Double Negative Charge Research Articles

Anions as Lewis Acids in Noncovalent Bonds.

The ability of an anion to serve as electron-accepting Lewis acid in a noncovalent bond is assessed via DFT calculations. NH3 is taken as the common base, and is paired with a host of ACln - anions, with central atom A=Ca, Sr, Mg, Te, Sb, Hg, Zn, Ag, Ga, Ti, Sn, I, and B. Each anion reacts through its σ or π-hole although the electrostatic potential of this hole is quite negative in most cases. Despite the contact between this negative hole and the negative region of the approaching nucleophile, the electrostatic component of the interaction energy of each bond is highly favorable, and accounts for more than half of the total attractive energy. The double negative charge of dianions precludes a stable complex with NH3.

Elucidation of the Effect of Phospholipid Charge on the Rate of Insulin Aggregation and Structure and Toxicity of Amyloid Fibrils.

The plasma membrane is a dynamic structure that separates the cell interior from the extracellular space. The fluidity and plasticity of the membrane determines a large number of physiologically important processes ranging from cell division to signal transduction. In turn, membrane fluidity is determined by phospholipids that possess different charges, lengths, and saturation states of fatty acids. A growing body of evidence suggests that phospholipids may play an important role in the aggregation of misfolded proteins, which causes pathological conditions that lead to severe neurodegenerative diseases. In this study, we investigate the role of the charge of the most abundant phospholipids in the plasma membrane: phosphatidylcholine and phosphatidylethanolamine, zwitterions: phosphatidylserine and phosphatidylglycerol, lipids that possess a negative charge, and cardiolipin that has double negative charge on its polar head. Our results show that both zwitterions strongly inhibit insulin aggregation, whereas negatively charged lipids accelerate fibril formation. We also found that in the equimolar presence of zwitterions insulin yields oligomers that exert significantly lower cell toxicity compared to fibrils that were grown in the lipid-free environment. Such aggregates were not formed in the presence of negatively charged lipids. Instead, long insulin fibrils that had strong cell toxicity were grown in the presence of such negatively charged lipids. However, our results showed no correlation between the charge of the lipid and secondary structure and toxicity of the aggregates formed in its presence. These findings show that the secondary structure and toxicity are determined by the chemical structure of the lipid rather than by the charge of the phospholipid polar head.

Coexistence of Semiconducting Ferromagnetics and Piezoelectrics down 2D Limit from Non van der Waals Antiferromagnetic LiNbO3-Type FeTiO3.

Stable two-dimensional (2D) ferromagnetic semiconductors (FMSs) with multifunctional properties have attracted extensive attention in device applications. Non van der Waals (vdW) transition-metal oxides with excellent environmental stability, if ferromagnetic (FM), may open up an unconventional and promising avenue for this subject, but they are usually antiferromagnetic or ferrimagnetic. Herein, we predict an FMS, monolayer Fe2Ti2O9, which can be obtained from LiNbO3-type FeTiO3 antiferromagnetic bulk, has a moderate band gap of 0.87 eV, large perpendicular magnetization (6 μB/fu) and a Curie temperature up to 110 K. The intriguing magnetic properties are derived from the double exchange and negative charge transfer between O_p orbitals and Fe_d orbitals. In addition, a large in-plane piezoelectric (PE) coefficient d11 of 5.0 pm/V is observed. This work offers a competitive candidate for multifunctional spintronics and may stimulate further experimental exploration of 2D non-vdW magnets.

1,3‐Bis(tricyanoborane)imidazoline‐2‐ylidenate Anion—A Ditopic Dianionic N‐Heterocyclic Carbene Ligand

The 1,3‐bis(tricyanoborane)imidazolate anion 1 was obtained in high yield from lithium imidazolate and B(CN)3−pyridine adduct. Anion 1 is chemically very robust and thus allowed the isolation of the corresponding H5O2 + salt. Furthermore, monoanion 1 served as starting species for the novel dianionic N‐heterocyclic carbene (NHC), 1,3‐bis(tricyanoborane)imidazoline‐2‐ylidenate anion 3 that acts as ditopic ligand via the carbene center and the cyano groups at boron. First reactions of this new NHC 3 with methyl iodide, elemental selenium, and [Ni(CO)4] led to the methylated imidazolate ion 4, the dianionic selenium adduct 5, and the dianionic nickel tricarbonyl complex 6. These NHC derivatives provide a first insight into the electronic and steric properties of the dianionic NHC 3. Especially the combination of properties, such as double negative charge, different coordination sites, large buried volume and good σ‐donor and π‐acceptor ability, make NHC 3 a unique and promising ligand and building block.

