Additional Oxygen Atoms Research Articles

Dynamics of Edge Dislocation in Ti–O Single Crystal Alloys at the Atomic Scale

The addition of oxygen atoms in solid solution to α‐Ti alloy can increase not only its hardness but also its brittleness. Herein, the edge dislocation mobility of Ti–O single crystals at oxygen concentrations of 0–2 at% and temperatures of 100–900 K is investigated by molecular dynamics simulations. The results show that the interstitial oxygen atoms have a strong hindering effect on the a/3 [110] edge dislocations on the {100} prismatic planes, which is attributed to the pinning effect of the vacancy clusters on the dislocation movement due to the interstitial oxygen atoms, thus leading to pronounced dislocation strengthening and hardening. The critical resolved shear stress (CRSS) for dislocation movement increases with increasing oxygen content and decreases with increasing temperature. Moreover, the effect of oxygen concentration on dislocation mobility also diminishes with increasing temperature.

Adsorption chemistry of co-doped graphene nanoribbon and its derivatives towards carbon based gases for gas sensing applications: Quantum DFT investigation

Sensing of the toxic gases plays a vital role in the human life to improve their health aspects and the quality of life. Using the first-principles calculations combined with density functional theory (DFT), the authors in this research work have explored the adsorption energy and electronic features of co-doped armchair graphene nanoribbon (ArGNR) and its derivatives, such as the co-doped armchair graphene oxide nanoribbon (ArGONR) and co-doped armchair reduced graphene oxide nanoribbon (ArRGONR) with boron and phosphorus (BP) atoms. A comparative study of detection of toxic carbon based gases (CO, CO2, CH4) on co-doped graphene nanoribbon (BP-ArGNR), and its derivatives such as BP-ArGONR (addition of more oxygen atoms in pristine ArGNR) and BP-ArRGONR (addition of less oxygen atoms in pristine ArGNR) has been performed. To evaluate the sensing of carbon based gases, their adsorption energies, binding distances, charge transfer, band structures and density of states have been studied for different variants. Before modification, adsorption energies for BP-ArGNR have been found to be smaller than the BP-ArGONR for CO, CO2 and CH4 molecules, thereby showing physisorption mechanism. Our computational results also revealed that after modification with oxygen atoms, BP-ArGONR shows relatively more negative value of adsorption energy in comparison to the pristine ArGNR (PR-ArGNR) for CO, CO2 and CH4 molecules, thereby showing chemisorption phenomenon. Band structure analysis predicts large band gap variations for BP-ArGONR as compared to PR-ArGNR. Thus, the authors concluded that after modification of graphene surface, enormous changes are observed in adsorption energies and band gap for BP-ArGONR towards all carbon based gases under study and hence significantly enhance the sensing performance of pristine graphene.

Synthesis, characterization and X-ray crystal structure of a mononuclear ampyrone based zinc complex

A novel mononuclear zinc complex derived from a pyrazole-based ligand was studied. The structure of the complex was explored using C, H, N, FT-IR, NMR, and UV/Vis studies, thermogravimetric analysis, and single-crystal X-ray crystallography. The single XRD study shows the coordination of the zinc ion to the alkoxide oxygen atom, two chloride ions, and one additional oxygen atom from the ethanol molecule in the complex. The intermolecular interactions in the complex were investigated using Hirshfeld surface analysis and revealed that the H…H is the most important interaction, accounting for 45.9% of the overall crystal packing contribution of the complex.

Size Exclusion and Ion Exchange Chromatographic Hardware Modified with a Hydrophilic Hybrid Surface.

