High Electronegativity Research Articles

Influence of Yb Substitution for La on Thermophysical Property of La2AlTaO7 Ceramics

The (La1−xYbx)2AlTaO7 ceramics were synthesized by pressureless sintering process at 1600°C for 10h in air. The crystal phase, microstructure and thermophysical properties were investigated. Results show that pure (La1−xYbx)2AlTaO7 cermics with single weberite structure are prepared successfully. Owing to the reduction of crystal-lattice tolerance-factor, the thermal conductivity of (La1−xYbx)2AlTaO7 (x>0) ceramics increases with increasing Yb2O3 fraction at identical temperatures, which is lower than that of La2AlTaO7. Due to the relatively high electro-negativity of Yb element, the addition of Yb2O3 increases the thermal expansion coefficient of (La1−xYbx)2AlTaO7 ceramics.

Structural and electronic properties of monolayer group III monochalcogenides

We investigate the structural, mechanical, and electronic properties of the two-dimensional hexagonal structure of group III-VI binary monolayers, $MX$ ($M=\text{B}$, Al, Ga, In and $X=\text{O}$, S, Se, Te) using first-principles calculations based on the density functional theory. The structural optimization calculations and phonon spectrum analysis indicate that all of the 16 possible binary compounds are thermally stable. In-plane stiffness values cover a range depending on the element types and can be as high as that of graphene, while the calculated bending rigidity is found to be an order of magnitude higher than that of graphene. The obtained electronic band structures show that $MX$ monolayers are indirect band-gap semiconductors. The calculated band gaps span a wide optical spectrum from deep ultraviolet to near infrared. The electronic structure of oxides ($M\mathrm{O}$) is different from the rest because of the high electronegativity of oxygen atoms. The dispersions of the electronic band edges and the nature of bonding between atoms can also be correlated with electronegativities of constituent elements. The unique characteristics of group III-VI binary monolayers can be suitable for high-performance device applications in nanoelectronics and optics.

The Existence of Non-negatively Charged Dust Particles in Nonthermal Plasmas

Particles in nonthermal dusty plasmas tend to charge negatively. However several effects can result in a significant fraction of the particles being neutral or positively charged, in which case they can deposit on surfaces that bound the plasma. Monte Carlo charging simulations were conducted to explore the effects of several parameters on the non-negative particle fraction of the stationary particle charge distribution. These simulations accounted for two effects not considered by the orbital motion limited theory of particle charging: single-particle charge limits, which were implemented by calculating electron tunneling currents from particles; and the increase in ion current to particles caused by charge-exchange collisions that occur within a particle’s capture radius. The effects of several parameters were considered, including particle size, in the range 1–10 nm; pressure, ranging from 0.1 to 10 Torr; electron temperature, from 1 to 5 eV; positive ion temperature, from 300 to 700 K; plasma electronegativity, characterized in terms of n+/ne ranging from 1 to 1000; and particle material, either SiO2 or Si. Within this parameter space, higher non-negative particle fractions are associated with smaller particle size, higher pressure, lower electron temperature, lower positive ion temperature, and higher electronegativity. Additionally, materials with lower electron affinities, such as SiO2, have higher non-negative particle fractions than materials with lower electron affinities, such as Si.