Omega-3 polyunsaturated fatty acids and hypertension: a review of vasodilatory mechanisms of docosahexaenoic acid and eicosapentaenoic acid.

Hypertension is often characterised by impaired vasodilation involving dysfunction of multiple vasodilatory mechanisms. ω-3 polyunsaturated fatty acids (PUFAs), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) can reduce blood pressure and vasodilation. In the endothelium, DHA and EPA improve function including increased NO bioavailability. However, animal studies show that DHA- and EPA-mediated vasodilation persists after endothelial removal, indicating a role for vascular smooth muscle cells (VSMCs). The vasodilatory effects of ω-3 PUFAs on VSMCs are mediated via opening of large conductance calcium-activated potassium channels (BKCa ), ATP-sensitive potassium channels (KATP ) and possibly members of the Kv 7 family of voltage-activated potassium channels, resulting in hyperpolarisation and relaxation. ω-3 PUFA actions on BKCa and voltage-gated ion channels involve electrostatic interactions that are dependent on the polyunsaturated acyl tail, cis-geometry of these double bonds and negative charge of the carboxyl headgroup. This suggests structural manipulation of ω-3 PUFA could generate novel, targeted, therapeutic leads.

Electron paramagnetic resonance and theoretical study of gallium vacancy in β -Ga2O3

Unintentionally doped n-type β-Ga2O3 becomes highly resistive after annealing at high temperatures in oxygen ambient. The annealing process also induces an electron paramagnetic resonance (EPR) center, labeled IR1, with an electron spin of S = 1/2 and principal g-values of gxx = 2.0160, gyy = 2.0386, and gzz = 2.0029 with the principal axis of gzz being 60° from the [001]* direction and gyy along the b-axis. A hyperfine (hf) structure due to the hf interaction between the electron spin and nuclear spins of two equivalent Ga atoms with a hf splitting of ∼29 G (for 69Ga) has been observed. The center can also be created by electron irradiation. Comparing the Ga hf constants determined by EPR with corresponding values calculated for different Ga vacancy-related defects, the IR1 defect is assigned to the double negative charge state of either the isolated Ga vacancy at the tetrahedral site (V2−Ga(I)) or the VGa(I)–Gaib–VGa(I) complex.

Understanding the Ion Exchange Process in LDH Nanomaterials by Fast In Situ XRPD and PCA-Assisted Kinetic Analysis

Layered double hydroxides (LDHs) are nanomaterials with interesting properties finding applications in many fields, such as catalysis, environmental chemistry, and pharmaceuticals. They are anionic clays with positively charged layers and anions within the layers to reach neutrality. Their properties are defined by both composition and morphology. The composition can be tuned by exchanging the interlayer anion. The far more stable, common, and highly prevalent among natural LDHs is the carbonate anion thanks to its double negative charge. To adapt the properties of LDHs for technological applications, the challenge is to exchange the carbonate with the functionalizing monovalent anions in an effective and cheap way. In this study, the exchange of carbonate with nitrate ions is studied by in situ X-ray powder diffraction (XRPD). The exchange is carried out by a liquid-assisted grinding approach, inserting the mechanically ground dry sample in a capillary and then wetting it with a drop of nitric acid, while measuring the XRPD pattern. The kinetics of the process was investigated by the Avrami-Erofe’ev method; the reaction mechanism was determined using the advancing interface model and by analyzing the XRD peak shapes, which evidentiate changes in the crystallinity during the reaction. The reaction starts from the faces perpendicular to the layers and occurs along the channels, increasingly limited by diffusion when approaching the internal part of the crystals.

