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Liquid-crystal materials exhibiting up to three nematic phases are reported. Dielectric response measurements show that while the lower temperature nematic phase has ferroelectric order and the highest temperature nematic phase is apolar, the intermediate phase has local antiferroelectric order. The modification of the molecular structure by increasing the number of lateral fluorine substituents leads to one of the materials showing a direct isotropic- ferronematic phase transition.

Intense interests in mid-infrared (MIR) nonlinear optical (NLO) crystals have erupted in recent years due to the development of optoelectronic applications ranging from remote monitoring to molecular spectroscopy. Here, two polar crystals Ca3(TeO3)2(MO4) (M = Mo, W) were grown from TeO2-MO3 flux by high-temperature solution methods. Ca3(TeO3)2(MoO4) and Ca3(TeO3)2(WO4) are isostructural, which feature novel structures consisting of asymmetric MO4 tetrahedra and TeO3 trigonal pyramids. Optical characterizations show that both crystals display ultrawide transparency ranges (279 nm to 5.78 μm and 290 nm to 5.62 μm), especially high optical transmittance over 80% in the important atmospheric transparent window of 3-5 μm, and superhigh laser damage thresholds (1.63 GW/cm2 and 1.50 GW/cm2), 54.3 and 50 times larger than that of state-of-the-art MIR NLO AgGaS2, respectively. Notably, they exhibit the widest band gaps and the loftiest laser-induced threshold damages among the reported tellurates so far. Moreover, Ca3(TeO3)2(MO4) exhibit type I phase matching at two working wavelengths owing to their large birefringence and strong second-harmonic generation responses from the distorted anions, as further elucidated by the first-principles calculations. The above characteristics indicate that Ca3(TeO3)2(MO4) crystals are high-performance MIR NLO materials, especially applying in high-power MIR laser operations.

Ice surfaces are widely present in our environment and participate in many important chemical reactions. We study the adsorption of acetone, a typical polar small organic molecule, on ice by combin...

Magnetic polar materials feature an astonishing range of physical properties, such as magnetoelectric coupling, chiral spin textures, and related new spin topology physics. This is primarily attributable to their lack of space inversion symmetry in conjunction with unpaired electrons, potentially facilitating an asymmetric Dzyaloshinskii-Moriya (DM) exchange interaction supported by spin-orbital and electron-lattice coupling. However, engineering the appropriate ensemble of coupled degrees of freedom necessary for enhanced DM exchange has remained elusive for polar magnets. Here, we study how spin and orbital components influence the capability of promoting the magnetic interaction by studying two magnetic polar materials, α-Cu(IO3)2 (2D) and Mn(IO3)2 (6S), and connecting their electronic and magnetic properties with their structures. The chemically controlled low-temperature synthesis of these complexes resulted in pure polycrystalline samples, providing a viable pathway to prepare bulk forms of transition-metal iodates. Rietveld refinements of the powder synchrotron X-ray diffraction data reveal that these materials exhibit different crystal structures but crystallize in the same polar and chiral P21 space group, giving rise to an electric polarization along the b-axis direction. The presence and absence of an evident phase transition to a possible topologically distinct state observed in α-Cu(IO3)2 and Mn(IO3)2, respectively, imply the important role of spin-orbit coupling. Neutron diffraction experiments reveal helpful insights into the magnetic ground state of these materials. While the long-wavelength incommensurability of α-Cu(IO3)2 is in harmony with sizable asymmetric DM interaction and low dimensionality of the electronic structure, the commensurate stripe AFM ground state of Mn(IO3)2 is attributed to negligible DM exchange and isotropic orbital overlapping. The work demonstrates connections between combined spin and orbital effects, magnetic coupling dimensionality, and DM exchange, providing a worthwhile approach for tuning asymmetric interaction, which promotes evolution of topologically distinct spin phases.

The spectral and luminescent properties of solutions of bis(hydroxynaphthoazomethine) of the pyridine family have been studied in comparison with the analogue of the benzene family. The presence of the pyridine nitrogen atom in the ortho position to the azomethine group favors the formation of the keto form of the azomethine moiety in the ground state of the molecule. The position of the luminescence maxima of solutions weakly depends on the presence of a nitrogen atom in the heterocycle and is more determined by the solvent polarity. Longer-wavelength and more efficient luminescence is observed in polar media.