Gas-Phase Ion-Molecule Reactions of Copper Hydride Anions [CuH2]- and [Cu2H3

Gas-phase reactivity of the copper hydride anions [CuH2]- and [Cu2H3]- toward a range of neutral reagents has been examined via multistage mass spectrometry experiments in a linear ion trap mass spectrometer in conjunction with isotope labeling studies and Density Functional Theory (DFT) calculations. [CuH2]- is more reactive than [Cu2H3]-, consistent with DFT calculations, which show it has a higher energy HOMO. Experimentally, [CuH2]- was found to react with CS2 via hydride transfer to give thioformate (HCS2-) in competition with the formation of the organometallic [CuCS2]- ion via liberation of hydrogen; CO2 via insertion to produce [HCuO2CH]-; methyl iodide and allyl iodide to give I- and [CuHI]-; and 2,2,2-trifluoroethanol and 1-butanethiol via protonation to give hydrogen and the product anions [CuH(OCH2CF3)]- and [CuH(SBu)]-. In contrast, the weaker acid methanol was found to be unreactive. DFT calculations reveal that the differences in reactivity between CS2 and CO2 are due to the lower lying π* orbital of the former, which allows it to accept electron density from the Cu center to form the initial three-membered ring complex intermediate, [H2Cu(η2-CS2)]-. In contrast, CO2 undergoes the barrierless side-on hydride transfer promoted by the high electronegativity of the oxygen atoms. Side-on SN2 mechanisms for reactions of [CuH2]- with methyl iodide and allyl iodide are favored on the basis of DFT calculations. Finally, the DFT calculated barriers for protonation of [CuH2]- by methanol, 2,2,2-trifluoroethanol, and 1-butanethiol correlate with their gas-phase acidities, suggesting that reactivity is mainly controlled by the acidity of the substrate.

First principle investigation of halogen-doped monolayer g-C3N4 photocatalyst

Element doping is an efficient strategy for tuning the electronic structure and improving the photocatalytic activity of graphitic carbon nitride (g-C3N4). Employing the density functional theory computation performed by CASTEP module, we investigated the band structures, electronic and optical properties of monolayer g-C3N4 doped with halogens (F, Cl, Br or I). First, the halogen atoms occupying the interstitial space enclosed by three tri-s-triazine units in the monolayer g-C3N4 unit cell was demonstrated to be the most stable configuration in terms of adsorption energy. On the basis of these interstitial-doped monolayer g-C3N4 systems, it is found that the introduction of halogen atoms leads to various density of states (DOS) and redistribution of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). The F atom tends to occupy the valance band and HOMO due to its extremely high electronegativity. By contrast, the Cl, Br and I atoms are involved in the conduction band and LUMO. In sum, the calculation results show that the halogen-doped monolayer g-C3N4 systems have narrowed band gap, increased light absorption and reduced work function, which are conducive to high photocatalytic activity. The conclusions presented in this work indicate the availability of halogen-doped monolayer g-C3N4 with considerable photocatalytic performance.

Relevance of GaAs(001) surface electronic structure for high frequency dispersion on n-type accumulation capacitance

This study investigates the origin of long-puzzled high frequency dispersion on the accumulation region of capacitance-voltage characteristics in an n-type GaAs-based metal-oxide-semiconductor. Probed adatoms with a high Pauling electronegativity, Ag and Au, unexpectedly donate charge to the contacted As/Ga atoms of as-grown α2 GaAs(001)-2 × 4 surfaces. The GaAs surface atoms behave as charge acceptors, and if not properly passivated, they would trap those electrons accumulated at the oxide and semiconductor interface under a positive bias. The exemplified core-level spectra of the Al2O3/n-GaAs(001)-2 × 4 and the Al2O3/n-GaAs(001)-4 × 6 interfaces exhibit remnant of pristine surface As emission, thereby causing high frequency dispersion in the accumulation region. For the p-type GaAs, electrons under a negatively biased condition are expelled from the interface, thereby avoiding becoming trapped.

The Effect of Temperature and Agitation in AMD with FeCl3 and Metal Hydroxides

Acid mine drainage (AMD) from decant in Krugersdorp (South Africa) was dosed with acid-free polyferric chloride (af- PFCl) of CaOH2 or MgOH2 (PFCl-Ca(OH)2 or-Mg(OH)2). A 200 mL sample was poured into five 500 mL glass beakers and the flocculent was added in a jar test respectively using different methods of mixing and dosing. The mechanism tests were performed employing two methods of dispersing reagents throughout the colloidal suspension, i.e., rapid mixing and shaking in order to find the removal mechanism of mineral salts and relationship between the removal and characteristics of flocculent/pollutants. The results showed that the turbidity removal efficiency exhibited by FeCl3, PFCl-Ca(OH) 2 or Mg(OH)2, and hydroxides of Ca or Mg is identical, all above 90%. It also revealed that the effective AMD treatment is not necessarily dependent upon the pH, but the ability of the coagulant to destabilize the double layer (high electronegativity) of an aqua-colloid and optimal hydrolysis. The residual turbidity of the AMD samples at 15, 25 and 35°C does not exhibit significant deviations. The turbidity removal of the samples with low temperature shows that dynamic viscosity of the colloidal suspension has an influence in the destabilization-hydrolysis reaction.

