Shell Charge Research Articles

Microvascular behavior of microbubbles is strongly influenced by shell charge and polyethyleneglycol coat

Microvascular behavior of microbubbles is strongly influenced by shell charge and polyethyleneglycol coat

Unified study of lattice dynamics of NiO

A unified study of lattice dynamics of paramagnetic NiO has been studied by correcting the basic equations of the three-body force shell model for the valency of the cations and anions. The shell charge and core charge parameters are also modified. This approach explains the complete lattice dynamics of NiO successfully only when both the ions are taken to be polarizable. There is good scope for fresh determination of positive ion polarizability and Debye temperature variation.

Charge density distribution and bond characterization of metal dialkyldithiocarbamate complexes (M=Co, Ni)

Electron density distribution of metal dithiocarbamate complexes, Co(S 2CNMe 2) 3 and Ni(S 2CNEt 2) 2, are studied both by single X-ray diffraction method and by theoretical quantum molecular orbital calculation. Bond characterization is made in terms of deformation density, topological analysis on total electron density and Fermi hole distribution. The cobalt(III) ion is coordinated with three ‘chemically equivalent’ planar bidentate ligands. The structure of the complex is like a ‘three-bladed propeller’. The Ni(II) ion is coordinated with two ligands in a square planar fashion. Deformation density distribution and topological analysis based on multipole model and molecular orbital calculations (DFT) are performed. The asphericity in electron density around the metal ion is clearly demonstrated; where local electron density accumulation is found at d π directions but local electron density depletion is found at d σ direction. The agreement between experiment and theory is good. The comparison between ligand dimer (S 2CNEt 2) 2, and metal complexes are made. With the topological analysis, the shape of valence shell charge concentration (VSCC) of each atom is illustrated. The bond characterization is made through topological properties associated with bond critical point (BCP). The linear relationship between the electron density at the bond critical point, ρ( r c), and the bond length leads to the conclusion that ρ( r c) is a good indicator of bond strength. The bond type is determined by the Laplacian at BCP, the total energy density at BCP and the Fermi-hole function.

On the Full Topology of the Laplacian of the Electron Density II: Umbrella Inversion of the Ammonia Molecule

The full topology of L(r), which is defined as minus the Laplacian of the electron density, ∇2ρ, has recently been explored for the water molecule (Coord. Chem. Rev. 2000, 197, 169). In this work, we have investigated the changing topology during the “umbrella” inversion in ammonia. The maxima in L(r) are points of local charge concentration, which can be associated with the electron pairs of VSEPR theory. We examine changes in three valence shell charge concentration (VSCC) and three depletion (VSCD) graphs as a function of the angle between the C3 axis and a hydrogen. Through the use of planar graphs, the transition mechanisms can be easily rationalized. The previously noted double maxima in L(r), corresponding to the lone-pair of nitrogen, found at the transition state for inversion is shown to persist for geometries distorted considerably from planar. The transitions between structures in the valence shell charge concentration and charge depletion graphs do not occur simultaneously.

Charge Density and Topological Analysis of Pentafluorobenzoic Acid

A charge density study of crystalline pentafluorobenzoic acid has been carried out using high-resolution X-ray diffraction data collected at 110 K. Two multipole refinement models based on the rigid-pseudoatom formalism were used for topological analysis, and the results were compared to those of theoretical calculations for the isolated molecule. In an analysis of the topological parameters at the bond critical points, the discussion focuses on the C−F bond, the hydrogen bond, and intramolecular and intermolecular weak F···O and F···F‘ interactions. Moreover, the geometrical distribution of the nonbonded valence shell charge concentrations was studied at oxygen and fluorine atoms on the basis of experimental data.

Lattice Dynamics of Transition Metal Oxides-An Application to FeO in the Paramagnetic Phase

The basic equations of three-body force shell model have been corrected for the ionic charge parameter Z . This correction also modifies the expressions for the shell and core charge parameters. Our model has been applied to study the phonon dispersion curves, Debye temperatures variation, combined density of states and two-phonon Raman scattering spectra of wustite. This approach has been found successful in interpreting the complete lattice dynamics of FeO only when both the ions are considered to be polarizable. There is good scope for the fresh determination of positive ion polarizability and Debye temperatures variation. It is concluded that the presence of magnetic and anharmonic interactions have no effect on the lattice dynamics of FeO in its paramagnetic phase.