Ionic liquids (ILs) are an important class of media that are usually used in combination with polar solvents to reduce costs and tune their physicochemical properties. In this regard, it is essential to understand the influence of adding solvents on the properties of ILs. In this work, the micro-heterogeneity and H-bonding interactions between a hydroxyl-functionalized IL, [HOEmim][TFSI], and acetonitrile (ACN) were investigated by attenuated total reflection Fourier transform infrared spectroscopy and molecular simulations. All studied IL-ACN mixtures were found to deviate from the ideal mixtures. The degree of deviations reaches the maximum at about x(ACN)=0.7 with the presence of both homogeneous clusters of pure IL/ACN and heterogeneous clusters of IL-ACN. With the addition of ACN to IL, the mixtures undergo the transformation from "ACN solvated in [HOEmim][TFSI]" to "[HOEmim][TFSI] solvated in ACN". It is found that the newly formed H-bonding interactions between the IL and ACN is the main factor that contributes to the red shifts of O-H, C2 -H, C4,5 -H, and Calkyl -H of [HOEmim]+ cation, and the blue shifts of C-D, C≡N of ACN, and C-F, S=O of [TFSI]- anion. These in-depth studies on the mixtures of hydroxyl-functionalized IL and acetonitrile would help to understand the micro-heterogeneity and H-bonding interactions of miscible solutions and shed light on exploring their applications.

It has long been anticipated that dielectric constants of polar liquids are reduced in the interfacial layer. Recent experiments and computer simulations support these expectations. A strong reduction of the dielectric constant is found in the direction perpendicular to a planar substrate, while the parallel response is bulk-like. This Perspective highlights recent theoretical calculations and simulations with an eye on relating them to properties observable in the laboratory. The average interface dielectric constant computed from simulations connects to thin films experiments, but this cannot be extended to screening of charges. In contrast to dielectric theories where a single dielectric constant gauges both the polarization energy and screening, these two signatures of dielectric polarization diverge on the molecular scale. The reduction of the dielectric constant of water in thin films is currently viewed as a combined effect of geometric confinement imposed by the substrate and the reconstruction of water hydrogen bonds in the surface layer.

The role of a polarized transition state and solvent effects on nitrate radical reactions was examined with a previously under-reported class of substrates, ethers, for their atmospheric implications. Absolute rate constants for hydrogen abstraction from a series of alcohols, ethers, and alkanes by nitrate radical have been measured in acetonitrile, water, and mixtures of these two solvents. Across all of these classes of compounds, using a modified form of the Evans-Polanyi relationship, it is demonstrated that the observed structure/reactivity trends can be reconciled by considering the number of abstractable hydrogens, strength of the C-H bond, and ionization potential (IP) of the substrate. Hydrogen abstractions by nitrate radical occur with low selectivity and are characterized by an early transition state (α ≈ 0.3). The dependence of the rate constant on IP suggests a polar transition state with some degree (

Photoredox-catalyzed C-O bond formation reactions are reported. The decarboxylative esterification reaction allows the conversion of a variety of arylacetic acids into the corresponding benzyl carboxylates. Furthermore, the use of (diacetoxyiodo)benzene allows the conversion of the benzylic C-H bond through hydrogen atom transfer. The reactions were applied to the divergent transformation of pharmaceuticals via decarboxylative or C-H esterification reactions.

Singlet fission (SF) is an intriguing process in which a singlet exciton produces two triplet excitons in molecular aggregates. Perylenediimide (PDI) derivatives are promising materials for SF-based photovoltaics, and the SF process in PDI aggregates is important to investigate for their applications. In this work, we studied the entire SF process occurring in the colloidal nanoparticles of a PDI derivative in solutions by using time-resolved fluorescence and transient absorption (TA) experiments. PE-PDI was found to form the colloidal nanoparticles of H- and J-aggregates in polar solvents. The TA signals of PE-PDI aggregates in solutions were selectively measured by wavelength-dependent excitation. The TA signals were analyzed by using a global fitting analysis, and all kinetic parameters involved in the entire SF process were determined. Our current investigation has confirmed that fast SF occurs on the surface of the colloidal nanoparticles of PDI aggregates via the charge transfer mediated mechanism, giving a high quantum yield of triplet excitons.

The built-in electric field generated by polar materials is one of the most effective strategies to promote the separation of photogenerated electron-hole pairs in the field of photocatalysis. However, because of the complexity and diversity of the built-in electric field in polar materials, it is not clear how to enhance the photocatalytic performance and how to control the polar electric field effectively. To this end, four-layered bismuth oxyhalides, BiOX, and BiOXO3 (X = Br, I) were synthesized by a simple hydrothermal method. X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis confirmed that they all have the structure characteristics of a sillenite phase. Scanning electron microscopy images show that they all have the morphology of nanosheets. Among them, BiOBrO3 was successfully synthesized and characterized for the first time in the present work. The order of photocatalytic performance (including carrier's lifetime, photocurrent density, and H2 evolution rate) of the four compounds is listed as follows: BiOBrO3 > BiOI > BiOIO3 > BiOBr. In the bulk of the BiOXO3 photocatalyst, the spontaneous polar built-in electric field along the [001] direction is the crucial factor to inhibit the recombination of photogenerated electron-hole pairs, while the surface polar electric field in BiOI can outstandingly inhibit the recombination of photogenerated electron-hole pairs due to the breaking of the mirror symmetry. Therefore, regulating the microstructure and composition of the structure unit, which generates the built-in electric field, can indeed control the magnitude, direction, and effects of built-in electric fields. In practice, we should carefully adjust the strategy according to the actual situation so as to reasonably design and use the polar electric field, giving full play to its role and enhancing the photocatalytic performance.

