Search results for "Chemical bond"
showing 10 items of 123 documents
First Principles Calculations of Atomic and Electronic Structure of Ti3+Al- and Ti2+Al-Doped YAlO3
2021
M.G.B. appreciates support from the Chongqing Recruitment Program for 100 Overseas Innovative Talents (grant no. 2015013), the Program for the Foreign Experts (grant no. W2017011), Wenfeng High-end Talents Project (grant no. W2016-01) offered by the Chongqing University of Posts and Telecommunications (CQUPT), Estonian Research Council grant PUT PRG111, European Regional Development Fund (TK141), and NCN project 2018/31/B/ST4/00924. This study was supported by a grant from Latvian Research Council No. LZP-2018/1-0214 (for AIP). Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Program H202…
Competitive arsenate and phosphate adsorption on α-FeOOH, LaOOH, and nano-TiO2: Two-dimensional correlation spectroscopy study
2021
Abstract Competitive adsorption of arsenate (AsO43−) and phosphate (PO43−) on α-FeOOH, LaOOH, and nano-TiO2 was studied using batch adsorption experiments and in-situ flow cell ATR-FTIR coupled with two-dimensional correlation spectroscopy (2D-COS) for the first time. With a higher temporal resolution, our results found a highly dynamic adsorption sequence for AsO43− and PO43−. When AsO43− and PO43− were simultaneously exposed to the adsorbents at the same concentrations, AsO43− was preferentially adsorbed by α-FeOOH and TiO2, but PO43− adsorption was dominant on LaOOH. The results implied that the PO43− adsorbed on LaOOH had to be remobilized to allow for AsO43− adsorption, but that PO43− …
Bond length compressibility in hard ReB2 investigated by x-ray absorption under high pressure
2010
International audience; This work describes x-ray absorption measurements under high pressure in ReB2 , complemented by ab initio calculations. The EXAFS analysis yields the average Re–B bond compressibility, which turns out to be χReB = 5.6(9) × 10− 4 GPa−1 . Combining this information with previous x-ray diffraction experiments we have characterized the network of covalent bonds responsible for the rigidity of the structure. The main conclusion is that the compression is anisotropic and nonhomogeneous, reflecting bonding differences between Re–B and B–B bonds and also between nonequivalent Re–B bonds. The layer defined by boron atoms tends to become flatter under high pressure. As a conse…
Bending Carbon Nanoforms for Supramolecular Recognition: A Topological Study on Hemifullerene-Based Aggregates
2018
International audience; Buckybowls have risen as appealing fullerene fragment derivatives. Their intrinsic curvature has been exploited in the generation of host–guest supramolecular assemblies, not only through concave–convex complementarity but also through less-known concave–concave staggered arrangements. Whereas the stabilization of bowl-in-bowl dispositions has been ascribed to efficient π–π forces together with favorable dipole–dipole interactions, a detailed analysis on the forces guiding the formation of the staggered arrangements is missing so far. Herein, we present a thorough theoretical characterization of bowl-in-bowl vs staggered hemifullerene-based homodimers and heterodimer…
Radiation induced generation of non-bridging oxygen hole center in silica: Intrinsic and extrinsic processes
2007
Abstract The generation of non-bridging oxygen hole center ( Si–O ) was investigated in a wide variety of natural (fused quartz) and synthetic silica samples exposed to different γ- and β-irradiation doses by looking at its optical bands. We distinguish two different generation processes: intrinsic associated with the cleavage of Si–O bond and characterized by a sublinear law and extrinsic due to the conversion of OH precursor characterized by a growth curve with a saturating tendency. The interplay between the two processes and the role of H are discussed.
Computer modelling of point defects in ABO3 perovskites and MgO
2004
We present results for basic intrinsic defects: F-type electron centers (O vacancy which trapped one or two electrons) and hole polarons bound to Mg or K vacancy in ionic MgO and partly covalent KNbO3 perovskite, respectively. We demonstrate that a considerable covalency of the perovskite chemical bonding makes the F-type centers therein much more similar to defects in partly-covalent quartz-type oxides rather than the conventional F centers in alkali halides and ionic MgO. Both one-site (atomic) and two-site (molecular) polarons are expected to coexist in KNbO3 characterized by close absorption energies. Our calculations confirm existence of the self-trapped electron polarons in KNbO3, KTa…
Oxidation of small gas phase Pd clusters: A density functional study
2006
The adsorption sites of O2 on neutral PdN clusters (N = 1–4) were studied using spin density functional theory. Only for Pd1O2 molecular adsorption is found to be favorable. For Pd2–4O2 dissociative adsorption with the oxygen sitting on Pd bridge sites is preferred. Most Pd clusters remain in the same high spin states found for pure gas phase Pd clusters. Only the ground state of Pd4O2 increase its spin from a triplet to a quintet state. For molecular adsorption the O–O bond gets activated to a superoxo-like state.
In silico identification and experimental validation of hits active against KPC-2 β-lactamase
2018
Bacterial resistance has become a worldwide concern, particularly after the emergence of resistant strains overproducing carbapenemases. Among these, the KPC-2 carbapenemase represents a significant clinical challenge, being characterized by a broad substrate spectrum that includes aminothiazoleoxime and cephalosporins such as cefotaxime. Moreover, strains harboring KPC-type β-lactamases are often reported as resistant to available β-lactamase inhibitors (clavulanic acid, tazobactam and sulbactam). Therefore, the identification of novel non β-lactam KPC-2 inhibitors is strongly necessary to maintain treatment options. This study explored novel, non-covalent inhibitors active against KPC-2, …
Local structure of gallate proton conductors
2009
Lanthanum barium gallate proton conductors are based on disconnected GaO4 groups. The insertion of hydroxyls in the LaBaGaO4 network proceeds through self-doping with Ba2+, consequent O2- vacancy formation to fulfill charge neutrality. With a structural investigation on self-doped LaBaGaO4 oxides using synchrotron XRD and EXAFS on the Ga K-edge, we find that: (a) the GaO4 tetrahedra retain their size throughout the whole series; (b) the GaO4 tetrahedra rotate as rigid bodies on hydration, leading to the formation of a network of shorter O-O configurations that are stabilized by hydrogen bonds; (c) contraction of the lattice occurs along the a unit cell axis, as a consequence of an overall s…
Application of 61Ni Mössbauer spectroscopy to chemical problems
1996
Using the possibility to produce 61Co sources at the MAinz MIcrotron, 61Ni Mossbauer spectroscopy was applied to different kinds of chemical problems. Measurements of isomer shifts and V zz values in some common compounds and compounds with unusual chemical bonding for comparison with band structure calculations, measurement of 61Ni Mossbauer parameters in model compounds for hydrogenase and dehydrogenase with an active [NiS4] centre, and study of novel binary NiF3 compounds at helium temperature are presented.