Electrostatic Charge Distributions Research Articles

Research cloud electrification model in the Wisconsin dynamic/microphysical model 2: Charge structure in an idealized thunderstorm and its dependence on ion generation rate

This paper presents a cloud electrification model, which we embedded in the Wisconsin Dynamic and Microphysical Model-2 and labels it CEMW. WISDYMM-2 makes use of two-moment cloud microphysics to produce 5 hydrometeor types (e.g., cloud-droplets, raindrops, cloud-ice, snow, and graupel) that are used by CEMW for storm electrification where storm convection is initiated by a warm air bubble that is placed over an assumed flat terrain with no surface friction. In this paper, CEMW was used to examine cloud electrification in a simulated (idealized) thundercloud and to examine the impact of various formulations of the ion generation rate by cosmic rays (G) on how the storm and individual hydrometeor charges were structured. Results showed that the CEMW generates reasonable electric charge structures, which is qualitatively similar to those published by Brothers et al. (2018) in that it consists of a number of smaller positively and negatively charged regions. This structure differs from a charge structure generally depicted by conceptual models based on conventional balloon measurements of electric field. However, simulated balloon measurements in the idealized thunder clouds further revealed that CEMW produces electrostatic charge distributions and electric field profiles that are in good agreement with those reported by real balloon measurements. How charge is structured by CEMW was tested by formulating G (the ion generation rate) in two different ways. First, we derived G assuming fair weather conditions, which is the usual way applied in cloud electrification modelling. Second, we calculated Gs using the Cosmic Ray Atmospheric Cascade: Cosmic Ray Induced Ionization model for several values of solar modulation potential and cut-off rigidity. The results show that the structure of the electric charge fields does not differ much depending on G, but the fundamental difference between G is in the amount of electric discharges.

Protein C-GeM: A Coarse-Grained Electron Model for Fast and Accurate Protein Electrostatics Prediction.

The electrostatic potential (ESP) is a powerful property for understanding and predicting electrostatic charge distributions that drive interactions between molecules. In this study, we compare various charge partitioning schemes including fitted charges, density-based quantum mechanical (QM) partitioning schemes, charge equilibration methods, and our recently introduced coarse-grained electron model, C-GeM, to describe the ESP for protein systems. When benchmarked against high quality density functional theory calculations of the ESP for tripeptides and the crambin protein, we find that the C-GeM model is of comparable accuracy to ab initio charge partitioning methods, but with orders of magnitude improvement in computational efficiency since it does not require either the electron density or the electrostatic potential as input.

EFFICIENT SYNTHESIS OF NOVEL TRICYCLIC BENZOXAZINE DERIVATIVE VIA RING OPENING OF EPOXIDE ALONG THE MP AND DFT STUDIES OF STRUCTURAL, SPECTROSCOPIC (IR, RAMAN, UV-VIS), THERMODYNAMIC, ORBITALS AND NLO PROPERTIES OF DESIRED TRICYCLIC BENZOXAZINE DERIVATIVE

Ring opening of 2-nitro phenyl glycidyl ether by chelated amino acid ester enolate provides access to desired novel benzoxazine derivative just over a few steps. Theoretical study on the molecular structure of 2,2,2-trifluoro-N-(1-oxo-2,3,3a,4-tetrahydro-1H-benzo[b]pyrrolo[1,2-d][1,4]ox-azin-2-yl) acetamide (S11) is presented by using second order Moller Plesset (MP2) as well as density functional theory (DFT) level calculations. The calculated vibrational frequencies were assigned into normal modes of vibration by the use of potential energy distribution (PED). The positive charge on all hydrogen atoms were obtained by charge distribution calculations using Mulliken, electrostatic and natural charge distributions. Similar electrophilic and nucleophilic regions were observed from the calculated electrostatic potential surface calculations. The time dependent density functional theory (TD-DFT) calculations were performed to obtain electronic transitions within the molecule. The frontier molecular orbital (FMO) analysis was leading to the possible charge transfer within the molecule. The natural bond orbital (NBO) analysis provided information regarding the interaction between the donor and acceptor in bond. The statistical thermodynamic functions (dipole moment, internal energy, enthalpy, Gibbs free energy, entropy, heat capacities and partition functions) were calculated at the range of temperature from 10-500 K