The solubility of 1-imino-2-phenyl-1H-indene-3-amine with fragments of 1,4-phenylenediamine and 1,3,4-, 1,2,4-thiadiazoles in ethanol and DMF in the 298–318 K range of temperatures. Patterns of the dissolution of macroheterocyclic compounds are discussed. The thermodynamic parameters of the dissolution of the synthesized compounds are calculated.

In this work the photodissociation process for ICN in ethanol, a moderately polar solvent, was simulated using semi-classical molecular dynamics. Comparisons of the results with previous simulations of the photodissociation of ICN in highly polar and nonpolar solvents were made. The results that were compared include the probabilities for recombination as ICN or the isomer INC, or cage escape as I + CN or I* + CN, as well as the different kinetic and potential energy properties that allow further insight into the influence of the solvent on energy dissipation of the photoproducts. In excellent agreement with experiment, we observed a 59% recombination probability in ethanol, significantly lower than in water. The energy dissipation of the translational, rotational, and vibrational kinetic energy of the photofragments was found to be slower in ethanol than in water primarily due to a weaker caging effect exerted by ethanol.

Light-driven unidirectional molecular rotary motors have the potential to power molecular machines. Consequently, optimizing their speed and efficiency is an important objective. Here, we investigate factors controlling the photochemical yield of the prototypical unidirectional rotary motor, a sterically overcrowded alkene, through detailed investigation of its excited-state dynamics. An isoviscosity analysis of the ultrafast fluorescence decay data resolves friction from barrier effects and reveals a 3.4 ± 0.5 kJ mol-1 barrier to excited-state decay in nonpolar media. Extension of this analysis to polar solvents shows that this barrier height is a strong function of medium polarity and that the decay pathway becomes near barrierless in more polar media. Thus, the properties of the medium can be used as a route for controlling the motor's excited-state dynamics. The connection between these dynamics and the quantum yield of photochemical isomerization is probed. The photochemical quantum yield is shown to be a much weaker function of solvent polarity, and the most efficient excited-state decay pathway does not lead to a strongly enhanced quantum yield for isomerization. These results are discussed in terms of the solvent dependence of the complex multidimensional excited-state reaction coordinate.

Equations of state (EoSs) have always been one the most interesting field of study for scientists and engineers, due to their extensive applications in various industries and scientific research. Accordingly, scientists have extensively studied useful modifications of the original EoSs. In this study, the temperature dependent part of the Peng–Robinson cubic equation of state is modified. The new dual parameter α-function is able reproduce the vapor pressure data accurately for a large variety of pure components. Mono-atomic and di-atomic molecules, hydrocarbons, polar and associating compounds are well represented by the Peng–Robinson–Saali equation of state with negligible deviation with experimental data. Moreover, the thermodynamic consistency test of P–T–x solubility data based on the fundamental Gibbs–Duhem equation, for binary mixtures including acid gases (CO2 and H2S)/polar and associating solvents at low and high pressure were also investigated. The proposed EoS coupled with a three-parameter binary interaction term, namely the Panagiotopoulos–Reid mixing rule, was used in order to present the PR–Saali EoS as a versatile equation for analyzing thermodynamic consistency of experimental data. Modeling processes were carried out by using MATLAB 2018a.

Interfacial tension (IFT) is important in developing oilfield exploration and production strategies, enhanced oil recovery, and oil-water separation. Tests using reservoir simulators such as Eclipse show that the selected IFT has significant impact on prediction of water coning and production. In petroleum engineering, IFT is often assessed through correlations based on bulk properties excluding the impact of surface-active components. Crude oil contains many different types of surface-active components among which naphthenic acids and asphaltene-like molecules play an important role in IFT between oil and water. It is desirable to be able to link the IFT to the concentration of the natural surfactants to predict variations across a petroleum reservoir. To develop this relation, the equilibrium IFT was investigated in various systems of varying acid content. As expected, naphthenic acids reduce IFT of oil and water significantly. The IFT reduction is however dependent on the structure and composition of naphthenic acids as well as the nature of the solvent. To include the natural surfactancy in the model a Gibbs-Langmuir approach is used to describe the impact of naphthenic acids content in crude oil on IFT. This is compared to two models currently used to estimate IFT in the petroleum industry. The current models are not equipped to capture the role of natural surfactants and hence results may lead to erroneous predictions on crude oil production. We therefore propose an approach where bulk properties that estimate the bulk IFT is used in combination of a term based on the Gibbs-Langmuir model to capture the perturbation by the naphthenic acids to yield more accurate estimates of IFT. This require fitting to at least two experimental points to yield accurate results.

