Magnitude Of Dipole Moment Research Articles

Revisiting Dynamic Processes and Relaxation Mechanisms in a Heterocyclic Glass-Former: Direct Observation of a Transient State.

Despite decades of studies, a clear understanding of near-Tg phenomena remains challenging for glass-forming systems. This review delves into the intricate molecular dynamics of the small, heterocyclic thioether, 6-methyl-2,3-dihydro-1,4-benzodithiine (MeBzS2), with a particular focus on its near-Tg cold crystallization and relaxation mechanisms. Investigating isothermal crystallization kinetics at various temperatures reveals a significant interplay between its molecular dynamics and recrystallization from a supercooled liquid. We also identify two independent interconversion paths between energetically privileged conformers, characterized by strained transition states. We demonstrate that these spatial transformations induce substantial alterations in the dipole moment orientation and magnitude. Our investigation also extends to the complex salt PdCl2(MeBzS2), where we observe the transient conformers directly, revealing a direct relationship between their abundance and the local or macroscopic electric field. The initially energetically privileged isomers in an undisturbed system become less favored in the presence of an external electric field or ions, resulting even in an unexpected inversion of states. Consequently, we confirm the intramolecular character of secondary relaxation in MeBzS2 and its mechanism related to conformational changes within the heterocyclic ring. The research is based on the combination of broadband dielectric spectroscopy, X-ray diffraction, and quantum density functional theory calculations.

Performance improvement on the cold flow properties of crude oil with high asphaltene by adjusting the polarity of the third monomer in polymers

AbstractAsphaltenes and waxes are the primary factors affecting the cold flow properties of crude oil. In this paper, based on the binary polymer of acrylate‐maleic anhydride (PM22‐MA), different third polar groups of acrylamide, N‐(hydroxymethyl) acrylamide, N‐phenylacrylamide (NPA), and styrene (SM) were introduced to synthesize a series of ternary pour point depressants (PPDs) to explore the effect of asphaltene on the cold flow properties of Xijiang (XJ) crude oil. Thereinto, PM22‐MA‐NPA containing amide group and benzene ring exhibited the best depressive effect, which decreased pour point by 14°C at 1500 ppm. The mechanism of interaction of the polar groups in PPDs with asphaltene was studied. The polar groups could form stronger hydrogen bonds with asphaltene, delaying the asphaltene macromolecule bonding, allowing the synergistic effect of PPDs and asphaltene to be better utilized to improve the cold flow properties of crude oil. Furthermore, the dipole moment magnitude and electron cloud density were calculated with Gaussian. It was found that the polar group with a dipole moment magnitude of 3.2244 debye and an electron cloud density ranging from −1.6364 to 1.9944 eV was the most suitable third polar monomer for the PPDs of XJ crude oil.

The Influence of Large Pendent Groups on Chain Anisotropy and Electrical Energy Loss of Polyimides at High Frequency through All-Atomic Molecular Simulation.

Polyimide is a potential material for high-performance printed circuit boards because of its chemical stability and excellent thermal and mechanical properties. Flexible printed circuit boards must have a low static dielectric constant and dielectric loss to reduce signal loss in high-speed communication devices. Engineering the molecular structure of polyimides with large pendant groups is a strategy to reduce their dielectric constant. However, there is no systematic study on how the large pendant groups influence electrical energy loss. We integrated all-atomic molecular dynamics and semi-empirical quantum mechanical calculations to examine the influence of pendant groups on polymer chain anisotropy and electrical energy loss at high frequencies. We analyzed the radius of gyration, relative shape anisotropy, dipole moment, and degree of polarization of the selected polyimides (TPAHF, TmBPHF, TpBPHF, MPDA, TriPMPDA, m-PDA, and m-TFPDA). The simulation results show that anisotropy perpendicular to chain direction and local chain rigidity correlate to electrical energy loss rather than dipole moment magnitudes. Polyimides with anisotropic pendant groups and significant local chain rigidity reduce electrical energy loss. The degree of polarization correlated well with the dielectric loss with a moderate computational cost, and difficulties in directly calculating the dielectric loss were circumvented.

