Electrostatic Energy Research Articles

Relation between Electrostatic Charge Density and Spin Hamiltonian Models of Ligand Field in Lanthanide Complexes.

Understanding the ligand field interactions in lanthanide-containing magnetic molecular complexes is of paramount importance for understanding their magnetic properties, and simple models for rationalizing their effects are much desired. In this work, the equivalence between electrostatic models, which derive their results from calculating the electrostatic interaction energy of the charge density of the 4f electrons in an electrostatic potential representing the ligands, and the common quantum mechanical effective spin Hamiltonian in the space of the ground J multiplet is formulated in detail. This enables the construction of an electrostatic potential for any given ligand field Hamiltonian and discusses the effects of the ligand field interactions in terms of an interaction of a generalized 4f charge density with the electrostatic potential. Such models often allow for an easier rationalization of the ligand field interactions, and it can be hoped that the results in this work will help us to better understand the effects of ligand field in lanthanide complexes.

Effect of Polymer Network Architecture on Adsorption Kinetics at Liquid–Liquid Interfaces: A Comparison Between Poly(NIPAM-co-AA) Copolymer Microgels and Interpenetrating Network Microgels

Understanding the adsorption features of polymer microgels with different chemical compositions and structures is crucial in studying the mechanisms of respective emulsion stabilization. Specifically, the use of stimuli-responsive particles can introduce new properties and broaden the application range of such complex systems. Recently, we demonstrated that emulsions stabilized by microgels composed of interpenetrating networks (IPNs) of poly-N-isopropylacrylamide (PNIPAM) and polyacrylic acid (PAA) exhibit higher colloidal stability upon heating compared to PNIPAM homopolymer and other relevant PNIPAM-based copolymer counterparts. In the present work, using pendant drop tensiometry, we studied the evolution of water–tetradecane interfacial tension during the adsorption of PNIPAM-PAA IPN particles, comparing them with single-network P-(NIPAM-co-AA) and PNIPAM microgels. The results showed that, despite having the same chemical composition, copolymer particles exhibit completely different adsorption behavior in comparison to other microgel architectures. The observed disparity can be attributed to the nonuniform distribution of charged acrylic acid groups within the P-(NIPAM-co-AA) network obtained through precipitation polymerization. Oppositely, the presence of IPN architecture provides a uniform distribution of different monomers inside respective microgels. Additionally, hydrogen bonding between PNIPAM and PAA subchains appears to reduce the electrostatic energy barrier, enhancing the ability of IPN particles to successfully cover the liquid interface. Overall, our findings confirm the efficiency of using PNIPAM-PAA IPN microgels for the preparation of oil-in-water emulsions and their stability, even when the temperature rises above the lower critical solution temperature of PNIPAM.

Bluues_cplx: Electrostatics at Protein-Protein and Protein-Ligand Interfaces.

(1) Background: Electrostatics plays a capital role in protein-protein and protein-ligand interactions. Implicit solvent models are widely used to describe electrostatics and complementarity at interfaces. Electrostatic complementarity at the interface is not trivial, involving surface potentials rather than the charges of surfacial contacting atoms. (2) Results: The program bluues_cplx, here used in conjunction with the software NanoShaper to compute molecular surfaces, has been used to compute the electrostatic properties of 756 protein-protein and 189 protein-ligand complexes along with the corresponding isolated molecules. (3) Methods: The software we make available here uses Generalized Born (GB) radii, computed by a molecular surface integral, to output several descriptors of electrostatics at protein (and in general, molecular) interfaces. We illustrate the usage of the software by analyzing a dataset of protein-protein and protein-ligand complexes, thus extending and refining previous analyses of electrostatic complementarity at protein interfaces. (4) Conclusions: The complete analysis of a molecular complex is performed in tens of seconds on a PC, and the results include the list of surfacial contacting atoms, their charges and Pearson correlation coefficient, the list of contacting surface points with the electrostatic potential (computed for the isolated molecules) and Pearson correlation coefficient, the electrostatic and hydrophobic free energy with different contributions for the isolated molecules, their complex and the difference for all terms. The software is readily usable for any molecular complex in solution.