While traditional microemulsions are versatile media for nanoscience and nanotechnology, stimulus-responsive microemulsions are more challenging to realize, and only a handful of cases have been reported. We here introduce magnetic microemulsions (MMEs) stabilized by alkyltrimethylammonium-based magnetic ionic liquids surfactants (MILSs), paired with water as the polar phase, aliphatic oils as the nonpolar phase, and aliphatic alcohols as the cosurfactant. n-Hexane coupled with n(MILSs/1-butanol) = 1:4 showed the most excellent ability to form MMEs, and the range of the monophasic region was expanded with increasing alkyl chain length of MILSs cation. Classical oil-in-water (O/W), bicontinuous (BC) sponge structure, and inverse water-in-oil (W/O) subregions were clarified by conductivity method. Dynamic light scattering showed that the diameter of W/O microemulsions droplets were about 2-6 nm. Magnetic susceptibility and rheological measurements revealed that these MMEs are with high magnetic susceptibility and low viscosity, which show interesting potential applications based on a manipulation via external magnetic field. Moreover, these MMEs showed Newtonian-like flow behavior within respective subregions, and their magnetic susceptibility was not affected by the subregion structure but MILSs mass fraction.

The preparation of a high-quality perovskite film is very important for improving the device performance of perovskite photodetectors (PPDs). At present, one of the most commonly used methods to ob...

Five antitumor drugs are selected as examples of polyfunctional organic compounds to test the possibilities of approximating their retention parameters in reversed-phase high-performance liquid chromatography using recurrent relationships of the form of tR(C + ΔС) = atR(C) + b, where C is the concentration of organic modifier in the composition of the eluent (acetonitrile), ΔC = const is a constant step of its change in concentration, and a and b are coefficients calculated using the least squares method. Examples of both ideally linear dependences in all ranges of acetonitrile concentrations and deviations from linearity in different ranges of its concentrations are revealed. Discussion of the possible reasons for such deviations (both structural factors and physicochemical properties) suggests that acid–base equilibria in the eluent are not the main ones, the positions of which depend on the concentration of the organic component. The reversible formation of hydrated forms typical of compounds whose molecules contain such polar fragments as amide ‒CO–NH– and sulfonamide –SO2–NH groups, seems more likely. Recurrent approximation of the retention parameters can be considered the simplest and most obvious way to reveal the specific interactions of the test compounds with components of the eluent.

Low-dimensional ferroelectricity has attracted enormous attention due to its applications in miniaturized devices and understanding the dimension effect on ferroelectricity is of significant importance. Based on first-principles calculations, we have investigated the dimension effect on the ferroelectricity of group-IV monochalcogenide MX nanoribbons. Our results reveal that H-terminated armchair GeSNRs exhibit large in-plane polarization along the ribbon direction which converges to the value of 2D GeS as the width increases, while out-of-plane polarization only arises in those with n = odd number. Interestingly, for bare A-GeSNRs, the structure with small n transforms into a paraelectric phase and the critical width for the PE/FE transition is calculated to be n = 10. On the side of zigzag GeSNRs, H-terminated ribbons possess polarization along both the out-of-plane and width directions, while bare Z-GeSNRs are expected to be polar ferromagnetic metals.

Tunneling electroresistance (TER) is the change in tunneling resistance induced by ferroelectric polarization reversal in ferroelectric tunnel junctions (FTJs), and how to achieve a giant TER has always been a central topic in the study of FTJs. In this work, by considering the NaTiO3/BaTiO3/LaTiO3 junction with asymmetric polar interfaces as an example, we propose a novel scheme to realize a giant TER based on the reversible partial metallization of ferroelectric barrier upon the switching of ferroelectric polarization. Density functional theory calculations indicate that high on-state and low off-state conductances are obtained and the TER ratio is as high as 3.20 × 108% due to the reversible partial barrier metallization, which leads to a great difference in the effective tunneling barrier widths. The reversible partial barrier metallization, accompanied by the ferroelectric polarization reversal, is driven by the parallel or anti-parallel alignment of the depolarization electrical field of the ferroelectrical barrier and a strong built-in electrical field cooperatively contributed by the asymmetric polar interfaces and the difference in the work functions of the two leads. The findings suggest a feasible scheme for constructing promising high performance FTJ memory devices by combining both asymmetric polar interfaces and substantially different work functions.

It has remained a big challenge to grow large crystals of compounds at very anisotropic crystal growth rates. GdPO4 is such an example, which usually grows into a needle-like shape. This work solved this problem by using Li+ ions, predicted by first-principles calculations, to adjust the crystal morphology of GdPO4. Based on the calculated surface energies and the polar properties of the surfaces, we identified two crystal planes, i.e. (−102) and (−111), which can be used to adjust the morphology of the GdPO4 crystal by using extrinsic cations in the flux system. With a predicted Li containing flux system, Li2O–MoO3–B2O3, a large crystal with a record size, 10.0 × 9.0 × 18.2 mm3, was grown by using the top-seeded solution growth (TSSG) method. Based on the grown large crystal and the polarized Raman measurements, four new Raman bands missing in early studies and other bands were unambiguously assigned. By introducing a new formula, the phonon–phonon interactions were shown to be weak in the temperature range from 83 to 803 K. Our study indicates that the crystal of GdPO4 can be used as a promising laser host material working under relatively high temperature conditions.