Enolate-Based Strategies to Construct <i>gem</i>-Difluoromethylene Compounds

Fluorine is a key element by virtue of the unique properties associated with the atom itself and its bond to carbon, its high electronegativity and relatively small size. Due to these attractive properties, organofluorine compounds find diverse applications in the medicinal, agricultural, and material sciences. In particular, difluoromethylene compounds have received a great deal of attention due to their biological activities. This article deals with the synthetic applications of difluoroenol ethers and their derivatives, which are useful building blocks for a wide variety of difluoromethylene compounds.

Enhanced visible-light response of metal-free doped bulk h-BN as potential efficient photocatalyst: a computational study

We have provided a straightforward route to screen a series of metal-free doped bulk h-BN as potential visible-light photocatalysts via the first-principle computations. Various nonmetal dopants are considered including Si, P, C, S, Cl, O, and F atoms according to increasing electronegativity. The results show that the introduction of nonmetals leads to small lattice distortions but significant modifications of band structures, electron transition paths and chemical bonding interactions. Generally, all doped h-BN except Si doping have an active response to the visible-light, and dopants with higher electronegativity can significantly narrow the band gaps, which could induce easier optical transition under visible-light excitation. Based on the electronic structures and absorption spectra, three different mechanisms of enhanced visible-light response for the doping effect are proposed. It is expected that F, Cl, and S-doped h-BN could be used as potential efficient visible-light driven photocatalysts. This study could aid in the design of novel efficient h-BN photocatalysts. Graphical Abstract The mechanisms of the enhancedvisible-light response of metal-free doped bulk h-BN.

Hole-Injection Properties Characteristics of Fluorinated Self-Assembled Monolayer on Polymeric and Organic Light-Emitting Diodes

We examine the electro-optic effects of a fluorinated self-assembled monolayer (FSAM) on polymeric light-emitting diodes (PLEDs) and organic light-emitting diodes (OLEDs). Owing to the high electronegativity of fluorine atoms, which decreases the hole-injection barrier-height, the LEDs with FSAM as the hole-injection layer (HIL) have the highest current density. The current densities of the LEDs with FSAM, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), and without HIL were estimated to be approximately 1, 0.24, and 0.06 A/cm2 respectively at 10 V. During the operational lifetime of the PLEDs, the driving voltage with FSAM is suppressed owing to the ohmic contact of the FSAM-modified ITO.

A Relativity Enhanced, Medium-Strong Au(I)···H-N Hydrogen Bond in a Protonated Phenylpyridine-Gold(I) Thiolate.

Gold is an electron-rich metal with a high electronegativity comparable to that of sulfur. Hence, hydrogen bonds of the Au(I)···H-E (E = electronegative element) type should be possible, but their existence is still under debate. Experimental results are scarce and often contradictory. As guidance for possible preparative work, we have theoretically investigated (ppyH)Au(SPh) (ppy = 2-phenylpyridine) bearing two monoanionic ligands which are not strongly electronegative at the same time to further increase the charge density on the gold(I) atom. The protonated pyridine nitrogen atom in ppy is geometrically ideally suited to place a proton in close proximity to the gold atom in a favorable geometry for a classical hydrogen bond arrangement. Indeed, the results of the calculations indicate that the hydrogen bonded conformation of (ppyH)Au(SPh) represents a minimum geometry with bond metrics in the expected range for medium-strong hydrogen bonds [r(N-H) = 1.043 Å, r(H···Au) = 2.060 Å, a(N-H···Au) = 141.4°]. The energy difference between the conformer containing the H···Au bond and another conformer without a hydrogen bond amounts to 7.8 kcal mol-1, which might serve as an estimate of the hydrogen bond strength. Spectroscopic properties were calculated, yielding further characteristics of such hydrogen bonded gold species.

