Reactivation pathway of the hydrogenase H‐cluster: Density functional theory study

This work puts forth a reaction pathway for the reactivation of exogenous ligand inhibited H‐cluster, the active site of Fe‐only hydrogenases. The H‐cluster is a dimetal complex, Fe–Fe, with the metal centers bridged by di(thiomethyl)amine. Exogenous ligands, H₂O, and OH^?, are bound to the distal iron (Fe_d). Density functional theory (DFT) calculations on the native and ruthenium‐modified H‐cluster have been performed using the B3LYP functional with 6‐31+G** and 6‐311+G** basis sets. We have ascertained that there is a thermodynamically favorable pathway for the reactivation of the OH^? inhibited H‐cluster, which proceeds by an initial protonation of the Fe_d–OH^? complex. The proposed reaction pathway has all its intermediate reactions ensue exothermically. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Preparation of a highly active nanocrystalline TiO2 photocatalyst from titanium oxo cluster precursor

Nanocrystalline TiO₂ (sample S1) was prepared from a titanium oxo cluster (Ti₇O₄(OEt)₂₀) precursor via a sol-gel route. This photocatalyst showed a higher photocatalytic activity than the TiO₂ (sample S2) obtained from titanium tetraisopropoxide. The samples were characterized by thermal analysis (TGA/DSC), X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy, N₂ adsorption (BET surface area), infrared absorption spectroscopy (FT-IR) and X-ray photoelectron spectroscopy. The characterization results show that both samples are anatase nanocrystals with particle sizes of about 12 nm, but the more photocatalytically active sample S1 has more surface hydroxyl groups and larger surface area and pore volume than sample S2.     

Hydrothermal synthesis and characterization of (enH2)3.5[As8V14O42(PO4)]·2H2O

The compound (enH₂)_3.5[As₈V₁₄O₄₂(PO₄)]·2H₂O 1 (en=ethylenediamine) has been synthesized and characterized by means of elemental analysis, IR spectrum, ESR spectrum, XPS spectrum, TG analysis and single crystal X-ray diffraction analysis. The compound 1 crystallizes in monoclinic system, space group C2/c, β=105.59(3), Z=8 and R₁(wR₂)=0.0398(0.0885). The compound 1 is constructed from [As₈V₁₄O₄₂(PO₄)]⁷⁻ anions and H₂en cations linked through hydrogen bonds into a network. The [As₈V₁₄O₄₂(PO₄)]⁷⁻ cluster consists of 14 VO₅ square pyramids linked by 4 As₂O₅ handle-like units, and includes at its center an ordered PO₄³⁻ anion.     

Topologisch und elektronisch bemerkenswerte „reduzierte”︁ Cluster des Typs [V18O42(X)]n− (X = SO4, VO4) mit Td-Symmetrie und davon abgeleitete Cluster [V(18–p)As2pO42(X)]m− (X = SO3, SO4, H2O; p = 3, 4)

Reduced Clusters with Remarkable Topological and Electronic Properties of the Type of [V₁₈O₄₂(X)]^n? (X = SO₄, VO₄) with T_d-Symmetry and Related Clusters [V_(18—p)As_2pO₄₂(X)]^m? (X = SO₃, SO₄, H₂O; p = 3, 4) The novel cluster-compounds Na₆[V₁₈O₄₂H₉(VO₄)] · 21 H₂O, (NH₄)₈[V₁₈O₄₂(SO₄)] · 25 H₂O, K₆[V₁₅As₆O₄₂(H₂O)] · 8 H₂O, (NH₄)₆[V₁₄As₈O₄₂(SO₃)], (NH₄)₆[V₁₄As₈O₄₂(SO₄)] and [N(CH3)₃]₄[₄V₁₄As₈0₄₂(H₂0)] were prepared and characterized by IR- and UV/Vis/NIR-spectroscopy, magnetic measurements and complete crystal structure analysis. For structural data see Inhaltsübersicht. Topological relations to the rhombicuboctahedron spanned by 24 0-atoms of the genuine hypothetical a-Keggin ion, at which the square planes are capped by V?O or As₂O groups, are discussed. Of particular interest are the ?extended”? Keggin ions [V₁₈O₄₂(X)]ⁿ- (X = SO₄ VO₄), (formaly derived from the hypothetical genuine a-Keggin ion by addition of six V?O groups) which have quite different electron populations in spite of the same structure of their cluster shells.     