Theoretical study of the structural and electronic properties of impurities in non-passivated silicon thin nanowires

In this work, we report theoretical results for the presence of the B, C, N, O and F as impurities in non-passivated [001] thin silicon nanowires. The results for the formation energies show that some dopants tend to segregate to the nanowire surfaces, as observed for passivated [110] ones, but at the double negative charge state. The most stable site for the considered impurities is the interstitial one, where the dopants make bridges with the lateral surface Si atoms, below to this surface, except for the oxygen and fluorine ones, which stay close to the central Si atom. For the neutral carbon, nitrogen and fluorine impurities, the surface π-states located at the facets are filled and a small bandgap appears in the calculated impurity band structures. However, if they were at the double negative charge state, the nanowire metallicity is recovered. Considering the boron and oxygen dopants, the neutral charge state enhances the metallic character at the opposite side of the nanowire where they are, which is reduced when two extra electrons are injected in the system and thus, opening slightly the nanowire bandgap. Our results clearly indicate that doping (or creating vacancies in) these nanowires with acceptors, as well as with hydrogen atoms, can reduce the thin nanowire metallic behavior.

Electrically active induced energy levels and metastability of B and N vacancy-complexes in 4H–SiC

Electrically active induced energy levels in semiconductor devices could be beneficial to the discovery of an enhanced p or n-type semiconductor. Nitrogen (N) implanted into 4H–SiC is a high energy process that produced high defect concentrations which could be removed during dopant activation annealing. On the other hand, boron (B) substituted for silicon in SiC causes a reduction in the number of defects. This scenario leads to a decrease in the dielectric properties and induced deep donor and shallow acceptor levels. Complexes formed by the N, such as the nitrogen-vacancy centre, have been reported to play a significant role in the application of quantum bits. In this paper, results of charge states thermodynamic transition level of the N and B vacancy-complexes in 4H–SiC are presented. We explore complexes where substitutional N/N or B/B sits near a Si (V) or C (V) vacancy to form vacancy-complexes (NV, NV, NV, NV, BV, BV, BV and BV). The energies of formation of the N related vacancy-complexes showed the NV to be energetically stable close to the valence band maximum in its double positive charge state. The NV is more energetically stable in the double negative charge state close to the conduction band minimum. The NV on the other hand, induced double donor level and the NV induced a double acceptor level. For B related complexes, the BV and BV were energetically stable in their single positive charge state close to the valence band maximum. As the Fermi energy is varied across the band gap, the neutral and single negative charge states of the BV become more stable at different energy levels. B and N related complexes exhibited charge state controlled metastability behaviour.

Diffusivity of the double negatively charged mono-vacancy in silicon

Lightly-doped silicon (Si) samples of n-type conductivity have been irradiated with 2.0 MeV ions at a temperature of 30 K and characterized in situ by deep level transient spectroscopy (DLTS) measurements using an on-line setup. Migration of the Si mono-vacancy in its double negative charge state (V2−) starts to occur at temperatures above ∼70 K and is monitored via trapping of V2− by interstitial oxygen impurity atoms (), leading to the growth of the prominent vacancy-oxygen () center. The center gives rise to an acceptor level located at ∼0.17 eV below the conduction band edge (Ec) and is readily detected by DLTS measurements. Post-irradiation isothermal anneals at temperatures in the range of 70 to 90 K reveal first-order kinetics for the reaction in both Czochralski-grown and Float-zone samples subjected to low fluences of ions, i.e. the irradiation-induced V concentration is dilute (1013 cm−3). On the basis of these kinetics data and the content of , the diffusivity of V2− can be determined quantitatively and is found to exhibit an activation energy for migration of ∼0.18 eV with a pre-exponential factor of ∼ cm2 s−1. The latter value evidences a simple jump process without any entropy effects for the motion of V2−. No deep level in the bandgap to be associated with V2− is observed but the results suggest that the level is situated deeper than ∼0.19 eV below Ec, corroborating results reported previously in the literature.