Unraveling the excitonic states in bulk 2H−MoS2 via their giant Stark shift

The interlayer exciton ($IL$) in bilayer $2H\text{\ensuremath{-}}{\mathrm{MoS}}_{2}$ has earlier been shown to undergo large Stark splitting under electric field ${F}_{z}\ensuremath{\parallel}\mathbf{c}$ axis. We show that the excited state exciton ${A}_{2s}$ in bulk $2H\text{\ensuremath{-}}{\mathrm{MoS}}_{2}$ undergoes nearly three times as large splitting, with a dipole moment magnitude 1.46 enm. The nature and evolution of different exciton species with ${F}_{z}$ is verified by comparison with ab initio GW-Bethe-Salpheter equation (BSE) calculations that include the full electron-hole correlations. The excitonic wave functions reveal the individual character of the exciton states at high ${F}_{z}$ as the ground state ${A}_{1s}$, split interlayer $I{L}_{\ensuremath{-}}, I{L}_{+}$, and split excited state ${A}_{2s\ensuremath{-}}$. Extrapolation to low ${F}_{z}$ indicates that $IL$ and ${A}_{2s}$ mix strongly. We try to rationalize the large dipole moment values by comparing GW-BSE results with the hydrogenic exciton model. Although the dominant ${A}_{1s}$ shows an insignificant Stark shift, its large anticrossing with ${A}_{2s\ensuremath{-}}$ provides a pathway for its modulation and control using an electric field.

Exposure to the electric field: A potential way to block the aggregation of histidine tautomeric isomers of β-amyloid

Controlling protein misfolding and accumulation in neurodegeneration is a challenge in chemical neuroscience. The application of appropriate electric fields (EFs) can be a potential noninvasive therapy to treat neuro disorders. The effect of EFs of varying intensities and directions on the conformational dynamics of β-Amyloid40 (Aβ40) under histidine tautomerism has been investigated for the first time. Our findings suggest that peptides tend to align their dipole moments with the orientation of EF. Irrespective of the EF direction, the dipole moment magnitude is affected by the EF strength. With the conformational changes, the EF strength equal to 0.5 V/nm destroyed the β-sheet content of the δδδ isomer as a potentially toxic agent. The content of the alpha-helical structure which can be transformed into the β-sheet is reduced. The strength of the EF showed a significant influence on the reduction of the number of intra-protein hydrogen bonds especially when EF is equal to 0.5 V/nm which could facilitate destabilization of the structure of the peptides. Current findings provide quantitative insights into the tautomerization-mediated Aβ40 dynamic and conformational changes induced by the external EFs in aqueous solutions, which may provide beneficial information for use as a therapeutic technique.

Dilution-induced changes in room temperature ionic liquids. Persistent compositional heterogeneity and the importance of dipolar interactions

Room temperature ionic liquids (RTILs) exhibit several unusual properties, including the ability to support an induced free charge density gradient, ρf. Upon dilution with water, RTILs form micelle-like structures, and compositional non-uniformity has been reported in other solvents, such as methanol and acetonitrile. The dependence of ρf on dilution is not consistent with uniform dissolution of the RTIL in the diluent. We report here our examination of two imidazolium RTILs diluted with polar aprotic solvents dimethyl sulfoxide (DMSO) and propylene carbonate (PC). Using the cationic fluorophore cresyl violet (CV+), we evaluate the dependence of ρf magnitude and persistence length on dilution with these two solvents. These properties are found to depend on the identity of the RTIL anion (BF4- and TFSI-). In regions of the RTILs not affected by the induced charge density gradient, we find evidence for the formation of aggregated domains of RTIL in the binary systems. The characteristic domain size is seen to depend on the identity of the diluent and RTIL anion, and for all systems examined, domain size increases with increasing dilution. We discuss these findings in the context of the magnitude of the RTIL ion pair dipole moments.