Certain biomolecules have proven to be difficult to analyze by liquid chromatography (LC), especially under certain chromatographic conditions. The separation of proteins in aqueous mobile phases is one such example because there is the potential for both hydrophobic and ionic secondary interactions to occur with chromatographic hardware to the detriment of peak recovery, peak shape, and the overall sensitivity of the LC analysis. To decrease non-specific adsorption and undesired secondary interactions between column hardware and biomolecules, we have developed and applied a new hydrophilically modified hybrid surface (h-HST) for size exclusion chromatography (SEC) and anion exchange (AEX) separations of proteins and nucleic acids. This surface incorporates additional oxygen and carbon atoms onto an ethylene bridge hybrid siloxane polymer. As a result, it exhibits reduced electrostatic properties and hydrophilicity that facilitates challenging aqueous separations. Flow injection tests with a phosphate buffer showed superior protein recovery from an h-HST frit when compared to unmodified ethylene-bridged hybrid HST, titanium, stainless steel, and PEEK frits. When applied to SEC of rituximab, ramucirumab, and trastuzumab emtansine with a 50 mM ammonium acetate buffer, this new hydrophilic chromatographic hardware yielded improved monomer and aggregate recovery, higher plate numbers, and more symmetrical peaks. AEX columns also benefited from h-HST hardware. An acidic mAb (eculizumab) showed improved recovery, more stable retention, and a sharper peak when eluted from an h-HST versus SS column. Moreover, AEX separations of intact mRNA samples (Cas9 and EPO mRNA) were improved, where it was seen that h-HST column hardware provided higher sensitivity and more repeatable peak areas from injection to injection. As such, there is significant potential in the use of h-HST chromatographic hardware to facilitate more robust and more sensitive analyses for a multitude of challenging separations and analytes.

The influence of temperature on the Ti4+ coordination in sodium titanosilicate melts: In-situ high-temperature Raman spectroscopy study

The structure of xTiO2-(100-x)[40Na2O-60SiO2] (x = 10, 15, 25 and 30 mol%) glasses and melts was studied in situ in the temperature range of 20–1150 °C using high-temperature Raman spectroscopy. The fraction of five-fold coordinated Ti4+ ions gradually decreases as temperature increases above ∼ 600 °C in the samples with x ≤ 25 mol%. No similar changes were found for the sample with x = 30 mol%. The change in titanium coordination is related to the transformation of square-based TiO5 pyramids into TiO4 tetrahedra with the formation of additional non-bridging oxygen atoms (NBO) in the melt structure. This transformation can be described by [TiØ4O]2− + SiØ3O− ↔ TiØ3O− + SiØ2O22− and [TiØ4O]2− + SiØ4 ↔ TiØ3O− + SiØ3O− (Ø is bridging oxygen atom) disproportional reactions, which are shifted toward the right with increasing temperature. All studied melts exhibit a more uniform titanium distribution in comparison with glasses of corresponding composition.

Effect of oxygen impurities on the electronic and mechanical properties of penta-graphene sheet

The electronic and mechanical properties of a penta-graphene monolayer (PGM) in attendance and nonattendance of oxygen impurities were investigated using the SIESTA computational code, based on density functional theory calculations. The results of the first-principles (ab-initio) calculations show that PGM in the nonattendance of oxygen atoms is a semiconductor with indirect band gap. By adding the oxygen, the bandgap size of PGM changes. Analyzing the results indicates that oxygen absorption increases the stability of the structure. The results display that, the addition of oxygen atoms affects the electrical and mechanical properties of penta-graphene, such as converting the band structure from semiconductor to insulating, reducing Young’s modulus, and changing the Poisson’s coefficient sign. Penta-graphene has received a lot of attention from researchers as a mechanical metamaterial or auxetic material due to its negative Poisson coefficient.

ИЗОТИУРОНИЕВЫЕ СОЛИ, СОДЕРЖАЩИЕ АТОМЫ КИСЛОРОДА ИЛИ АЗОТА В ОРГАНИЧЕСКОМ ФРАГМЕНТЕ – НОВЫЙ ТИП БЛЕСКООБРАЗОВАТЕЛЕЙ ПРИ ЭЛЕКТРОХИМИЧЕСКОМ НИКЕЛИРОВАНИИ

Based on chlorex, bis (2-chloroethyl) disubstituted isothiuronium salts containing 
 additional oxygen or nitrogen atoms have been synthesized for amine and thiourea. The resulting salts 
 were studied as gloss-forming additives in the Watts electrolyte for the electrochemical production of 
 shiny nickel coatings. The electrolysis modes that ensure the production of high-quality coatings are 
 found.