Multivariate comparison of concentration profiles in materials analysis

Hierarchical cluster analysis (HCA) and principal components analysis (PCA) were applied to find groups between similar depth-profiles in thin-layers investigated by Rutherford backscattering spectrometry (RBS).HCA yields in one run an objective hierarchy of similarity for several profiles. Among the similarity coefficients examined the linear measure, the Euclidean distance and the exponential measure respond with different sensitivity to overall shifts in direction of the concentration axis, whereas the correlation measure relates to parallelism of the profiles.For agglomerative HCA with Euclidean distance, a lowest significant linkage level has been defined by use of Fisher'sF-test. For divisive HCA based also on Euclidean distance, the maximum of a separating function marks the most separating cluster step. The outcomes of both proposals agree for the data set investigated.PCA is useful for verifying the results of HCA and yields additional information about the data structure. In the actual example quite different positions of features (concentrations at definite depths) in the space of the two first principal components hint at peculiarities during the metallurgical coating process.     

基于聚类分析的初三化学学业质量发展研究

以2013-2016年广州市各区（县级市）中考化学成绩的4种数据为指标，运用聚类分析研究广州市区域初三化学学业质量的发展状况。研究发现各区（县级市）主要分为3大类，部分区在不同年份的类别中移动，倾向于建立一个包括越来越多区域的第1大类。广州市区域初三化学学业质量逐步向优质均衡发展。系统的中学生化学探究活动和化学教师研训活动是实现这一发展的重要原因。     

Reaction of Tetracopper(I)-Phosphonitocavitand with PhSeSiMe3: Synthesis and Structure of a Polyanionic Cluster [pyH]6[(CuCl)9(μ3-SePh)5(μ4-SePh)]

Treatment of tetracopper(I)-phosphonitocavitand [1·Cu₄(μ-Cl)₄(μ₄-Cl)] (2) (1 = tetraphosphonitocavitand [rccc-2,8,14,20-tetrakis-(iso-butyl)-phosphonitocavitand (C₄₄H₄₈O₈P₄Ph₄)]) with PhSeSiMe₃ in THF at low temperature afforded a novel polyanionic cluster [pyH]₆[(CuCl)₉(μ₃-SePh)₅(μ₄-SePh)] (4) as a major product along with a new tetracopper(I)-phosphonitocavitand (3) with a centered μ₃-Cl. Molecular structure of anionic cluster in 4 consists of six PhSe⁻ bridging ligands containing five μ₃-SePh and one exceptional μ₄-SePh bridging nine copper atoms, of which eight copper atoms have trigonal coordination geometry and the other has distorted tetrahedral geometry. Dedicated to Professor Han-Qin Liu on the occasion of his 70th birthday.     

Stability of neutral and charged Si50 cage and stacked structure and in comparison with Si60 structures

We have performed calculations on the fullerene cage and stacked structures of neutral and ionic Si₅₀ cluster by full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method. It is found that the neutral and charged fullerene cages relax into distorted structures resembling puckered balls. Their electronic structures are remarkably similar besides their geometrical structures. However, the relaxed cages are still not so stable as the stacked structure built from tricapped trigonal prism. By comparison, for the fullerene cages and stacked structures of neutral and ionic Si₆₀ cluster, similar characteristics are found.     

Gas-Chromatographic Studies of the Interaction between Water and Methanol Molecules and the Surface of Carbon Materials

The gas-chromatographic method is used to study the interaction of water and methanol molecules with active hydrophilic centres existing at the surface of thermally exfoliated graphite and graphitized thermal carbon black. The concentration of carboxyl and phenol hydroxyl groups at the surface of these sorbents is determined, and heats of adsorption of the studied molecules are shown to be and 28−25 kJ/mol, respectively. It is also shown that adsorption of water at the hydrophilic centres at lowest relative pressure values takes place with formation of clusters consisting of n = 2 water molecules.     

Erratum: Separability between valence and conduction bands in transition metal clusters

Density Functional Theory (DFT) and direct ab initio molecular dynamics (MD) calculations were applied to the hydrogen molecule trapped in a water cluster composed of 12 water molecules (H₂O)₁₂. The static DFT calculation showed that the H₂ molecule is trapped in the center of mass of (H₂O)₁₂. The vibrational frequency of the H–H stretching mode of the H₂ molecule trapped in the water cluster was blueshifted from that in vacuo. On the other hand, the vibrational frequency of H₂ in water‐hydrogen 1:1 complex (H₂O–H₂) was redshifted. A direct ab initio MD calculation of H₂(H₂O)₁₂ at 50 K indicated that the H₂ molecule is rotated freely around the center of mass of the water cluster. The origin of the spectral shift of H₂ in water ice is discussed on the basis of the theoretical results. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005