Agro-ecological risk of pesticides application for protecting apple plantations in the conditions of Pre-Carpathian Province of the Carpathian mountains in Ukraine

It was found that the rate of detoxification of pesticides depends on their physicochemical properties and correlates with the polarity of the compounds. According to the magnitude of dipole moments, the studied pesticides are divided into three groups: nonpolar with µ from 0 to 2 Debye (D), low-polar with µ from 2 to 6 Debye and polar with µ more than 6 Debye. Non-polar pesticides are practically insoluble in water and their decay period in the ecosystem is longer than that of low-polar and polar pesticides. Peculiarities, speed and dynamics of pesticide detoxification in the apple orchard ecosystem have been studied. It was found that non-polar pesticides decompose at a rate of 0.07–0.12±0.05 parts per day, and low-polar pesticides — at a rate of 0.15–0.22±0.05 parts per day. On the tenth day after spraying, 0.05 to 1.24 mg/kg of the studied pesticides were detected in apple fruits and from 0.15 to 4.41 mg/kg in apple leaves. The classification of pesticides according to the degree of danger was carried out and it was found that the studied drugs have a degree of danger from 3 to 6. Pesticides with 3 degrees of danger are more dangerous to humans and biota and require more detailed regulation, regulation and control. The seasonal load of pesticides (H) for the intensive chemical system was 29.5 kg/ha, for the advanced system — 10.5 kg/ha and for the system of biological and chemical protection — 0.45 kg/ha. The weighted average hazard (Q) in the intensive chemical protection system was 5.0, for the advanced system — 4.9, and for the biological and chemical protection system — 6.8. It was found that the agroecotoxicological index for all protection systems was less than 1, all protection systems are not very dangerous and do not lead to ecosystem pollution. For the intensive system of chemical protection, this figure ranged from 0.24 to 0.49, for the advanced — from 0.014 to 0.025, and for the system of biological and chemical protection — from 6·10–5 to 8·10–5.

Application of Helbig integrals to magnetic gradient tensor multi-target detection

We extended the magnetic gradient tensor Helbig integrals (MGTHI) from classical Helbig integrals (HI), which can be perfectly adapted to the grid measurement of planar-cross magnetic gradient tensor system. With different sizes of windows, we can estimate the MGTHI by using the two-dimensional trapezoidal rule algorithm and calculate the total magnetization direction of grids, where the node with the smallest change in the magnetization direction is target horizontal position. In the targets recognition area determined by the invariant improved tilt angles, the source depth and dipole moment magnitude can be calculated with magnetic vector and tensor field data directly above the source. In experiments, the horizontal position deviation of multiple small magnets in the survey area of 2.1 m × 2.1 m and 1.2 m × 1.2 m is less than 0.08 m, and the buried depth deviation is less than 0.15 m, the positioning accuracy is improved by more than 5 times from the classical HI method.

Modeling the First-Order Molecular Hyperpolarizability Dispersion from Experimentally Obtained One- and Two-Photon Absorption.

The search for optical materials, particularly organic compounds, is still an attractive and essential field for developing several photonic devices and applications. For example, some applications are based on light scattering with twice the energy of the incoming photon for selected compounds, that is, the nonlinear optical effect related to the second-order susceptibility term from the electronic polarization expression. The microscopic interpretation of this phenomenon is called the first-order molecular hyperpolarizability or incoherent second harmonic generation of light. Understanding such phenomena as a function of the incoming wavelength is crucial to improving the optical response of future materials. Still, the experimental apparatus, hyper-Rayleigh scattering, apparently simple, is indeed a challenging task. Therefore, we proposed a proper alternative to obtain the dispersion of the first-order hyperpolarizability using the well-known one- and two-photon absorption techniques. By the spectral analysis of both the spectra, we gathered spectroscopic parameters and applied them for predicting the first-order hyperpolarizability dispersion. This prediction is based on an n-level energy system, taking into account the position and magnitude of transition dipole moments and the difference between the permanent dipole moment of the n-excited states. Moreover, using the presented method, we can avoid underestimating the first-order hyperpolarizability by not suppressing higher-energy transitions. Quantum chemical calculations and the hyper-Rayleigh scattering technique were used to validate the proposed method.