In silico mutation on a mutant lipase from Acinetobacter haemolyticus towards enhancing alkaline stability

Alkaline-stable lipases are highly valuable biocatalysts that catalyze reactions under highly basic conditions. Herein, computational predictions of lipase from Acinetobacter haemolyticus and its mutant, Mut-LipKV1 was performed to identify functionally relevant mutations that enhance pH performance under increasing basicity. Mut-LipKV1 was constructed by in silico site directed mutagenesis of several outer loop acidic residues, aspartic acid (Asp) into basic ones, lysine (Lys) at positions 51, 122 and 247, followed by simulation under extreme pH conditions (pH 8.0–pH 12.0). The energy minimized Mut-LipKV1 model exhibited good quality as shown by PROCHECK, ERRAT and Verify3D data that corresponded to 79.2, 88.82 and 89.42% in comparison to 75.2, 86.15, and 95.19% in the wild-type. Electrostatic surface potentials and charge distributions of the Mut-LipKV1 model was more stable and better adapted to conditions of elevated pHs (pH 8.0 − 10.0). Mut-LipKV1 exhibited a mixture of neutral and positive surface charge distribution compared to the predominantly negative charge in the wild-type lipase at pH 8.0. Data of molecular dynamics simulations also supported the increased alkaline-stability of Mut-LipKV1, wherein the lipase was more stable at a higher pH 9.0 (RMSD = ∼0.3 nm, RMSF = ∼0.05–0.2 nm), over the optimal pH 8.0 of the wild-type lipase (RMSD = 0.3 nm, RMSF = 0.05–0.20 nm). Thus, the adaptive strategy of replacing surface aspartic acid to lysine in lipase was successful in yielding a more alkaline-stable Mut-LipKV1 under elevated basic conditions.Communicated by Ramaswamy H. Sarma

Structural Basis for the Selective Inhibition of Cdc2-Like Kinases by CX-4945.

Cdc2-like kinases (CLKs) play a crucial role in the alternative splicing of eukaryotic pre-mRNAs through the phosphorylation of serine/arginine-rich proteins (SR proteins). Dysregulation of this processes is linked with various diseases including cancers, neurodegenerative diseases, and many genetic diseases. Thus, CLKs have been regarded to have a potential as a therapeutic target and significant efforts have been exerted to discover an effective inhibitor. In particular, the small molecule CX-4945, originally identified as an inhibitor of casein kinase 2 (CK2), was further revealed to have a strong CLK-inhibitory activity. Four isoforms of CLKs (CLK1, CLK2, CLK3, and CLK4) can be inhibited by CX-4945, with the highest inhibitory effect on CLK2. This study aimed to elucidate the structural basis of the selective inhibitory effect of CX-4945 on different isoforms of CLKs. We determined the crystal structures of CLK1, CLK2, and CLK3 in complex with CX-4945 at resolutions of 2.4 Å, 2.8 Å, and 2.6 Å, respectively. Comparative analysis revealed that CX-4945 was bound in the same active site pocket of the CLKs with similar interacting networks. Intriguingly, the active sites of CLK/CX-4945 complex structures had different sizes and electrostatic surface charge distributions. The active site of CLK1 was somewhat narrow and contained a negatively charged patch. CLK3 had a protruded Lys248 residue in the entrance of the active site pocket. In addition, Ala319, equivalent to Val324 (CLK1) and Val326 (CLK2), contributed to the weak hydrophobic interactions with the benzonaphthyridine ring of CX-4945. In contrast, the charge distribution pattern of CLK2 was the weakest, favoring its interactions with benzonaphthyridine ring. Thus, the relatively strong binding affinities of CX-4945 with CLK2 are consistent with its strong inhibitory effect defined in the previous study. These results may provide insights into structure-based drug discovery processes.

Halogen and Hydrogen Bonding Interplay in the Crystal Packing of Halometallocenes.

