Construction and characterization of double mutants in nitrogenase of<Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis>

Two mutants in nitrogenase of Klebsiella pneumoniae are constructed by site-directed mutagenesis and gene replacement procedure, which express the nitrogenases with Lysine and Glutamine substituting for α-Glutamine 190 and α-Histidine 194 respectively (Kp-Q α190 K and Kp-Hα194 Q). The above two substitutions are respectively introduced into a nifV mutant (expressing a citrate-containing nitrogenase) and sequentially two double mutants are obtained (Kp-Q α190 K-nifV and Kp-H α194 Q-nifV). All four mutants exhibit strict Nif phenotype under the N2-fixation condition and fail to grow diazotrophically. Altered nitrogneases are effectively depressed and the C2H2 reduction analysis shows that the double substitutions in Kp-Q α190 K-nifV abolish cell C2H2 reduction activity, but Kp-H α194 Q-nifV cells maintain a C2H2 reduction activity at 10% of that of wild type. Whole cell C2D2 reduction by all four mutants in comparison to the wild type and nifV mutant is also detected. The results show that only single α-Gln^194 substitution does not perturb the stereospecificity of protonation of C2D2. These results indicate that the α-Glutamine 190 and its combination with homocitrate are essential to the catalytic activity of nitrogenase and it is proposed that α-Glutamine 190 and its combination with homocitrate are involved in the proton and/or electron transfer to FeMoco. The nitrogenases from these double mutants will be useful in further analysis of the entry of the proton and/or electron to FeMoco and the substrate binding sites.     

Influence of structure and atom sites on Sn-based anode materials for lithium ion batteries: a first-principle study

To understand the influence of structure and atom sites on the electrochemical properties of Sn-based anode materials,the lithium intercalation–deintercalation mechanisms into SnNi2Cu and SnNiCu2phases were studied using the first-principle plane wave pseudo-potential method.Calculation results showed that both SnNi2Cu and SnNiCu2were unsuitable anode materials for lithium ion batteries.The Sn-based anode structure related to the number of interstitial sites,theoretical specific capacity,and volume expansion ratio.Different atom sites led to different forces at interstitial sites,resulting in variations in formation energy,density of states,and hybrid orbital types.In order to validate the calculated model,the SnNi2Cu alloy anode material was synthesized through a chemical reduction-codeposition approach.Experimental results proved that the theoretical design was reasonable.Consequently,when selecting Snbased alloy anodes,attention should be paid to maximizing the number of interstitial sites and distributing atoms reasonably to minimize forces at these sites and facilitate the intercalation and deintercalation of lithium ion.     

The influence of molar ratios of Ce/Zr on the selective catalytic reduction of NOx with NH3 over Fe2O3-WO3/CexZrl-xO2 （0 〈 x 〈 1） monolith catalyst

A series of CexZrl_xO2 （0 ≤ x ≤ 1） with dif- ferent molar ratios of Ce/Zr were syhthesized via coprecip- itation method, and Fe2O3-WO3/CexZrl-xO2 monolithic catalysts were prepared, for selective catalytic reduction of nitrogen oxides by ammonia （NH3-SCR）. The structural properties and redox behavior of the catalysts were com- prehensively characterized by N2 physisorption, X-ray diffraction （XRD）, X-ray photoelectron spectra （XPS）, H2-temperature programmed reduction （H2-TPR） and activity measurement for NH3-SCR. The results showed that the NH3-SCR activities of the catalysts were gradually enhanced by increasing the molar ratios of Ce/Zr, especially the low- temperature catalytic activity and the reaction temperature window. Fe2O3-WO3/Ceo.68Zro.3202 monolithic catalyst presented the best NH3-SCR activity among the investigated catalysts, more than 90 % NOx could be removed in the temperature range of 247-454 ℃ on the catalyst under the gas hourly space velocities of 30,000 h- 1. And it always held more than 99 % N2 selectivity and less than 20 ppm （1 ppm =10-6 L/L ） N20 generation concentration between 200 and 500 ℃, the catalyst also displayed its strong resistance of H20 and SO2. Good textural and structural properties, more surface Fe, Ce and active oxygen were together contributed to the excellent NH3-SCR performance of Fe2O3-WO3/ Ce0.68Zr0.32O2 catalyst.     