Impact of distribution of carboxymethyl substituents in the stabilizer of carboxymethyl cellulose on the stability of acidified milk drinks

The influences of molecular parameters such as molecular weight (Mw), the degree of substitution (DS) and especially the distribution of carboxymethyl substituents within the anhydroglucose unit (AGU) of carboxymethylcellulose (CMC) on the rheological properties of CMC solutions and the stability of acidified milk drinks (AMDs) induced by this cellulose ether have been comprehensively investigated and evaluated by LUMi-Sizer. The DS and the distribution of carboxymethyl substituents are characterized by means of 1H NMR spectroscopy using a set of acid-hydrolyzing CMC samples. A new CMC molecular parameter of Ri indicating the individual degree of substitution at the position of either C-2 (R2) or C-6 (R6) in AGU is proposed to evaluate the influence of distribution of carboxymethyl substituents on the stability of the milk drinks. It is found that the distribution of carboxymethyl substituents also plays a key role in the stability of AMDs. The stability of the drinks increases not only with increasing the Mw and DS but also with decreasing the R2 or increasing the R6 of CMC. This fact is explained on the basis of CMC with a higher individual DS at C-2 position resulting in higher electronegativity, thus increasing the electrostatic repulsion between CMC-adsorbed casein particles in the colloidal system, thereby contributing to a better stability to AMDs. These findings provide an insight into fabricating better stability of AMDs induced by CMC.

Comparison of hydrogen absorption in metallic and semiconductor single-walled Ge- and GeO2-doped carbon nanotubes

First-principles calculations were carried out to compare hydrogen absorption in pristine metallic and semiconductor carbon nanotubes (CNTs) with the situation in their Ge- and GeO2-doped counterparts. We found out that the pristine carbon nanotubes have low absorption efficiency (−1.53 eV in the metallic, and −2.06 eV in the semiconductor carbon nanotube). When Ge was doped into both carbon nanotubes, the hydrogen absorption was enhanced to −5.29 eV in the metallic and −3.99 eV in the semiconductor carbon nanotubes. Investigating the Partial density of states proved that there was considerable overlap between Ge 4p and hydrogen 1s orbitals in both CNTs. When CNTs were doped with GeO2, hydrogen atoms were bound to oxygen atoms, due to high electronegativity of oxygen atom. The hydrogen absorption was found to be increased remarkably in the metallic carbon nanotube (−6.59 eV). In order to compare the binding energy of Ge and GeO2 doped metallic and semiconductor carbon nanotubes, the partial density of states and the magnetization of the samples were studied.

Cancer Cell Hyperactivity and Membrane Dipolarity Monitoring via Raman Mapping of Interfaced Graphene: Toward Non-Invasive Cancer Diagnostics.

Ultrasensitive detection, mapping, and monitoring of the activity of cancer cells is critical for treatment evaluation and patient care. Here, we demonstrate that a cancer cell's glycolysis-induced hyperactivity and enhanced electronegative membrane (from sialic acid) can sensitively modify the second-order overtone of in-plane phonon vibration energies (2D) of interfaced graphene via a hole-doping mechanism. By leveraging ultrathin graphene's high quantum capacitance and responsive phononics, we sensitively differentiated the activity of interfaced Glioblastoma Multiforme (GBM) cells, a malignant brain tumor, from that of human astrocytes at a single-cell resolution. GBM cell's high surface electronegativity (potential ∼310 mV) and hyperacidic-release induces hole-doping in graphene with a 3-fold higher 2D vibration energy shift of approximately 6 ± 0.5 cm-1 than astrocytes. From molecular dipole-induced quantum coupling, we estimate that the sialic acid density on the cell membrane increases from one molecule per ∼17 nm2 to one molecule per ∼7 nm2. Furthermore, graphene phononic response also identified enhanced acidity of cancer cell's growth medium. Graphene's phonon-sensitive platform to determine interfaced cell's activity/chemistry will potentially open avenues for studying activity of other cancer cell types, including metastatic tumors, and characterizing different grades of their malignancy.