On the full topology of the Laplacian of the electron density

In this work we briefly review the use of the function L( r ), which is defined as minus the Laplacian of the electron density, ∇ 2 ρ, in the context of the theory of ‘atoms in molecules’. The topology of L( r ) can be almost faithfully mapped onto the electron pairs of the VSEPR model. The computation of the gradient vector field L( r ) opens new avenues for the further quantification of this mapping. Although major questions are still outstanding this contribution explores for the first time the full topology of L( r ) for a molecule. In water there are four regions: the Core Shell Charge Concentration (CSCC), the Core Shell Charge Depletion (CSCD), the Valence Shell Charge Concentration (VSCC) and the Valence Shell Charge Depletion (VSCD). Each region has a set of L( r ) critical points coagulating in a graph, except the CSCC. In analogy with the topology of the electron density we propose the term basin interaction line for the pair of gradient paths linking two basins in L( r ), and the term interbasin surface for the surface separating two basins. We present a systematic study of the water molecule, which possesses 43 critical points in L( r ). The question is raised how a basin in L( r ) can be linked with the domain of the VSEPR model.

CCD Charge Density Study on Crystals with Large Unit Cell Parameters: The Case of Hexagonall-Cystine

The electron density of l-cystine has been analyzed using 110 K single-crystal Mo Kα X-ray diffraction data to a resolution of (sin θ/λ)max = 1.123 A-1 with a CCD area detector. Due to the large c-parameter (55.9 A), a discussion is made for choosing the best experimental data collection strategy and data reduction. A multipolar pseudo-atom density model was fitted against the 2309 observed data with I > 3σ(I), [R(F) = 0.014, RW(F) = 0.019, S = 0.73]. The deformation density distribution and topological analysis of charge density clearly reveals disulfide bridge characteristic features and sulfur lone pair electron regions which validate high-level ab initio calculations. The valence shell charge concentration (VSCC) suggests sp3 hybridization of sulfur atoms.

Laplacian and bond critical point properties of the electron density distributions of sulfide bonds; a comparison with oxide bonds

Topological and bond critical point properties of electron density distributions, ρ(r), were calculated for a series of sulfide molecules, containing first- and second-row main group M-cations. Laplacian maps of the distributions, ∇ 2 ρ(r), show that the valence shell charge concentration (VSCC) of the sulfide anion is highly polarized and extended into the internuclear region of the M-S bonds, coalescing with the VSCCs of the more electronegative first-row cations. On the other hand, maps for a corresponding set of oxide molecules show that the oxide anion tends to be less polarized and more locally concentrated in the vicinity of its valence shell, particularly when bonded to second-row M-cations. A search for extrema in the ∇ 2 ρ(r) distributions reveals maxima in the VSCCs that can be ascribed to bonded and nonbonded electron pairs. The different and distinctive properties of sulfides and oxides are examined in terms of the number and the positions of the electron pairs and the topographic features of the Laplacian maps. The evidence provided by the electron density distributions and its topological properties indicates that the bonded interactions in sulfides are more directional, for a given M-cation, than in oxides. The value of the electron density distribution at the bond critical point and the length of a given M-S bond are reliable measures of a bonded interaction, the greater the accumulation of the electron density and the shorter the bond, the greater its shared (covalent) interaction.

Core distortions in metal atoms and the use of effective core potentials

The recent experimental determination of the geometry of Ti(CH 3) 2Cl 2 shows it to be inconsistent with the VSEPR model, a result not uncommon for molecules containing transition metal atoms. The valence shell charge concentrations (CCs) that appear as maxima in L( r)=−∇ 2 ρ( r), provide a physical basis for the VSEPR model of molecular geometry for main group molecules. The same model accounts for the geometry of transition metal molecules with the proviso that the CCs are formed within the outer shell of the core of the metal atom, as defined by the shell structure of L( r). This observation appears to be in conflict with calculations for Ti(CH 3) 2Cl 2 showing that its geometry can be predicted using an effective core potential for the metal atom, a procedure that would appear to preclude the presence of core distortions. The apparent contradiction is resolved by distinguishing between the definition of the core using L( r) and one based on the orbital model.

Monopole and electrically charged dust thin shells in general relativity: Classical and quantum comparison of hollow and atomlike configurations

We give a comparative description of monopole and electrically charged spherically symmetric dust thin shells. Herewith we consider two of the most interesting configurations: the hollow shell and shell, surrounding a body with opposite charge. The classification of shells in accordance with the types of black holes and traversable wormholes is constructed. The theorems for the parameters of turning points are proved. Also for atomlike configurations the effects of screening (electrical case) and amplification (monopole case) of the internal mass by shell charge are studied. Finally, one considers the quantum aspects; herewith, exact solutions of wave equations and bound states spectra are found.