Delayed Gadolinium-enhanced MR Imaging of Cartilage: A Comparative Analysis of Different Gadolinium-based Contrast Agents in an ex Vivo Porcine Model

Purpose To compare the delayed gadolinium-enhanced magnetic resonance (MR) imaging of cartilage (dGEMRIC) indexes acquired with different gadolinium-based contrast agents (GBCAs), with emphasis on the difference in electrical charge, and to evaluate the feasibility of the use of GBCAs other than gadopentetate dimeglumine with a double negative charge (Gd-DTPA2-) as alternatives at dGEMRIC. Materials and Methods Intact porcine patellae (n = 44) were divided into four groups according to GBCA used: Gd-DTPA2-, double negative gadobenate dimeglumine (Gd-BOPTA2-), single negative gadoterate meglumine (Gd-DOTA-), and nonionic gadobutrol (Gd-DT-DO3A). Patellae in each group were further assigned to control (n = 3) or trypsin-treated (n = 8) groups and were immersed in GBCA solutions prepared at a concentration of 2.5 mmol/L. T1 maps were acquired at 10-minute intervals at 0-120 minutes. The difference between postcontrast R1 and precontrast R1 (ΔR) and the time ΔR curves were plotted. Patellae were stained with safranin-O to evaluate the proteoglycan content of the cartilage. A linear mixed-effects model was used to analyze the time ΔR curves, and Student t tests and Mann-Whitney U tests were used to compare dGEMRIC indexes between groups. Results The difference in the estimated slopes of the time ΔR curves between control and trypsin-treated groups were greatest with Gd-BOPTA2-, followed by Gd-DTPA2-, Gd-DOTA-, and Gd-DT-DO3A, with differences in the estimated slopes of 0.037, 0.022, 0.018, and 0.011, respectively. The slope difference between control and trypsin-treated groups was significantly greater with Gd-BOPTA2- (P < .001) and significantly smaller with Gd-DT-DO3A (P = .004) in comparison with that with Gd-DTPA2-. Only the GBCAs with double negative charges showed significant differences in both the T1 measured after equilibration of cartilage with GBCA solution and the ΔR at 90 and 120 minutes between the control and trypsin-treated groups. Conclusion Double negative GBCAs produced better contrast between normal and degenerated cartilage than did those with a single negative charge and nonionic GBCAs at the same concentration for dGEMRIC. Because Gd-BOPTA2-, a high-relaxivity GBCA, showed higher contrast than did Gd-DTPA2-, Gd-BOPTA2-may be useful as an alternative GBCA for dGEMRIC. © RSNA, 2016 Online supplemental material is available for this article.

Formation kinetics of trivacancy-oxygen pairs in silicon

The formation of donor and acceptor states of the trivacancy-oxygen (V3O) complex in p- and n-type silicon, respectively, has been studied in detail by means of deep level transient spectroscopy. The samples were irradiated with 1.8 MeV protons, and it was found that acceptor and donor states of V3 disappear at annealing temperatures below 200 °C, with a transition from the metastable (110) planar configuration to the stable fourfold coordinated configuration. Annealing above 200 °C unveils the formation of two levels with energy positions at Ec − 0.34 eV and Ec − 0.46 eV in n-type samples and two levels at Ev + 0.24 eV and Ev + 0.11 eV in p-type samples. (Ec and Ev denote the conduction and valence band edge, respectively.) The amplitudes of these levels show an almost one-to-one correlation with those of the V3-related levels occurring after irradiation. In accordance with recent reports in the literature, the emerging levels are ascribed to the V3O complex; single and double negative charge states in n-type samples and single and double positive charge states in p-type samples. By undertaking isothermal formation of the V3O complex in p-type samples which exhibits first-order kinetics, the diffusivity of V3 in the neutral charge state is determined to be (8.5 ± 3.5) × 10−2 exp [−(1.50 ± 0.04) eV/kT] cm2/s.

