Analysis of active sites for N2 and H^＋ reduction on FeMo-cofactor of nitrogenase

Dinitrogen (N2) and proton (H ),which act as physiological substrates of nitrogenase,are reduced on FeMo-co of the MoFe protein. However,researchers have different opinions about their exact reduction sites. Nitrogenases were purified from the wild type (WT) and five mutants of Azotobacter vinelandii (Av),including Qα191K,Hα195Q,nifV-,Qα191K/nifV- and Hα195Q/nifV-; and the activities of these en-zymes for N2 and H reduction were analyzed. Our results suggest that the Fe2 and Fe6,atoms closed to the central sulfur atom (S2B) within FeMo-co,are sites for N2 binding and reduction and the Mo atom of FeMo-co is the site for H reduction. Combining these data with further bioinformatical analysis,we propose that two parallel electron channels may exist between the 8Fe7S cluster and FeMo-co.     

Crystal structure and negative thermal expansion of solid solution Lu<Subscript>2</Subscript>W<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Mo<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>12</Subscript>

A new series of solid solutions Lu₂W_3−x Mo _x O₁₂ (0.5≤x≤2.5) were successfully synthesized by the solid-state method. Their crystal structure and negative thermal expansion properties were studied using high-temperature X-ray powder diffraction and the Rietveld method. All samples of rare-earth tungstates and molybdates are found to crystallize in the same orthorhombic structure with space group Pnca and show the negative thermal expansion phenomena related to transverse vibration of bridging oxygen atoms in the structure. Thermal expansion coefficients (TEC) of Lu₂W_3−x Mo _x O₁₂ are determined as −20.0×10⁻⁶ K⁻¹ for x=0.5 and −16.1×10⁻⁶ K⁻¹ for x=2.5 but -18.6×10⁻⁶ and −16.9×10⁻⁶ K⁻¹ for unsubstituted Lu₂W₃O₁₂ and Lu₂Mo₃O₁₂ in the identical temperature range of 200 to 800°C. High-temperature X-ray diffraction (XRD) data and bond length analysis suggest that the difference between W-O and Mo-O bond is responsible for the change of TECs after the element substitution in this series of solid solutions.     

Magnetoelectric and converse magnetoelectric res ponses in TbxDy1-xFe2-y alloy ＆ Pb（Mg1/3Nb2/3）（1-x）TixO3 crystal laminated composites

Measured results of magnetoelectric （ME） and converse magnetoelectric （CME） effects of TbxDy1-xFe2-y/ Pb（Mg1/3Nb2/3）（1-x）TixO3/TbxDy1-xFe2-y （TD/PMNT/TD） and PMNT/TD/PMNT laminated composites are presented. ME effect was determined by measuring laminate voltage output under a Helmholtz-generated AC field biased by a DC field （0-1 kOe） （1Oe = 79.58 A/m）. The CME effect was measured by recording the voltage induced in a solenoid encompassing the ME sample while exposed to a DC bias field and PMNT layer driven by a 10 V AC source. The ME and CME responses in the two laminated structure are linear. The highest values of ME coefficients in TD/PMNT/TD and PMNT/TD/PMNT composites are 384 mV/Oe and 158 mV/Oe, respectively, while the highest values of CME coefficients in the two composites are 118 mG/V and 162 mG/V （1 G=10^-4 T）, respectively.     

Preliminary Mo isotope data of Phanerozoic clastic sediments from the northern margin of the Yangtze block and its implication for paleoenvironmental conditions

Mo isotopes along with Nd isotopes and other geochemical characteristics of the Phanerozoic clastic sediments from the northern margin of the Yangtze block were analyzed by MC-ICP-MS and some other techniques, spanning the period from Cambrian to Jurassic. The δ 98Mo values and εNd(t ) in these sedimets were observed to exhibit a large range of variation (?0.65‰―+1.87‰, ?1.46―?10.90, respec-tively). Specifically, the sample from Late Permian Maokou Formation has relatively positive values in both δ 98Mo and...     

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.     

Influence of O2/Ar ratio on the properties of transparent conductive niobium-doped ZnO films

Niobium-doped ZnO transparent conductive films are deposited on glass substrates by radio frequency sputtering at 300℃. The influence of O2/Ar ratio on the structural, electrical and optical properties of the as-deposited films is investigated by X-ray diffraction, Hall measurement and optical transmission spectroscopy. The lowest resistivity of 4.0×10^-4Ω· cm is obtained from the film deposited at the O2/Ar ratio of 1/12. The average optical transmittance of the films is over 90%.     

