A versatile entry into aqueous niobium chemistry: isolation and structure of the intermediate Nb4(μ2-O)2(μ2-OC2H5)4Cl4(OC2H5)4(HOC2H5)4

The reduction of ethanolic solutions of niobium pentachloride with zinc, followed by treatment with aqueous acids serves as a versatile entry into the aqueous solution chemistry of niobium. From the zinc-reduced solution, the major intermediate, Nb₄(μ₂-O)₂(μ₂-OC₂H₅)₄Cl₄(OC₂H₅)₄(HOC₂H₅)₄, was isolated and the crystal structure determined by X-ray crystallography. The complex crystallizes in the orthorhombic space group Pccn, with Z=4, a=21.0105(9), b=11.0387(5), c=19.1389(8), V=4438.9(3) ų, M_r=1090.19,R₁=0.0327 and wR₂=0.0876. The structure revealed a centrosymmetric tetrameric Nb(IV) complex, consisting of a pair of edge-sharing bi-octahedral Nb₂(μ₂-OC₂H₅)₄Cl₂(OC₂H₅)₂(HOC₂H₅)₂ units that are joined by two axial oxo ligands. The Nb-Nb distance of 2.7458(3) Å is consistent with a single metal-metal bond.     

C3与C4植物的环境调控

环境条件决定着不同光合类型植物的地理分布范围和区域 ,一般来说 ,C4 植物分布于高温、强光的环境而 C3植物分布于阴凉、湿润的环境 ,且 C4 比 C3植物光合速率高。但环境条件影响着不同光合类型植物的光合潜能的发挥 ,C4 植物在高温、强光、干旱条件下所表现出来的优势在其它环境条件下未必就显现出来。环境条件甚至可以引起 C3、C4 光合途径间的相互转化 ,这使得目前几种鉴别植物光合类型的方法出现不一致的结果。因此 ,在判断植物的光合类型时 ,要注意多种手段的综合利用 ,同时注意植物所处环境条件的影响。     

Oxidation of [Ir(η-C5Me5)(C8H4S8)] and crystal structures of [IrI(η-C5Me5)(C8H4S8)](I3) and [IrI(η-C5Me5)(C8H4S8)](I3)1/2(I7)1/2

[Ir(η⁵-C₅Me₅)(C₈H₄S₈)] (1) [ = 2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithionate(2−)] was reacted with iodine in dichloromethane to afford one-electron- and two-electron-oxidized species [IrI(η⁵-C₅Me₅)(C₈H₄S₈)] (2), [IrI(η⁵-C₅Me₅)(C₈H₄S₈)](I₃) (3) and [IrI(η⁵-C₅Me₅)(C₈H₄S₈)](I₅) (4). The oxidized species exhibit electrical conductivities of (1.1-5.0) × 10⁻⁶ S cm⁻¹ measured for compacted pellets at room temperature. The X-ray crystal structures of the two-electron-oxidized complexes 3 and 4 revealed the Ir-I bonds for both of them and the presence of for 3 and ions for 4 as the counter anions. They have many S-S and S-I non-bonding contacts to form two-dimensional molecular interaction sheets in the solid state.     

Thallium(III) complexes of the metalloligands [Pt2(μ-S)2(PPh3)4] and [Pt2(μ-Se)2(PPh3)4]

Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with the diarylthallium(III) bromides Ar₂TlBr [Ar = Ph and p-ClC₆H₄] in methanol gave good yields of the thallium(III) adducts [Pt₂(μ-S)₂(PPh₃)₄TlAr₂]⁺, isolated as their salts. The corresponding selenide complex [Pt₂(μ-Se)₂(PPh₃)₄TlPh₂]BPh₄ was similarly synthesised from [Pt₂(μ-Se)₂(PPh₃)₄], Ph₂TlBr and NaBPh₄. The reaction of [Pt₂(μ-S)₂(PPh₃)₄] with PhTlBr₂ gave [Pt₂(μ-S)₂(PPh₃)₄TlBrPh]⁺, while reaction with TlBr₃ gave the dibromothallium(III) adduct [Pt₂(μ-S)₂(PPh₃)₄TlBr₂]⁺[TlBr₄]⁻. The latter complex is a rare example of a thallium(III) dihalide complex stabilised solely by sulfur donor ligands. X-ray crystal structure determinations on the complexes [Pt₂(μ-S)₂(PPh₃)₄TlPh₂]BPh₄, [Pt₂(μ-S)₂(PPh₃)₄TlBrPh]BPh₄ and [Pt₂(μ-S)₂(PPh₃)₄TlBr₂][TlBr₄] reveal a greater interaction between the thallium(III) centre and the two sulfide ligands on stepwise replacement of Ph by Br, as indicated by shorter Tl-S and Pt?Tl distances, and an increasing S-Tl-S bond angle. Investigations of the ESI MS fragmentation behaviour of the thallium(III) complexes are reported.     

