Gas adsorption sites in a large-pore metal-organic framework

The primary adsorption sites for Ar and N2 within metal-organic framework-5, a cubic structure composed of Zn4O(CO2)6 units and phenylene links defining large pores 12 and 15 angstroms in diameter, have been identified by single-crystal x-ray diffraction. Refinement of data collected between 293 and 30 kelvin revealed a total of eight symmetry-independent adsorption sites. Five of these are sites on the zinc oxide unit and the organic link; the remaining three sites form a second layer in the pores. The structural integrity and high symmetry of the framework are retained throughout, with negligible changes resulting from gas adsorption.     

An octahedral coordination complex of iron(VI)

The hexavalent state, considered to be the highest oxidation level accessible for iron, has previously been found only in the tetrahedral ferrate dianion, FeO4(2-). We report the photochemical synthesis of another Fe(VI) compound, an octahedrally coordinated dication bearing a terminal nitrido ligand. M?ssbauer and x-ray absorption spectra, supported by density functional theory, are consistent with the octahedral structure having an FeN triple bond of 1.57 angstroms and a singlet d2(xy) ground electronic configuration. The compound is stable at 77 kelvin and yields a high-spin Fe(III) species upon warming.     

Interwoven metal-organic framework on a periodic minimal surface with extra-large pores

Interpenetration (catenation) has long been considered a major impediment in the achievement of stable and porous crystalline structures. A strategy for the design of highly porous and structurally stable networks makes use of metal-organic building blocks that can be assembled on a triply periodic P-minimal geometric surface to produce structures that are interpenetrating-more accurately considered as interwoven. We used 4,4',4"-benzene-1,3,5-triyl-tribenzoic acid (H(3)BTB), copper(II) nitrate, and N,N'-dimethylformamide (DMF) to prepare Cu(3)(BTB)(2)(H(2)O)(3).(DMF)(9)(H(2)O)(2) (MOF-14), whose structure reveals a pair of interwoven metal-organic frameworks that are mutually reinforced. The structure contains remarkably large pores, 16.4 angstroms in diameter, in which voluminous amounts of gases and organic solvents can be reversibly sorbed.     

Hydrocarbon sex pheromone in tiger moths (Arctiidae)

2-Methylheptadecane is a sex pheromone compound in many sibling species of the Holomelina aurantiaca complex, in Holomelina laeta, and in Pyrrharctia isabella, which are all arctiids. Habitat preference, temporal distribution , and differing diurnal cycles help effect reproductive isolation among the species, but secondary sex pheromone chemicals are also suggested by the field studies.     

First solvation shell of the Cu(II) aqua ion: evidence for fivefold coordination

We determined the structure of the hydrated Cu(II) complex by both neutron diffraction and first-principles molecular dynamics. In contrast with the generally accepted picture, which assumes an octahedrally solvated Cu(II) ion, our experimental and theoretical results favor fivefold coordination. The simulation reveals that the solvated complex undergoes frequent transformations between square pyramidal and trigonal bipyramidal configurations. We argue that this picture is also consistent with experimental data obtained previously by visible near-infrared absorption, x-ray absorption near-edge structure, and nuclear magnetic resonance methods. The preference of the Cu(II) ion for fivefold instead of sixfold coordination, which occurs for other cations of comparable charge and size, results from a Jahn-Teller destabilization of the octahedral complex.     

Benzene Complexes with Copper(II)montmorillonite

Benzene formed a stable coinplex through its pi electrons to the copper ion in copper(II)montmorillonite. Copper(II)was the only exchangeable metal cation in montmorillonite to form a complex with benzene. Only those clay minerals whose charge arises in the octahedral layer produced the complex.     

A compound ovary with open carpels in winteraceae (magnoliales): evolutionary implications

"Bubbia" perrieri, a primitive angiosperm collected once in 1909 in northwestern Madagascar, differs from all other members of its genus and family (Winteraceae) in its bicarpellate, unilocular ovary. Moreover, its inflorescences are terminal, and its development is partially sympodial. It therefore represents the survivor of a previously undetected evolutionary line that should be accorded at least subfamilial status. If so, Winteraceae might, more likely than previously, be considered as allied to Canellaceae, a group of primitive angiosperms that has an ovary of "Bubbia" perrieri type and is specialized in some other respects.     

固相萃取─高效液相色谱法测定水中多环芳烃PAHs

介绍了7种水中多环芳烃高效液相色谱的检测方法,其中以ACCUBOND ODS C18作为水中PAHs固相萃取柱的萃取效率最高,不仅各组分的回收效率和检测灵敏度高,而且具有操作简便、溶剂用量小的特点,符合水中多环芳烃检测的基本要求,其峰面积与质量浓度呈现良好的线性关系,相关系数≥0.9990,平均加标回收率为81.8%～107.4%,相对标准偏差为1.80%～5.73%。     

利用同位素研究苗木在不同土壤中对两种磷源的吸收

作者利用同位素示踪和苗木放射性自显影技术,用~(32)P制备的标记铁磷和过磷酸钙分别施用于杉木、银杏、马尾松、柏木和黑松等苗木的根际土壤中;分别采用红壤、黄壤和石灰性土壤进行试验。经两年试验,结果表明:铁磷是能够被吸收利用的磷源,只不过吸收利用的速度很侈。在施用标记过磷酸钙63天内测定苗木对~(32)P的吸收动态时发现,磷在苗木组织中有不断积累的趋势;未见磷被“固定”而逐渐降低其有效性。施标记肥63天时,银杏从铁磷中吸收的~(32)P为从过磷酸钙中吸收的~(32)P的4.1％(红壤中)。在3类不同土壤中的试验均有相类似的趋势。     