Borohydride - Oxide Isomorphism in Design of Energy Storage Materials

An increasing number of novel single, double and triple cation borohydrides has been structurally characterized in the last few years as hydrogen storage materials and solid state electrolytes for battery applications [1,2]. It is interesting to note that the majority of these novel metal borohydrides resemble structures of various metal oxides. This is not altogether surprising considering the fact that [BH4]-and O2-anions are isoelectronic. The particularity of the borohydride-oxide analogy is the double negative charge of O2-vs. the simply charged borohydride [BH4]-, this providing a superior structural flexibility in oxides with respect to mixed valence compounds. Though somewhat handicapped by its lower charge regarding this issue, the borohydride anion obtains its versatility as a building block due to being a non-spherical anion with a tetrahedral shape as opposed to the oxide, which is approximately spherical. This commonly results in a lower symmetry of the borohydride when compared to the related oxide, the prototype very often showing a close packing of a readily polarisable soft oxide anion. We will show by means of in-situ synchrotron X-ray powder diffraction and ab initio calculations in the solid state that structural distortions in metal borohydrides compared to oxide prototypes have their origin in close hydridic di-hydrogen contacts of repulsive nature. These contacts may be suggested as a tool to tailor the crystal symmetry in complex metal hydrides in the future. Nearly twice as big as the oxide, the borohydride anion allows for connectivities of the coordination polyhedra rarely observed among the oxides such as tetrahedral edge sharing. We will show how the borohydride-oxide isomorphism, and cationic heterovalent substitution allow the prediction and design of novel borohydrides with high hydrogen content or high cation mobility.

Bis(ammonium) Zoledronate Dihydrate

Neutralization of 2-(1-imidazole)-1-hydroxyl-1,1′-ethylidenediphosphonic acid (zoledronic acid) by an excess of ammonia yielded bis(ammonium) zoledronate dihydrate, {, 2(H4N+), 2(H2O)}. The product is readily soluble in water and forms monocrystals for which the X-ray structural analysis was carried out. The zoledronic anion is of double negative charge due to deprotonation of three P–OH groups and protonation of the nitrogen in the imidazole ring. The structure is stabilized by extensive network of N–H⋯O and O–H⋯O hydrogen bonds expanding through the crystal in plane (002). The imidazole ring is involved in - stacking interactions with its symmetry equivalents related by inversion centers at (1 0 0) and (1 1/2 0), with distances between centroids (Cg–Cg) of 3.819 (2) and 3.881 (2) Å, respectively.

Bis(ethanamidinium) (1,10-phenanthroline-2,9-dicarboxylato)manganate(II) heptahydrate

In the title complex, (C2H7N2)2[Mn(C14H6N2O4)2]·7H2O, the MnII atom is coordinated by four N atoms and four O atoms from two 1,10-phenanthroline-2,9-dicarboxyl­ate ligands in a distorted dodeca­hedral geometry. The double negative charge is balanced by two ethanamidinium cations. A three-dimensional supra­molecular structure is formed through N—H⋯O and O—H⋯O hydrogen bonds and π–π stacking inter­actions [centroid–centroid distance = 3.553 (2) Å].

Study of the noncovalent interaction of squarylium dyes with serum albumins

The noncovalent interaction of zwitterionic indolium squarylium dyes (hydrophilic and hydrophobic) and a structurally analogous ionic indodicarbocyanine (hydrophilic) dye with serum albumins was studied by spectral and fluorescent methods. It has been found that the hydrophilic squarylium dye with sulfonate groups most efficiently interacts with albumins, which is probably due to the double negative charge of the dye molecule at the expense of the sulfonate groups and the possibility to form hydrogen bonds with albumin. The hydrophobic squarylium dye, as well as the hydrophilic indodicarbocyanine dye without the squarylium fragment in its structure, bind with albumins much weaker than the structurally relevant hydro- philic squarylium dye. The properties of the latter dye permit us to recommend it for using as a spectral and fluorescent probe for serum albumins in extracellular media of living organisms.

Spectral and fluorescent study of the interaction of squarylium dyes, derivatives of 3H-indolium, with albumins

Noncovalent interactions of intraionic squarylium dyes, derivatives of 3H-indolium, as well as the structurally analogous ionic indodicarbocyanine dye with serum albumins (human, bovine, rat) and, for comparison, with ovalbumin has been studied by spectral and fluorescent methods. The hydrophilic squarylium dye with sulfonate groups was found to interact with albumins more efficiently, which is probably due to the double negative charge on the dye molecule at the expense of the sulfonate groups and the ability to form hydrogen bonds with albumin. The hydrophilic indodicarbocyanine dye without the squarylium group in its structure binds to albumins much more weaker than the structurally analogous squarylium dye. The dyes bind to ovalbumin less efficiently than to serum albumins. Along with the binding of monomeric dye molecules, the aggregation of the dyes on albumins is also observed. The hydrophobic squarylium dye without sulfonate groups tends to form aggregates in aqueous solutions, which partially decompose upon the introduction of albumin into the solution. The hydrophilic squarylium dye with sulfonate groups can be recommended for tests as a spectral-fluorescent probe for serum albumins in extracellular media of living organisms.

