Variações temporais de uma sucessão de alfafa e de propriedades físicas do solo a elas relacionadas no Loess Plateau, China

The objective of this work was to investigate the relationship between changes in the plant community and changes in soil physical properties and water availability, during a succession from alfalfa (Medicago sativa L.) to natural vegetation on the Loess Plateau, China. Data from a succession sere spanning 32 years were collated, and vegetative indexes were compared to changes related to soil bulk density and soil water storage. The alfalfa yield increased for approximately 7 years, then it declined and the alfalfa was replaced by a natural community dominated by Stipa bungeana that began to thrive about 10 years after alfalfa seeding. Soil bulk density increased over time, but the deterioration of the alfalfa was mainly ascribed to a severe reduction in soil water storage, which was lowest around the time when degradation commenced. The results indicated that water consumption by alfalfa could be reduced by reducing plant density. The analysis of the data also suggested that soil water recharge could be facilitated by rotating the alfalfa with other crops, natural vegetation, or bare soil.O objetivo deste trabalho foi investigar a relação entre variações em uma comunidade de plantas e variações nas propriedades físicas do solo e na disponibilidade de água, durante uma sucessão de alfafa (Medicago sativa L.) por vegetação natural, no Platô Loess, na China. Dados de uma sucessão de 32 anos foram examinados e índices vegetativos foram comparados em relação às variações de densidade do solo e do armazenamento de água no solo. A produção de alfafa aumentou aproximadamente por sete anos, e então decresceu, e a alfafa foi substituída por uma comunidade natural dominada pela Stipa bungeana, que começou a crescer vigorosamente dez anos após a semeadura da alfafa. A densidade do solo aumentou com o tempo, e a deterioração da alfafa se deu principalmente em razão da redução severa da água armazenada no solo, que atingiu o mínimo quando a degradação da alfafa começou. Os resultados indicam que o consumo de água pela alfafa poderia ser reduzido pela redução na densidade de plantas e que a recarga de água no solo poderia ser facilitada pela rotação entre a alfafa e outras culturas, vegetação natural ou solo nu

Structural Basis of Chemokine Sequestration by CrmD, a Poxvirus-Encoded Tumor Necrosis Factor Receptor

Pathogens have evolved sophisticated mechanisms to evade detection and destruction by the host immune system. Large DNA viruses encode homologues of chemokines and their receptors, as well as chemokine-binding proteins (CKBPs) to modulate the chemokine network in host response. The SECRET domain (smallpox virus-encoded chemokine receptor) represents a new family of viral CKBPs that binds a subset of chemokines from different classes to inhibit their activities, either independently or fused with viral tumor necrosis factor receptors (vTNFRs). Here we present the crystal structures of the SECRET domain of vTNFR CrmD encoded by ectromelia virus and its complex with chemokine CX3CL1. The SECRET domain adopts a β-sandwich fold and utilizes its β-sheet I surface to interact with CX3CL1, representing a new chemokine-binding manner of viral CKBPs. Structure-based mutagenesis and biochemical analysis identified important basic residues in the 40s loop of CX3CL1 for the interaction. Mutation of corresponding acidic residues in the SECRET domain also affected the binding for other chemokines, indicating that the SECRET domain binds different chemokines in a similar manner. We further showed that heparin inhibited the binding of CX3CL1 by the SECRET domain and the SECRET domain inhibited RAW264.7 cell migration induced by CX3CL1. These results together shed light on the structural basis for the SECRET domain to inhibit chemokine activities by interfering with both chemokine-GAG and chemokine-receptor interactions

Catalytic selective oxidation or oxidative functionalization of methane and ethane to organic oxygenates

Selective oxidation or oxidative functionalization of methane and ethane by both homogeneous and heterogeneous catalysis is presented concerning: (1) selective oxidation of methane and ethane to organic oxygenates by hydrogen peroxide in a water medium in the presence of homogeneous osmium catalysts, (2) selective oxidation of methane to formaldehyde over highly dispersed iron and copper heterogeneous catalysts, (3) selective oxidation of ethane to acetaldehyde and formaldehyde over supported molybdenum catalysts, and (4) oxidative carbonylation of methane to methyl acetate over heterogeneous catalysts containing dual sites of rhodium and iron.National Natural Science Foundation of China [20433030, 20625310, 20773099, 20873110]; National Basic Program of China [2005CB221408, 2010CB732303]; Key Scientific Project of Fujian [2009HZ0002-1]; Program for New Century Excellent Talents in Fujia