Fabrication of SrFe_(12-x)Ni_xO_(19) nanoparticles and investigation on their structural,magnetic and dielectric properties

Sr Fe12-xNixO19 nanoparticles(x = 0–1) were synthesized by a combustion sol–gel method. Their structure, dielectric and magnetic properties were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM), an LCR metry, and vibrating sample magnetometry(VSM).The results reveal that all samples of Ni doped compounds(Sr Fe12-xNixO19) with x 0.2 are single phase. It appears that the Fe3+ ions are substituted by Ni2+ ions on the crystallographic sites of the Sr Fe12O19 structure; however, for x ≥ 0.2, the secondary Ni phase ferrite(Ni Fe2O3) appears, which reduces the saturation magnetization and coercivity. In addition, Ni doping reduces the dielectric constant, dielectric loss, and alternating current(ac) electrical conductivity of the samples. The variation in ac conductivity(σac) with frequency shows that the electrical conductivity in these ferrites is mainly attributed to the electron hopping mechanism.Therefore; all the single-phase Ni doped samples are suitable for use in magnetic recording media and microwave devices.     

Molecular characterization of H1N1 influenza A viruses from human cases in North America

Subtypes of H1N1 influenza virus can be found in humans in North America, while they are also associated with the infection of swine. Characterization of the genotypes of viral strains in human populations is important to understand the source and distribution of viral strains. Genomic and protein sequences of 10 isolates of the 2009 outbreak of influenza A （H1N1） virus in North America were obtained from GenBank database. To characterize the genotypes of these viruses, phylogenetic trees of genes PB2, PB1, PA, HA, NP, NA, NS and M were constructed by Phylip3.67 program and N-Linked glycosylation sites of HA, NA, PB2, NS1 and M2 proteins were analyzed online by NetNGlyc1.0 program. Phylogenetic analysis indicated that these isolates are virtually identical but may be recombinant viruses because their genomic fragments come from different viruses. The isolates also contain a characteristic lowly pathogenic amino acid motif at their HA cleavage sites （IPSIQSR↓GL）, and an E residue at position 627 of the PB2 protein which shows its high affinity to humans. The homologous model of M proteins showed that the viruses had obtained the ability of anti-amantadine due to the mutation at the drug-sensitive site, while sequence analysis of NA proteins indicated that the viruses are still susceptible to the neuraminidase inhibitor drug （i.e. oseltamivir and zanamivir） because no mutations have been observed. Our results strongly suggested that the viruses responsible for the 2009 outbreaks of influenza A （H1N1） virus have the ability to cross species barriers to infect human and mammalian animals based on molecular analysis. These findings may further facilitate the therapy and prevention of possible transmission from North America to other countries.     

Isolation and characterization of H7N9 viruses from live poultry markets--Implication of the source of current H7N9 infection in humans

On March 31, 2013, the National Health and Family Planning Commission announced that human infections with a previously undescribed influenza A (H7N9) virus had occurred in Shanghai and Anhui Province, China. To investigate the possible origins of the H7N9 viruses causing these human infections, we collected 970 samples, including drinking water, soil, and cloacal and tracheal swabs of poultry from live poultry markets and poultry farms in Shanghai and Anhui Province. Twenty samples were positive for the H7N9 influenza virus. Notably, all 20 viruses were isolated from samples collected from live poultry markets in Shanghai. Phylogenetic analyses showed that the six internal genes of these novel human H7N9 viruses were derived from avian H9N2 viruses, but the ancestor of their HA and NA genes is uncertain. When we examined the phylogenetic relationship between the H7N9 isolates from live poultry markets and the viruses that caused the human infections, we found that they shared high homology across all eight gene segments. We thus identified the direct avian origin of the H7N9 influenza viruses that caused the human infections. Importantly, we observed that the H7N9 viruses isolated from humans had acquired critical mutations that made them more "human-like". It is therefore imperative to take strong measures to control the spread of H7N9 viruses in birds and humans to prevent further threats to human health.     