Novel titanium(IV) diolate complexes with additional O‐donor as precatalyst for the synthesis of ultrahigh molecular weight polyethylene with reduced entanglement density: Influence of polymerization conditions and its implications on mechanical properties

New alkoxo‐titanium(IV) complexes with diolate ligand containing additional donor oxygen atom have been synthesized from readily available and scalable precursors. The structure of complex 4 was established by X‐ray diffraction. Titanium atom adopts a distorted tetrahedral geometry formed by six oxygen atoms of ligands. The resulting complexes 3–4 are moderately or highly active in ethylene polymerization in the presence of {EtnAlCl3–n + Bu2Mg} binary cocatalysts. The influence of the nature of the solvent, the organoaluminum cocatalyst and the polymerization temperature on the activity of catalytic systems, and the properties of the resulting polymers were studied. The obtained polymers are linear polyethylene of ultrahigh molecular weight (up to 5.8·106 g mol−1) with a broad molecular weight distribution. The polymers are suitable for the modern methods of polymer processing—the solventless solid‐state formation of super high‐strength (breaking strength up to 2.8 GPa) and high‐modulus (elastic modulus up to 140 GPa) oriented films and film tapes. The possibility of scaling up the synthesis of ultrahigh molecular weight polyethylene (UHMWPE) without a significant drop in the productivity of the catalytic system and polymer properties is shown. UHMWPE samples have been investigated by small‐angle X‐ray scattering (SAXS) methods to study the structural changes induced by solid‐state drawing of nascent reactor powders.

A Diesel Engine with a Catalytic Piston Surface to Propel Small Aircraft at High Altitudes—A Theoretical Study

Due to the oxygen shortage at high altitudes, the use of diesel engines in small aircraft is limited to a low ceiling level. Here, we propose to significantly extend the ceiling level by introducing an in-cylinder steam reforming system. In this arrangement, the fuel direct-injection assembly comprises of a two-stage process. In the first stage, a blend of methanol and water is injected into the hot previously compressed cylinder charge onto an in-cylinder catalyst. Residual heat is absorbed due to the blend evaporation and the steam-reforming process to produce hydrogen. In the second stage, diesel fuel with a lower ignition temperature than the hydrogen fuel is injected to initiate combustion, while the absorbed heat (from the first stage) is released through the hydrogen oxidation. Essentially, the absorbed heat is exploited to produce extra hydrogen fuel, which increases the cycle efficiency. In this arrangement, the in-cylinder oxygen content is significantly increased due to the additional oxygen atoms that are included in the methanol and in particular in the water molecules. These are released when the methanol and water are decomposed during the steam-reforming process. We show that owing to the addition of the oxygen content in the cylinder, the flight ceiling level can be extended from 5000 to 9000 ft, and that the indicated efficiency can be increase up to 6%.

Evolution of fumarolic anhydrous copper sulfate minerals during successive hydration/dehydration

AbstractHydration processes of primary anhydrous minerals as well as dehydration of the hydrated phases are relevant not only for answering geochemical and petrological questions, but are also interesting in the context of the theory of the ‘Evolution of minerals’. Our study of the evolution of anhydrous exhalative sulfates in hydration and dehydration processes has demonstrated the complexity of the processes for a number of minerals from the active high-temperature fumaroles of Tolbachik volcano (chalcocyanite Cu(SO4), dolerophanite Cu2O(SO4), alumoklyuchevskite K3Cu3AlO2(SO4)4 and itelmenite Na2CuMg2(SO4)4). Hydration and dehydration experiments were carried out for all four minerals using powder X-ray diffraction. A typical structural characteristic of several anhydrous copper sulfate minerals of fumarolic origin is the presence of oxygen-centred OCu4 tetrahedra. These are absent in the structures of all known hydrated minerals or synthetic compounds of the class under consideration. Hydration of minerals initially containing O2– anions as part of oxocomplexes, proceeds with sequential formation of a large series of hydroxysalts. On the contrary, hydration of itelmenite with its relatively complex ‘initial’ structure, but without additional oxygen atoms that are strong Lewis bases, results in formation of simpler hydrates. The lower the temperature and the larger the excess of water, the stronger the tendency of the cations to adopt higher hydration numbers thus outcompeting the sulfate anions as ligands. Ultimately, the water molecules completely expel the bridging sulfate anions from the metal coordination sphere yielding relatively simple fully hydrated structures.

Dynamic Activation of Adsorbed Intermediates via Axial Traction for the Promoted Electrochemical CO2 Reduction.