Selective Conversion of Cellobiose and Cellulose into Gluconic Acid in Water in the Presence of Oxygen, Catalyzed by Polyoxometalate-Supported Gold Nanoparticles

National Natural Science Foundation of China [21173172, 21103143, 21033006, 20873110]; National Basic Research Program of China [2010CB732303]; Program for Changjiang Scholars and Innovative Research Team in University [IRT1036]Gold nanoparticles loaded onto Keggin-type insoluble polyoxometalates (CsxH3-xPW12O40) showed superior catalytic performances for the direct conversion of cellobiose into gluconic acid in water in the presence of O-2. The selectivity of Au/CsxH3-xPW12O40 for gluconic acid was significantly higher than those of Au catalysts loaded onto typical metal oxides (e.g., SiO2, Al2O3, and TiO2), carbon nanotubes, and zeolites (H-ZSM-5 and HY). The acidity of polyoxometalates and the mean-size of the Au nanoparticles were the key factors in the catalytic conversion of cellobiose into gluconic acid. The stronger acidity of polyoxometalates not only favored the conversion of cellobiose but also resulted in higher selectivity of gluconic acid by facilitating desorption and inhibiting its further degradation. On the other hand, the smaller Au nanoparticles accelerated the oxidation of glucose (an intermediate) into gluconic acid, thereby leading to increases both in the conversion of cellobiose and in the selectivity of gluconic acid. The Au/CsxH3-xPW12O40 system also catalyzed the conversion of cellulose into gluconic acid with good efficiency, but it could not be used repeatedly owing to the leaching of a H+-rich hydrophilic moiety over long-term hydrothermal reactions. We have demonstrated that the combination of H3PW12O40 and Au/Cs3.0PW12O40 afforded excellent yields of gluconic acid (about 85%, 418 K, 11 h), and the deactivation of the recovered H3PW12O40Au/Cs3.0PW12O40 catalyst was not serious during repeated use

Catalytic behavior and kinetic features of FeOx/SBA-15 catalyst for selective oxidation of methane by oxygen

FeOx/SBA-15 catalysts with different iron contents were studied for the selective oxidation of methane by oxygen. The catalyst with an iron content of 0.05 wt% exhibited the highest single-pass formaldehyde yield (similar to 2% at 898 K). The selectivity to formaldehyde and the specific site rate for formaldehyde formation decreased with increasing iron content. The structure-performance correlation suggests that the isolated iron species account for the selective oxidation of methane to formaldehyde, whereas the FemOn clusters are less active and the crystalline Fe2O3 mainly catalyzes the complete oxidation of methane. Kinetic investigations over the 0.05 wt% FeOx/SBA-15 catalyst reveal that formaldehyde is the major primary product, and the consecutive oxidation of formaldehyde produces carbon monoxide as the main by-product. The reaction orders with respect to methane and oxygen were 1.0 and 0.20, respectively, and the activation energy was 102 kJ mol(-1), which was significantly lower than those reported for other catalysts such as MoOx/SBA-15. Pulse reaction studies clarify that methane can react with the lattice oxygen but the products are only CO and CO2. Thus, the lattice oxygen cannot be responsible for formaldehyde formation. It is proposed that the activation of molecular oxygen on the reduced iron sites generated by methane molecules produces active oxygen species for the selective oxidation of methane. (C) 2008 Elsevier B.V. All rights reserved.NSF of China [20433030, 20625310, 20773099]; National Basic Program of China [2005CB221408]; Key Scientific Project of Fujian Province [2005HZ01-3]; Program for New Century Excellent Talents in Fujian Provinc

Copper-catalyzed selective oxidation of methane by oxygen: Studies on catalytic behavior and functioning mechanism of CuOx/SBA-15

While copper is the active center of particulate methane monooxygenase in methanotrophic bacteria, there are few studies to utilize synthetic copper catalysts for the selective oxidation of methane by oxygen. In this work, we have found that the copper ions attached on mesoporous silica SBA-15 with high dispersion can catalyze the selective oxidation of methane to formaldehyde by oxygen efficiently. The catalyst with a copper content of 0.008 wt % (Si/Cu = 13200) exhibits the best catalytic performance, and the specific site rate for formaldehyde formation can reach 5.6 mol (mol Cu)(-1) s(-1), significantly higher than those reported to date for other catalysts. We have elucidated that the oxidation of methane produces formaldehyde as a major primary product together with a small amount of carbon dioxide, while carbon monoxide is formed mainly via the consecutive oxidation of formaldehyde over our copper-based catalyst. Pulse reaction studies have indicated that methane molecules can react with the lattice oxygen of the catalyst, producing carbon oxides, and Cull in the catalyst is reduced at the same time. Detailed pulse reaction studies combined with EPR characterizations suggest that the reduced copper (probably Cut) sites generated by methane molecules during the reaction account for the activation of molecular oxygen, forming active oxygen species for the selective oxidation of methane to formaldehyde.NSF of China [20433030, 20625310, 20773099]; National Basic Program of China [2003CB615803, 2005CB221408]; Key Scientific Project of Fujian Province [2005HZ01-3