Effects of smelting parameters on the slag/metal separation behaviors of Hongge vanadium-bearing titanomagnetite metallized pellets obtained from the gas-based direct reduction process

Smelting separations of Hongge vanadium-bearing titanomagnetite metallized pellets (HVTMP) prepared by gas-based direct reduction were investigated, and the effects of smelting parameters on the slag/metal separation behaviors were analyzed. Relevant mechanisms were elucidated using X-ray diffraction analysis, FACTSAGE 7.0 calculations, and scanning electron microscopy observations. The results show that, when the smelting temperature, time, and C/O ratio are increased, the recoveries of V and Cr of HVTMP in pig iron are improved, the recovery of Fe initially increases and subsequently decreases, and the recovery of TiO₂ in slag decreases. When the smelting CaO/SiO₂ ratio is increased, the recoveries of Fe, V, and Cr in pig iron increase and the recovery of TiO₂ in slag initially increases and subsequently decreases. The appropriate smelting separation parameters for HVTMP are as follows: smelting temperature of 1873 K; smelting time of 30–50 min; C/O ratio of 1.25; and CaO/SiO₂ ratio of 0.50. With these optimized parameters (smelting time: 30 min), the recoveries of Fe, V, Cr, and TiO₂ are 99.5%, 91.24%, 92.41%, and 94.86%, respectively.     

Heterogeneous oxidation of carbonyl sulfide on mineral oxides

Heterogeneous oxidation of carbonyl sulfide (OCS) on mineral oxides including SiO2,Fe2O3,CaO,MgO,ZnO and TiO2,which are the main components of atmospheric particles,were investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS),ion chromatography (IC),temperature-programmed desorption (TPD),X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) methods. The main products and intermediates of the heterogeneous oxidation of OCS on these oxides were identified with in situ DRIFTS and IC. The reaction mechanism and kinetics were also discussed. It is found that the reaction mechanism on these mineral oxides is the same as that on Al2O3 for the same final products and the intermediates at room temperature. Namely,OCS can be catalytically oxidized to produce surface SO42- species and gaseous CO2 through the surface hydrogen thiocarbonate (HSCO2-) and HSO3- species. The activity series for heterogeneous oxidation of OCS follows: Al2O3 ≈ CaO > MgO > TiO2 ≈ ZnO > Fe2O3 > SiO2. The specific area,basic hydroxyl and surface basicity of these oxides have effect on the reactivity. This study suggests that heterogeneous reactions of OCS on mineral dust may be an unneglectable sink of OCS.     

Two-stage reduction for the preparation of ferronickel alloy from nickel laterite ore with low Co and high MgO contents

The preparation of ferronickel alloy from the nickel laterite ore with low Co and high MgO contents was studied by using a pre-reduction-smelting method. The effects of reduction time, calcination temperature, quantity of reductant and calcium oxide (CaO), and pellet diameter on the reduction ratio of Fe and on the pellet strength were investigated. The results show that, for a roasting temperature >800℃, a roasting time >30 min, 1.5wt% added anthracite coal, 5wt% added CaO, and a pellet size of~10 mm, the reduction ratio of Fe exceeds 70% and the compressive strength of the pellets exceeds 10 kg per pellet. Reduction smelting experiments were performed by varying the smelting time, temperature, quantity of reductant and CaO, and reduction ratio of Fe in the pellets. Optimal conditions for the reduction smelting process are as follows:smelting time, 30-45 min; smelting temperature, 1550℃; quantity of reductant, 4wt%-5wt%; and quantity of CaO, 5wt%; leading to an Fe reduction ratio of 75% in the pellets. In addition, the mineral composition of the raw ore and that during the reduction process were investigated by process mineralogy.     

Resonance-enhanced multiphoton ionization spectroscopy on the B′2Σ+ and B2Π states of NS

Resonance-enhanced multiphoton ionization （REMPI） spectra of N^32S and N^34S have been recorded in the range of 35700-40200 cm^-1. The radical was generated by a pulsed dc discharge of a mixture of SF6 and N2 under a supersonic free jet condition. All the 16 observed bands of N^32S radicals have been assigned, among which 12 bands belong to three transition progressions （v′=0-4, 0）, （v′=1-4, 1） and （v′=2-4, 2） from the X^2П ground state to the B′^2∑^＋ upper state and the rest correspond to （9, 0）, （10, 0）, （11, 0） and （12, 0） bands of B^2П-X^2П transition, respectively. Analysis of the rotationally resolved spectra yields exhaustive spectroscopic constants of both the X^2П ground state and the B′^2∑^＋ excited state. The electronic transition bands of the isotopic molecule N^34S have been rotationally analyzed for the first time and the rotational constants of the ground and upper states have been determined simultaneously.     