Probe on the pivotal role of green rust in improving the enzymatic activity and facilitating the formation of 1O2 in Fenton-like process for degradation of 4-chlorophenol

Iron-based materials have demonstrated significant efficacy in catalyzing hydrogen peroxide (H2O2) for the removal of antibiotics from aquatic environments. Green rust (GR), a hybrid valence state iron-based catalyst, was synthesized. By exploiting the catalytic properties of glucose oxidase (GOx) to generate H2O2 from glucose (Glu), a GR-GOx/Glu system for the removal of recalcitrant organic compound 4-chlorophenol (4-CP) was constructed. In terms of pollutant degradation efficiency, an increase of 30% was observed compared to Fe2+/H2O2 system. Utilizing density functional theory (DFT), we calculated the electrostatic potential energy and charge density distribution, demonstrating the existence of active electron transfer between GR and flavin adenine dinucleotide (FAD), which subsequently enhanced the activity of GOx. The enhancement was pivotal for the sustained generation of preferred oxidative species and rapid degradation of pollutants within the system. Furthermore, the acids and H2O2 generated during enzyme catalysis not only neutralized the alkalinity released by the Fenton-like reaction but also promoted the conversion of superoxide radical (·O2-) to singlet oxygen (1O2). Overall, this study elucidates the fundamental motivation underlying the enhancement of enzymatic activity and highlights the critical role of 1O2 within the system, providing valuable insights into the potential mechanisms by which metal hydroxides catalyze the H2O2 process.

Electrostatic energy of a solid spherical sector with uniform volume charge density

Electrostatic energy of a solid spherical sector with uniform volume charge density

Molecular dynamics analysis for aggregation phenomenon of aged asphalt and depolymerisation mechanism of regenerants

ABSTRACT The depolymerisation mechanism of various regenerants, when applied to the aged asphalt aggregate structure, was investigated to provide insights for the design and development of regenerants. This study focused on the molecular aggregation of the regenerant-aged asphalt system using molecular dynamics simulation technology. Simulation showcased that the uneven charge distribution in asphaltene molecules and the absence of charge in the central region are prerequisites for the electrostatic attraction of asphaltene molecules, which significantly affects their aggregation, and asphaltene molecules in heavy-aged asphalt are prone to forming stable aggregation structures. Among the four components of aged asphalt, asphaltene molecules exhibited the most significant self-aggregation, followed by saturates, while resin and aromatic molecules showed relatively weaker self-aggregation. Low temperatures encouraged aggregation, whereas high temperatures discouraged it, and ageing elevated the molecular self-aggregation, intensifying with the progression of asphalt ageing. Regenerants improved the depolymerisation of asphaltene aggregates, and fatty acid glycerides presented the most effective depolymerisation, followed by aromatic hydrocarbons and alkanes, while glycerol’s performance was the least effective. To choose regenerant composition materials, those with low electrical potential energy, weak polarity, low polar functional group content or non-polarity should be selected to ensure superior depolymerisation, permeation fusion, and regeneration effects.

A drug-drug co-amorphous system for highly improved solubility of breviscapine: an experimental and computational study

Drug-drug co-amorphous systems are a promising approach to improve the aqueous solubility of poorly water-soluble drugs. This study explores the combination of breviscapine (BRE) and matrine (MAT) form an amorphous salt, aiming to synergistically enhance the solubility and dissolution of BRE. In silico analysis of electrostatic potential and local ionization energy were conducted on BRE-MAT complex to predict the intermolecular interactions, and solvent-free energies were calculated using thermodynamic integration and density functional theory. The co-amorphous mixture, prepared by solvent evaporation, was characterized using various analytical techniques, including polarized microscopy, differential scanning calorimetry, and powder X-ray diffraction, confirming its amorphous nature. Fourier transform infrared spectroscopy and molecular dynamic simulations revealed strong hydrogen bonding, with a proton transfer from the carboxyl group of BRE to the tertiary amine nitrogen of MAT. The resulting co-amorphous salt demonstrated substantial solubility improvement (> 8000-fold in water) and enhanced in vitro dissolution of BRE. The study also confirmed that the co-amorphous salt maintained physical stability at 40 °C and 75% relative humidity over 6 months. These findings provide a viable strategy for developing drug-drug co-amorphous formulations to enhance solubility and stability, with significant potential for pharmaceutical applications.