Organochromium(II) and Organonitridochromium(V) N-Heterocyclic Carbene Complexes: Synthesis and Structural Characterization

The N-heterocyclic carbene-stabilized chromium(II) alkyl, aryl, and alkynyl complexes (IPM)(2)CrR(2) [R = Me (2), Ph (3), C equivalent to CPh (3); IPM = 1,3-diisopropyl-4,5-dimethylimidazole-2-ylidene] were prepared by metathesis reactions of (IPM)(2)CrCl(2) (1) with the corresponding organolithium reagents. Further reaction of 3 with an organic azide, 1-azidoadamantane, yielded an organonitridochromium(V) compound (IPM)(2)Ph(2)Cr equivalent to N (5). Compounds 2-5 are fully characterized by (1)H NMR and IR spectroscopy, X-ray crystallography as well as by elemental analysis. The structural analysis shows that the metal atom adopts a nearly square-planar arrangement in the respective 2, 3, and 4 and a square-pyramidal one in 5. The reaction of 3 with the organic azide to 5 appears a novel way to the organonitridochromium compound.National Nature Science Foundation of China (NNSFC)[20842006, 20972129, 20902112]; Research Fund for New Teacher of Higher Education[2009060011500466]; Chinese Postdoctoral Science Foundation[20090460748

Copper grafted on SBA-15 as efficient catalyst for the selective oxidation of methane by oxygen

CuOx/SBA-15 catalysts prepared by a grafting approach (denoted as CuOx/SBA-15-gra) have been characterized and studied for the selective oxidation of methane to formaldehyde by oxygen Our characterizations using XRD H-2-TPR UV-vis and ESR suggest that Cu2+ ions are almost isolated on the surface of SBA-15 at a Cu content 06 wt% decreased the fraction of isolated Cu2+ ions and increased that of aggregated CuOx clusters On the other hand the fraction of isolated Cu2+ ions was much smaller in the CuOx/SBA-15 catalyst prepared by the impregnation method (denoted as CuOx/SBA-15-imp) even with a lower Cu content (0 5 wt%) The CuOx/SBA-15-gra provided significantly higher HCHO selectivity in the selective oxidation of CH4 than the CuOx/SBA-15-imp and the CuOx/SBA-15-gra catalyst with a Cu content of 0 6 wt% showed the best performance for HCHO formation In situ FT-IR spectroscopy of adsorbed CO and XPS measurements suggest the generation of Cu+ after the reaction and the Cu+ site is likely responsible for the activation of oxygen forming an active oxygen species for the selective oxidation of CH4 to HCHO (C) 2010 Elsevier B V All rights reserve

Selective oxidation of methane to formaldehyde by oxygen over silica-supported iron catalysts

FeOx-SiO2 catalysts prepared by a sol-gel method were studied for the selective oxidation of methane by oxygen. A single-pass formaldehyde yield of 2.0% was obtained over the FeOx-SiO2 with an iron content of 0.5 wt% at 898 K This 0.5 wt% FeOx-SiO2 catalyst demonstrated significantly higher catalytic performances than the 0.5 wt% FeOx-SiO2 prepared by an impregnation method. The correlation between the catalytic performances and the characterizations with UV-Vis and H-2-TPR suggested that the higher dispersion of iron species in the catalyst prepared by the sol-gel method was responsible for its higher catalytic activity for formaldehyde formation. The modification of the FeOx-SiO2 by phosphorus enhanced the formaldehyde selectivity, and a single-pass formaldehyde yield of 2.4% could be attained over a P-FeOx-SiO2 catalyst (P/Fe = 0.5) at 898 K Raman spectroscopic measurements indicated the formation of FePO4 nanoclusters in this catalyst, which were more selective toward formaldehyde formation.National Natural Science Foundation of China [20625310, 20773099, 20873110]; National Basic Program of China [2005CB221408]; National Science Fund for Talent Training in Basic Science [J0630429