Near-infrared to visible up-conversion emissions of Er^3＋ doped Al2O3 powders derived from the sol-gel method

The Er3 doped Al2O3 powders were prepared by the sol-gel method using the aluminium isopropoxide [Al(OC3H7)3]-derived Al2O3 sols with addition of the erbium nitrate [Er(NO3)3.5H2O]. The different phase structure, including three crystalline types of (Al,Er)2O3 phases, γ, θ, α, and two Er-Al-O phases, ErAlO3 and Al10Er6O24, was obtained with the 1 mol% Er3 doped Al2O3 powders at the different sintering temperatures of 600―1200℃. The green and red up-conversion emissions centered at about 523, 545 and 660 nm, corresponding respectively to the 2H11/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3 , were detected by a 978 nm semiconductor laser diodes excitation. The phase structure and OH content had evident influence on the up-conversion emissions intensity. The maximum intensities of both the green and red emissions were obtained respectively for the Er3 doped Al2O3 powders sintered at 1200 ℃, which was composed mainly of α-(Al,Er)2O3, less of ErAlO3 and Al10Er6O24 phases, and with the least OH content. The two-photon absorption up-conversion process was involved in the green and red up-conversion emissions of the Er3 doped Al2O3 powders.     

Synthesis, Characterization and Calorimetry of Ni（C4H8N2O3）2Cl2

A coordination complex was synthesized from NiCl2 and dipeptide glycylglycine（GG）. It was characterized by element analysis, NMR and TG methods, and then was determined to be Ni（C4HsN2O3）2Cl2. Using an isoperibolic reaction calorimeter, the standard molar enthalpy of formation of Ni（GG）2Cl2（solid） has been determined to be -（1 674.66±2.02） kJ · mol^-1 at 298.15 K.     

Compression behavior and equation of state of Ni77P23 amorphous alloy

The compression behavior of Ni77P23 amorphous alloy is investigated at room temperature in a diamond-anvil cell instrument using insitu high pressure energy dispersive X-ray diffraction with a syn- chrotron radiation source. The equation of state is determined by fitting the experimental data accord- ing to Birch-Murnaghan equation: -ΔV/V0=0.08606P-3.2×10-4P2 5.7×10-6P3. It is found that the structure of Ni77P23 amorphous alloy is stable under pressures up to 30.5 GPa.     

Kinetic studies of the decomposition reaction of adducts of dinuclear Fe(Ⅱ)/O2

Kinetic studies of the decomposition reaction of dinuclear Fe(Ⅱ) adducts [Fe₂(N-Et-HPTB){O₂P(OPh)₂}](Cl- O₄)₂ (1) and [Fe₂(N-Et-HPTB) {O₂P(Ph)₂}] (ClO₄)₂ (2) with O₂ have been carried out at low temperature using UV-vis spectra. The decomposition reaction of Fe(Ⅱ)/O₂ adducts was first-order in the experimental conditions, and the activation parameters were obtained. ?H^¹ = 85.62 kJ·mol^-1, ?S¹ = 19.43 J·mol^-1·K^-1 for compound (1) and ?H^¹ = 97.97 kJ·mol^-1, ?S^¹ = 55.68 J·mol^-1·K^-1 for compound (2). These results are similar to those of dioxygen adducts of other metals complexes and natural enzymes such as methane mono- oxygenase (MMOH).     

Investigation of the cross-reaction mechanism of C<Subscript>6</Subscript>H<Subscript>5</Subscript>F-HNO<Subscript>2</Subscript> aqueous solution irradiated at 355 nm by transient absorbance spectrum technique

The transient absorption spectrum technique was employed to investigate the cross-reaction mechanism of C6H5F-HNO2 aqueous solution irradiated at 355 nm. The characteristic and the kinetic parameters of transient species were also detected. Hydroxyl radical derived from the photolysis of HNO2 was added to monofluorobenzene with a second-order rate constant of （5.83±0.17）×10^9 L·mol^-1·s^-1 to form an adduct, C6H5F…OH, which was able to react with HNO2 as the main reaction pathway with a rate constant of （8.3±0.1）×10^7 L·mol^-1·s^-1. The C6F6…OH adduct can also be decayed by elimination of H2O to yield monofluorophenyl radical C6H4F-. By GC-MS technique, the final products were identified to be monofluorophenol, nitro-monofluorobenzene, nitro-monofluorophenol and para-fluorobiphenyl.     