The arylation of [Pt2(μ-S)2(PPh3)4]

Routes to the synthesis of the mixed sulfide-phenylthiolate complex [Pt₂(μ-S)(μ-SPh)(PPh₃)₄]⁺ have been explored; reaction of [Pt₂(μ-S)₂(PPh₃)₄] with excess Ph₂IBr proceeds readily to selectively produce this complex, which was structurally characterised as its PF₆⁻ salt. Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with other potent arylating reagents (1-chloro-2,4-dinitrobenzene and 1,5-difluoro-2,4-dinitrobenzene) also produce the corresponding nitroaryl-thiolate complexes [Pt₂(μ-S){μ-SC₆H₂(NO₂)₂X}(PPh₃)₄]⁺ (X = H, F). The complex [Pt₂(μ-S)(μ-SPh)(PPh₃)₄]⁺ reacts with Me₂SO₄ to produce the mixed alkyl/aryl bis-thiolate complex [Pt₂(μ-SMe)(μ-SPh)(PPh₃)₄]²⁺, but corresponding reactions with the nitroaryl-thiolate complexes are plagued by elimination of the nitroaryl group and formation of [Pt₂(μ-SMe)₂(PPh₃)₄]²⁺. [Pt₂(μ-S)(μ-SPh)(PPh₃)₄]⁺ also reacts with Ph₃PAuCl to give [Pt₂(μ-SAuPPh₃)(μ-SPh)(PPh₃)₄]²⁺.     

C3、C4和CAM途径的生态学意义

本文通过C_3,C_4和CAM植物在不同环境中的分布,从3个方面阐述了这3种碳同化途径在利用环境资源时的生态学意义——资源分隔: 1.光合途径的空间分异:(1)不同光合类型植物的气候带(水平和垂直带)和地理区域分布;(2)不同光合类型植物在微环境中的分布。 2.光合途径的时间分异。 3.光合途径在资源分隔中的重叠。     

Synthesis of some pentanuclear platinum clusters [Pt5(CO)6(L)4]. The X-ray structure of [Pt5(μ-CO)5(CO)(PCy3)4]

[Pt₅(μ-CO)₅(CO)L₄] (L = PPh₃1, PPh₂Bz 2, AsPh₃3, PEt₃4, PCy₃5) have been synthesized by reacting [Pt₃(μ-CO)₃(PR₃)₃] with H₂O₂ (1 and 2), by reduction of cis-[PtCl₂(CO)(PEt₃)] with Zn dust (4), and by the Zn reduction of [Pt₃(μ-CO)₃(PCy₃)₃] in the presence of [PtCl₂(CH₃CN)₂] (5). Complex 5 has not been observed previously and has been characterized by X-ray crystallography. Oxidation of the phosphine ligands with H₂O₂ is a new way to synthesize 1 and 2. The first complete NMR characterization of these complexes has also been achieved, and showed that these pentanuclear cluster complexes exhibit similar stereochemistries in solution and in the solid state. The observed ¹J_Pt-Pt values do not have any correlation with the corresponding bond lengths, again pointing out the irregular behaviour of such parameter in Pt complexes.     

Heterobimetallic platinum-bismuth aggregates derived from [Pt2(μ-S)2(PPh3)4]

The metalloligand [Pt₂(μ-S)₂(PPh₃)₄] reacts with Bi(S₂CNEt₂)₃ or Bi(S₂COEt)₃ in methanol to produce the orange cationic adducts [Pt₂(μ-S)₂(PPh₃)₄Bi(S₂CNEt₂)₂]⁺ and [Pt₂(μ-S)₂(PPh₃)₄Bi(S₂COEt)₂]⁺, respectively, isolated as their hexafluorophosphate salts. An X-ray structure determination on [Pt₂(μ-S)₂(PPh₃)₄Bi(S₂CNEt₂)₂]PF₆ reveals the presence of a six-coordinated bismuth centre with an approximately nido-pentagonal bipyramidal coordination geometry. Fragmentation pathways for both complexes have been probed using electrospray ionisation mass spectrometry; ions [Pt₂(μ-S)₂(PPh₃)₂Bi(S₂CXEt_n)₂]⁺ (X = O, n = 1, X = N, n = 2) are formed by selective loss of two PPh₃ ligands, and at higher cone voltages the species [(Ph₃P)PtS₂Bi]⁺ is observed. Ions formed by loss of CS₂ are also observed for the xanthate but not the dithiocarbamate ions.     

