Importance Of Electrostatic Forces Research Articles

Importance of Electrostatic Forces in Supracolloidal Self-Assembly of Polymer-Functionalized Gold Nanorods

Importance of Electrostatic Forces in Supracolloidal Self-Assembly of Polymer-Functionalized Gold Nanorods

Toward a Physics Based Model of Hypervelocity Dust Impacts

AbstractThere has been important understanding of the process by which a hypersonic dust impact makes an electrical signal on a spacecraft sensor, leading to a fuller understanding of the physics. Zaslavsky (2015), https://doi.org/10.1002/2014ja020635 showed that the most important signal comes from the charging of the spacecraft, less from charging of an antenna. The present work is an extension of the work of Zaslavsky. An analytical treatment of the physics of a hypersonic dust impact and the mechanism for generating an electrical signal in a sensor, an antenna, is presented. The treatment is compared with observations from STEREO and Parker Solar Probe. A full treatment of this process by simulations seems beyond present computer capabilities, but some parts of the treatment must depend on simulations but other features can be better understood through analytical treatment. Evidence for a somewhat larger contribution from the antenna part of the signal than in previous publications is presented. Importance of electrostatic forces in forming the exiting plasma cloud is emphasized. Electrostatic forces lead to a rapid expansion of the escaping cloud, so that it expands more rapidly than it escapes, and sometimes surrounds one or more antennas. This accounts for the ability of dipole antennas to detect dust impacts. Some progress toward understanding occasional negative charging of an antenna is presented, together with direct evidence of such charging. Use of laboratory measurements of charge to estimate size of spacecraft impacts are shown to be not reliable without further calibration work.

Endocytic Trafficking of Nanoparticles Delivered by Cell-penetrating Peptides Comprised of Nona-arginine and a Penetration Accelerating Sequence

Cell-penetrating peptides (CPPs) can traverse cellular membranes and deliver biologically active molecules into cells. In this study, we demonstrate that CPPs comprised of nona-arginine (R9) and a penetration accelerating peptide sequence (Pas) that facilitates escape from endocytic lysosomes, denoted as PR9, greatly enhance the delivery of noncovalently associated quantum dots (QDs) into human A549 cells. Mechanistic studies, intracellular trafficking analysis and a functional gene assay reveal that endocytosis is the main route for intracellular delivery of PR9/QD complexes. Endocytic trafficking of PR9/QD complexes was monitored using both confocal and transmission electron microscopy (TEM). Zeta-potential and size analyses indicate the importance of electrostatic forces in the interaction of PR9/QD complexes with plasma membranes. Circular dichroism (CD) spectroscopy reveals that the secondary structural elements of PR9 have similar conformations in aqueous buffer at pH 7 and 5. This study of nontoxic PR9 provides a basis for the design of optimized cargo delivery that allows escape from endocytic vesicles.

Effects of Molecular Sieving and Electrostatic Enhancement in the Adsorption of Organic Compounds on the Zeolitic Imidazolate Framework ZIF-8

In this work, the adsorption behavior of a range of organic vapors and gases on the zeolitic imidazolate framework, ZIF-8, is investigated using an inverse gas chromatography (IGC) methodology at the zero-coverage limit and elevated temperatures. The measured thermodynamic values and surface energies for the adsorption of n-alkanes on ZIF-8 are found to be reduced from those previously reported for IRMOF-1. This reduction is most likely an effect of the predominately organic accessible surface of ZIF-8 and the resulting weaker interactions in comparison to IRMOF-1. The pore aperture size of ZIF-8, which is significantly reduced from that of IRMOF-1, is seen to introduce molecular sieving effects for branched alkanes, aromatics, and heavily halogenated compounds. Deformation polarizabilities of the adsorbates were used to calculate the specific adsorption free energy, and it is determined that the specific effects account for around 1-5 kJ/mol, or between 10% and 70% of the total free energy of adsorption for the sorbates studied (at 250 °C). The importance of electrostatic forces was seen in the significantly enhanced adsorption of propylene and ethylene in comparison to their respective alkanes and in the direct correlation shown between the specific components of the free energy of adsorption and the adsorbate's dipole moment.

Electrostatic forces in wind-pollination—Part 2: Simulations of pollen capture

During fair-weather conditions, a 100 V m −1 electric field exists between positive charge suspended in the air and negative charge distributed on the surfaces of plants and on the ground. The fields surrounding plants are highly complex reaching magnitudes up to 3×10 6 V m −1. These fields possibly influence the capture of charged wind-dispersed pollen grains. In this article, we model the electric fields around grounded conductive spherical “plants” and then estimate the forces and resulting trajectories of charged pollen grains approaching the plants. Pollen grain capture depends on many factors: the size, density, and charge of the pollen; the size and location of the plant reproductive structures; as well as wind speed, ambient electric field magnitude, and air viscosity. Electrostatic forces become increasingly important as pollen grain charge increases and pollen grain size (mass) decreases. A positively charged pollen grain is attracted to plants, while a negatively charged pollen grain is repelled. The model suggests that a pollen grain (10 μm radius, carrying a positive charge of 1 fC) is captured if passing within 2 mm of the plant. A similar negatively charged pollen grain is repelled and frequently uncapturable. The importance of electrostatic forces in pollen capture is limited by wind, becoming virtually irrelevant at high wind speeds (e.g. 10 m s −1). However, during light wind conditions (e.g. 1 m s −1), atmospheric electricity may be a significant factor in the capture of wind-dispersed pollen.