Field emission of SiCN thin films bombarded by Ar<Superscript>+</Superscript> ions

SiCN thin films were synthesized by a radio frequency chemical vapor deposition (RFCVD) system on P-type Si (1 0 0) wafers using C₂H₄, SiH₄ and N₂ as raw materials, In order to get rid of the oxygen absorbed on the surface and improve the characteristics of electron field emission, Ar⁺ ions of low energy were used to bombard the samples. The field emission characteristics of SiCN thin films before and after Ar⁺ bombardment were studied in the super vacuum environment of 10⁻⁶ Pa. It was showed that the turn-on field (defined as the point where the current-voltage curve shows a sharp increase in the current density) decreased from 38 V/μm before bombardment to 25 V/μm after bombardment. And the maximum emission current density increased from 159.2 to 267.4 μA/cm². The composition before and after Ar⁺ bombardment was compared using X-ray photoelectron spectroscopy (XPS). Our results illustrated that the field emission characteristics were improved after the bombardment of Ar⁺. Foundation item: Supported by the National Natural Science Foundation of China (19975035) Biography: Ma You-peng (1978), male, Master candidate, research direction: novel functional materials film and ion beam modification of materials.     

Nitric oxide suppresses stomatal opening by inhibiting inward-rectifying K<Stack><Subscript>in</Subscript><Superscript>+</Superscript></Stack> channels in <Emphasis Type="Italic">Arabidopsis</Emphasis> guard cells

We explore nitric oxide （NO） effect on K^＋in, channels in Arabidopsis guard cells. We observed NO inhibited K^＋in, currents when Ca^2＋ chelator EGTA （Ethylene glycol-bis（2-aminoethylether）-N,N,N′,N;tetraacetic acid） was not added in the pipette solution; K^＋in currents were not sensitive to NO when cytosolic Ca^2＋ was chelated by EGTA. NO inhibited the Arabidopsis stomatal opening, but when EGTA was added in the bath solution, inhibition effect of NO on stomatal opening vanished. Thus, it implies that NO elevates cytosolic Ca^2＋ by activating plasma membrane Ca^2＋ channels firstly, then inactivates K^＋in, chartnels, resulting in stomatal opening suppressed subsequently.     

Comparative analysis of the dissolution kinetics of galena in binary solutions of HCl/FeCl<Subscript>3</Subscript> and HCl/H<Subscript>2</Subscript>O<Subscript>2</Subscript>

A comparative study of the dissolution kinetics of galena ore in binary solutions of FeCl₃/HCl and H₂O₂/HCl has been undertaken. The dissolution kinetics of the galena was found to depend on leachant concentration, reaction temperature, stirring speed, solid-to-liquid ratio, and particle diameter. The dissolution rate of galena ore increases with the increase of leachant concentration, reaction temperature, and stirring speed, while it decreases with the increase of solid-to-liquid ratio and particle diameter. The activation energy (E _a) of 26.5 kJ/mol was obtained for galena ore dissolution in 0.3 M FeCl₃/8.06 M HCl, and it suggests the surface diffusion model for the leaching reaction, while the E _a value of 40.6 kJ/mol was obtained for its dissolution in 8.06 M H₂O₂/8.06 M HCl, which suggests the surface chemical reaction model for the leaching reaction. Furthermore, the linear relationship between rate constants and the reciprocal of particle radius supports the fact that dissolution is controlled by the surface reaction in the two cases. Finally, the rate of reaction based on the reaction-controlled process has been described by a semiempirical mathematical model. The Arrhenius and reaction constants of 11.023 s⁻¹, 1.25×10⁴ and 3.65×10² s⁻¹, 8.02×10⁶ were calculated for the 0.3 M FeCl₃/8.06 M HCl and 8.06 M H₂O₂/8.06 M HCl binary solutions, respectively.     

Theoretical investigations of ESR and optical spectra of crystalline KHSO4：Mn^2＋

Calculations of d-d transitions and the axial zero-field splitting parameter D in crystalline KHSO4:Mn2+ have been undertaken, with consideration of the ninth O2– ligand. Energy level values calculated in a tetragonal field are in good agreement with experimentally observed values. Occasionally degenerate energy levels of 4A1(4Eg(G)) and 4A1(4A1g(G)) were found in the tetragonal crystal field. The calculated value of D is in good agreement with experimental value for KHSO4:Mn2+.