Herein, a new protocol dealing with the preparation of 1,2-allenyl ketones has been successfully developed via the reactions of enynes with radicals enabled by dual photoredox/copper catalysis. Based on the results of a deuteration experiment and the competition reaction between cyclopropanation and allenation, the mechanism based on a photoredox-neutral-catalysed radical-polar crossover process has been proposed. Synthetic applications of allenes have also been demonstrated.

There are many effective medium models that accurately describe the dielectric properties of mixtures. However, these models assume that the components are non-interacting. This assumption is not valid for solutions of polar liquids, resulting in significant deviations between the measured and theoretically predicted values of the complex index of refraction of the mixtures. We present three effective medium theories by expanding the well-known Debye relaxation model for solutions of polar liquids in the terahertz (THz) regime. The new effective medium models proposed in this paper predict the individual relaxation Debye parameters based on the cooperative motion dynamics and self-associative properties of each mixture, and therefore explain the deviation of the dielectric functions of the solutions from the traditional effective medium models. These models are verified through reflection measurements of four alcohol-water solutions acquired through THz time-domain spectroscopy (THz-TDS). Compared to the current mixed medium models, the new effective Debye theorem predicts the dielectric properties of polar solutions more accurately and has the potential to explain inter-species mixing schemes and interactions.

Various experimental reports address the stability of G-quadruplex DNA inside a close confinement such as α-hemolysin, nanocavity water pool and different metal-organic-frameworks (MOFs). To understand the conformational change of G-quadruplex DNA at the atomistic level, we have carried out a total of 40 μs simulation run under both non-polar and polar confinement conditions. To investigate the dynamics, we have considered two different KCl salt concentrations, i.e., 0.47 M (minimal salt concentration) and higher than 2 M (higher salt concentration), at two distinct temperatures, 300 K and 350 K. Here, we have observed that the human telomeric G-quadruplex DNA deviates more from its crystal structure at minimal salt concentration under both non-polar and polar confinement conditions. Besides, the loop regions deviate and fluctuate more compared to the other regions, i.e., sugar-phosphate backbone and tetrad regions. The presence of K+ ions is found to be primarily responsible for this phenomenon. From the spatial density function (SDF) plots, a higher density of K+ ions is observed in the backbone region. Furthermore, from the residue-wise first solvation shell estimation, we have noticed that the K+ ions mainly accumulate in the tetrad region under both non-polar and polar confinement conditions due to which the tetrad regions are more rigid than the loop regions. Higher salt concentration results in increased rigidity of the G-quadruplex DNA. Our study provides valuable insight into the conformational deviation of the G-quadruplex DNA under nanoconfinement conditions.

A generalized energy-based fragmentation (GEBF) approach has been combined with a universal solvation model based on solute electron density (SMD) to compute the solvation energies of general large systems (such as protein molecules) in solutions. In the GEBF-SMD method, the solvation energy of a target system could be combined by the corresponding solvation energies of various subsystems, each of which is embedded in the background point charges and surface charges on the surface of solute cavity at the positions of its atoms and neighbouring atoms outside of the subsystem. Our results show that the GEBF-SMD model could reproduce the conventional SMD solvation energies quite well for various proteins in solutions, and could significantly reduce the computational costs for the SMD calculations of large proteins. In addition, the GEBF-SMD approach is almost independent of the basis sets and the types of solvents (including protic, polar, and nonpolar ones). Also, the GEBF-SMD approach could reproduce the relative energies of various conformers of large systems in solutions. Therefore, the GEBF-SMD method is expected to be applicable for computing the solvation energies of a broad range of large systems.

Density functional theory (DFT) calculations are performed to predict the structural, electronic and magnetic properties of electrically neutral or charged few-atomic-layer (AL) oxides whose parent systems are based on polar perovskite $KTaO_{3}$. Their properties vary greatly with the number of ALs ($n_{AL}$) and the stoichiometric ratio. In the few-AL limit ($n_{AL}\leqslant 14$), the even AL (EL) systems with chemical formula $(KTaO_{3})_{n}$ are semiconductors, while the odd AL (OL) systems with formula ($K_{n+1}Ta_{n}O_{3n+1}$ or $K_{n}Ta_{n+1}O_{3n+2}$) are half-metal except for the unique $KTa_{2}O_{5}$ case which is a semiconductor due to the large Peierls distortions. After reaching certain critical thickness ($n_{AL}>14$), the EL systems show ferromagnetic surface states, while ferromagnetism disappears in the OL systems. These predictions from fundamental complexity of polar perovskite when approaching the two-dimensional (2D) limit may be helpful for interpreting experimental observations later., Phys. Chem. Chem. Phys., 2021

