Correction for 'Electrostatic control of regioselectivity viaion pairing in a Au(i)-catalyzed rearrangement' by Vivian M. Lau et al., Chem. Sci., 2014, 5, 4975-4979.
Triboelectrification due to frictional contacts between particles and surfaces is prevalent in many powder handling processes. Aiming to explore the friction‐induced electrostatic charging behavior, ...a discrete element method (DEM) is developed for the first time in the current article, in which a frictional charging model and electrostatic interaction models are implemented. The charge accumulation on both the particles and the surface in a rotational container is then analyzed numerically and experimentally to evaluate the developed DEM. The numerical results for the frictional electrification between insulant particles and an insulant wall agree well with the experimental measurement. It is also shown that both the net charge on the particles and the degree of the particle dispersion are a function of the charging time. Moreover, it is revealed that the friction‐induced particle charge enhances particle dispersion, and increases the granular temperature due to the electrostatic interactions.
Arginine: Its pKa value revisited Fitch, Carolyn A; Platzer, Gerald; Okon, Mark ...
Protein science,
05/2015, Volume:
24, Issue:
5
Journal Article
Peer reviewed
Open access
Using complementary approaches of potentiometry and NMR spectroscopy, we have determined that the equilibrium acid dissociation constant (pKa value) of the arginine guanidinium group is 13.8 ± 0.1. ...This is substantially higher than that of ∼ 12 often used in structure-based electrostatics calculations and cited in biochemistry textbooks. The revised intrinsic pKa value helps explains why arginine side chains in proteins are always predominantly charged, even at pH values as great as 10. The high pKa value also reinforces the observation that arginine side chains are invariably protonated under physiological conditions of near neutral pH. This occurs even when the guanidinium moiety is buried in a hydrophobic micro-environment, such as that inside a protein or a lipid membrane, thought to be incompatible with the presence of a charged group.
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•Tribocharging models often depend on ill-defined or poorly quantified parameters.•An effective empirical model parameter evaluation method is presented and validated.•The efficacy of ...2D/3D DEM models using these parameters is compared and evaluated.•2D and 3D models simulate successfully tribocharging due to single contacts.•Only 3D models agree experimental data in complex (multi-particle/contact) systems.
Many discrete element method (DEM) tribocharging models presented in the literature rely on ill-defined or poorly quantified charging parameters. This work presents a straightforward experimental method to quantify key parameters, namely the charge transfer limit, Γ, and the charging efficiency, κc. These parameters are then used in both 2D and 3D DEM simulations to evaluate the applicability of faster 2D models to tribocharge modelling. Both the 2D and 3D models are found to perform well against the experimental data for single-contact and single-particle, multi-contact systems. However, the 2D model fails to produce good agreement with experimental data for multi-contact, multi-particle systems. This approach for determining experimentally the parameters for the DEM tribocharging model is found to be effective and produces good agreement between simulated and experimental data. This method will improve and simplify the DEM modelling of triboelectric charging in dry material handling processes.
The Adaptive Poisson–Boltzmann Solver (APBS) software was developed to solve the equations of continuum electrostatics for large biomolecular assemblages that have provided impact in the study of a ...broad range of chemical, biological, and biomedical applications. APBS addresses the three key technology challenges for understanding solvation and electrostatics in biomedical applications: accurate and efficient models for biomolecular solvation and electrostatics, robust and scalable software for applying those theories to biomolecular systems, and mechanisms for sharing and analyzing biomolecular electrostatics data in the scientific community. To address new research applications and advancing computational capabilities, we have continually updated APBS and its suite of accompanying software since its release in 2001. In this article, we discuss the models and capabilities that have recently been implemented within the APBS software package including a Poisson–Boltzmann analytical and a semi‐analytical solver, an optimized boundary element solver, a geometry‐based geometric flow solvation model, a graph theory‐based algorithm for determining pKa values, and an improved web‐based visualization tool for viewing electrostatics.
Predators and prey benefit from detecting sensory cues of each other's presence. As they move through their environment, terrestrial animals accumulate electrostatic charge. Because electric charges ...exert forces at a distance, a prey animal could conceivably sense electrical forces to detect an approaching predator. Here, we report such a case of a terrestrial animal detecting its predators by electroreception. We show that predatory wasps are charged, thus emit electric fields, and that caterpillars respond to such fields with defensive behaviors. Furthermore, the mechanosensory setae of caterpillars are deflected by these electrostatic forces and are tuned to the wingbeat frequency of their insect predators. This ability unveils a dimension of the sensory interactions between prey and predators and is likely widespread among terrestrial animals.
Molecular surface electrostatic potentials of SeCl2 reflect the anisotropies of the electronic densities of both the selenium (left) and chlorines (right) in this molecule; both atoms have regions of ...both positive (red, yellow, green) and negative (blue) electrostatic potential. Display omitted
► An overview of the “σ-hole” concept is given. ► σ-Holes on Groups IV–VII atoms explain many long known noncovalent interactions. ► Density difference plots of halogen bonding interactions are presented. ► Electrostatic potentials point to the fallacy of atomic charges. ► Electrostatics/polarization and dispersion can usually explain σ-hole bonding.
Many covalently-bonded atoms of Groups IV–VII have regions of positive electrostatic potential (σ-holes) opposite to the bonds, along their extensions. Through these positive regions, the atoms can interact highly directionally with negative sites. (Halogen bonding, in which the σ-hole is on a Group VII atom, is an example of this, and we suggest that hydrogen bonding is as well.) The formation and observed properties of the resulting noncovalent complexes can be fully explained in terms of electrostatics/polarization plus dispersion as the driving forces; this straightforward interpretation is based largely upon physical observables – electrostatic potentials, geometries, interaction energies and electric fields. More elaborate interpretations, involving less physically-based methods and models, have also been advanced. In this paper, we try to reconcile some of these seemingly different approaches.
Ionic Liquid Crystals: Versatile Materials Goossens, Karel; Lava, Kathleen; Bielawski, Christopher W ...
Chemical reviews,
04/2016, Volume:
116, Issue:
8
Journal Article
Peer reviewed
This Review covers the recent developments (2005–2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive ...overview of the “state-of-the-art” in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.
The net electrostatic charge of most folded proteins has never been measured in solution at pH values different from the isoelectric point. The authors discuss how measuring the net electrostatic ...charge Z of folded, solvated proteins can provide new information about fundamental electrostatic properties of metalloproteins or about processes in which they are involved, for example, electron transfer or metal coordination. For more details see the Concept by B. F. Shaw and C. T. Zahler on page 7581 ff.
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