Dipole control of Rashba spin splitting in a type-II Sb/InSe van der Waals heterostructure

InSe monolayer, belonging to group III–VI chalcogenide family, has shown promising performance in the realm of spintronic. Nevertheless, the out-of-plane mirror symmetry in InSe monolayer constrains the electrons' degrees of freedom, and this will confine its spin-related applications. Herein, we construct Sb/InSe van der Waals heterostructure to extend the electronic and spintronic properties of InSe. The density functional theory is utilized to verify the tunable electronic properties and Rashba spin splitting (RSS) of Sb/InSe heterostructure. According to the obtained results, the Sb/InSe heterostructure can be considered as a direct band gap semiconductor with typical type-II band alignment, where the electrons and holes are localized in the InSe and Sb layers, respectively. The RSS is recognized at conduction band minimum around Γ point in Sb/InSe, which is induced by the spontaneous internal electric field with electric dipole moment of 0.016 e Å from Sb to InSe. The vertical strain, in-plane strain, and external electric field are employed to modulate the strength of RSS. The Rashba coefficient and dipole moment exhibit the similar variation tendency, suggesting the strength of RSS depends on the magnitude of dipole moment. The controllable RSS makes Sb/InSe heterostructure become an appropriate candidate material for spintronic devices.

Photoconductivity along the Polymer/Polymer Interface

The effect of photoexcitation on the electrical conductivity of the interface between two polydiphenylenephthalide (PDP) polymer films is discovered. It is shown that ultraviolet radiation makes the main contribution to the generation of photoconductivity. Long-term relaxation of photoconductivity is observed after extinction of illumination. Based on electrophysical measurements and comparing the results of optical studies, it is concluded that ultraviolet radiation has an effect on the dipole moment magnitude.

Single-Molecule-Doped Crystalline Nanosheets for Delicate Photophysics Studies and Directional Single-Photon-Emitting Devices

Single molecules in solids have been considered as an attractive class of solid-state single quantum systems because they can be chemically synthesized at low cost to have stable narrow transitions at desired wavelengths. Here we report and demonstrate single dibenzoterrylene molecules in crystalline anthracene nanosheets as a robust and versatile solid-state platform for delicate photophysics studies and building blocks of single-photon devices. The high-quality nanosheet sample enables robust studies of delicate single-molecule photophysics at room temperature, including the first real-time observation of single molecule insertion site jump, quantitative measurements of the associated changes of dipole moment orientation and magnitude, unambiguous determination of excitation-power dependent intersystem crossing rate and triplet lifetime. Moreover, we demonstrate the flexible assembly of the nanosheets into a planar antenna device to achieve bright single-molecule emission with a Gaussian emission pattern. The thin thickness, good photostability and mechanical stability make the dibenzoterrylene-in-anthracene nanosheet system an excellent candidate of static quantum nodes in integrated photonic circuit.

Фотопроводимость вдоль границы раздела полимер/полимер

Abstract The effect of photoexcitation on the electrical conductivity of the interface between two polydiphenylenephthalide (PDP) polymer films is discovered. It is shown that ultraviolet radiation makes the main contribution to the generation of photoconductivity. Long-term relaxation of photoconductivity is observed after extinction of illumination. Based on electrophysical measurements and comparing the results of optical studies, it is concluded that ultraviolet radiation has an effect on the dipole moment magnitude.

Computational mathematics applied to astrophysics: Three cases of study

The role of computational mathematics on the study of the fundamental properties of neutrinos and axions and their impact on the energy loss within stellar structure is illustrated in this work. The theoretical predictions, done with the aid of a numerical code for simulating stellar evolution, are used in three cases of interest: the number of neutrinos reaching our planet from the closest stellar system, calculated by modelling its two main stars and their corresponding neutrino spectrum; the magnitude of the neutrino magnetic dipole moment and the axion-electron coupling constant is estimated by comparing stellar models to the tip-RGB of fifty globular clusters; and, finally, the survival of the Earth, after the Sun becomes a red giant is tested for an scenario in which axions and neutrinos are being simultaneously produced within the solar core.