This paper focuses in the influence of halogen atoms in the design and structural control of the crystal packing of Group VIII halogenated metallocenes. The study is based on the present knowledge on new types of intermolecular contacts such as halogen (X⋯X, C-X⋯H, C-X⋯π), π⋯π, and C-H⋯π interactions. The presence of novel C-H⋯M interactions is also discussed. Crystal packings are analysed after database search on this family of compounds. Results are supported by ab initio calculations on electrostatic charge distributions; Hirshfeld analysis is also used to predict the types of contacts to be expected in the molecules. Special attention is given to the competition among hydrogen and halogen interactions, mainly its influence on the nature and geometric orientations of the different supramolecular motifs. Supramolecular arrangements of halogenated metallocenes and Group IV di-halogenated bent metallocenes are also compared and discussed. Analysis supports halogen bonds as the predominant interactions in defining the crystal packing of bromine and iodine 1,1′-halometallocenes.

The role of halogen interactions in the crystal structure of biscyclopentadienyl dihalides

The purpose of this survey is to examine the crystal packing of bent metallocenes, namely, group IV, V and VI biscyclopentadienyl dihalides and dihydrides, first synthesized in the late 1950s. This analysis is based on the present knowledge on new types of intermolecular contacts such as halogen and C–H⋯π interactions as well as dihydrogen bonds. Results are also supported by ab initio calculations that provide information on electrostatic charge distributions, in particular the effect of two V-shaped metal–halogen bonds on the molecular electron density distribution. Type I halogen interactions do not appear to be affected by this feature, specifically the geometric parameters and variation of atom polarizability, but the resultant electronic density distribution precludes the presence of Type II halogen bonds. Special attention is given to the competition among hydrogen and halogen interactions, in particular its influence on the nature and geometric orientations of the different supramolecular motifs and, ultimately, on the space groups observed for each crystal.

Detection of Moisture Adsorption on Joining Surface Using Static Electricity Distribution

Condition of a material surface is an important factor in strength of bond for adhesion. Especially, penetration of water into the adhesive joint part have negative effects on the strength of bond such as degradation of a polymer, corrosion degradation of an adherend, and degradation of a mechanical properties in the interfacial surface. Technologies of some surface analyses have been developed in order to evaluate the moisture adsorption on the material surface. The technologies, they are necessary to use specific materials or vacuum environments, are limited to tools usage. However, various adhesion between different materials have carried out in the air at production site, so the existing techniques cannot be applied as the surface analysis and evaluation at the production site. Therefore development of a new surface analysis technique adaptable a variety of materials in air, non-contact and non-destructive in order to evaluate the moisture adsorption on the surface is demanded. So, we have focused on a relationship between static electricity and moisture as a means of observing the state of the material surface. Static electricity is less likely to occur with high humidity, also static electricity on the insulator surface is inhomogeneously charged. If it is possible to observe the two-dimensional distribution of static electricity with high spatial resolution, it may be possible to detect indirectly the influence of moisture adsorbed locally to the surface. So far, static electricity measurement technologies using targeted electrostatic fields include the static induction type, vibrating reed induction type fieldmeters and chopper stabilized instruments. Their sensors using the technologies are often used at the production site. However, when the sensors are used to measure electrostatic charge distributions within an object surface, it is necessary to narrow the sensing area for high spatial resolution and scan point by point over the whole surface. As a result, measurements of the charge distributions are quite costly in terms of time. State of the charge distribution on the surface change over time, it is important key to measure the static electricity distribution in a short period of time. We developed a sensor that can visualize static electricity with a spatial resolution at 1 mm. Moreover, technology of measuring static electricity distribution with high spatial resolution in a short period of time using the 30 parallel sensor. In this study, it was examined on detection of a moisture adsorption by survey changes of the charge distribution on the object surface using the developed measurement technology of the static electricity distribution. First, static electricity distribution in an area of 30 mm × 30 mm on an acrylic surface was evaluated when the acrylic and a dried nylon cloth was friction. As a result, irregularly charged distribution of surface potential in the range of -1000 V ~ +1000 V was observed. Although absolute amount of the surface potential distribution was slightly changed, the shape of the distribution even after three minutes of the friction was unchanged. This result indicates that the electrostatic charges are unable to move within the same surface by reason of the insulating acrylic surface. Next, the part of the same acrylic surface and the wet nylon cloth was contacted lightly, it was completely dry the sample surface by natural evaporation. The charge distribution on the acrylic surface in the state was evaluated. As the result, the charges of the part on the surface contact with the wet nylon was lost. These results imply that the electrostatic charges flow as surface current through the formed water film on the sample surface, and the charges leaks in the air. Thus, it was revealed that the influence of moisture adsorption on the surface was able to detect indirectly by utilizing static electricity distribution. The measurement technique of static electricity distribution is possible to adapt to various materials in air, non-contact and non-destructive. Therefore, it was suggested the possibility of simply evaluating the influence of moisture adsorption on joining surface at production site of the adhesion.

