Substitution Of Oxygen Research Articles

Calculations of the relative energies of the low‐lying electronic states of 2,7‐naphthoquinodimethane and 2,7‐naphthoquinone. Substitution of oxygen for CH2 is predicted to increase the singlet‐triplet energy difference (ΔEST)

Abstract(12/12)CASSCF and CASPT2 calculations have been performed on the triplet and two lowest‐lying singlet states of the 2,7‐naphthoquinodimethane (NQDM) and 2,7‐naphthoquinone (NQ) diradicals. Both diradicals are predicted to have triplet ground states but to differ in the ordering of the two lowest singlet states, with E(1A1) < E(1B2) in NQDM, but E(1A1) > E(1B2) in NQ. The reason for the difference in ordering of the singlet states in these two diradicals is discussed. The state reordering is shown to be responsible for the prediction that the substitution of the oxygens in NQ for the CH2 groups in NQDM increases, rather than decreases, the singlet‐triplet energy separation (ΔEST).

Cytotoxicity of acetylcholinesterase reactivators evaluated in vitro and its relation to their structure

The development of acetylcholinesterase reactivators, i.e., antidotes against organophosphorus poisoning, is an important goal of defense research. The aim of this study was to compare cytotoxicity and chemical structure of five currently available oximes (pralidoxime, trimedoxime, obidoxime, methoxime, and asoxime) together with four perspective oximes from K-series (K027, K074, K075, and K203). The cytotoxicity of tested substances was measured using two methods – colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay and impedance based real-time cytotoxicity assay – in three different cell lines (HepG2, ACHN, and NHLF). Toxicity was subsequently expressed as toxicological index IC50. The tested compounds showed different cytotoxicity ranging from 0.92 to 40.06 mM. In HepG2 cells, K027 was the least and asoxime was the most toxic reactivator. In ACHN and NHLF cell lines, trimedoxime was the compound with the lowest adverse effects, whereas the highest toxicity was found in methoxime-treated cells. The results show that at least five structural features affect the reactivators’ toxicity such as the number of oxime groups in the molecule, their position on pyridinium ring, the length of carbon linker, and the oxygen substitution or insertion of the double bond into the connection chain. Newly synthetized oximes with IC50 ≥ 1 mM evaluated in this three cell lines model might appear suitable for further testing.

Temperature Dependence of Structural and Transport Properties for Na3V2(PO4)2F3 and Na3V2(PO4)2F2.5O0.5

Among polyanionic-based electrode materials developed for Na-ion batteries, one of the most promising families turns out to be Na3V2(PO4)2F3–yOy (0 ≤ y ≤ 2). Here, we present the influence of the oxygen substitution for fluorine on the structural and transport properties of Na3V2(PO4)2F3–yOy, as a function of temperature, through the comparison of the two compositions y = 0 and y = 0.5. An order–disorder phase transition is observed, whatever the content in oxygen, in relation with changes in the ionic conductivity and thus with the mobility of the Na+ ions within the tunnels of the tridimensional structure. The richer the content in oxygen in Na3V2(PO4)2F3–yOy, the higher is the electronic conductivity, in relation with the mixed valence state V3+/V4+ within the bioctahedral units V2O8F3–yOy, and the better are the electrochemical performances in Na-ion batteries.

Stereoselective Total Synthesis of Hetisine-type C20 -Diterpenoid Alkaloids: Spirasine IV and XI.

The first total synthesis of the architecturally complex hetisine-type heptacyclic C20 -diterpenoid alkaloids (±)-spirasine IV and XI is reported. The A/F/G/C tetracyclic skeleton with the challenging N-C6 and C14-C20 linkages was efficiently constructed by an intramolecular azomethine-ylide-based 1,3-dipolar cycloaddition with unusual regioselectivity. SmI2 -mediated free-radical addition to the arene moiety without prior dearomatization and a stereoselective intramolecular aldol reaction further enabled rapid access to the hetisine core, providing a bicyclo[2.2.2]octane ring with a new oxygen substitution pattern.

