Refinement of the cation distribution in Nb-Mo double oxide

The structure of Nb₂Mo₃O₁₄ double oxide is refined from powder data using synchrotron radiation and the anomalous scattering effect; space group P $ \bar 4 The structure of Nb₂Mo₃O₁₄ double oxide is refined from powder data using synchrotron radiation and the anomalous scattering effect; space group P 2₁ m is found for the material. It is demonstrated that in the tetragonal unit cell with parameters a = 23.173 ?, c = 4.0027 ? Nb⁵⁺ and Mo⁶⁺ ions are stochastically distributed in MO₆ octahedra and MO₇ pentagonal bipyramids of the polygonal network structure of the Mo₅O₁₄ type. Original Russian Text Copyright ? 2008 by T. Yu. Kardash, L. M. Plyasova, V. M. Bondareva, and A. N. Shmakov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 4, pp. 729–735, May–June, 2008.     

Unfolding ESIPT in Bis-2,5-(2-benzoxazolyl) Hydroquinone and 2,5-Bis(benzo[d]oxazol-2-yl)-4-methoxyphenol: a Comprehensive Computational Approach

The photo-physical behaviour of bis-2,5-(2-benzoxazolyl) hydroquinone and 2,5-bis (benzo[d]oxazol-2-yl)-4-methoxyphenol was studied using the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT). All the possible rotamers were optimized to obtain global minimum optimized structure. The theoretical absorption and emission values of rotamers estimated by using TD-DFT [TD-B3LYP/6–31G(d)] are in good agreement with experimental absorption and emission wavelengths. Based on the absorption values, the contribution of respective rotamer is determined theoretically.     

Dioxidomolybdenum(VI) complexes of allyl N'-2-hydroxy-3-methoxybenzylidenecarbamohydrazonothioate: synthesis,spectral, and theoretical investigations

The new dibasic NNO ligand H₂L (H₂L = allyl N′-2-hydroxy-3-methoxybenzylidenecarbamohydrazonothioate) was synthesized by condensation of 2-hydroxy-3-methoxybenzaldehyde with the product resulting from the reaction of thiosemicarbazide with allyl bromide. Four dioxidomolybdenum(VI) complexes with the general formula [MoO₂L(S)] (S=MeOH, EtOH, DMSO, and 1-methylimidazole) were synthesized and characterized by elemental analysis, FT-IR, EI-MS and UV-Vis spectroscopy, and by X-ray crystallography. Spectroscopic evidence indicates that the cis-MoO₂ chelates have octahedral geometry in which H₂L coordinates via the phenolate oxygen, azomethine nitrogen and deprotonated thioamide nitrogen. The other sites are occupied by two oxido and an additional ligand (S). Density functional theory calculations of spectral parameters were also carried out for these systems.     

Effect of SiO<Subscript>2</Subscript> on the physicochemical and catalytic properties of VMoTeNbО catalyst in oxidative conversion of ethane

Supported oxide catalysts of the overall composition V_0.3Mo₁Te_0.23Nb_0.12/n SiO₂ (n = 0, 10, 25, 35, and 50 wt %) were tested in oxidative conversion of ethane to ethylene and were characterized by chemical analysis, X-ray diffraction, and high-resolution transmission electron microscopy. On introducing SiO₂, coarse crystals of the active М1 phase become partially coated with layers of amorphous SiO₂. The support does not influence the selectivity with respect to the reaction products. The catalysts with 10–25 wt % SiO₂ content exhibit the highest activity owing to the presence of nanodomains of the M1 phase.     

Parents’ Attitudes Toward Mathematics and the Influence on Their Students’ Attitudes toward Mathematics: A Quantitative Study

The purpose of this study was to investigate parents’ attitudes toward mathematics, their students' attitude toward mathematics, and the influence of the parents’ attitude on the students' attitude toward mathematics. Data analyses revealed statistically significant positive correlations between parents’ and students’ attitudes toward mathematics. Additionally, parents’ mathematics attitude significantly predicted students’ attitudes toward mathematics (n=146). By understanding the influence of parents’ attitudes on students’ attitudes toward mathematics, school efforts can be geared toward fostering favorable attitudes toward mathematics among parents.     

Normal‐to‐Abnormal NHC Rearrangement of AlIII,GaIII, and InIII Trialkyl Complexes: Scope,Mechanism, Reactivity Studies,and H2 Activation

The present contribution reports experimental and theoretical mechanistic investigations on a normal‐to‐abnormal (C2‐to‐C4‐bonded) NHC rearrangement processes occurring with bulky group 13 metal NHC adducts, including the scope of such a reactivity for Al compounds. The sterically congested adducts (nItBu)MMe₃ (nItBu=1,3‐di‐tert‐butylimidazol‐2‐ylidene; M=Al, Ga, In; 1 a – c ) readily rearrange to quantitatively afford the corresponding C4‐bonded complexes (aItBu)MMe₃ ( 4 a – c ), a reaction that may be promoted by THF. Thorough experimental data and DFT calculations were performed on the nNHC‐to‐aNHC process converting the Al‐nNHC ( 1 a ) to its aNHC analogue 4 a . A nItBu/aItBu isomerization is proposed to account for the formation of the thermodynamic product 4 a through reaction of transient aItBu with THF–AlMe₃. The reaction of benzophenone with (nItBu)AlMe₃ afforded the zwitterionic species (aItBu)(CPh₂‐O‐AlMe₃) ( 6 ), reflecting the unusual reactivity that such bulky adducts may display. Interestingly, the nItBu/Al(iBu)₃ Lewis pair behaves like a frustrated Lewis pair (FLP) since it readily reacts with H₂ under mild conditions. This may open the way to future reactivity developments involving commonly used trialkylaluminum precursors.     

