近十年国内农村贫困研究的文献分析

基于CNKI数据库提供的数据,对1999-2008年我国农村贫困期刊论文进行统计,概述了国内农村贫困研究论文的数量、机构、地区、基金等的结构分布,分析了国内农村贫困研究取得的成绩与今后进一步发展的建议。     

Proton radiography of inertial fusion implosions

A distinctive way of quantitatively imaging inertial fusion implosions has resulted in the characterization of two different types of electromagnetic configurations and in the measurement of the temporal evolution of capsule size and areal density. Radiography with a pulsed, monoenergetic, isotropic proton source reveals field structures through deflection of proton trajectories, and areal densities are quantified through the energy lost by protons while traversing the plasma. The two field structures consist of (i) many radial filaments with complex striations and bifurcations, permeating the entire field of view, of magnetic field magnitude 60 tesla and (ii) a coherent, centrally directed electric field of order 10(9) volts per meter, seen in proximity to the capsule surface. Although the mechanism for generating these fields is unclear, their effect on implosion dynamics is potentially consequential.     

Crystal structures of Fe2+ dioxygenase superoxo, alkylperoxo, and bound product intermediates

We report the structures of three intermediates in the O2 activation and insertion reactions of an extradiol ring-cleaving dioxygenase. A crystal of Fe2+-containing homoprotocatechuate 2,3-dioxygenase was soaked in the slow substrate 4-nitrocatechol in a low O2 atmosphere. The x-ray crystal structure shows that three different intermediates reside in different subunits of a single homotetrameric enzyme molecule. One of these is the key substrate-alkylperoxo-Fe2+ intermediate, which has been predicted, but not structurally characterized, in an oxygenase. The intermediates define the major chemical steps of the dioxygenase mechanism and point to a general mechanistic strategy for the diverse 2-His-1-carboxylate enzyme family.     

Structure,mechanism, and regulation of the Neurospora plasma membrane H+-ATPase

Proton pumps in the plasma membrane of plants and yeasts maintain the intracellular pH and membrane potential. To gain insight into the molecular mechanisms of proton pumping, we built an atomic homology model of the proton pump based on the 2.6 angstrom x-ray structure of the related Ca2+ pump from rabbit sarcoplasmic reticulum. The model, when fitted to an 8 angstrom map of the Neurospora proton pump determined by electron microscopy, reveals the likely path of the proton through the membrane and shows that the nucleotide-binding domain rotates by approximately 70 degrees to deliver adenosine triphosphate (ATP) to the phosphorylation site. A synthetic peptide corresponding to the carboxyl-terminal regulatory domain stimulates ATPase activity, suggesting a mechanism for proton transport regulation.     

养殖池塘底泥磷酸酶活性与释磷关系及其调控的研究

以天津市东丽区和西青区2个养殖池塘为对象,采用用室内试验方法,研究了底泥中各有机磷组分与上覆水中可溶性磷(DRP)含量、底泥磷酸酶活性与有机磷各组分及上覆水中可溶性磷之间的关系,并采取不同处理对底泥酸性磷酸酶(ACP)和碱性磷酸酶(ALP)活性进行调控.结果表明,底泥中活性有机磷(LOP)、中等活性有机磷(MLOP)、中稳性有机磷(MROP)与上覆水中DRP之间呈显著正相关.底泥中ALP与MLOP、MROP之间相关显著,并对其直接影响较大;ACP与MLOP之间相关显著,对其产生的直接影响也很大.A、B两池塘底泥中ALP与上覆水中DRP随时间变化规律基本一致,二者之间呈显著正相关.在养殖水体中加入酶抑制剂和沸石能抑制ALP和ACP活性,并以酶抑制剂加沸石的处理效果最好.     

碱催化三聚氰胺甲醛体系中的竞争关系

通过电喷雾电离质谱仪(ESI-MS)和核磁共振碳谱(~(13)C-NMR)分析方法研究了碱催化三聚氰胺甲醛(MF)体系中三聚氰胺(M)羟甲基化机理和缩聚反应结构中的竞争关系。结果表明,MF反应体系中羟甲基化程度大于缩聚程度,OH~-离子作为催化剂参与反应,形成M氮负离子或羟甲基氧负离子中间体后参与羟甲基化和缩聚反应。由于ESI-MS中存在同分异构现象,无法清晰描述MF体系中生成桥键和醚键等结构的竞争关系;在~(13)C-NMR研究中表明甲醛(F)与M的摩尔比可以显著影响缩聚产物分布,在低F与M摩尔比条件下醚键与桥键具有明显竞争关系,随着摩尔比升高,醚键逐渐占据绝对优势。在MF体系中醚键结构一直具有优势的原因可能与π-π堆积超分子现象有关。     

Visualizing ribosome biogenesis: parallel assembly pathways for the 30S subunit

Ribosomes are self-assembling macromolecular machines that translate DNA into proteins, and an understanding of ribosome biogenesis is central to cellular physiology. Previous studies on the Escherichia coli 30S subunit suggest that ribosome assembly occurs via multiple parallel pathways rather than through a single rate-limiting step, but little mechanistic information is known about this process. Discovery single-particle profiling (DSP), an application of time-resolved electron microscopy, was used to obtain more than 1 million snapshots of assembling 30S subunits, identify and visualize the structures of 14 assembly intermediates, and monitor the population flux of these intermediates over time. DSP results were integrated with mass spectrometry data to construct the first ribosome-assembly mechanism that incorporates binding dependencies, rate constants, and structural characterization of populated intermediates.     