The processes occurring in hydrated powders and concentrated suspensions of hydrophobic silica were studied by 1H NMR spectroscopy. It is shown that a mixture of methyl silica and water with a hydration of less than 1 g / g is a wet powder, where water is in the form of submicron clusters filling the interparticle voids of nanosilica, and the interfacial energy is directly proportional to the amount of added water. It was found that at high water concentrations there is a spontaneous increase in the size of water structures, which is accompanied by a sharp decrease in interfacial energy, that may reflect the disappearance of narrow interparticle voids or their filling with air. It is shown that aqueous suspensions of AM-1 are easily mixed with a weakly polar organic solvent chloroform, forming a stable suspension with close the amounts both of water and chloroform. It was revealed that the aqueous suspension of methyl silica has high thixotropic properties, which depend on the time and the magnitude of the applied mechanical loads.

The search for magnetoelectric materials typically revolves around the struggle to make magnetic and ferroelectric orders simultaneously coexist in the same material, using either an intrinsic or an extrinsic/composite approach. Via ab initio calculations of a prototypical Fe/BaTiO3 interface, we predict that it is possible to tune the magnitude of the individual magnetic moments even for non-polar BaTiO3. By comparing polar and non-polar Fe/BaTiO3 heterostructures, we show that the Fe, Ti and equatorial O atomic magnetic moments are induced and enhanced as a result of their local crystal field. The crystal field may be controlled solely by manipulation of the inter-atomic distances of their neighbouring atoms (which will affect their electrostatic fields and orbital hybridizations), or by the BaTiO3 electric dipole moments, working as a local polarization. When this polarization is present, it dominates the crystal field contributions, thus constraining the effects of other perturbations such as strain. We also find that, contrary to conventional expectations, the non-polar heterostructure shows higher strain induced magnetization sensitivity than its polar counterpart.

Two novel selenite oxychlorides Pb2MCu(SeO3)4Cl(H2O) (M = Fe, Ga) were hydrothermally synthesized and structurally characterized. They are isostructural and crystallize in the two-dimensional [MCu(SeO3)4Cl(H2O)]4- anionic layer structure mediated with hydrogen bonds and aligned between neighboring layers which assist in building the three-dimensional framework with a polar space group. Optical properties measurements revealed that the optical band gaps are 2.61 and 3.22 eV for Pb2FeCu(SeO3)4Cl(H2O) (1) and Pb2GaCu(SeO3)4Cl(H2O) (2) and the SHG responses are about 0.12 and 0.18 times that of KDP, respectively. Furthermore, 1 exhibits an interesting metamagnetic phenomenon under varied applied fields from around 1 to 4 T at 2 K, and 2 behaves with potential ferromagnetic ordering at low temperature.

This paper describes the test methods that were applied to three ingots of high-copper converter matte with the weight ratio of Cu:Ni ~ 2.3 at Polar Division of PJSC MMC Norilsk Nickel to determine their cooling rate. The obtained results are also discussed. A test heat was done in the converter of the Nadezhdinski Metallurgical Plant, during which the following compositions were closely monitored: that of middlings; that of the finished matte that was discharged at 1,255–1,260 оС and poured in molds at 1,200 and 1,140 оС; and that of metallized matte that was intentionally overheated to 1,285–1,290 оС and poured at 1,200 оС. The cooling time was 82 and 93 hours (for capped ingots). The temperature was monitored with the help of six chromel-alumel thermocouples located at the level of 1,350, 850 and 350 mm from the bottom; three of them in the centre and the other three on a side. The ingots were crushed at the Nickel Plant, and a ~300 kg representative sample with the size of 3 mm was taken from each ingot for flotation tests. Spot samples were taken from the temperature monitoring areas for structural characterization. Based on experimental data, functional dependencies were derived with R2 0.99 that describe the obtained cooling curves. It is shown that due to the use of insulation cap in the structure defining temperature range of 1,150–750 оС, the cooling rate of the ingot top can be considerably decreased (approximately by three times). It is equal to 28–29 оС/h. In the vertically central part of all test ingots — i. e. ~850 mm from the bottom both in the centre and on a side, the cooling rates vary in the range of ~9–10.5 оС/h; in lower monitoring points — i. e. 350 mm from the bottom, they are equal to 24–33 оС/h. The cooling rate of the overheated matte at the top drops to 67 versus 87 оС/h for the uncapped ingot, whereas in the centre and at the bottom it almost remains the same.

The effect of termination and cation distribution on the stability of low-index MgAl2O4 and ZnFe2O4 surfaces is investigated theoretically at the generalized gradient approximation and self-consist...

The formation and properties of binary thiolate self-assembled monolayers (SAMs), comprised of precursors featuring a short heteroaromatic backbone, consisting of a nonpolar phenyl ring and a polar...