Regulating the local environment and structure of metal center coordinated by nitrogen ligands (M-N4 ) to accelerate overall reaction dynamics of the electrochemical CO2 reduction reaction (CO2 RR) has attracted extensive attention. Herein, we develop an axial traction strategy to optimize the electronic structure of the M-N4 moiety and construct atomically dispersed nickel sites coordinated with four nitrogen atoms and one axial oxygen atom, which are embedded within the carbon matrix (Ni-N4 -O/C). The Ni-N4 -O/C electrocatalyst exhibited excellent CO2 RR performance with a maximum CO Faradic efficiency (FE) close to 100 % at -0.9 V. The CO FE could be maintained above 90 % in a wide range of potential window from -0.5 to -1.1 V. The superior CO2 RR activity is due to the Ni-N4 -O active moiety composed of a Ni-N4 site with an additional oxygen atom that induces an axial traction effect.

Dynamic Activation of Adsorbed Intermediates via Axial Traction for the Promoted Electrochemical CO2 Reduction

AbstractRegulating the local environment and structure of metal center coordinated by nitrogen ligands (M‐N4) to accelerate overall reaction dynamics of the electrochemical CO2 reduction reaction (CO2RR) has attracted extensive attention. Herein, we develop an axial traction strategy to optimize the electronic structure of the M‐N4 moiety and construct atomically dispersed nickel sites coordinated with four nitrogen atoms and one axial oxygen atom, which are embedded within the carbon matrix (Ni‐N4‐O/C). The Ni‐N4‐O/C electrocatalyst exhibited excellent CO2RR performance with a maximum CO Faradic efficiency (FE) close to 100 % at −0.9 V. The CO FE could be maintained above 90 % in a wide range of potential window from −0.5 to −1.1 V. The superior CO2RR activity is due to the Ni‐N4‐O active moiety composed of a Ni‐N4 site with an additional oxygen atom that induces an axial traction effect.

Silver(I)-mediated base pairing in DNA involving the artificial nucleobase 7,8-dihydro-8-oxo-1,N6-ethenoadenine

The artificial nucleobase 7,8-dihydro-8-oxo-1,N6-ethenoadenine (X) was investigated with respect to its ability to engage in Ag(I)-mediated base pairing in DNA. Spectroscopic data indicate the formation of dinuclear X–Ag(I)2–X homo base pairs and mononuclear X–Ag(I)–C base pairs (C, cytosine). Density functional theory calculations and molecular dynamics simulations indicate that the nucleobase changes from its lactam tautomeric form prior to the formation of the Ag(I)-mediated base pair to the lactim form after the incorporation of the Ag(I) ions. Fluorescence spectroscopy indicates that the two Ag(I) ions of the homo base pair are incorporated sequentially. Isothermal titration calorimetry confirms that the affinity of one of the Ag(I) ions is about tenfold higher than that of the other Ag(I) ion. The computational analysis by means of density functional theory confirms a much larger reaction energy for the incorporation of the first Ag(I) ion. The thermal stabilization upon the formation of the dinuclear Ag(I)-mediated homo base pair exceeds the one previously observed for the closely related nucleobase 1,N6-ethenoadenine by far, despite very similar structures. This additional stabilization may stem from the presence of water molecules engaged in hydrogen bonding with the additional oxygen atom of the artificial nucleobase X. The highly stabilizing Ag(I)-mediated base pair is a valuable addition to established dinuclear metal-mediated base pairs.

An isotopic study of abiotic nitrite oxidation by ligand-bound manganese (III)

Redox transformations of nitrogen (N) play a critical role in determining its speciation and biological availability, thus defining the magnitude and extent of productivity in many ecosystems. A range of important nitrogen transformations often co-occur in regions hosting other redox-active elements, including sulfur, iron, and manganese (Mn), especially along sharp redox gradients within aquatic sediments. This proximity in “redox real estate” produces conditions under which multi-element interactions and coupled cycling are thermodynamically favored. While previous work has reported anoxic nitrification linked to the presence of manganese (Mn) oxides in sediments, a clear connection between the cycling of Mn and N has remained elusive. Soluble Mn(III), which is stabilized via ligand-complexation, has recently been shown to represent the dominant dissolved Mn species in many environments. Here, we examined the reactivity of ligand-stabilized Mn(III) with nitrite, using natural abundance stable nitrogen and oxygen isotopes to explore reaction dynamics under a range of conditions. Oxidation of nitrite to nitrate by Mn(III)-pyrophosphate proceeded abiotically under both oxygen replete and nitrogen-purged conditions. Kinetics and isotope systematics of this reaction were measured over a range of pH (5–8), with reaction rates decreasing with increasing pH. Under all treatments, an inverse kinetic isotope effect of −19.9 ± 0.7‰ was observed for N, remarkably similar to previously documented fractionation by nitrite-oxidizing organisms. Experiments using 18O-labeled water confirmed that the source of the additional oxygen atom was from water. These findings suggest that nitrite oxidation in environments hosting abundant ligand-bound Mn(III), including porewaters, estuaries, and coastal waters, may be facilitated in part by abiotic reactions with Mn, even under functionally anoxic conditions.