Icariin suppresses bone resorption activity of rabbit osteoclasts in vitro

The effect of icariin on the bone resorption activity of rabbit osteoclasts is assessed in vitro. Osteoclasts were isolated from Japanese white rabbits and cultured on plates with a sterilized bone slice in each well. After treatment with icariin at various concentrations, the bone resorption activity of osteoclasts was evaluated by examining pit areas, superoxide anion (·O2-) generation, size and number of actin rings and intracellular calcium concentration [Ca2 ]i. As revealed by these data, icariin elicited continuous decline of [Ca2 ]i, making actin ring constricted and ·O2- generation decreased. These events resulted in smaller and fewer pits which indicate suppressed bone resorption activity of rabbit osteoclasts by icariin.     

Direct electrochemistry and electrocatalysis of horseradish peroxidase in MnO2 nanosheet film

A novel material MnO2 nanosheet has been used as the support matrix for the immobilization of horseradish peroxidase （HRP）. HRP entrapped in MnO2 nanosheet film exhibits facile direct electron transfer with the electron transfer rate constant of 6.86 s^-1. The HRP/MnO2 nanosheet film gives a reversible redox couple with the apparent formal peak potential （E^0＇） of -0.315 V （vs. Ag/AgCl） in pH 6.5 phosphate buffer solution （PBS）. The formal potential E^0＇ of HRP shifts linearly with pH with a slope of -53.75 mV.pH^-1, denoting that an electron transfer accompanies single-proton transportation. The immobilized HRP shows an electrocatslytic activity to the reduction of H2O2. The response time of the biosensor for H2O2 is less than 3 s, and the detection limit is 0.21 μmol · L^-1 based on signal/noise = 3.     

Second organic aerosol formation by irradiation of α-pinene-NO<Subscript>x</Subscript>-H<Subscript>2</Subscript>O in an indoor smog chamber for atmospheric chemistry and physics

Ozone（O3） and secondary organic aerosol （SOA） are considered to be the most serious secondary air pollutants of concern in most metropolitan areas, as well as for Beijing. In this study, 03 and SOA formation potential of α-pinene, the most abundant biogenic VOCs, is investigated at Tsinghua Indoor Chamber Facility. The experiments were conducted under atmospheric relevant HCs/NOx ratios in both presence and absence of ammonia sulfate seed aerosol. A Scanning Mobility Particle Sizer system （3936, TSI） and a Condensation Particle Counter （3010, TSI） were used to study the SOA formation and a gas chromatograph （GC） equipped with a DB-5 column and a flame ionization detector （FID） was used to measure α-pinene simultaneously. The results show that the presence of ammonia sulfate seed aerosol did not change the formation trend of 03, but significantly contribute to SOA formation. A strong linear relationship （r^2 = 0.90） between SOA yield enhancement （△Y＊） and surface concentration of seed aerosol （PM1, s）has been found, denoting that the PMi, s is the control factor for SOA yield enhancement. And the possible reason for the enhancement is acid-catalyzed heterogeneous reactions.     

Rate constants for the reaction of ozone with <Emphasis Type="Italic">n</Emphasis>-butyl, <Emphasis Type="Italic">s</Emphasis>-butyl and <Emphasis Type="Italic">t</Emphasis>-butyl methyl sulfides

The rate constants for the ozone reactions with n-butyl methyl sulfide （n-BMS, CHaCH2CH2CH2SCH3）, sec-butyl methyl sulfide （s-BMS, CH3CH2（CH3）CHSCHa） and tert-butyl methyl sulfide （t-BMS, （CH3）3CSCH3） were measured using our smog chamber under supposedly pseudo-first-order conditions at 30002 K and 760 Torr. The experimental determined rate constants for n-butyl, s-butyl and t-butyl methyl sulfide are （1.23 ± 0.06）×10-19, （5.08 ± 0.19）×10-20 and （2.26 ± 0.14）×10-20 cm3 molecule-1· s-1, respectively. The reactivity-structure relationship of the reactions was discussed and used to illustrate the mechanism of the ozone reaction with thioethers. The results enrich the kinetics data of atmospheric chemistry.     