Analytical expressions for electrostatics of graphene structures

This study focuses on electrostatics of various graphene structures as graphene monolayer, graphene nanoribbons, as well as multi-layer graphene or graphene flakes. An atomistic moment method based on classical electrostatics is utilized in order to evaluate the charge distribution in each nanostructure. Assuming a freestanding graphene structure in an infinite or in a semi-infinite space limited by a grounded infinite plane, the effect of the length, width, number of layers and position of the nanostructure on its electrostatic charge distributions and total charge and capacitance is examined through a parametric analysis. The results of the present show good agreement with corresponding available data in the literature, obtained from different theoretical approaches. Performing nonlinear regression analysis on the numerical results, where it is possible, simple analytical expressions are proposed for the total charge and charge distribution prediction based on structure geometry.

Mapping the electrostatic potential of Au nanoparticles using hybrid electron holography

Electron holography is a powerful technique for characterizing electrostatic potentials, charge distributions, electric and magnetic fields, strain distributions and semiconductor dopant distributions with sub-nm spatial resolution. Mapping internal electrostatic and magnetic fields within nanoparticles and other low-dimensional materials by TEM requires both high spatial resolution and high phase sensitivity. Carrying out such an analysis fully quantitatively is even more challenging, since artefacts such as dynamical electron scattering may strongly affect the measurement. In-line electron holography, one of the variants of electron holography, features high phase sensitivity at high spatial frequencies, but suffers from inefficient phase recovery at low spatial frequencies. Off-axis electron holography, in contrast, can recover low spatial frequency phase information much more reliably, but is less effective in retrieving phase information at high spatial frequencies when compared to in-line holography. We investigate gold nanoparticles using hybrid electron holography at both atomic-resolution and intermediate magnification. Hybrid electron holography is a novel technique that synergistically combines off-axis and in-line electron holography, allowing the measurement of the complex wave function describing the scattered electrons with excellent signal-to-noise properties at both high and low spatial frequencies. The effect of dynamical electron scattering is minimized by beam tilt averaging.

Bipolar electrostatic charge and mass distributions of powder aerosols – Effects of inhaler design and inhaler material

This study investigated the effect of modifying the Aerolizer® inhaler design and material on bipolar charging of a powder aerosol. The modified inhalers included various grid configurations, mouthpiece lengths, air inlet sizes, and were also constructed of different materials (acrylonitrile butadiene styrene, acetal, low density polyethylene, nylon, polypropylene, and stainless steel). The novel BOLAR™ (Dekati Ltd., Kangasala, Finland) was used to characterise bipolar charge and mass distributions. All of the tested inhalers showed spray-dried mannitol powder carried significantly different positive and negative charges that had higher magnitudes than the measured net charge. The estimated elementary charges per particle indicated the aerosols carried significant levels of charge that may potentially influence particle deposition in the lungs. Increasing the grid voidage decreased the magnitude of charging, as did reducing the air inlet size, whereas mouthpiece length had no obvious effect. The observed effects on charging due to modifications to the inhaler design could be explained by a difference in the level of contacts due to impaction between the particles and the inhaler internal surface. Bipolar charge of mannitol did not differ when dispersed by inhalers constructed of different materials. This could be attributed to various potential factors such as the very brief contact time between the powder and the inhaler material, as well as coating of the inhaler interior by the powder which effectively renders the surface to be mannitol-like. Overall, the comparable q/m profiles across all the inhaler designs and inhaler materials indicated charging correlated with the mass distributions and modifications to the inhaler did not affect the qualitative bipolar charge characteristics of mannitol powder.

Measuring Bipolar Charge and Mass Distributions of Powder Aerosols by a Novel Tool (BOLAR).