Effect of an interfacial oxygen monolayer on the spin-polarization at the Fe/MgO interface: First-principles calculations

Density functional theory is applied to calculate the structural, electronic, and magnetic properties of the Fe/MgO/Fe (001) magnetic tunnel junctions (MTJs) as well as the influence of an interfacial oxygen monolayer by the addition of oxygen atoms at the Fe/MgO interface. The formation of Fe–O bonded atoms, as well as the changes in the spin polarization around the Fermi level of the Fe/MgO/Fe (001) with an interfacial FeO layer, is observed. The calculated spin-polarized density of states of the Fe/MgO/Fe with a Fe–O interface layer showed that the peaks of the O 2s, O 2p, and Fe 3d states are shifted due to the coupling between the O atoms and Fe layer. The Fe/MgO/Fe structure exhibits metallic behavior due to the position of the density of states (DOS) peak at the Fermi level with both majority and minority spins. The calculated spin polarization (P) is only 7% for the metallic Fe/MgO/Fe structure, whereas the metallic Fe/MgO/Fe structure with FeO interfacial layer has P of 24%. Thus, the polarization is found to be extremely sensitive to the nature of the interface layer. Likewise, the nature of spin-charge transfer in both investigated MTJ structures was found to be different at the Fe/MgO interface due to the hybridization interaction between Fe and O. We have also calculated the structural, magnetic, and electronic properties of Fe/MgO/Fe with FeO layer with different sizes of the junction by varying the number of MgO layers, with Fe thickness fixed at 5 ML.

Pure and Tm3+-doped Ca3(VO4)2 crystals: Growth, statistical and local structure, and luminescent properties

Pure and Tm3+-doped Ca3(VO4)2 crystals (CVO and CVO:Tm) were grown by the Czochralski method. Activator ions were introduced in the form of Tm2O3 (0.5 and 1.0 wt%) over CVO stoichiometry. The single-crystal X-ray diffraction analysis revealed for the first time the actual crystal compositions with a splitting of one Ca5 site into two, Ca5 and Ca5A, defective sites and a partial occurrence of Tm3+ ions in two, Ca3 and Ca4, sites. X-ray absorption spectroscopy showed that the Tm3+ ions have octahedral coordination with an additional oxygen atom (coordination number, 6 + 1) and the V5+ ions have tetrahedral coordination (coordination number, 4). The structure of CVO:Tm crystals is proposed based on the local structure of Tm3+ ions, taking into account their structural organization in Tm2O3 and structural features of the CVO crystal matrix. Spectral-luminescent properties of CVO:1.0 wt%Tm crystal are consistent with structural results obtained: two pronounced peaks at λ = 470.5 and 473.5 nm in the absorption spectra (77 K), two different fluorescence spectra for different excitation wavelengths, and two components with significantly different lifetimes (1380 and 370 μs) in the decay curves indicate the presence of two different Tm3+ optical centers in the Ca3(VO4)2 crystal with excellent spectroscopic properties.