DFT and TDDFT study on cation-π complexes of diboryne (NHC → B ≡ B←NHC).

In this study, density functional theory calculation on mono-cationic cation-π complexes of diborynes has been made to understand the interaction in cation-π complexes of diboryne. Results suggest that apart from the smaller cations Li+ and Na+, larger cation like K+ ion could also form complexes with diboryne compounds via cation-π interaction. From the calculated structural and spectroscopic analysis 11B, 13C NMR (Nuclear Magnetic Resonance), FTIR (Fourier Transform Infra red) (force constant, value), and UV-vis spectra, it is found that the interaction between the cations and π-electron cloud of the diboryne is purely electrostatic. It is also observed that smaller cation (Li+) with high electronegativity interacts more strongly compared to larger cation (K+). Calculated interaction energy advocates that the π-electron cloud of the B2 unit contributes more to the cation-π interaction than the two aromatic phenyl rings of the NHC (N-heterocyclic carbene) substituted with 2,6-diisopropylphenyl group. The aryl substituent at the NHC-ligands undergoes a change in spatial orientation with respect to the size of cations in order to provide suitable space to the cations for effective cation-π interaction. Quantum theory of atoms in molecules study clarifies further the nature and extent of B-B and B2-cation interactions.11B-NMR, 13C-NMR, and time dependent density functional theory analysis indicate that cation-π interaction annihilates the B → C (NHC) π-back donation and favours the B≡B bond formation.

Pyrrolidino Analogues of Gefitinib with Improved EGFR Inhibition, Cancer Cell Cytotoxicity, and Pharmacokinetic Properties.

The binding mode analysis of Gefitinib revealed that 6-propylmorpholino group (sidechain) shows no interactions due to its weak electron density. In order to modify the electron density of Gefitinib's sidechain, novel pyrrolidino analogs of Gefitinib where morpholino groups were replaced by substituted pyrrolidino groups were synthesized. Gefitinib derivatives with high electronegativity atoms or groups in the pyrrolidino moiety always exhibit high potent activity against EGFR and human cancer cell lines, A431, MDA-MB-231 and A549. Among these derivatives, 16 displayed the best pharmacokinetic properties that make it to be a promising candidate for developing drugs to replace Gefitinib.

Gold Complexes for Therapeutic Purposes: an Updated Patent Review (2010-2015).

Gold has always aroused great interest in the history of mankind. It has been used for thousands of years for jewelry, religious cult valuables, durable goods and in the art world. However, few know that such a precious and noble metal was exploited in the past by the ancients also for its therapeutic properties. More recently, in the twentieth century some complexes containing gold centers in the oxidation state +1 were studied for the treatment of the rheumatoid arthritis and the orally-administered drug Auranofin was approved by the FDA in 1985. From the chemical point of view, gold derivatives deserve special attention due to the unique position of this metal within the periodic table, which results in unconventional relativistic effects and, ultimately, in the highest electronegativity, electron affinity and redox potential among all metals. In this review, after an introduction concerning the use of gold complexes in medicine, we have examined all the patents internationally or nationally published in the years 2010-2015 (until December 31, 2015) and describing new inorganic compounds containing gold(I) and gold(III) with proved therapeutic properties. These patents were filed to mainly protect compounds with promising anticancer and anti-inflammatory activities (total 18 and 4, respectively). In particular, this work explores both coordination compounds containing ligands with various donor atoms (e.g., N-, O-, S- and -P) and organo-gold derivatives with at least one Au-C bond. The toxicological profile and the intracellular targets reported for some among the patented gold derivatives are discussed.