The Bipolar Charge Analyzer (BOLAR) was evaluated for measuring bipolar electrostatic charge and mass distributions of powder aerosols generated from a dry powder inhaler. Mannitol powder (5, 10, and 20 mg) was dispersed using an Osmohaler inhaler into the BOLAR at air flow rates of 30 or 60 L/min. As the aerosol sample was drawn through the BOLAR, the air flow was divided into six equal fractions. Five of them entered individual detection tubes with a defined cutoff diameter in the range of 0.95 to 16.36 μm (depending on the flow rate) and the remaining (i.e., the sixth) fraction passed through a reference chamber. The aerosols that entered the detection tubes were separated according to the particle charge polarity (positive, negative, or neutral) and charge was measured by separate electrometers. The deposited powder of a single actuation from the inhaler was chemically assayed using high performance liquid chromatography. Additionally, the aerosol measurements were conducted on a modified Classic Electrical Low Pressure Impactor (ELPI) for comparison of the net specific charge per size fraction. Spray-dried mannitol carried significantly different positively and negatively charged particles in each of the five defined particle size fractions. The charge-to-mass ratio (q/m) of positively charged particles ranged from +1.11 to +32.57 pC/μg and negatively charged particles ranged from -1.39 to -9.25 pC/μg, resulting in a net q/m of -3.08 to +13.34 pC/μg. The net q/m values obtained on the modified ELPI ranged from -5.18 to +4.81 pC/μg, which were comparable to the BOLAR measurements. This is the first full report to utilize the BOLAR to measure bipolar charge and mass distributions of a powder aerosol. Positively and negatively charged particles were observed within each size fraction, and their corresponding q/m profiles were successfully characterized. Despite some potential drawbacks, the BOLAR has provided a new platform for investigating bipolar charge in powder aerosols for inhalation.

Molecular dynamics studies on the NMR structures of rabbit prion protein wild type and mutants: surface electrostatic charge distributions

Prion diseases are invariably fatal and highly infectious neurodegenerative diseases that affect a wide variety of mammalian species such as sheep and goats, cattle, deer and elk, and humans. But for rabbits, studies have shown that they have a low susceptibility to be infected by prion diseases. This paper does molecular dynamics (MD) studies of rabbit NMR structures (of the wild type and its two mutants of two surface residues), in order to understand the specific mechanism of rabbit prion proteins (RaPrPC). Protein surface electrostatic charge distributions are specially focused to analyze the MD trajectories. This paper can conclude that surface electrostatic charge distributions indeed contribute to the structural stability of wild-type RaPrPC; this may be useful for the medicinal treatment of prion diseases.

Point charges optimally placed to represent the multipole expansion of charge distributions.

We propose an approach for approximating electrostatic charge distributions with a small number of point charges to optimally represent the original charge distribution. By construction, the proposed optimal point charge approximation (OPCA) retains many of the useful properties of point multipole expansion, including the same far-field asymptotic behavior of the approximate potential. A general framework for numerically computing OPCA, for any given number of approximating charges, is described. We then derive a 2-charge practical point charge approximation, PPCA, which approximates the 2-charge OPCA via closed form analytical expressions, and test the PPCA on a set of charge distributions relevant to biomolecular modeling. We measure the accuracy of the new approximations as the RMS error in the electrostatic potential relative to that produced by the original charge distribution, at a distance the extent of the charge distribution–the mid-field. The error for the 2-charge PPCA is found to be on average 23% smaller than that of optimally placed point dipole approximation, and comparable to that of the point quadrupole approximation. The standard deviation in RMS error for the 2-charge PPCA is 53% lower than that of the optimal point dipole approximation, and comparable to that of the point quadrupole approximation. We also calculate the 3-charge OPCA for representing the gas phase quantum mechanical charge distribution of a water molecule. The electrostatic potential calculated by the 3-charge OPCA for water, in the mid-field (2.8 Å from the oxygen atom), is on average 33.3% more accurate than the potential due to the point multipole expansion up to the octupole order. Compared to a 3 point charge approximation in which the charges are placed on the atom centers, the 3-charge OPCA is seven times more accurate, by RMS error. The maximum error at the oxygen-Na distance (2.23 Å ) is half that of the point multipole expansion up to the octupole order.

