleneimine (PEI)-coated BNNTs. BNNTs conjugated with fluorescent markers (quantum dots) are employed to enable tracking of their uptake by living cells. The results demonstrate good cytocompatibility together with unequivocal BNNT cellular uptake by an energy-dependent endocytic process.     

Electronic,transport, magnetic,and optical properties of graphene nanoribbons and their optical sensing applications: A comprehensive review

Low dimensional materials have attracted great research interest from both theoretical and experimental point of views. These materials exhibit novel physical and chemical properties due to the confinement effect in low dimensions. The experimental observations of graphene open a new platform to study the physical properties of materials restricted to two dimensions. This featured article provides a review on the novel properties of quasi one-dimensional (1D) material known as graphene nanoribbon. Graphene nanoribbons can be obtained by unzipping carbon nanotubes (CNT) or cutting the graphene sheet. Alternatively, it is also called the finite termination of graphene edges. It gives rise to different edge geometries, namely zigzag and armchair, among others. There are various physical and chemical techniques to realize these materials. Depending on the edge type termination, these are called the zigzag and armchair graphene nanoribbons (ZGNR and AGNR). These edges play an important role in controlling the properties of graphene nanoribbons. The present review article provides an overview of the electronic, transport, optical, and magnetic properties of graphene nanoribbons. However, there are different ways to tune these properties for device applications. Here, some of them, such as external perturbations and chemical modifications, are highlighted. Few applications of graphene nanoribbon have also been briefly discussed.     

An azomethin-zinc complex for organic electroluminescence: Crystal structure, thermal stability and optoelectronic properties

An azomethin-zinc complex, bis[salicylidene(4-dimethylamino)aniline]zinc(II) (Zn(sada)₂) was synthesized and structurally characterized by single-crystal X-ray crystallography. Crystal data for Zn(C₁₅H₁₅N₂O)₂ was determined as follows: space group, triclinic, ; a = 10.2791(9) Å, b = 16.5008(14) Å, c = 17.5984(15) Å, α = 114.830(2)°, β = 96.579(2)°, γ = 97.674(2)°, Z = 4. Through thermal analysis characterization and FT-IR spectra, this complex was proved to have good thermal stability. The vapor-deposited films exhibited uniform and environment-stable morphology. The light emission and charge transporting performance of Zn(sada)₂ in organic light emitting diodes (OLEDs) were investigated preliminarily, and the results indicated the superior electron transporting property of this complex. Compared with the typical bilayer device of N,N′-diphenyl-N,N′-bis(1-naphthyl)-benzidine (NPB)/tris-(8-hydroxyquinoline)aluminum (Alq₃), the device with Zn(sada)₂ as the electron transporting layer exhibited a much lower turn-on voltage of 2.5 V (it is usually 3.5 V for an NPB/Alq₃ device).     

Correction to: An analysis of structural phase transition and allied properties of cubic ReN and MoN compounds

The dependence of sensitivity of an explosive on its molecular structure may be mainly attributed to the molecular deformability, which can be expressed by some characteristic parameters, resonance energy for aromatic an explosive, strain energy for a strained-ring or strained-cage explosive, large π-π separation energy for a large π-π linked-explosive, bond rotational energy barriers of C–NO₂, N–NO₂, O–NO₂ for C–NO₂, N–NO₂, O–NO₂ bond-based explosives, and so on. Molecular polarizability of an explosive is also an important molecular deformability index, which can be effectively used to compare impact sensitivities of explosive’s isomers, isoelectronic species, and similar structures. Interestingly, comparing the molecular polarizabilities under external electric fields with different energy levels of isomeric N₂₀(Ih) and N₂₀(D_3d) clusters and the Mo₂N₂₀ and Re₂N₂₀ complex compounds, it is found that there are different energy thresholds of significant molecular expansion.

     

Pivotal surfaces in inverse hexagonal and cubic phases of phospholipids and glycolipids

Data on the location and dimensions of the pivotal surfaces in inverse hexagonal (H_II) and inverse cubic (Q_II) phases of phospholipids and glycolipids are reviewed. This includes the H_II phases of dioleoyl phosphatidylethanolamine, 2:1 mol/mol mixtures of saturated fatty acids with the corresponding diacyl phosphatidylcholine, and glucosyl didodecylglycerol, and also the Q_II^230/G gyroid inverse cubic phases of monooleoylglycerol and glucosyl didodecylglycerol. Data from the inverse cubic phases are largely compatible with those from inverse hexagonal H_II-phases. The pivotal plane is located in the hydrophobic region, relatively close to the polar–apolar interface. The area per lipid at the pivotal plane is similar in size to lipid cross-sectional areas found in the fluid lamellar phase (L_α) of lipid bilayers.     

Boron nitride nanotube-based biosensor for acetone detection: molecular structural mechanics-based simulation

In this study, an ultra-sensitive biosensor based on a single-walled boron nitride nanotube (SWBNNT) structure is proposed for acetone detection. The molecular structural mechanics-based simulation approach has been used to model the atomic structure of SWBNNTs. The cantilevered and bridged configurations of SWBNNT-based biosensor have been considered for analysis. The resonant frequency shift due to attached mass has been analysed for the mass-based detection of acetone molecules. The present simulation approach is validated by comparing obtained simulated results with the continuum mechanics-based analytical results. Along with detection of the attached molecule, identification of its intermediate landing position along the length of the nanotube is equally important for the better performance of the biosensor systems. The frequency shift-based analysis has been reported for the mass-based detection of acetone molecules as well as its intermediate landing position along the length of the nanotube. The resonant frequency shift variations of the higher order modes of vibration for both the considered configurations of SWBNNTs have been assistive for the identification of intermediate landing position of the acetone molecule. The proposed molecular structural mechanics-based simulation approach is found to be very effectual in terms of simulation of the real atomic structures of the nanotube. The proposed biosensor can achieve extremely high sensitivity at molecular level and it can be potentially used for real-time sensing capability for the acetone concentration for future health monitoring.