Molecular mechanisms of the adsorption of a model protein (human serum albumin) on poly(methylidene malonate 2.1.2) nanoparticles.

To understand the molecular mechanisms involved in protein-methylidene malonate 2.1.2 polymer interactions. To assess the importance of electrostatic forces in polymer-protein interactions use was made of HSA and its derivatives, which were anionized by succinylation and aconitylation. Surface plasmon resonance measurements, using the three HSA molecules as immobilized ligands and polymer nanoparticles as analytes in the liquid phase, allowed the determination of initial kinetic constants and affinity constants at equilibrium at two different temperatures. Saturation of binding for the three proteins occurred at approximately 900 protein molecules/nanoparticle. The apparent affinity decreased with increasing electronegativity of the proteins. Surface plasmon resonance measurement of proteins, covalently linked to the chip matrix, showed a high affinity for the nanoparticles (K(A) approximately 10(10) M(-1) and confirmed the moderate decrease of affinity with increasing electronegativity of the modified albumins. Measurements at 25 and 37 degrees C showed no significant increase in the albumin-nanoparticle interactions. Dissociation of the proteins from the nanoparticles could only be realized with chaotropic salt solutions. These results suggest the molecular forces initiating the protein-nanoparticle interactions are mainly of electrostatic nature followed by stabilization by hydrophobic forces. The high affinity confirms the nanoparticles as excellent carriers for protein delivery.

Capillary electroseparations of some di-, tri-, and tetrapeptides and enkephalin-related peptides

Electrophoretic mobilities and capacity factors for short peptides were determined in micellar electrokinetic systems (MEKC) using UV detection at 210 nm. On the basis of determined capacity ratios, taurodeoxycholic acid was found to be a selective micellar agent for peptides. Structural features other than hydrophobicity were found to be decisive for the distribution of the peptides to the micellar phase. Basic peptides of enkephalin-type containing arginine were more highly distributed to the micelles than others, indicating the importance of electrostatic forces in the distribution mechanism. In systems with polyacrylamide-coated capillaries, the micellar velocity toward the anode is larger than the electroosmosis, and conditions permitting splitting of a series of related peptides, i.e., some peptides migrating with the micelles and others toward the cathode resulting in infinite selectivities, were developed. Separation by micellar electrokinetic chromatography is demonstrated to be a suitable alternative for peptides that are difficult to separate by capillary zone electrophoresis.

Substitution of glycine 48 with glutamic acid alters the substrate specificity of the HIV protease: second site revertants demonstrate the importance of electrostatic forces

Substitution of glycine 48 with glutamic acid alters the substrate specificity of the HIV protease: second site revertants demonstrate the importance of electrostatic forces

Electromagnetic energy and power in terms of charges and potentials instead of fields

It has been shown in a previous paper by Konopinski that there are important advantages, particularly to the engineer, in an electro-magnetic theory in which the properties, which are customarily associated with the fields, are assigned instead to the source charges, and measured by the potentials. These properties include stored energy and energy flow. The objective of the paper is to reformulate Poynting's theorem in charge-potential terms, and it is shown that the energy flow vector which is obtained simplifies the quantitative description of electromagnetic power transfer. It is closely related to the circuit concepts familiar to all electrical engineers, and, unlike the Poynting vector, is equally useful in communications and in power-frequency applications. It demonstrates the fundamental importance of electrostatic forces in all electromagnetic devices. The paper also shows that practical difficulties in applying field theory, and, in particular, the Poynting vector, have led to the use of hybrids in which two wholly different viewpoints are mixed.

On the Bacteriolysis by Lysozyme

Summary The bacteriolysis by lysozyme was studied by measuring the light-absorption of a lysing suspension, with a Moll-extinctiometer. In addition to a morphological study, this procedure was applied to the determination of lysozyme, which could be made within 5 per cent, and to a study of the influence of pH and electrolytes. The optimal pH was found to be about 6.2. The optimum is caused by an interaction of two factors: at lower pH's the action of lysozyme increases, but below pH 6.2 the visible lysis is inhibited. The same is the case in distilled water, where a phenomenon, analogous to Nakamura's alkali-phenomenon was found. High concentrations of electrolytes inhibit the primary reaction, adsorption of lysozyme. In this respect the valency of the ions is predominant. Some general remarks are made on the importance of electrostatic forces in similar reactions.