VDAC Solvation Free Energy Calculation by a Nonuniform Size Modified Poisson-Boltzmann Ion Channel Model.

Voltage-dependent anion channel (VDAC) is the primary conduit for regulated passage of ions and metabolites into and out of a mitochondrion. Calculating the solvation free energy for VDAC is crucial for understanding its stability, function, and interactions within the cellular environment. In this article, numerical schemes for computing the total solvation free energy for VDAC-comprising electrostatic, ideal gas, and excess free energies plus the nonpolar energy-are developed based on a nonuniform size modified Poisson-Boltzmann ion channel (nuSMPBIC) finite element solver along with tetrahedral meshes for VDAC proteins. The current mesh generation package is also updated to improve mesh quality and accelerate mesh generation. A VDAC Solvation Free Energy Calculation (VSFEC) package is then created by integrating these schemes with the updated mesh package, the nuSMPBIC finite element package, the PDB2PQR package, and the OPM database, as well as one uniform SMPBIC finite element package and one Poisson-Boltzmann ion channel (PBIC) finite element package. With the VSFEC package, many numerical experiments are made using six VDAC proteins, eight ionic solutions containing up to four ionic species, including ATP4- and Ca2+, two reference states, different boundary values, and different permittivity constants. The test results underscore the importance of considering nonuniform ionic size effects to explore the varying patterns of the total solvation free energy, and demonstrate the high performance of the VSFEC package for VDAC solvation free energy calculation.

Dynamic Modulation of Ions Solvation Sheath by Butyramide as Molecular Additives in Aqueous Batteries.

The high activity of water in aqueous battery electrolytes can trigger side reactions, limiting their large-scale application. Additives that form contact pairs (CPs) with cations by coordinating with them can effectively reduce water's activity. However, due to the complex interactions between ions, additives, and solvent molecules and the fact that current strategies for additive screening primarily rely on static physical parameters, the dynamic mechanisms that govern the modulation of ion solvation sheaths are still poorly understood. In this study, we introduce butyramide (BUT) as a molecular additive and employ molecular simulations to demonstrate its regulatory effect on the hydration sheath of Ca2+, which is more pronounced than that for Na+. The dynamic process by which BUT replaces water molecules in the tight hydration sheath of Ca2+ is elucidated by forming a stable [BUT-Ca2+(H2O)7] complex that suppresses water molecule activity. At a 2 M concentration, the free energy barrier for the transition from contact pair (CP) to solvent-shared pair (SP) for Ca2+ is 11.7 kJ/mol higher than that for Na+ at 8.5 kJ/mol, consistent with the cationic Hofmeister series. Furthermore, the stability and dynamic fluctuations among solvent-separated pair (SSP), SP, and CP states are attributed to the balance between electrostatic attractive potential energy and hydration repulsive potential energy, supported by quantum chemical calculations of the ion desolvation process. Using BUT as an additive presents a promising strategy to enhance battery performance by modulating the solvation environment of metal ions, addressing the growing demand for safer and more sustainable energy storage solutions.

The impact of charge regulation and ionic intranuclear environment on the nucleosome core particle.