Redox reactions of the hydrogenase-cytochrome C3 system from Desulfovibrio gigas with the synthetic analogue of ferredoxin active sites [Fe4S4 (SCH2CH2OH)4]2−

The synthetic cluster [Fe₄S₄ (SCH₂CH₂OH)₄]^2? and ferredoxin I from $\text{Desulfovibrio}\text{gigas}$ have been comparatively reacted in the presence of hydrogen with two enzyme components isolated from the $\text{D.}\text{gigas}$ electron carrier system: hydrogenase and cytochrome c₃. The reactions have been followed by spectrophotometric and manometric methods. No reduction is detected unless both enzymes are simultaneously present. The easy reduction in the presence of hydrogenase-cytochrome c₃ combination takes place in two stages corresponding each to one equivalent of reduction. The first stage is reversible while the second is not and yields a super reduced species deriving from the cluster complex.     

中国东北草原植物中的C3和C4光合作用途径

以光合作用关键羧化酶ＰＥＰＣ和ＲｕＢＰＣ活性化,并且参照叶片ＣＯ补偿浓度,δ＾１３Ｃ值和叶片解剖结构特点来鉴定东北草原区２３３种植物的Ｃ３,或Ｃ４光全作用途径,这些植物隶属于１４４属７３科,其中１３７种为首次鉴定。８９种具有Ｃ４光合作用途径,隶属于５５属１７科;１４４种人有Ｃ３光俣作用途径;隶属于９４属２８在多数Ｃ４种分布在禾本科、莎草科、苋科和藜科。苋属、地肤属、狗昌属和虎尾草属中的均为Ｃ４植物     

添加氧化铁对水稻土中H2、CO2和CH4形成的影响

水稻土是甲烷产生的重要源地.厌氧条件下甲烷的形成与有机质厌氧降解产生的乙酸、H₂和CO₂有关.氧化铁作为电子受体可有效地竞争有机质向甲烷的转化,其抑制作用机理可能与乙酸、H₂和CO₂的有效消耗有关.通过向水稻土泥浆中添加无定形氧化铁和纤铁矿,分别测定了25℃厌氧恒温培养105d过程中的H₂、CO₂和CH₄的浓度变化.结果表明,添加无定形氧化铁及纤铁矿可导致H₂浓度显著降低;无定形氧化铁对H₂消耗的影响明显大于纤铁矿;添加不同氧化铁对CO₂浓度的影响与H₂浓度的变化有相同的趋势;添加氧化铁能显著抑制水稻土中甲烷形成,并导致有机碳的转移发生变化,使得CH₄-C显著降低,气相中CO₂-C量减少,而由土壤泥浆固定的CO₃^2--C量显著增加.     

C4作物FACE(free-air CO2 enrichment)研究进展

持续迅速上升的大气二氧化碳浓度([CO₂])是全球变暖最大的驱动因子,但其作为光合作用底物直接增加了作物的生产力。相比C₃作物,人们对未来高浓度CO₂情形下C₄作物的响应规律认识较少。与封闭或半封闭气室研究相比,FACE(free-air CO₂ enrichment)试验在空气自由流动的大田条件下对作物表现进行研究,它提供了对未来作物生长环境的真实模拟,因此提供了评估CO₂肥料效应以及揭示植物响应机制的最好机会。作为人类重要的粮食和饲料来源,高粱和玉米是最重要的C₄作物。在简介美国玉米和高粱FACE系统的基础上,综述了FACE情形下高浓度CO₂(模拟本世纪中叶大气CO₂浓度,即550 μmol/mol)对两大作物生理、生长和产量以及土壤特性等方面的影响,同时比较了与气室研究结果的异同点。(1)FACE使干旱条件下两作物光合作用显著增强,但湿润条件下没有影响;FACE条件下高粱出现光合适应现象,而玉米没有;(2)FACE使两作物气孔导度大幅下降,导致叶温升高、蒸腾速率下降、蒸发蒸腾总量减少或没有变化、叶片总水势和水分利用效率增加或没有变化;(3)FACE对两作物物候期和化学组分影响很少;(4)FACE使干旱条件下两作物生长和产量略有增加,但湿润条件下没有影响;(5)FACE使高粱田土壤丛枝状菌根真菌的长度和易提取胶状物质浓度显著增加,导致水稳性土壤团聚体增加;FACE对高粱田N₂O或含氮气体(N₂O+N₂)的排放没有影响;(6)高浓度CO₂对两作物气孔导度的影响FACE试验明显大于气室试验,而对生长和产量的影响呈相反趋势。阐明CO₂与基因型、土壤湿度和大气温度间的互作效应及其机制是下一轮C₄作物FACE研究优先考虑的方向,技术的不断进步已为利用大型FACE系统来研究这些互作效应提供了可能。     