Valence shell structures in the distributions of the Laplacian of the electron density and the one-electron potential for diatomic molecules

The valence shell charge concentration, VSCC, in an atom is defined by Bader as the outermost spherical region for which ∇2ρ(r)<0. We compare and contrast an alternate definition of the VSCC as the outermost spherical region for which ∇2ρ(r)/2ρ(r)<0. The quantity ∇2ρ(r)/2ρ(r), termed the one-electron potential (OEP), is implicit in the (exact) one-electron Schrödinger equation. In a homonuclear diatomic bound by shared interaction, the VSCCs of the atoms are merged. Provided that the merged VSCCs persist, the diatomic is enclosed by an outermost zero-valued surface encompassing the VSCC of the molecule. The outermost ∇2ρ(r)=0 surface is termed the reactive surface while the outermost OEP=0 surface is termed the molecular envelope. In cases where the VSCCs are not revealed in the atoms, the reactive surfaces and molecular envelopes are incomplete or absent in the diatomics. We show that in many diatomics the molecular envelope is present although the reactive surface is missing. In an ionic diatomic bound by closed-shell interaction, the VSCC of the cation can disappear. Otherwise, fragments of the cationic VSCC, termed ligand-opposed charge-concentration (LOCC), may remain opposite to the anion. In general, the LOCC is absent when the VSCC is not revealed in the atom. We show that the LOCC is more widespread in the distribution of OEP than ∇2ρ(r).

EMPIRICAL PARAMETERIZATION OF INTER-IONIC POTENTIALS FOR ALKALINE EARTH FLUORIDES

When the functional forms of non-coulombic inter-ionic short-range potentials have been defined, the bulk properties of ionic crystals can be calculated. The parameters presented in potential functions are determined by fitting procedure, to reproduce as colsely as possible the measured crystal data. In the present study, the shell model is employed for the investigations of CaF2, SrF2 and BaF2 ionic crystals. Remarkable feature of the present fitting procedure is that shell charges are sure to be negative and recent experimental data are adopted. The anion (F-) charge, which is assumed to be common to the three fluorides, is adjusted to 0.97e. In so doing, the obtained model parameter set is able to produce a satisfactory agreement between the calculated results and the experimental data, such as lattice formation energies, elastic constants, dielectric constants, ionic polarizabilities, transverse optic and Raman frequencies, for the alkaline earth fluorides.

Experimental Determination of the Electron Density Topology in a Non-centrosymmetric Transition Metal Complex: [Ni(H3L)][NO3][PF6] [H3L =N,N‘,N‘‘-Tris(2-hydroxy-3-methylbutyl)-1,4,7-triazacyclononane

We have determined the experimental charge density of the title compound, a large pendant arm macrocyclic complex, by fitting a multipole model to high-resolution X-ray diffraction data. We find redistribution of the charge density from the ligating nitrogen and oxygen atoms to the central nickel ion which considerably reduces the charge on the metal. While the d-orbital populations are in agreement with ligand-field theory, the charge density of the metal shows diffuse features which are ascribed to metal 4s and 4p participation in the metal−ligand bonding. Additionally, the trigonal-planar arrangement of critical points in −∇2ρ(r) within the valence shell charge concentration (VSCC) of the ligating oxygen atom provides evidence for metal−oxygen π-bonding.

The topology of the valence shell and the electric field gradient at the nitrogen nucleus in aziridines

The ab initio molecular charge density ρ(r) of substituted aziridines was calculated at the MP2 level for R = -H, -CH3, -CF3, -Cl, -NO2, -CN, -OH, -NO, and -F. The use of the topology of the Laplacian of ρ(r) allowed the analysis of the electric field gradient (EFG) at the nitrogen nucleus directly in terms of its valence shell charge concentration. The EFG changed sign and the orientation of its y- and z-axes with respect to aziridine when R = -Cl, -NO2, -CN, -OH, -NO, and -F. The changes in the EFG in these aziridines upon substitution were correlated with those calculated in the valence charge concentrations along the direction of the N—R bond. The sign of the qzz component and the orientation of the principal axes of the EFG tensor were found to be determined by the relative value of the contributions from the charge concentrations at the points in the valence shell along the N—C and N—R bond directions. Key words: molecular charge distribution, aziridines, Laplacian of the charge density, electric field gradient.