​According to Mayr, polar organic synthesis can be rationalized by a simple empirical relationship linking bimolecular rate constants to as few as three reactivity parameters. Here, we propose an extension to Mayr’s reactivity method that is rooted in uncertainty quantification and transforms the reactivity parameters into probability distributions. Through uncertainty propagation, these distributions can be transformed into uncertainty estimates for bimolecular rate constants. Chemists can exploit these virtual error bars to enhance synthesis planning and to decrease the ambiguity of conclusions drawn from experimental data. We demonstrate the above at the example of the reference data set released by Mayr and co-workers [J. Am. Chem. Soc. 2001, 123, 9500; J. Am. Chem. Soc. 2012, 134, 13902]. As by-product of the new approach, we obtain revised reactivity parameters for 36 π-nucleophiles and 32 benzhydrylium ions.

The initial adsorption behavior of different GaN surfaces (the polar Ga-face (+c) and N-face (−c) and the nonpolar (1010) (m)-plane) under O2 molecule beam irradiation was studied by continuous re...

ZnO-based catalysts have been widely used in industrial reactions involving syngas conversions. Hydrogen dynamics on the surface of the catalyst is an essential process for understanding the mechan...

Vibrational energy transport through oligomeric polyethylene glycol (PEG) chains can occur ballistically via optical vibrational chain bands, showing fast and constant transport speed and high efficiency of the transport, thus offering means to transfer significant quanta of energy, exceeding 1000 cm–1, to large distances exceeding 60 A. We report how the intramolecular energy transport time, through-chain transport speed, and end-group cooling rate depend on the rigidity and polarity of the environment. The experiments were performed with end-group labeled PEG oligomers using two-dimensional infrared (2DIR) spectroscopy. The ballistic energy transport was initiated at one end of the chain by exciting an azido moiety at ca. 2100 cm–1 and recorded at another end of the chain by probing the carbonyl stretching mode of succinimide ester. We found that the rigidity of the environment, polystyrene (PS) matrix vs. a solution of similar polarity, did not change the energy transport times much, nor the through-chain transport speed. These results suggest that in mildly polar media, dynamic fluctuations, occurring in solution but largely frozen in a solid matrix, are not the dominant cause of the dephasing of the chain states, despite the presence of fast relaxation components in the solution. The similarity of the transport times in different media suggests that the secondary chain structure does not affect much the transport in PEG chains. The solvent polarity affected the intramolecular transport significantly: the transport efficiency in polar DMSO is ca. 1.6 fold smaller than that in nonpolar CCl4 or PS. The cooling time of the succinimide ester end group is reduced in more polar solvents affecting the waiting time dependence shape and thus the energy arrival time to the reporter. The analysis of different ways of extracting the energy arrival time from the data is presented. The observed dependences of the through-chain transport time on the solvent polarity suggests the presence of multiple wavepackets propagating in the PEG chain with different group velocities.

Epoxy resin is widely used in metal surface protection, because of corrosion resistance and adhesion. However, it’s water solubility, oxygen, and water impermeability are not enough. In this paper, linoleic acid (LOFA) and epoxy resin (E20) were used to synthesize epoxy ester (EL) and grafted with phosphonate esterified acrylic resin (AR-P) to prepare acrylic grafted epoxy ester (EL@AR-P). After modification, water solubility and film-forming property were improved, and the oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) decreased. At the addition of PM-2 at 2%, the OTR, WVTR, and water-uptake rate decreased by 12.9%, 25.0%, and 12.1%, respectively. Subsequently, the modified material was subjected to electrochemical impedance spectroscopy. The low-frequency impedance of EL@AR-P2 is three times higher than EL@AR-P0. After 16 days of immersion, the low-frequency impedance of EL@AR-P2 is 20 times higher than EL@AR-P. Energy dispersive spectrometer and X-ray photoelectron spectroscopy results showed that the P elements were concentrated on the substrate surface and found the presence of P–O–Fe bonds, demonstrating that the phosphonate groups were migrated to the substrate surface to form a chelate layer with the substrate and enhancing the coating adhesion and corrosion resistance. This paper modifies the molecular structure of epoxy resin, which is expected to be an excellent material for anti-corrosion coatings.

Molecular dynamics simulations of the villin headpiece subdomain HP36 have been carried out to examine relations between rates of vibrational energy transfer across non-covalently bonded contacts and equilibrium structural fluctuations, with focus on van der Waals contacts. Rates of energy transfer across van der Waals contacts vary inversely with the variance of the contact length, with the same constant of proportionality for all nonpolar contacts of HP36. A similar relation is observed for hydrogen bonds, but the proportionality depends on contact pairs, with hydrogen bonds stabilizing the α-helices all exhibiting the same constant of proportionality, one that is distinct from those computed for other polar contacts. Rates of energy transfer across van der Waals contacts are found to be up to 2 orders of magnitude smaller than rates of energy transfer across polar contacts.