云南不同地点及海拔异色瓢虫鞘翅色斑变异比较

2006年5月至2007年3月,分别在云南香格里拉、东川、元江和昆明进行野外标本采集．对4个地点的异色瓢虫Harmonia axyridis（Pallas）色斑变异进行了研究。结果显示,4个地点的异色瓢虫体色多以黄色为基本色调,鞘翅变化可分为黑底和黄底两大系列,共有43种色斑变异型。香格里拉、东川和昆明等3个地点黑底系色斑变异个体数量小于黄底系个体数量,而在元江则是黑底系个体数量占优势。在不同海拔地带中,异色瓢虫色斑变异出现个体数量最高是中海拔地带。异色瓢虫色斑变异是对生活环境的一种积极适应。图3表2参12     

5-氯甲基水杨醛缩 L-酪氨酸锰(II)配合物的合成及生物活性的研究

【目的】在甲醇溶剂体系中合成5-氯甲基水杨醛缩L-酪氨酸Schiff碱配体及其Mn(Ⅱ) 配合物.【方法】通过元素分析、摩尔电导、红外光谱、紫外光谱及差热-热重方法确定它们的分子组成;采用滤纸片法、光还原NBT法及荧光猝灭法测定该配合物的抗菌活性、SOD活性及其与牛血清白蛋白（BSA）的相互作用.【结果和结论】 5-氯甲基水杨醛缩L-酪氨酸Schiff碱配体及其Mn(Ⅱ) 配合物的分子组成分别为K₂L·3H₂O（L=C₁₇H₁₄NO₄Cl^2-）和K［MnL(CH₃COO)］·2H₂O,配合物中Schiff碱配体上的亚胺基N、羧基O及酚羟基O均与Mn(Ⅱ)配位.该配合物的抗菌活性高于配体,且对革兰阴性菌大肠埃希菌的抗菌活性高于对革兰阳性菌金黄色葡萄球菌的;该配合物具有较高的SOD活性,其IC₅₀为1.616 μmol·L^-1;基于静态猝灭机理,该配合物能有效猝灭BSA的内源荧光,并与BSA结合形成1种基态复合物,25 ℃条件下与BSA的结合位点数n约为1,结合常数K_A为1.62×10⁶ L·mol^-1,且分子内可能发生非辐射能量转移.     

邻二氮菲分光光度法同时测定水稻土中Fe(Ⅱ)和Fe(Ⅲ)

在HAc—NaAc缓冲系中,Fe(Ⅱ)和Fe(Ⅲ)的邻二氮菲络合物的吸收光谱在390.5nm有等吸收交叉点,同时Fe(Ⅱ)络合物的最大吸收波长为510nm.在此波长下Fe(Ⅲ)也有吸收.本文选择上述两波长,按双组分分光光度计算法,导出了吸光度与Fe(Ⅱ)和Fe(Ⅲ)浓度的相关计算公式.在0～15μg/mL Fe(Ⅱ)及0～25μg/mL Fe(Ⅲ)范围服从Beer定律.标准混合物测定误差Fe(Ⅱ)为-3.43％～2.33％;Fe(Ⅲ)为-1.15％～+1.55％.并用于水稻土中Fe(Ⅱ)和Fe(Ⅲ)的同时测定.铁的回收率为Fe(Ⅱ)90,6％～98,3％;Fe(Ⅲ)97.4％～102％.对19种阴阳离子作了干扰试验。     

土壤微团聚体中氧化铁的异化还原能力

选取有代表性的吉林、湖南、四川和广东4个省份的水稻土,采用超声波分散提取不同粒级的微团聚体,通过30℃恒温厌氧培养,测定培养过程中Fe( )产生量的变化。结果表明,不同土壤中铁还原程度大小与土壤的地带性分布有一定关系,吉林和四川水稻土中铁还原量大,而湖南和广东水稻土中铁还原量较小;对不同大小的微团聚体来说,除广东水稻土外,不同大小的微团聚体之间的铁还原程度均表现为:<0.001mm的微团聚体(14～35mg/g)>0.001～0.05mm的微团聚体(5～15mg/g)>0.05～0.25mm的微团聚(<6mg/g);不同组分中的铁还原主要由盐酸可溶性氧化铁的数量决定,不同土壤及不同团聚体中铁还原差异主要是由不同组分中氧化铁的化学形态决定。对于广东水稻土,其<0.001mm和0.05～0.25mm的微团聚体中的有机质数量可能是限制铁还原的关键因素。     

A manganese(IV)/iron(III) cofactor in Chlamydia trachomatis ribonucleotide reductase

In a conventional class I ribonucleotide reductase (RNR), a diiron(II/II) cofactor in the R2 subunit reacts with oxygen to produce a diiron(III/IV) intermediate, which generates a stable tyrosyl radical (Y*). The Y* reversibly oxidizes a cysteine residue in the R1 subunit to a cysteinyl radical (C*), which abstracts the 3'-hydrogen of the substrate to initiate its reduction. The RNR from Chlamydia trachomatis lacks the Y*, and it had been proposed that the diiron(III/IV) complex in R2 directly generates the C* in R1. By enzyme activity measurements and spectroscopic methods, we show that this RNR actually uses a previously unknown stable manganese(IV)/iron(III) cofactor for radical initiation.