Influence of CH3 group of μ-N-C-S ligand on the properties of [Fe2(C4H5N2S)2(NO)4] complex

Bi-nuclear neutral sulfur-nitrosyl iron complex [Fe₂(SR)₂(NO)₄] (I) has been obtained by replacement of thiosulfate ligands in dianion [Fe₂(S₂O₃)₂(NO)₄]²⁻ by 1-methyl-imidazole-2-yl. From X-ray analysis data, the complex has centrosymmetrical dimeric structure, with the iron atoms being linked via μ-N-C-S bridge. From Mossbauer spectroscopy, isomeric shift δ_Fe is 0.180(1) mm/s and quadrupole splitting ΔE_Q is 0.928(2) mm/s at T = 290 K. By comparative studying the mass-spectra in the gaseous phase of solid samples decomposition and kinetics of NO release in 1% aqueous solutions of dimethylsulfoxide, using of the ligand with CH₃ substituent in position 1 of imidazole-2-thiol was shown to yield a more stable donor of nitrogen monoxide than earlier obtained analog with imidazole-2-thiol, [Fe₂(C₃H₃N₂S)₂(NO)₄].     

Synthesis and characterisation of [Pt2(μ-S)(μ-I)(PPh3)4] - A cationic iodo analogue of the metalloligand [Pt2(μ-S)2(PPh3)4]

Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with a number of transition metal-iodo complexes leads to the formation of the cationic iodo analogue [Pt₂(μ-S)(μ-I)(PPh₃)₄]⁺, identified using electrospray ionisation mass spectrometry (ESI MS). Synthetic routes to this complex were developed, using the reaction of [Pt₂(μ-S)₂(PPh₃)₄] with either [PtI₂(PPh₃)₂] or elemental iodine. The complex was characterised by NMR spectroscopy, ESI MS and an X-ray structure determination, which reveals the presence of a planar, disordered {Pt₂SI}⁺ core. Monitoring the iodine reaction by ESI MS allows the identification of various iodine species, including the short-lived intermediate [Pt₂(μ-S)₂(PPh₃)₄I]⁺, which allows a mechanism for the reaction to be proposed.     

苦瓜籽蛋白的PEG/（NH4）2SO4双水相分离及抑菌作用的研究

优化试验条件影响因素,建立PEG/(NH4)2SO4双水相系统,确定出分离苦瓜籽蛋白的最适PEG6000和(NH4)2SO4质量分数分别是22%、25%,分配系数为0.089,回收率为96%。双水相分离的苦瓜籽蛋白经SDS-PAGE凝胶电泳显示,主要蛋白质是50 KD4、3 KD和10 KD亚基结合形成的多聚体12S(327 KD)球蛋白,还原条件下出现诸多小于35 kD的蛋白组分,表明蛋白质亚基是通过二硫键结合。抑菌试验显示苦瓜籽蛋白对受试细菌菌和真菌产生明显的抑菌活性,其MIC远低于苯甲酸钠,而且在不同盐离子浓度、温度、pH及紫外线等因素处理时,均具有一定的稳定性。此外试验还表明苦瓜籽蛋白也具有较强的清除羟自由基能力和总抗氧化能力。     

Hydrido-derivatives of [Ir4(CO)10(diphosphine)]: X-ray analyses of [Ir4H(CO)9(μ-Ph2PH(CH3)PPh2)] and [Ir4 H(CO)9(μ-Ph2P(CH2)nPPh2)] (n = 2, 3)

Some novel hydrido-anions of general formula [Ir₄H(CO)₉(μ-L-L)]⁻ (L-L = Ph₂PCH(CH₃)PPh₂, Ph₂P(CH₂)₂PPh₂, Ph₂P(CH₂)₃PPh₂ and Ph₂AsCH₂AsPh₂) have been obtained by the reaction of [Ir₄(CO)₁₀(μ-L-L)] with the base 1,8-diazabicyclo[5.4.0]undec-7-ene in wet dichloromethane. According to IR and ¹H, ³¹P and ¹³C NMR data at low temperature, these anionic derivatives display a single conformation in solution: three edge-bridging COs around the triangular basal face and both the hydride and the bidentate ligands located in axial positions relative to this face. The structures of four compounds were established by X-ray diffraction studies, which confirmed the configuration proposed on the basis of spectroscopic data.     