A time-resolved luminescent competitive assay to detect L-selectin using aptamers as recognition elements

L-selectin is a protein with potential importance for numerous diseases and clinical disorders. In this paper, we present a new aptamer-based luminescent assay developed to detect L-selectin. The sensing system working principle is based on Förster Resonance Energy Transfer (FRET) from a donor terbium complex (TbC) to an acceptor cyanine dye (Cy5). In the present approach, the biotinylated aptamer is combined with Cy5-labelled streptavidin (Cy5-Strep) to yield an aptamer-based acceptor construct (Apta-Cy5-Strep), while L-selectin is conjugated using luminescent TbC. Upon aptamer binding to the TbC-labelled L-selectin (L-selectin-TbC), permanent donor-acceptor proximity is established which allows for radiationless energy transfer to occur. However, when unlabelled L-selectin is added, it competes with the L-selectin-TbC and the FRET signal decreases as the L-selectin concentration increases. FRET from the TbC to Cy5 was observed with time-gated time-resolved luminescence spectroscopy. A significant change in the corrected luminescence signal was observed in the dynamic range of 10–500 ng/mL L-selectin, the concentration range relevant for accelerated cognitive decline of Alzheimer's disease, with a limit of detection (LOD) equal to 10 ng/mL. The aptasensor-based assay is homogeneous and can be realized within one hour. Therefore, this method has the potential to become an alternative to tedious heterogeneous analytical methods, e.g. based on enzyme-linked immunosorbent assay (ELISA).     

Towards Structural‐Functional Mimics of Acetylene Hydratase: Reversible Activation of Acetylene using a Biomimetic Tungsten Complex

The synthesis and characterization of a biomimetic system that can reversibly bind acetylene (ethyne) is reported. The system has been designed to mimic catalytic intermediates of the tungstoenzyme acetylene hydratase. The thiophenyloxazoline ligand S‐Phoz (2‐(4′,4′‐dimethyloxazolin‐2′‐yl)thiophenolate) is used to generate a bioinspired donor environment around the W center, facilitating the stabilization of W–acetylene adducts. The featured complexes [W(C₂H₂)(CO)(S‐Phoz)₂] ( 2 ) and [WO(C₂H₂)(S‐Phoz)₂] ( 3 ) are extremely rare from a synthetic and structural point of view as very little is known about W–C₂H₂ adducts. Upon exposure to visible light, 3 can release C₂H₂ from its coordination sphere to yield the 14‐electron species [WO(S‐Phoz)₂] ( 4 ). Under light‐exclusion 4 re‐activates C₂H₂ making this the first fully characterized system for the reversible activation of acetylene.     

Photochemical Strain-Release-Driven Cyclobutylation of C(sp3)-Centered Radicals

A new photoredox-catalyzed decarboxylative radical addition approach to functionalized cyclobutanes is described. The reaction involves an unprecedented formal Giese-type addition of C(sp³)-centered radicals to highly strained bicyclo[1.1.0]butanes. The mild photoredox conditions, which make use of a readily available and bench stable phenyl sulfonyl bicyclo[1.1.0]butane, proved to be amenable to a diverse range of α-amino and α-oxy carboxylic acids, providing a concise route to 1,3-disubstituted cyclobutanes. Furthermore, kinetic studies and DFT calculations unveiled mechanistic details on bicyclo[1.1.0]butane reactivity relative to the corresponding olefin system.     

Structure, electronic properties and catalytic behaviour of an activity-enhancing CYP102A1 (P450(BM3)) variant

The substrate-free crystal structure of a five-mutation directed evolution variant of CYP102A1 (P450(BM3)) with generic activity-enhancing properties ("KT2") has been determined to 1.9-? resolution. There is a close resemblance to substrate-bound structures of the wild-type enzyme (WT). The disruption of two salt bridges that link the G- and I-helices in WT causes conformational changes that break several hydrogen bonds and reduce the angle of the kink in the I-helix where dioxygen activation is thought to take place. The side-chain of a key active site residue, Phe87, is rotated in one molecule of the asymmetric unit, and the side-chains of Phe158 and Phe261 cascade into the orientations found in fatty-acid-bound forms of the enzyme. The iron is out of the porphyrin plane, towards the proximal cysteine. Unusually, the axial water ligand to the haem iron is not hydrogen-bonded to Ala264. The first electron transfer from the reductase domain to the haem domain of substrate-free KT2 is almost as fast as in palmitate-bound WT even though the reduction potential of the haem domain is only slightly more oxidising than that of substrate-free WT. However, NADPH is turned over slowly in the absence of substrate, so the catalytic cycle is gated by a step subsequent to the first electron transfer-a contrast to WT. Propylbenzene binding slightly raises the first electron transfer rate in WT but not in KT2. It is proposed that the generic rate accelerating properties of KT2 arise from the substrate-free form being in a catalytically ready conformation, such that substrate-induced changes to the structure play a less significant role in promoting the first electron transfer than in WT.