Study of Oxygen Diffusion in Polycrystalline ZnO by SIMS

Oxygen diffusion coefficients were measured in polycrystalline ZnO by means of the gas-solid exchange method using the isotope 18O as the oxygen tracer. The diffusion annealings were performed at 892oC and 992oC, in an Ar+18O2 atmosphere under oxygen partial pressures from 0.1 to 1atm. After the diffusion annealings, the 18O diffusion profiles were established by secondary ion mass spectrometry (SIMS). Increasing the oxygen pressure leads to an increase of the oxygen diffusion in ZnO. The bulk diffusion coefficients depends on oxygen pressure according to , at 882oC, or , at 992oC, which indicates that the oxygen bulk diffusion mechanism should preferentially take place by means of interstitial oxygen having a null effective charge. The grain boundary diffusion coefficients show little dependence on oxygen pressure at 882oC, given by , which should correspond to a diffusion mechanism by means of interstitial oxygen, with a double negative charge, but at 992oC this dependence is corresponding to a diffusion mechanism by interstitial oxygen having a null effective charge. The results also show that the grain boundary is a fast path for the oxygen diffusion in polycrystalline ZnO.

Homo‐ and Heterodimetallic Geminal Dianions Derived from the Bis(phosphinimine) {Ph2P(NSiMe3)}2CH2 and the Alkali Metals Li, Na, and K

The geminal organodimetallic complexes [({Ph2P(NSiMe3)}2C)2M4], where M4=Na4, 3; Li2Na2, 4; LiNa3, 5; Li2K2, 6; Na2K2, 7, and Na3K, 8, have been prepared through a variety of methods including direct or sequential deprotonation of the neutral ligand with strong bases (tBuLi, nBuNa, (Me3Si)2NNa, PhCH2K or (Me3Si)2NK), transmetalation of the homometallic derivatives (M4=Li4, 2 or Na4, 3) with tBuONa or tBuOK, and by cation exchange upon mixing the homometallic complexes in an arene solution. Complexes 3-8 have been characterized by single-crystal X-ray diffraction and are found to form a homologous series of dimeric structures in the solid-state, in accord with the previously reported structure of 2. Each complex is composed of a plane of four metals, M4, in which the ligands adopt capping positions to form distorted M4C2 octahedral cores. The metals in homometallic complexes 2 and 3 define an approximate square, whereas the heterometallic derivatives 4-8 have distinctly rhombic arrangements. The lighter metals in 4-8 interact strongly with the carbanions and the heavier metals are pushed towards the periphery of the structures. 1H, 13C, 7Li, 31P, and 29Si multinuclear NMR spectroscopic studies, cryoscopic measurements, and electrospray ionization-mass spectroscopic studies are consistent with the dimers being retained in solution. Dynamic solution behavior was discovered for Li2Na2 complex 4, in which all five possible tetrametallic derivatives Li4, Li3Na, Li2Na2, LiNa3 and Na4 coexist. Density functional theory (DFT) and natural bond order (NBO) calculations in association with natural population analyses (NPA) reveal significant differences in the electronic structures of the variously metalated dianions. The smaller cations are more effective in localizing the double negative charge on the carbanion (in the form of two lone pairs), leading to differences in the distribution of the electron density within the ligand backbones. In turn, a complex interplay of hyperconjugation, electrostatics and metal-ligand interactions is found to control the resulting electronic structures of the geminal organodimetallic complexes.

Oxygen defect in silicon studied by semi-empirical calculations

The atomic and electronic structure of interstitial oxygen in bulk silicon is studied by a semi-empirical Hartree--Fock technique. The calculations are performed in real space on a hydrogen terminated cluster in combination with a new parameterization of oxygen within the framework of the modified neglect of diatomic overlap (MNDO) technique. We find that the results on the silicon cluster are in good agreement with experiment as well as with the results of ab initio calculations. Moreover, the various charge states of the oxygen have been analyzed. It has been found that interstitial oxygen in both neutral and double negative charge state forms a stable configuration but the single negative state forms an instable configuration with a strong level in the band gap at E v +0.55 eV.