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.     

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.     

Export and remineralization of POM in the Southern Ocean and the South China Sea estimated from 210Po/210Pb disequilibria

Disequilibria between ^210Po and ^210Pb in the upper water and their potential applications as a proxy of particle export and remineralization were examined in the Southern Ocean （station IV3） and the South China Sea （NS44）. ^210po was deficit in surface waters but excessive relative to ^210Pb in subsurface waters. Good positive correlation between ^210Po and particulate organic carbon （POC） indicated deficits and excess of ^210Po resulted from particulate organic matter （POM） export and remJneralization respectively, which was also supported by the decreased δ^13C and increased δ^15N downwards as a result of particle remineralization. On the basis of ^210Po/^210Pb box-model, POC export flux out of the surface waters were 1.2 mmol C. m^-2. d^-1 and 2.3 mmol C. m^-2. d^-1 for station NS44 and IV3, respectively. In the subsurface waters, remineralization fluxes of ^210Po were 0.062 Bq. m^-2.d^-1 and 0.566 Bq.m^-2.d^-1 for station NS44 and IV3 along with the recycle efficiency of 52±26% and 119±52%, respectively. Remineralized fluxes of POM derived from ^210Po and exported POC were 0.6 mmol C.m^-2.d^-1 and 2.7 mmol C. m^-2. d^-1 for NS44 and IV3. This study suggested that ^210Po was a powerful tracer of particle export and remineralization.     

The Distribution of a CP-asymmetric quantity in the decay channel J / Ψ → π + π ? π 0

The distribution of a CP-asymmetric quantityA in the decay channelJ/ψ→π ⁺ π ⁻ π ⁰ is investigated. This dimensionless quantityA is constructed from the momenta of the π-meson final states, namely A=P _x ^{π +} P _y ^{π −} -P _x ^{π −} P _y ^{π −}, whereP _h,P _x ^h andP _y ^h are the module of the momentum of a hadron h, the x- and y-components of that momentum respectively, theJ/ψ particle is produced by e⁺ e⁻ collision, and the direction of the momentum of e⁺ is taken to be the positive direction ofz axis. There would exists the violation under the combined transformation of charge conjugation and space reflection (CP violation) when the average ofA among a lot of events, 〈A〉, be examined to be nonzero clearly from data. In this way, 748 events are selected from the BES experimental data, and analyzed. The corresponding averageA-value is measured to be 〈A〉 = 0.010 39 ± 0.014 61 ± 0.015 2. Further, some discussion of our result, the size of the data sample being need for further attempt and a possible perspective are given.     

Comparison of the carbon isotope composition of total organic carbon and long-chain <Emphasis Type="Italic">n</Emphasis>-alkanes from surface soils in eastern China and their significance

Surface soil samples collected over a high spatial resolution in eastern China were analyzed for carbon isotope composition （δ^13C） of total organic carbon （TOC） and higher plant-derived long-chain n-alkanes, with the latter reported as weighted mean values. The two sets of δ^13C values are significantly correlated and show similar trends in spatial variation. The spatial distribution of δ^13C shows less negative values in the mid-latitudes between 31°N and 40°N and more negative ones at higher and lower latitudes. This is consistent with previously reported carbon isotope data from surface soil phytoliths in the same region and suggests that the mid-latitude area provides relatively favorable growing condi- tions for C4 plants. Furthermore, δ^13C values of both TOC and long-chain n-alkanes from 12 surface soil samples collected from a small grassland in north China displayed similar carbon isotope values and the difference between paired δ^13C of a soil samples remains relatively constant. Our data demonstrate that in eastern China, soil δ^13C composition of both TOC and long-chain n-alkanes is effective indicators of C3/C4 ratios of the prevailing vegetation. This work suggests that -22‰ and -32‰ are good es- timated end members for the weighted mean δ^13C values of long-chain n-alkanes （C27, C29 and C31 n-alkanes） from soils under dominant C4 or C3 vegetation, allowing us to reconstruct paleovegetation trends.     