Valence Shell Charge Topology, Atomic Graphs, and Electric Field Gradients in One- to Four-Bonded Nitrogen Atoms

The atomic graph containing the extremes of the Laplacian of the charge distribution −▿2ρ(r) of the valence shell for each type of coordinated N atom in some nitriles, imines, diimides, planar and nonplanar amines, and substituted ammonium ions was obtained. Each bonding configuration showed specific correlations between the values of −▿2ρ(r) at some of the extremes present in the N atomic graph and the components of the electric field gradient (EFG) tensor. It was found that the qzz principal component of the EFG was generated mainly by the nonbonding charge concentration “lone pair” of the N valence shell for coordination one to three studied in this work. For the four-coordinated N atom with Td symmetry, a relationship was obtained with a difference between the values of −▿2ρ(r) at the bonded maxima corresponding to the different bonds. The asymmetry parameter of the EFG was found to be connected with the atomic graphs through the values of −▿2ρ(r) at specific sets of saddle points of the N valence she...

Geometry distorting intramolecular interactions to an alkyne group in 1-(2-aminophenyl)-2-(2-nitrophenyl)ethyne: a joint experimental? theoretical study

X-Ray diffraction studies on the title compound show that in the crystalline state the amino and nitro groups lie to the same side of the triple bond and are hydrogen bonded to each other. There is a short contact to each alkyne carbon atom; one from a nitro oxygen atom, which leads to a trans bend in the alkyne, and one from an amino hydrogen atom. The analyses of the ab initio electron densities for this molecule and for its conformer with functional groups lying on opposite sides of the triple bond, using the theory of atoms in molecules, indicate that in both cases there is a bond path and associated (3, –1) critical point between the nitro oxygen atom and the nearer alkyne carbon atom, but not between the amino hydrogen atom and its alkyne carbon neighbour. Plots of the Laplacian for both conformers indicate local concentrations of ‘lone-pair’ density on the nitro oxygen atom, with local depletions in the valence shell charge concentration on the alkyne carbon atom, indicative of a nucleophilelelectrophile type interaction. The geometry of the interaction of the alkyne with the amino hydrogen atom is far from optimal in the trans conformer.

Um Modelo Macroscópico para a Força de Reação Radiativa.

We present a simple macroscopic system, a spherical shell with a uniform charge distribution, inside of which we put a test charge. We show that the spherical shell charge distribution, when accelerated, produces a non null electromagnetic field that acts on the test charge i nducing, near the spherical shell center, force such as the Lorentz-Dirac radiation reaction one.

Effects of chromium on DNA replication in vitro.

Chromium is an environmentally significant human carcinogen with complicated metabolism and an unknown mechanism of mutagenesis. Chromium(VI) is taken up by cells as the chromate anion and is reduced intracellularly via reactive intermediates to stable Cr(III) species. Chromium(III) forms tight complexes with biological ligands, such as DNA and proteins, which are slow to exchange. In vitro, CrCl3.6H2O primarily interacts with DNA to form outer shell charge complexes with the DNA phosphates. However, at micromolar concentrations, the Cr(III) binds to a low number of saturable tight binding sites on single-stranded M13 DNA. Additional chromium interacts in a nonspecific manner with the DNA and can form intermolecular DNA cross-links. Although high concentrations of Cr(III) inhibit DNA replication, micromolar concentrations of Cr(III) can substitute for Mg2+, weakly activate the Klenow fragment of E. coli DNA polymerase I (Pol I-KF), and act as an enhancer of nucleotide incorporation. Alterations in enzyme kinetics induced by Cr(III) increase DNA polymerase processivity and the rate of polymerase bypass of DNA lesions. This results in an increased rate of spontaneous mutagenesis during DNA replication both in vitro and in vivo. Our results indicate that chromium(III) may contribute to chromate-induced mutagenesis and may be a factor in the initiation of chromium carcinogenesis.

Shell boundaries and core-valence regions within atomic isoelectronic series using electrostatic potential-density ratio

It is shown the locations of the characteristic topological featues in the average electrostatic potential defined by the ratio of the electrostatic potential V( r) and the spherically averaged electron density p( r) can be identified with the inter-shell boundaries. Numerical tests using the nonrelativistic numerical Hartree-Fock wave functions corresponding to the Ne, Ar, Kr, Xe and Rn isoelectronic series provide excellent estimates of the formal shell charges. Accurate estimates of the core-valence regions for atoms beyond Ar and the other isoelectronic are provided for the first time.