Stereoselective Total Synthesis of Hetisine‐type C20‐Diterpenoid Alkaloids: Spirasine IV and XI

AbstractThe first total synthesis of the architecturally complex hetisine‐type heptacyclic C20‐diterpenoid alkaloids (±)‐spirasine IV and XI is reported. The A/F/G/C tetracyclic skeleton with the challenging N−C6 and C14−C20 linkages was efficiently constructed by an intramolecular azomethine‐ylide‐based 1,3‐dipolar cycloaddition with unusual regioselectivity. SmI2‐mediated free‐radical addition to the arene moiety without prior dearomatization and a stereoselective intramolecular aldol reaction further enabled rapid access to the hetisine core, providing a bicyclo[2.2.2]octane ring with a new oxygen substitution pattern.

Enhancement of the thermoelectric performance of oxygen substituted bismuth telluride

We carried out first-principles calculations based on density functional theory and the semi-classical Boltzmann transport theory to study the effect of oxygen substitution on the electronic structure and thermoelectric properties of bismuth telluride. The newly formed compound, Bi2O2Te, is found to be a narrow bandgap semiconductor with the bandgap of Eg = 0.13 eV. The presence of a flat band close to the valence band maximum gives rise to a steep slope of density of states near Fermi energy, leading to a significant enhancement of the Seebeck coefficient. As a result, the thermoelectric power factor of Bi2O2Te is significantly improved by controlling the carrier concentration, and the maximum power factor increased with temperature. Assuming the experiment-thermal conductivity, Bi2O2Te exhibits a high figure of merit of ZT ∼1.27 around 600 K for the p-type doping, which matches or exceeds ZT of the state-of-the-art thermoelectric materials in this temperature range. This suggests that Bi2O2Te with p-type doping is a new promising material for use in the moderate-temperature thermoelectric energy conversion.

A safe and efficient approach to fabricate black carbon-doped rutile titania by substitution of oxygen at carbon sites in titanium carbide film

A safe and efficient approach to fabricate black carbon-doped rutile titania by substitution of oxygen at carbon sites in titanium carbide film

Structure and superconducting characteristics of magnesium diboride, substitution of boron atoms by oxygen and carbon

An x-ray analysis of MgB2-based materials shows that they contain MgB2 and MgO phases. According to a quantitative Auger analysis (taken after removing the oxidized surface layer by Ar ion etching in the microscope chamber) the MgB2 phase contains some amount of oxygen that approximately corresponds to the composition MgB2.2-1.7O0.4-0.6. Rietveld refinement of the MgB2 phase, based on EDX data with varying B/O content, leads to the composition MgB1.68-1.8O0.2-0.32. Ab-initio modelling of boron substitution by oxygen in MgB2 (ΔHf = −150.6 meV/atom) shows that this is energetically favourable up to the composition MgB1.75O0.25 (ΔHf = −191.4 meV/atom). In contrast to carbon substitution, where very small levels of doping can dramatically affect the superconducting characteristics of the material with concomitant changes in the electron density, oxygen substitution results in very little change in the superconducting properties of MgB2. The formation of vacancies at the Mg site of both MgB2 and substituted MgB1.75O0.25 was modelled as well, but has shown that such processes are energetically disadvantageous (ΔHf of Mg0.875B2 and Mg0.75B1.75O0.25 are equal to −45.5 and −93.5 meV/atom, respectively).

Theoretical Elucidation of the Mechanism and Kinetic Experimental Phenomena on the Esterification of α-Tocopherol with Succinic Anhydride: Catalysis of a Histidine Derivative vs an Imidazolium-Based Ionic Liquid.

DFT calculations have been conducted to gain insight into the mechanism and kinetics of the esterification of α-tocopherol with succinic anhydride catalyzed by a histidine derivative or an imidazolium-based ionic liquid (IL). The two catalytic reactions involve an intrinsically consistent molecular mechanism: a rate-determining, concerted nucleophilic substitution followed by a facile proton-transfer process. The histidine derivative or the IL anion is shown to play a decisive role, acting as a Brönsted base by abstracting the hydroxyl proton of α-tocopherol to favor the nucleophilic substitution of the hydroxyl oxygen of α-tocopherol on succinic anhydride. The calculated free energy barriers of two reactions (15.8 kcal/mol for the histamine-catalyzed reaction and 22.9 kcal/mol for the IL-catalyzed reaction) together with their respective characteristic features, the catalytic reaction with a catalytic amount of histamine vs the catalytic reaction with an excessed amount of the IL, rationalize well the experimentally observed kinetics that the former has faster initial rate but longer reaction time while the latter is initiated slowly but completed in a much shorter time.