A novel tetranuclear hydrogenphosphate-bridged Cu(II) cluster. Synthesis, structure, spectroscopy and magnetism of [Cu4(dpyam)4(μ4,η-HPO4)2(μ-X)2]X2(H2O)6 (X = Cl, Br)

Two novel tetranuclear compounds with an unprecedented mode of a hydrogenphosphato bridge, [Cu₄(dpyam)₄(μ₄,η³-HPO₄)₂(μ-X)₂]²⁺ (in which dpyam = di-2-pyridylamine and X = Cl (1), Br (2)) have been synthesised and characterised structurally and magnetically. The Cu(II) ions in the structures each display a square-pyramidal geometry, with two tridentate hydrogenphosphato groups bridging four copper atoms in a μ₄,η³ coordination mode which is rarely found in hydrogenphosphate metal compounds. Each (different) pair of Cu(II) ions is additionally bridged by halide ions, with relatively long Cu-X distances (2.551(3)-2.604(3) Å for 1 and 2.707(1)-2.766(2) Å for 2) and subsequently also a small Cu-X-Cu angle (65.7(1)° and 65.1(1)° for 1 and 61.6(1)° and 62.4(1) for 2) and a large Cu-X-Cu angle (95.5(1)° and 96.5(1)° for 1 and 91.1(1)° and 92.6(1)° for 2). Cu?Cu distances in the tetranuclear units varies from 2.802(3) to 5.232(3) Å for 1 and from 2.834(1) to5.233(1) Å in 2. The lattice structures are stabilised by extensive intermolecular hydrogen bonds. The magnetic susceptibility measurements down to 5 K revealed a weak ferromagnetic interaction between the outer pairs of Cu(II) ions which vary from 22 to 46 cm⁻¹ in 1 and 12 to 33 cm⁻¹ in 2 and a moderately strong antiferromagnetic interaction between the inner Cu(II) ions of −79 cm⁻¹ in 1 and −83 cm⁻¹ in 2, via the Cu-O-P-O-Cu pathway.     

Binding of HIV-1 virions to α4β7 expressing cells and impact of antagonizing α4β7 on HIV-1 infection of primary CD4+ T cells

HIV-1 envelope glycoprotein is reported to interact with α4β7, an integrin mediating the homing of lymphocytes to gut-associated lymphoid tissue, but the significance of α4β7 in HIV-1 infection remains controversial. Here, using HIV-1 strain Ba L, the gp120 of which was previously shown to be capable of interacting with α4β7, we demonstrated that α4β7 can mediate the binding of whole HIV-1 virions to α4β7-expressing transfectants. We further constructed a cell line stably expressing α4β7 and confirmed the α4β7-mediated HIV-1 binding. In primary lymphocytes with activated α4β7 expression, we also observed significant virus binding which can be inhibited by an anti-α4β7 antibody. Moreover, we investigated the impact of antagonizing α4β7 on HIV-1 infection of primary CD4+ T cells. In α4β7-activated CD4+ T cells, both anti-α4β7 antibodies and introduction of shorthairpin RNAs specifically targeting α4β7 resulted in a decreased HIV-1 infection. Our findings indicate that α4β7 may serve as an attachment factor at least for some HIV-1 strains. The established approach provides a promising means for the investigation of other viral strains to understand the potential roles of α4β7 in HIV-1 infection.     

C3和C4植物叶片对光氧化响应的日变化

田间生长的C3植物花生和C4植物玉米分别于晴天上午9：00、中午12：00、下午15：00取样。中午12：00花生叶片的Fv／Fm较早上9：见下降16％,出现了光抑制现象,玉米叶片的Fv／Fm则未下降。不同时间取样的花生和玉米叶片经甲基紫精（MV） 强光的人为光氧化处理,叶绿素和类胡萝卜素出现不同程度的氧化降解,中午12：00降解幅度最大,15时降幅最小。植物叶片的抗氧化能力与其SOD活性相关,而与PEPCase的活性没有明显的相关性。光氧化处理后,花生和玉米的叶绿素荧光参数FV／Fm、qp、pSII都下降,花生在12：00的降幅最小,玉米的降幅最大。光氧化引起花生的qN和热耗散系数（KD）上升,玉米则都下降．结果显示C3植物花生和C4植物玉米对光氧化的响应可能存在不同的机制。