Stereoselective Synthesis of 1,6,9-Tri-oxaspiro[4.5]decanes From d-Glucose: Novel Structural Motifs of Spiroacetal Natural Products

Spiroacetals are the central structural core element of numerous natural products and are essential for their biological activity. A typical structural representative of a spiroacetal is the bicyclic 1,6-dioxaspiro[4.5]decane ring system. It represents the complete or partial structure of many biologically potent natural products such as the Paravespula pheromone 1, the antibiotic (+)-monensin A 2, the anticancer agent (−)-berkelic acid 3, the antimitotic ingredient spirastrellolide F, characterized after methylation as (+)-methyl ester 4, and the marine toxin (−)-calyculin A 5. In these compounds, the 1,6-dioxaspiro[4.5]decane ring system is found in either spiro ( R)-6 or ( S) - 6 configuration. The corresponding 1,6,9-trioxaspiro[4.5]decane framework ( S)-7 and ( R)-7 with opposite chirality at the spiro center due to an additional oxygen atom at position 9 in the pyran portion has so far not been found in living organisms or been synthesized. To close this gap and enable structure–activity relationship studies, potentially leading to novel antibiotics and selective anticancer agents, we have developed an efficient and stereocontrolled route to the ( R)- and ( S)-configurated 1,6,9-trioxaspiro[4.5]decane ring system leading to oxa analog motifs of the above natural products.

Investigation of interaction of borocarbon nanotubes with gas phase atoms

During the study of adsorption interaction by computer modeling, it was found that adsorption of oxygen, fluorine and chlorine atoms is possible on the surface of a carbon nanotube. In the course of comparing the surface sorption activity of BC5 nanotubes with respect to various chemical elements, it was found that the interaction of the oxygen atom with the surface of the borocarbon nanotube is the most energetically advantageous. The introduction of boron atoms promotes a more active addition of oxygen, fluorine and chlorine atoms to the surface of the nanotube, that is, structural modification leads to an increase in the sorption activity of carbon nanotubes.

Cu9O2(VO4)4Cl2, the First Copper Oxychloride Vanadate: Mineralogically Inspired Synthesis and Magnetic Behavior.

A new spin-1/2 frustrated antiferromagnet, Cu9O2(VO4)4Cl2, was synthesized via chemical vapor transport method that emulates mineral formation in volcanic fumaroles. Cu9O2(VO4)4Cl2 is the first copper oxychloride vanadate obtained in the ternary CuO-V2O5-CuCl2 anhydrous system. Copper ions constitute a three-dimensional complex framework with a topological structure novel for synthetic compounds but similar to that in the fumarolic mineral yaroshevskite. All of the oxygen atoms except for the O7 site are strongly bonded in the VO4 tetrahedra. The O7 site belongs to an additional oxygen atom (Oa) being tetrahedrally coordinated by four Cu atoms, thus forming the OCu4 tetrahedra. The structural formula can be represented as Cu3[Cu6O2](VO4)4Cl2 highlighting oxocentered units in the structure. IR spectra reveal several absorption bands at 526, 578, and 601 cm-1 interpreted as a characteristic feature of the OCu4 tetrahedra. Cu9O2(VO4)4Cl2 reveals ferrimagnetic behavior with the Curie temperature TC = 24 K and the uncompensated moment of Mr ∼ 1.9 μB/f.u.

Structures and Magnetism of Cationic Chromium–Manganese Bimetallic Oxide Clusters

The chromium–manganese bimetallic oxide clusters CrMnO4+, CrMn2O5,6+, Cr2MnO6,7+, CrMn3O6+, Cr2Mn2O7,8+, and Cr3MnO8,9+ were synthesized in a laser ablation cluster source and characterized by infrared multiple photon dissociation spectroscopy on the corresponding weakly bound cluster–O2 complexes. The geometric and electronic structures of CrMnO2–6+, CrxMnyO3–8+ (x,y = 2,1 and 1,2), and CrxMnyO5–10+ (x,y = 1,3, 2,2, and 3,1) were studied using density functional theory, and for certain sizes, the spectroscopic data allowed to assign the predicted structures. It is found computationally that, for a given number of metal atoms, neither the Cr:Mn ratio nor the presence of additional oxygen atoms significantly affects the geometric structures, but their magnetic properties are strongly dependent on the chemical composition. While total magnetic moments of the small CrMnOz+ (z = 2–6) clusters monotonically decrease upon addition of oxygen atoms, those of CrxMnyOz+ (x + y = 3, 4) are lower because of antiferromagnetic interactions and are less dependent on the number of oxygen atoms. The local magnetic moments of metallic sites significantly decrease with additional oxygen atoms, leading to almost quenched magnetism for the saturated oxide clusters. In general, the local magnetic moments on the Mn atoms are found to be higher than on the Cr atoms, and upon addition of oxygen, the local magnetic moments on Cr sites decrease first.