Effect of sulfur addition on the electrochemical performance of lithium‑vanadium-phosphate glasses as electrodes for energy storage devices

Glasses of the composition 37.5Li2O-25V2O5-37.5P2O5 mol% containing different sulfur (0, 10, 50, 100mol%) content were successfully synthesized and investigated as electrodes for electrochemical devices. Both galvanostatic charge/discharge (GCD) and cyclic voltammetry (CV) were performed to study of electrochemical properties. The results showed that glasses containing sulfur (S) exhibited a high performance, such as specific capacitance, energy density and power density, compared with the S-free glass. These properties increased with increasing of S content. The outstanding electrochemical performance of the glasses containing S can be attributed to the partial substitution of oxygen (O) atoms by S atoms. Since the radius of S ion is higher than O ion, this substitution can significantly enlarge the size of Li-ion transfer pathway. Besides, S ion has better polarization ability than O ion, thus weakens the interaction between Li ions and glass network. Therefore, the addition of S into oxide glasses may be an effective way to improve the performance of electrochemical devices electrodes.

Compositional effects on the crosslink density of Ca–(Mg)–(Y)–Si–Al–oxyfluoronitride glasses

AbstractThe effects of fluorine and nitrogen substitution for oxygen in aluminosilicate glasses, effectively oxyfluoronitride (OFN) glasses, modified by calcium, calcium–yttrium or calcium–magnesium on thermal and physical/mechanical properties have been compared. Thus, 42 glasses in the Ca–(Mg)–(Y)–Si–Al–O–(N)–(F) system have been prepared and characterized with respect to density (ρ), molar volume (MV), compactness (C), free volume (FV), glass transition temperatures measured by DTA (Tg,DTA) and dilatometry (Tg,dil), dilatometric softening point (TDS), microhardness (μHv) and Young's modulus (E). Gradients of property variation with nitrogen or fluorine substitutions for oxygen are similar for all three different oxyfluoronitride glass systems and are comparable with those reported for other OFN glasses, again indicating independent and additive effects of nitrogen and fluorine. In attempting to further understand how fluorine affects the cross‐link density (CLD) in OFN glasses, it becomes apparent that it is necessary to allow for a greater contribution by aluminum in a modifier role as fluorine content is increased. This modified calculation of CLD values results in good linear fits between Tg and CLD values. This analysis clearly demonstrates and endorses the concepts that thermal properties are related to CLD while physical/mechanical properties are dependent on glass compactness.

New direct consecutive formation of spinel phase in (Fe,Co,Ni)Al2O4 composites for enhanced Pd(II) ions removal

Spinel (Fe,Co,Ni)Al2O4 composites (FeCoNiAl) were prepared by an introduction of Ni, Co and Fe ions into a γ-Al2O3 framework via a simple electrochemical method. The physicochemical properties of the catalysts were studied by XRD, N2 adsorption-desorption, TEM, MP-AES, FTIR, XPS, ESR, and VSM analyses. The characterization data showed that an altered arrangement of the γ-Al2O3 framework was observed with a different structure, particularly with a formation of metal oxides and spinel phases as a consequence of dealumination, isomorphous substitution and surface oxygen defects that contributed to the magnetism properties. The adsorptivity toward Pd2+ was in the following order: FeCoNiAl > CoNiAl > NiAl. A strong coercive fields possessed by hercynite (FeAl2O4) in the FeCoNiAl was found to play an important role in the adsorption. The detailed adsorption equilibrium isotherms, kinetic, thermodynamics, and optimization were also studied to clarify the related results. The equilibrium data were fitted using the Langmuir model with 0.1 g L−1 FeCoNiAl giving the maximum monolayer adsorption capacity (qm) of 303 mg g−1 at 303 K and pH 5. The adsorption kinetics were best described by the pseudo-first-order model. Thermodynamic studies showed that the adsorption was exothermic and not spontaneous at high temperatures. Optimization by response surface methodology (RSM) with a central composite design (CCD) model supported this result by demonstrating that the reaction temperature played an important role in the adsorption.