We theoretically investigate how the intranuclear environment influences the charge of a nucleosome core particle (NCP)-the fundamental unit of chromatin consisting of DNA wrapped around a core of histone proteins. The molecular-based theory explicitly considers the size, shape, conformation, charge, and chemical state of all molecular species-thereby linking the structural state with the chemical/charged state of the system. We investigate how variations in monovalent and divalent salt concentrations, as well as pH, affect the charge distribution across different regions of an NCP and quantify the impact of charge regulation. The effective charge of an NCP emerges from a delicate and complex balance involving the chemical dissociation equilibrium of the amino acids and the DNA-phosphates, the electrostatic interaction between them, and the translational entropy of the mobile solution ions, i.e., counter ion release and ion condensation. From our results, we note the significant effect of divalent magnesium ions on the charge and electrostatic energy as well as the counterion cloud that surrounds an NCP. As a function of magnesium concentration, charge neutralization, and even charge inversion is predicted-in line with experimental observation of NCPs. The strong Mg-dependence of the nucleosome charge state arises from ion bridges between two DNA-phosphates and one Mg2+ ion. We demonstrate that to describe and predict the charged state of an NCP properly, it is essential to consider molecular details, such as DNA-phosphate ion condensation and the acid-base equilibrium of the amino acids that comprise the core histone proteins.

Effect of Aggregate Crystalline Surface Anisotropy on Asphalt–Aggregate Interface Interaction Based on Molecular Dynamics

To investigate the influence of aggregate crystalline surface anisotropy on the interfacial effects and understand the bonding mechanisms, molecular dynamics simulations were employed to analyze the spatial distribution, diffusion, and adhesion properties of asphalt on typical acidic (α-quartz, SiO2) and weakly alkaline (calcite, CaCO3) aggregates. The results indicated that different types and crystalline surfaces of aggregates did not alter the distribution patterns of the asphalt components on their surfaces. However, the magnitude of the radial distribution function (RDF) varied with different crystalline surfaces, and a higher RDF value was correlated with better adhesion performance. Different diffusion behaviors were exhibited by asphalt molecules on different crystalline surfaces: slower diffusion was correlated with stronger adhesion and faster diffusion with weaker adhesion. The adhesion performance was significantly affected by the anisotropy of the aggregates. In the asphalt–SiO2 system, the van der Waals energy and surface atomic density were the major influencing factors, whereas, in the asphalt–CaCO3 system, the electrostatic energy was significantly influenced by ionic bonding. Overall, alkaline aggregates showed greater adhesion performance with asphalt than acidic aggregates.

Seeding Control in Chirality Triggering of Red-Emitting Organic Charge-Transfer Cocrystal Helixes from Achiral Molecules.

Supramolecular chirality has gained immense attention for great potential, in which the rational engineering strategy facilitates unique helical stacking/assembly, high chiroptical behavior, and prime biomedical activity. In this study, we reported a novel chiral organic donor-acceptor cocrystal based on asymmetrical components of benzo(b)naphtho(1,2-d)thiophene (BNT) and 9-oxo-9H-indeno(1,2-b)pyrazine-2,3-dicarbonitrile (DCAF) that exhibited red emission using a simple solution approach. During the self-assembly, a kinetically controlled growth of polar solvent or substrate induction led to the chiral packing and helical morphology twisted by the cooperation of electrostatic potential energy and chirality. Intriguingly, a "seeding-control" mechanism was newly developed for the production of c-BNT-DCAF helical crystals with a defined uniform chiral form, which enables chirality transfer and amplification from the microscopic to macroscopic level via supramolecular stacking. By introducing chiral additives or even a small break at the edge, the first nucleus acted as a chiral seeding to guide the donor/acceptor molecule alignment into the same handedness. A remarkably high dissymmetry factor (glum) value of 0.1 was demonstrated on the chiral manipulated ribbons, which is the highest among the reported charge-transfer complexes. This work offers us more paths for the design of chiral supramolecular systems for vital applications in organic optoelectronics, micro/nanomechanics, and biomimetics.

Optimization of physicochemical properties of theophylline by forming cocrystals with amino acids.