Low Order Physical Multipoles

Point multipole expansions are widely used to gain physical insight into complex distributions of charges and to reduce the cost of computing interactions between such distributions. However, practical applications that typically retain only a few leading terms may suffer from unacceptable loss of accuracy in the near-field. We propose an alternative approach for approximating electrostatic charge distributions, Optimal Physical Multipoles (OPMs), which optimally represent the original charge distribution with a set of point charges. By construction, approximation of electrostatic potential based on OPMs retains many of the useful properties of the corresponding point multipole expansion, including the same asymptotic behavior of the approximate potential for a given multipole order. At the same time, OPMs can be significantly more accurate in the near field: up to 5 times more accurate for some of the charge distributions tested here which are relevant to biomolecular modeling. Unlike point multipoles, for point charge distributions the OPM always converges to the original point charge distribution at finite order. Furthermore, OPMs may be more computationally efficient and easier to implement into existing molecular simulations software packages than approximation schemes based on point multipoles. In addition to providing a general framework for computing OPMs to any order, closed-form expressions for the lowest order OPMs (monopole and dipole) are derived. Thus, for some practical applications Optimal Physical Multipoles may represent a preferable alternative to point multipoles.

Bonding patterns of [Ag2‐alanine]0,± hybrid complexes and the implementation of molecular logic gates

AbstractA structural and energetic computational analysis of various conformers of positive, neutral and negatively charged hybrid [Ag2‐alanine]0,± complexes is reported using density functional theory. We show that the overall charge on the hybrid complexes influence the silver coordination mode. The positively charged cluster forms stable conformers via chelate bonds between the carboxylic group and silver dimer while the neutral cluster exhibits covalent bonding between silver and the amine nitrogen. In negatively charged clusters, bonding occurs via a weaker Ag‐hydrogen bond. Unary and binary logic gates NOT, FAN‐OUT, AND, NAND, OR, XOR and NOR are designed using the dependence of bonding patterns on the overall charge state of the cluster. The outputs can be read using an IR readout protocol or electrostatic potential charge distributions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Polarization effects in 2-DEG and 2-DHG AlGaN/AlN/GaN multi-heterostructures measured by electron holography

The electrostatic potential profiles and charge distributions in modulation-doped n-type and p-type AlGaN/AlN/GaN heterostructures have been measured by electron holography with high spatial resolution. For n-type two-dimensional electron gas structure a negative curvature and for p-type two-dimensional hole gas structure a positive curvature in the potential profile at the AlN/GaN interface were observed, which demonstrated the accumulation of two-dimensional carriers. The measured electrostatic potential profiles were also compared with the calculated band diagram in the heterostructures.

Properties of Continuous and Discrete Electrostatic Charge Distributions

The exact form of the charge distribution on toner or carrier particles is a subject of some importance due to the effect of this distribution on forces between these particles and adjacent surfaces. The properties of some simple discrete and continuous charge distributions adjacent a conductive surface are calculated.

Simultaneous Characterization of Aerodynamic Size and Electrostatic Charge Distributions of Inhaled Dry Powder Inhaler Aerosols

Simultaneous Characterization of Aerodynamic Size and Electrostatic Charge Distributions of Inhaled Dry Powder Inhaler Aerosols

The NMR solution structure of recombinant RGD-hirudin

The solution structure of a new recombinant RGD-hirudin, which has the activities of anti-thrombin and anti-platelet aggregation, was determined by 1H nuclear magnetic resonance spectroscopy and compared with the conformations of recombinant wild-type hirudin and hirudin (variant 2, Lys47) of the hirudin thrombin complex. On the basis of total 1284 distance and dihedral angle constraints derived from a series of NMR spectra, 20 conformers were computed with ARIA/CNS programs. The structure of residues 3–30 and 37–48 form a molecular core with two antiparallel β-sheets as the other two hirudins. However, significant differences were found in the surface electrostatic charge distributions among the three hirudins, especially in the RGD segment of recombinant RGD-hirudin. This difference may be greatly beneficial to its additional function of anti-platelet aggregation. The difference in extended C-terminal makes its both ionic and hydrophobic interactions with the fibrinogen recognition exosite of thrombin more effective.