Fluorination of Bi1.8Fe1.2SbO7 pyrochlore solid solutions

A technique has been developed for fluorinating the pyrochlore oxide Bi1.8Fe0.2FeSbO7, and a compound with the composition Bi1.8Fe1.2SbO7–x/2Fx has been obtained. The synthesized oxyfluoride also has the pyrochlore structure (sp. gr. Fd3m), with a lattice parameter a = 10.4443(1) A (R wp = 5.2). It has been shown that the charge balance upon fluorine substitution for oxygen is maintained not through partial reduction of Fe3+ to Fe2+ but through the incorporation of fluorine into oxygen vacancies. The magnetic behavior of the fluorinated pyrochlore phase is determined by the persisting frustration of the octahedral sublattice, which is responsible for the development of a spin glass state below T f = 12 K. The fluorination-induced changes in the anion sublattice led to an increase in the antiferromagnetic exchange interaction between neighboring Fe3+ ions and changes in the dynamic properties of the spin glass phase.

Hole-Doping Induced Ferromagnetism in Monolayer SnO: A First-Principles Study

Hole-doping of monolayer SnO, which should result in a stable ferromagnetic order in this two-dimensional material, is theoretically studied, using first-principles simulations, based on density functional theory. Sn vacancies are predicted to behave like acceptors and to produce a spin-polarized gap state near the valence band edge. The formation energy of these defects is relatively low, especially under oxygen-rich growth conditions. Extrinsic doping of monolayer SnO is next investigated. It is found that the substitution of tin by indium as well as the substitution of oxygen by nitrogen should result in p-type doping of the material.

Fluoro-Carba-Sugars are Glycomimetic Activators of the glmS Ribozyme.

The glmS ribozyme is a bacterial gene-regulating riboswitch that controls cell wall synthesis, depending on glucosamine-6-phosphate as a cofactor. Due to the presence of this ribozyme in several human pathogen bacteria (e.g., MRSA, VRSA), the glmS ribozyme represents an attractive target for the development of artificial cofactors. The substitution of the ring oxygen in carbohydrates by functionalized methylene groups leads to a new generation of glycomimetics that exploits distinct interaction possibilities with their target structure in biological systems. Herein, we describe the synthesis of mono-fluoro-modified carba variants of α-d-glucosamine and β-l-idosamine. (5aR)-Fluoro-carba-α-d-glucosamine-6-phosphate is a synthetic mimic of the natural ligand of the glmS ribozyme and is capable of effectively addressing its unique self-cleavage mechanism. However, in contrast to what was expected, the activity is significantly decreased compared to its non-fluorinated analog. By combining self-cleavage assays with the Bacillus subtilis and Staphylococcus aureus glmS ribozyme and molecular docking studies, we provide a structure-activity relationship for fluorinated carba-sugars.

Exploration of the utility of CF3+ as a reagent for chemical ionisation reaction mass spectrometry

The utility of CF3+ as a chemical-ionisation reagent for the identification of volatile organic compounds (VOCs) is explored. CF3+ and CF2H+, produced from the discharge of CF4, have been used as chemical ionization (CI) precursor ions with a representative functional mixture of VOCs in Chemical Ionisation Reaction Mass Spectrometry (CIR-MS), a multi-reagent analogue of PTR-MS.Reacting CF3+ with a functionally varied range of VOCs, under 100Td and 120Td accelerating electric fields (E/N), produced markedly different fragmentation patterns. Whereas hydride ion transfer was found to be the main reaction mechanism with n-alkanes. CF3+ acts as a Lewis acid, a strong electrophile with aromatics and nitriles. In VOCs with carbonyl groups, CF3+ forms an intermediate complex leading to the substitution of oxygen by fluorine. Target VOCs with longer alkyl chains in general show greater fragmentation, starting at C5 and becoming progressively more significant by C7.A brief comparison is made with the comparable H3O+ reactivity. From the comparison between CF3+ and H3O+, it is clear that CF3+ is a “more aggressive” reagent ion but offers utility in terms of distinctive mass shifts with certain functional groups.

8OCB and 8CB Liquid Crystals Confined in Nanoporous Alumina: Effect of Confinement on the Structure and Dynamics.