Molecular structure, dynamics and adsorption behavior of water molecules and ions on [0 1 0] surface of γ-FeOOH: A molecular dynamics approach

The interaction between chloride ions and passivate film of steel bars determines the corrosion resistance of iron materials. In this study, the molecular structure, dynamics properties and adsorption behavior of water molecules and ions on passivate film surface is systematically investigated by molecular dynamics simulation method. This interfacial model is constructed for NaCl solution with 1.5 mol/L near the γ-FeOOH [0 1 0] surface. The FeO6 octahedron, exhibiting strong hydrophilic nature within the surface, provides a large amounts of oxygen sites to form H-bonds with the neighboring water molecules. The surface water molecules, distributed in the first adsorbed layer, not only show a comparably high magnitude of dipole moment but also tend to develop an H-down orientation with respect to the γ-FeOOH substrate. Solid oxygen and hydrogen atoms in the γ-FeOOH substrate, which replace the surrounding water molecules, change the hydration structure of ions and the adsorbed ions mobility. Furthermore, the sodium and chloride ions can be adsorbed by the iron hydroxyl surface in different ways. On the one hand, by forming NaO bond with solid oxygen in the iron hydroxyl, the sodium ions can penetrate into the vacancy areas between the neighboring FeO6 octahedrons. On the other hand, chloride ions form H-bonds with the neighboring FeOH groups and associate with sodium ions on the surface to form the cation-anion ionic pairs. Both H-bond connection and the cation-anion ionic pairs restrict the chloride ions in the γ-FeOOH substrate. Additionally, due to the attraction of the solid substrate, the diffusion coefficient of solution species within the surface dramatically decrease by 70% and the resident time of water and ions in the vicinity of γ-FeOOH substrate is elongated more than twice as compared with that in bulk solution. Hopefully, this paper can provide valuable insights and interpret the corrosion mechanism of iron materials at the molecular level.

Structure factor of colloidal magnetic fluid

We determined with Langevin dynamics simulations the structure factor of a monodisperse ferrofluid as a function of the density of the suspension, and dipole strength in the particles valid for hard ferrofluids. The structure factor shows the transition from a liquid-like ordering of the particles at low density and dipole moment up to the formations of chain structures at high dipole strength. The collective diffusion coefficient shows a decaying dependence on the dipole moment magnitude for low density of colloid, however, at a high density, such a dependence gets reversed, and the diffusion increases with the dipole moment.

Flexoelectric Effects in Corrugated Boron Nitride Nanoribbons

Hexagonal boron nitride (h-BN) monolayer is an isostructural analogue to graphene and promising dielectric. Inspired by recent experimental reports, we focus on suspended and corrugated boron nitride nanoribbons (BNRs) as model systems, and report an intriguing flexoelectric polar effect using a series of ab initio-based density functional theory and tight binding calculations. Our results decode various synergies of the complex flexoelectrical properties including the role of corrugation height, structural deformation, and orbital mixing in corrugated BNRs. We demonstrate structural deformation of BNRs significantly contribute to the magnitude of electric dipole moment and bandgap closing, converting the insulating BNRs to semiconductors. This important finding, combined with the fundamental insights into the nature of electromechanical coupling, provides key hypotheses for design and modulation of novel nanoelectronic and nanophotonic devices.