Theoretical study on photophysical property of C60M（CO）5 （M=Cr,Mo and W）

Configurations of three η2 models of transition-metal [60]fullerene derivatives C60M（CO）5（M=Cr, Mo and W） have been optimized at B3LYP/LanL2DZ level. On the basis of the optimized geometrical structures, their electronic spectra and the frequency dependence of third-order nonlinear optical polarizabilities γ in different optical processes of third-harmonic generation （THG）, electric-field-induced second-harmonic generation （EFISHG） and degenerate four-wave mixing （DFWM） are calculated by using TDB3LYP model based on LanL2DZ level coupled with the SOS （sum-over-state） method. The obtained results show that their electronic spectra have a red shift compared with that of [60]fullerene and different transition-metal functional groups added to C60 cage may result in different spectrum properties. For the three studied species, （η^2-C60）Mo（CO）5 has the largest third-order nonlinear optical polarizability.     

超声波下酸化碘酸钾和亚硫酸钠反应的反应速率研究

分别测定在有超声波作用和在无超声波作用条件下 ,酸化碘酸钾 (KIO3 )和亚硫酸钠 (Na2 SO3 )反应的反应速率方程式及活化能 ,从而研究该反应的机理以及超声波在该反应中的作用 ,并确定反应的最佳条件。实验得出 ,超声波对该反应有一定的促进作用 ,但是这种促进作用只提高反应的速率常数和降低反应的活化能 ,并没有改变反应机理。在超声波功率为 30 0W时 ,反应的速率方程表示式为 :v =k·c1 0 9(KIO3 ) ·c1 0 0 (Na2 SO3 )·c1 0 8(H+ ) ,其中 :k =95 0 (mol-1·L) 2 ·s-1,活化能为 17 35kJ·mol-1。实验还得出 ,在温度为2 98K时 ,当KIO3 与Na2 SO3 的初始浓度比为 2∶5 ,H+ 的初始浓度为 0 0 4 2 8mol·L-1,超声功率为 30 0W时 ,反应速率为最快 ,即v =4 31× 10 -4mol·L-1·s-1)。     

Effect of Cl- on photosynthetic bicarbonate uptake in two cyanobacteria Microcystis aeruginosa and Synechocystis PCC6803

Photosynthetic inorganic carbon utilization was investigated in two cyanobacteria Microcystis aeruginosa and Synechocystis PCC6803 grown in standing culture. Photosynthetic rates for the two algae reached about 10 times the theoretical CO₂ supply rate at low dissolved inorganic carbon (DIC) of 100 μmol/L, and the rates were unaffected by the addition of 20 mmol/L Na⁺, indicating that the two algae possessed Na+-independent HCO^-₃ utilization for photosynthesis under low DIC. Their photo- synthetic rates at low DIC were inhibited by higher Cl^- and the degrees of inhibition were increased with the rise of CI^- concentration, and in the presence of Diphenylamine-2-carboxylate (DPC), a reported Cl^- channel inhibitor, the rates decreased by 74%－82%, implying that putative DPC-sensitive Cl^- channels participate in Na+-independent HCO₃^- uptake for photosynthesis. The experiment of intracellular 14C-DIC accumulation for photosynthesis showed that internal DIC pools decreased by about 80% with 200 μmol/L DPC and by 64%－70% with 100 mmol/L Cl^-. The experiment of chlorophyll a fluorescence quenching showed that initial rates and extents of fluorescence quenching obviously decreased with 200 μmol/L DPC or 100 mmol/L Cl^-. The two experiments gave further evidence that putative DPC-sen- sitive Cl^- channels participate in Na+-independent HCO^-₃ uptake for photosynthesis in the two algae grown in standing culture.     

An in-situ DRIFTS study in the reaction between NO x and soot on BaAl2O4

The interactions between NO, O2 and their mixture on BaAl2O4, as well as the reaction of NOx with soot in the presence of O2, have been investigated using Diffuse Reflectance Infrared Fourier Transform Spectroscopy （DRIFTS）. NO adsorption produces only nitrites species in the absence of O2. NO2 adsorption produces nitrates species besides nitrites species. The produced nitrites will further react with O2, Osurf^-. and Olattice^2- to form nitrates. The reaction of NOx with soot begins with the reaction of nitrates with soot oxygenated complex （C（O））, which is regarded as the key and rate determining step. A reaction pathway is proposed for the catalyzed reaction of NOx with soot in the presence of O2.     

Heteroseneous 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 SO4^2- species and gaseous CO2 through the surface hydrogen thiocarbonate （HSCO2-） and HSO; 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.