The effect of oxygen substitution is studied in two homologous compounds of n-cyanobiphenyls with n = 8 in the bulk and under confinement within self-ordered nanoporous alumina (AAO). Oxygen substitution in 8OCB increases the dipole moment and stabilizes the crystalline, smectic, and nematic phases to higher temperatures relative to 8CB. Within their smectic- A (SmA) phase both 8CB and 8OCB behave as weak viscoelastic solids with low shear moduli reflecting the underlying supramolecular defect structure. Dielectric spectroscopy assisted by DFT calculations identified strong dipolar associations within the isotropic phases characterized by a Kirkwood-Fröhlich interaction parameter, g ∼ 0.36. Dielectric spectroscopy further identified a slow process (∼ kHz) of low dielectric strength. The proximity of this process to the rheology time scale suggests as common origin a cooperative relaxation of the defect structure. Confinement alters the phase diagram by stabilizing certain crystalline phases and by reducing the N-I transition temperature in agreement with surface tension effects. However, the N-I transition seems to retain its first order character. Surface treatment with n-decyltrichlorosilane results in destabilization of the SmA phase at the expense of the N phase. This is consistent with a picture of surface anchored LC molecules at the pore walls that stabilize the nematic phase.

Carrier-Induced Band-Gap Variation and Point Defects in Zn3N2 from First Principles

The semiconductor Zn${}_{3}$N${}_{2}$, composed of inexpensive, abundant, nontoxic elements, shows a very high electron mobility and is quite appealing for many applications. However, real-world samples remain puzzling, with reported band gaps ranging from 0.85 to 3.2 eV. Using advanced first-principles calculations, the authors solve this puzzle: Gaps of up to 2 eV are mainly due to either hydrogen interstitials or oxygen substitution at nitrogen sites, while larger values seem to be due to flawed interpretation of experimental data. This insight is key to the development of devices based on this interesting, but tricky, compound.

Crystallization pathways and some properties of lithium disilicate oxynitride glasses

Abstract Lithium silicates have been used as model glasses for scientific and technological studies of glass-ceramics because they easily crystallize in the interiors, even without the addition of any nucleating agent. On the other hand, partial replacement of oxygens with nitrogens affects most properties of oxide glasses, but its effect on the crystallization kinetics of the glasses has been poorly documented. In this work, we report, for the first time, on the crystallization kinetics of nitrited lithium silicate glasses. The oxynitride glasses were prepared by partial substitution of oxygen by nitrogen, up to 6 at% N/(N+O), by melt-quenching the liquid under N 2 atmosphere inside a glove box. As expected, the density, microhardness, and Young's modulus of the glasses improved with increasing nitrogen content. Higher values of glass transition and crystallization peak temperatures were also obtained with an increase in the nitrogen content. Rietveld refinement analysis after adequate thermal treatment revealed that addition of nitrogen led to increasingly higher contents of lithium metasilicate at the expense of the (expected) lithium disilicate crystal phase. Crystallization kinetic parameters such as the activation energy and Avrami index were calculated using Ozawa's equations. These two parameters also increased with increasing nitrogen content, whereas the crystal growth rates decreased with increasing nitrogen content. The above-described changes in the properties of the oxynitride glasses are straightforwardly explained by the increase in the connectivity of the glass network, which results in enhancement of the atomic packing density owing to partial substitution of two-coordinated oxygens by three-coordinated nitrogens.

Electronic Structures of LNA Phosphorothioate Oligonucleotides.

Important oligonucleotides in anti-sense research have been investigated in silico and experimentally. This involves quantum mechanical (QM) calculations and chromatography experiments on locked nucleic acid (LNA) phosphorothioate (PS) oligonucleotides. iso-potential electrostatic surfaces are essential in this study and have been calculated from the wave functions derived from the QM calculations that provide binding information and other properties of these molecules. The QM calculations give details of the electronic structures in terms of e.g., energy and bonding, which make them distinguish or differentiate between the individual PS diastereoisomers determined by the position of sulfur atoms. Rules are derived from the electronic calculations of these molecules and include the effects of the phosphorothioate chirality and formation of electrostatic potential surfaces. Physical and electrochemical descriptors of the PS oligonucleotides are compared to the experiments in which chiral states on these molecules can be distinguished. The calculations demonstrate that electronic structure, electrostatic potential, and topology are highly sensitive to single PS configuration changes and can give a lead to understanding the activity of the molecules.