Significant efforts in the past decade have given us highly accurate all-atom protein force fields for molecular dynamics (MD) simulations of folded and disordered proteins. These simulations, complemented with experimental data, provide new insights into molecular interactions that underlie the physical properties of proteins, especially for intrinsically disordered proteins (IDPs) for which defining the heterogeneous structural ensemble is hugely challenging by experiments alone. Consequently, the accuracy of these protein force fields is of utmost importance to ensure reliable simulated conformational data. Here, we first assess the accuracy of current state-of-the-art force fields for IDPs (ff99SBws and ff03ws) applied to disordered proteins of low amino acid sequence complexity that can undergo liquid-liquid phase separation. On the basis of a detailed comparison of NMR chemical shifts between simulation and experiment on several IDPs, we find that regions surrounding specific polar residues result in simulated ensembles with exaggerated helicity when compared to experiment. To resolve this discrepancy, we introduce residue-specific modifications to the backbone torsion potential of three residues (Ser, Thr, and Gln) in the ff99SBws force field. The modified force field, ff99SBws-STQ, provides a more accurate representation of helical structure propensity in these LC domains without compromising faithful representation of helicity in a region with distinct sequence composition. Our refinement strategy also suggests a path forward for integrating experimental data in the assessment of residue-specific deficiencies in the current physics-based force fields and improves these force fields further for their broader applicability.

Polar surfaces of solid oxides are intrinsically unstable and tend to reconstruct due to the diverging electrostatic energy and thus often exhibit unique physical and chemical properties. However, a quantitative description of the restructuring mechanism of these polar surfaces remains challenging. Here we provide an atomic-level picture of the refaceting process that governs the surface polarity compensation of cubic ceria nanoparticles based on the accurate reference data acquired from the well-defined model systems. The combined results from advanced infrared spectroscopy, atomic-resolved transmission electron microscopy, and density functional theory calculations identify a two-step scenario where an initial O-terminated (2 × 2) reconstruction is followed by a severe refaceting via massive mass transport at elevated temperatures to yield {111}-dominated nanopyramids. This significant surface restructuring promotes the redox properties of ceria nanocubes, which account for the enhanced catalytic activity for CO oxidation.

Ferroelectrics (FEs) are increasingly finding use as solar energy conversion materials. One of the hallmark signatures of a proper FE is a polar ground state whose polarization can be switched thro...

The proposed model of intermolecular interactions contains three independent groups of quantities describing non-polar forces, polar forces, and hydrogen bonds. The contribution of hydrogen bonding to the total energy of intermolecular interaction is represented as a product of some quantum-mechanical threshold value and the probability of molecular arrangement that makes this bonding possible. Two characteristics, “polarity” and “hydrophilicity”, distinguishing polar and non-polar species, are introduced. Along with the generalized charge, these characteristics are independent arguments of the three-parameter model for liquid phases used in chromatography. The model is applied to describe the interaction of polar molecules in the gas phase with liquid polyethylenee glycol (PEG). Theoretical dependences of PEG polarity and hydrophilicity on the polymer′s molecular mass are derived. The graph of these dependences plotted in “polarity–hydrophilicity” coordinates agrees well chromatography data for characteristics of PEGs used as stationary phases.

Although both pressure and temperature are essential parameters governing thermodynamics, the effects of the pressure on solution-phase equilibria have not been well studied compared to those of temperature. Here, we demonstrate the interesting pressure-dependent behavior of tetraphenylethylene (TPE) derivatives in multiphase systems composed of an organic phase and an aqueous phase in the presence and absence of γ-cyclodextrin (γ-CD). In this system, tetraphenylethylene monocarboxylic acid (TPE1H) and its dicarboxylic acid (TPE2H2) are distributed in the aqueous phase and dissociated into the corresponding anions, that is, TPE1- and TPE22-, when the pH is sufficiently high. The distribution ratios of TPE1H/TPE1- and TPE2H/TPE22- show opposing pressure dependencies: the distribution of the former in the organic phase increases with increasing pressure, whereas that of the latter decreases. The 1:1 complexation constants of TPE1- and TPE22- with γ-CD, which can be determined from the distribution ratios in the presence of γ-CD, also show opposing pressure dependencies: the former shows a positive pressure dependence, but the latter exhibits a negative one. These pressure effects on the distribution and complexation of TPE derivatives can be interpreted based on the differences in the molecular polarity of these solutes. The water permittivity is enhanced at high pressure, thus stabilizing the more polar TPE22- in the aqueous phase to a larger extent than TPE1- and, as a result, reducing its distribution in the organic phase, as well as its complexation with γ-CD. Fluorescence spectra in the aqueous phase suggest that the TPE derivatives form aggregates with γ-CD molecules, as detected by the specific fluorescence. In addition, the fluorescence intensities of the γ-CD complexes are enhanced at high pressures because of the restricted rotation of the phenyl rings in the TPE molecules. This study provides new perspectives for multiphase partitioning and an attractive alternative to conventional extraction methods.