This study presents the synthesis and characterization of novel cocrystal structures of theophylline (THE) with the amino acids gamma-aminobutyric acid (GABA) and l-arginine (ARG). Despite a large number of reports about THE cocrystals, no crystallographic parameters of cocrystals formed by THE and amino acids have been reported. THE is characterized by low solubility, while amino acids as cocrystal co-formers (CCFs) are increasingly recognized for their high solubility and safety. Consequently, the synthesis of cocrystals with amino acids has garnered considerable research interest. To optimize THE's physicochemical properties, amino acids were chosen as CCFs, resulting in the synthesis of two novel cocrystals: THE-GABA and THE-ARG-2H2O. Comprehensive characterization, such as X-ray diffraction analysis, spectral analysis, thermal analysis, and dynamic vapor sorption were conducted for THE-GABA and THE-ARG-2H2O, alongside stability and solubility assessments. To better explain the characterization and evaluation results, the theoretical calculation methods were adopted, including the molecular electrostatic potential (MESP), topological analysis, energy framework, Hirshfeld surface and crystal voids. The study's findings reveal that the solubility and permeability of THE in both novel cocrystals, THE-GABA and THE-ARG-2H2O, have increased, especially in the latter. Meanwhile, the hygroscopicity of them was at a low level which was basically consistent with THE.

Orbital XY models in moiré superlattices

Abstract Moiré superlattices provide a new platform to engineer various many-body problems. In this work, we consider arrays of quantum dots (QD) realized on semiconductor moiré superlattices with a deep moiré potential. We diagonalize single QD with multiple electrons, and find degenerate ground states serve as local degrees of freedom (qudits) in the superlattice. With a deep moiré potential, the hopping and exchange interaction between nearby QDs become irrelevant, and the direct Coulomb interaction of the density-density type dominates. Therefore, nearby QDs must arrange the spatial densities to optimize the Coulomb energy. When the local Hilbert space has a two-fold orbital degeneracy, we find that a square superlattice realizes an anisotropic XY model, while a triangular superlattice realizes a generalized XY model with geometric frustration.

Mirror resonances in Be9 and B9 within an α+α+N model

Using an α+α+N three-body model, we describe the ground and excited unbound states above the three-body threshold of A=9 mirror nuclei. We investigate the energy levels of low-lying and highly excited resonances below ≈10MeV excitation energy of Be9 and B9 mirror nuclei with the complex-scaling method. The same number of solutions are found for both mirror nuclei, namely, thirteen resonances, 3/21−4−, 5/21−3−, 1/21−3−, 7/21,2−, and 9/2−, including the ground state for odd parity states, and eight resonances 5/21,2+, 3/21,2+, 7/21,2+, and 9/21,2+, for even-parity states with the exception of the low-lying 1/2+ state. These results are compared with experimentally observed and other theoretically calculated results. The band structures of odd and even parity states for both Be9 and B9 mirror nuclei are discussed in relation to the effect of the Coulomb energy difference. Published by the American Physical Society 2024

Reversible Manipulation of Polar Topologies in Oxide Ferroelectrics via Electric Fields.

Polar topologies show great potentials in memories and other nano-micro devices. To integrate with silicon conducting circuits, it is vital to understand the dynamic evolution and the transformation of different domain configurations under external stimulus. Here in situ transmission electron microscopy is performed and the electrically controlled creation and annihilation of large-scale polar flux-closure array from typical c/a domains in PbTiO3/SrTiO3 bilayers is directly observed. It is found that the transformation is reversible after removal of external electric fields. Increasing external electric fields on (PbTiO3/SrTiO3)5 multilayered films, it is further found that the flux-closure domains are nucleated and propagated via the steps of first the formation of new c domains and then connection with neighboring c domains. The transition from a/c domains to flux-closure arrays under electric fields is collaborated with evaluating energy variations by phase-field simulations in which the electrostatic energy plays an important role. These results demonstrate the polar topologies can be reversibly manipulated by external stimuli, which sheds light on further understanding the dynamics behavior of polar topologies and helps for future nanoelectric applications.