Structure and Dynamics of the Bcl-2 Promoter G-Quadruplex using the Drude Polarizable Force Field

G-quadruplexes (GQ) are noncanonical nucleic acid structures that form in guanine-rich sequences and exist in a variety of topological forms. The guanine bases in GQ arrange in a square planar configuration and stack to form tetrads via Hoogsteen hydrogen bonding and coordination of ions like K+. These highly ordered secondary structures are implicated in the regulation of gene expression and genome maintenance, and alterations to their structures contribute to diseases such as cancer. The B-cell CLL/lymphoma 2 (bcl-2) oncogene is associated with a variety of cancers and its promoter features a GQ that arises due to two consecutive substitutions of guanine with thymine. Understanding the forces driving GQ folding and stabilization is required for developing novel therapeutics that target these structures. To develop a greater understanding of the atomistic details in the bcl-2 GQ, we performed molecular dynamics simulations using the CHARMM36 additive and Drude-2017 polarizable force fields. In the classical Drude oscillator model, electronic degrees of freedom are modeled as negatively charged particles attached harmonically to all heavy atoms. This approach overcomes limitations of nonpolarizable force fields, which approximate average polarization via assignment of partial charges. We performed simulations of the mutant bcl-2 promoter GQ and created the wild-type sequence by reverting the point mutations. The wild-type sequence was then thermally denatured and allowed to re-fold to determine the structural differences between the mutant bcl-2 GQ and the native, wild-type fold. Our analysis provides insight into the stability of the bcl-2 GQ structure, backbone conformational ensembles in dihedral space, base-ion interaction energetics, and the magnitude and fluctuation of dipole moments. These simulations illustrate that polarization is integral for tetrad stability and suggests that the Drude force field is essential for simulating GQ structures.

Assessment of Functionals for TDDFT Calculations of One- and Two-Photon Absorption Properties of Neutral and Anionic Fluorescent Proteins Chromophores

Performance of DFT functionals with different percentages of exact Hartree-Fock exchange energy (EX) is assessed for recovery of the CC2 reference one- (OPA) and two-photon absorption (TPA) spectra of fluorescent proteins chromophores in vacuo. The investigated DFT functionals, together with their EX contributions are BLYP (0%), B3LYP (20%), B1LYP (25%), BHandHLYP (50%), and CAM-B3LYP (19% at short range and 65% at long range). Our test set consists of anionic and neutral chromophores as naturally occurring in the fluorescent proteins. For the first time, we compare TDDFT and CC2 methods for higher excited states than the S1 state, exhibiting relatively large TPA intensity. Our TDDFT results for neutral chromophores reveal an increase in excitation energies as well as TPA and OPA intensities errors, compared to CC2-derived results, as the DFT functional contains less exact exchange. The long-range-corrected CAM-B3LYP functional performs the best, closely followed by BHandHLYP, while BLYP usually significantly underestimates all investigated spectral properties, hence being the worst in reproducing the reference CC2 results. The hybrid B3LYP and B1LYP functionals can be roughly placed in between. We propose that TDDFT may underestimate the TPA intensities for neutral chromophores of fluorescent proteins due to underestimated oscillator strengths between some excited states. In the case of anionic chromophores, we find that B3LYP and B1LYP functionals overcome others in terms of reproducing CC2 excitation energies. On the other hand, however, TPA intensity is usually significantly underestimated, and in this respect, CAM-B3LYP functional seems to be again superior. In contrast to the case of neutral chromophores, it seems that a large magnitude of excited-state dipole moments or changes in dipole moments upon excitation may be the driving force behind high TPA transition moments.

Dipole moment of polyhedral water clusters: mathematical relationships and their application

Polyhedral water clusters are characterized by exponential proton disorder and a complex molecular interaction. Nevertheless, a simple theory has been developed for these systems. It allows predicting classes of the most stable proton configurations that differ in the arrangement of hydrogen atoms (protons) in the hydrogen bonds. The stability for a particular configuration is evaluated on the basis of the analysis of local topological characteristics of the hydrogen bond network. However, the stability of water clusters is determined also by another, clearly non-topological global characteristic: the magnitude of the total dipole moment. In this article we show that the total dipole moment of polyhedral water clusters is proportional to the vector sum of polyhedron edges if their direction coincides with the direction of hydrogen bonds. This makes it possible not to take into account separately the contribution of free (dangling) hydrogen atoms when classifying proton configurations.