1.82 wt.% Pt/N, P co-doped carbon overwhelms 20 wt.% Pt/C as a high-efficiency electrocatalyst for hydrogen evolution reaction

Cost-effective electrocatalysts for the hydrogen evolution reaction (HER) play a key role in the field of renewable energy. Although tremendous efforts have been devoted to the search of alternative materials, Pt/C is still the most efficient electrocatalyst for the HER. Nevertheless, decreasing the loading of Pt in the designed eletrocatalysts is of significance. However, with low Pt loading, it is challenging to maintain excellent catalytic performance. Herein, a new catalyst (Pt/NPC) was prepared by dispersing Pt nanoparticles (PtNPs) with an average diameter of 1.8 nm over a three-dimensional (3D) carbon network co-doped with N and P. Because of the high electronegativity of the N and P dopants, PtNPs were uniformly dispersed on the carbon network via high electronic affinity between Pt and carbon, affording a Pt/NPC catalyst; Pt/NPC exhibited superior HER activity, attributed to the down-shift of the Pt d-band caused by the donation of charge from N and P to Pt. The results show that Pt/NPC with an ultralow Pt loading of 1.82 wt.% exhibits excellent HER performance, which corresponds to a HER mass activity 20.6-fold greater than that observed for commercial 20% Pt/C at an overpotential of 20 mV vs. RHE.

Influences of interstitial nitrogen with high electronegativity on structure and hydrogen storage properties of Mg-based metal hydride: A theoretical study

Interstitially doping nonmetal elements has been viewed as an effective way to improve the hydrogen storage properties of Mg-based metal hydride. In this work, the influences of the concentration of N with high electronegativity on the crystal structure, hydrogen absorption/desorption kinetics and thermodynamics of Mg-based system were systematically investigated by first-principle calculations. For Mg2NiNx (x = 0, 0.25, 0.5) system and its hydride, the doping positions of interstitial N atom in the crystal structures were firstly determined. The calculation results showed that the addition of N element has the favorable effects on the improvement of both the kinetic and thermodynamic properties. N-doped Mg-based system with x = 0.5 has the best hydrogen absorption/desorption performances. Compared with pure Mg-based system, the formation enthalpy and dehydrogenation energy of Mg2NiN0.5 system are reduced respectively by up to 98% and 59% due to the strong hybridization between the orbits of N and H. Besides, Mg2NiN0.5 system is able to achieve the reversible hydrogen absorption/desorption reactions at ambient temperature, which makes it suitable for most practical applications.

The Fluorine Gauche Effect: A Brief History

AbstractTransforming the fluorine gauche effect from an academic curiosity into a powerful acyclic conformational control strategy has enriched molecular design. This expansive approach to modulating structure has proven to be particularly valuable in the construction of functional small molecules, thereby finding application in diverse disciplines, ranging from therapeutic medicine to enantioselective catalysis. In contrast to the well‐established arsenal of conformational control tactics, in which conformer populations result from minimising nonbonding interactions, (e.g., A1,3‐ or A1,2‐strain), the fluorine gauche effect is attributable to stabilising interactions comprised of two components: stereoelectronic and electrostatic. Conformer populations are partially determined by favourable, hyperconjugative interactions involving proximal electron‐rich σ‐bonds, π‐systems, and nonbonding electron pairs with the antibonding orbital of the C−F σ‐bond: σ→σ*, π→σ*, and n→σ*, respectively. Electrostatic, charge‐dipole interactions (e.g., N+⋅⋅⋅Fδ−) also play a crucial role in stabilising what are often counter‐intuitive conformations. These noncovalent interactions, permissible on account of the low van der Waals radius and high electronegativity of the fluorine atom, render this effect fundamentally important and practically valuable in structural chemistry. In this contribution to the Rosarium Philosophorum in honour of Prof. Jack David Dunitz FRS, we endeavour to delineate, albeit in an abridged form, the evolution of the fluorine gauche effect from a fundamental spectroscopic study to a ubiquitous component of physical organic chemistry.