The C-terminal activating domain promotes pannexin 1 channel opening

Pannexin 1 (Panx1) constitutes a large pore channel responsible for the release of adenosine triphosphate (ATP) from apoptotic cells. Strong evidence indicates that caspase-mediated cleavage of the C-terminus promotes the opening of the Panx1 channel by unplugging the pore. However, this simple pore-plugging mechanism alone cannot account for the observation that a Panx1 construct ending before the caspase cleavage site remains closed. Here, we show that a helical region located immediately before the caspase cleavage site, referred to as the "C-terminal activating domain (CAD)", plays a pivotal role in facilitating Panx1 activation. Electrophysiology and mutagenesis studies uncovered that two conserved leucine residues within the CAD play a pivotal role. Cryoelectron microscopy (Cryo-EM) analysis of the construct ending before reaching the CAD demonstrated that the N terminus extends into an intracellular pocket. In contrast, the construct including the CAD revealed that this domain occupies the intracellular pocket, causing the N terminus to flip upward within the pore. Analysis of electrostatic free energy landscape in the closed conformation indicated that the intracellular side of the ion permeation pore may be occupied by anions like ATP, creating an electrostatic barrier for anions attempting to permeate the pore. When the N terminus flips up, it diminishes the positively charged surface, thereby reducing the drive to accumulate anions inside the pore. This dynamic change in the electrostatic landscape likely contributes to the selection of permeant ions. Collectively, these experiments put forth a mechanism in which C-terminal cleavage liberates the CAD, causing the repositioning of the N terminus to promote Panx1 channel opening.

Minimum energy principles in electrostatics

Abstract We employ the principle of minimum energy of the electrostatic field to derive Laplace’s equation for electric potential in charge-free space. We also apply the principle of minimum electrical potential energy of a system of discrete charges to explain the possibility of the existence of their stable equilibrium configuration on the surface of a conductor.

Bifuruzan skeleton: developing new high-energy and high-density energetic materials.

High-energy density materials (HEDMs) are integral to modern society and are in high demand. Consequently, the design and synthesis of energetic material molecules have garnered significant research interest. This study focuses on the furazan ring system as a core for developing superior HEDMs. We employed density functional theory (DFT) to assess the properties of 27 novel energetic compounds, including their geometries, densities, enthalpies of formation, detonation velocities, detonation pressures, and molecular orbital energies (HOMO-LUMO). The computation of detonation velocity and detonation pressure was based on theoretical density and enthalpy of formation. The findings revealed that incorporating energetic groups into the furazan framework, linked by sec-ammonia bridge (-NH-), enhances both the detonation performance and oxygen content of the materials. This enhancement guides the future synthetic endeavors aimed at creating advanced HEDMs. DFT has been employed to investigate the detonation performance and stability of energetic materials. Molecular optimization and performance metrics were all calculated using the DFT-B3LYP method with a 6-311 + G* basis set. The optimization and volume calculations were performed using the Gaussian 09 package. The electrostatic potential energy was computed using Multiwfn software. The impact sensitivity of the designed molecules was calculated using the heat of detonation model.

Probing the Nanostructure and Reactivity of Epoxy-Amine Interphases.

Understanding and controlling the structure of interphase regions in epoxy resins have been a long-standing goal in high-performance composite and coating development, since these are widely considered to be weak points in the microstructure of these materials, determining key properties such as fracture strength and barrier performance. These buried nanoscale regions are, however, inaccessible to conventional analytical techniques, and little is understood about their underlying formation mechanism. Here, we combine molecular dynamics (MD) simulation with nanoscale infrared chemical mapping to develop new understanding of the interphase using model epoxy-amine binders composed of diglycidyl ether of bisphenol A (DGEBA) cross-linked using m-xylylenediamine (MXDA). Iron oxide powders are used as exemplary surfaces, where we demonstrate that the electrostatic binding energies between the amine cross-linker and particles range from repulsive (magnetite, Fe3O4) to weakly attractive (hematite, Fe2O3) to strong immobilization (goethite, FeOOH). We find that interfacial binding occurs upon mixing and determines the overall level of residual amine content in the bulk matrix but does not correlate with a detectable amine depletion in the vicinity of particles. In all cases, an excess of both epoxy and amine functionality is detected close to particles, and the extent of matrix undercuring is found to be dependent on the entropic segregation of the unreacted material during the ambient cure. Detailed MD simulations demonstrate that spatial segregation of the unreacted precursors is expected in the interphase, leading to the experimental observation that, even after extensive postcure heating, individual particles remain embedded in a nanoscale underdeveloped environment.