Catalytic reduction of dinitrogen to ammonia at a single molybdenum center

Dinitrogen (N2) was reduced to ammonia at room temperature and 1 atmosphere with molybdenum catalysts that contain tetradentate [HIPTN3N]3- triamidoamine ligands (such as [HIPTN3N]Mo(N2), where [HIPTN3N]3- is [(3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2)3N]3-) in heptane. Slow addition of the proton source [(2,6-lutidinium)(BAr'4), where Ar' is 3,5-(CF3)2C6H3]and reductant (decamethyl chromocene) was critical for achieving high efficiency ( approximately 66% in four turnovers). Numerous x-ray studies, along with isolation and characterization of six proposed intermediates in the catalytic reaction under noncatalytic conditions, suggest that N2 was reduced at a sterically protected, single molybdenum center that cycled from Mo(III) through Mo(VI) states.     

Studying enzyme mechanism by 13C nuclear magnetic resonance

High-resolution carbon-13 nuclear magnetic resonance (NMR) spectra of enzyme-inhibitor and enzyme-substrate complexes provide detailed structural and stereochemical information on the mechanism of enzyme action. The proteases trypsin and papain are shown to form tetrahedrally coordinated complexes and acyl derivatives with a variety of compounds artificially enriched at the site or sites of interest. These results are compared with the structural information derived from x-ray diffraction. Detailed NMR studies have provided a clearer picture of the ionization state of the residues participating in enzyme-catalyzed processes than other more classical techniques. The dynamics of enzymic catalysis can be observed at sub-zero temperatures by a combination of cryoenzymology and carbon-13 NMR spectroscopy. With these powerful techniques, transient, covalently bound intermediates in enzyme-catalyzed reactions can be detected and their structures rigorously assigned.     

Water-mediated proton hopping on an iron oxide surface

The diffusion of hydrogen atoms across solid oxide surfaces is often assumed to be accelerated by the presence of water molecules. Here we present a high-resolution, high-speed scanning tunneling microscopy (STM) study of the diffusion of H atoms on an FeO thin film. STM movies directly reveal a water-mediated hydrogen diffusion mechanism on the oxide surface at temperatures between 100 and 300 kelvin. Density functional theory calculations and isotope-exchange experiments confirm the STM observations, and a proton-transfer mechanism that proceeds via an H(3)O(+)-like transition state is revealed. This mechanism differs from that observed previously for rutile TiO(2)(110), where water dissociation is a key step in proton diffusion.     

Mechanisms of proton conduction and gating in influenza M2 proton channels from solid-state NMR

The M2 protein of influenza viruses forms an acid-activated tetrameric proton channel. We used solid-state nuclear magnetic resonance spectroscopy to determine the structure and functional dynamics of the pH-sensing and proton-selective histidine-37 in M2 bound to a cholesterol-containing virus-envelope-mimetic membrane so as to better understand the proton conduction mechanism. In the high-pH closed state, the four histidines form an edge-face π-stacked structure, preventing the formation of a hydrogen-bonded water chain to conduct protons. In the low-pH conducting state, the imidazoliums hydrogen-bond extensively with water and undergo microsecond ring reorientations with an energy barrier greater than 59 kilojoules per mole. This barrier is consistent with the temperature dependence of proton conductivity, suggesting that histidine-37 dynamically shuttles protons into the virion. We propose a proton conduction mechanism in which ring-flip-assisted imidazole deprotonation is the rate-limiting step.     

Oxygen activation and reduction in respiration: involvement of redox-active tyrosine 244

Cytochrome oxidase activates and reduces O(2) to water to sustain respiration and uses the energy released to drive proton translocation and adenosine 5'-triphosphate synthesis. A key intermediate in this process, P, lies at the junction of the O(2)-reducing and proton-pumping functions. We used radioactive iodide labeling followed by peptide mapping to gain insight into the structure of P. We show that the cross-linked histidine 240-tyrosine 244 (His240-Tyr244) species is redox active in P formation, which establishes its structure as Fe(IV) = O/Cu(B)2+-H240-Y244. Thus, energy transfer from O2 to the protein moiety is used as a strategy to avoid toxic intermediates and to control energy utilization in subsequent proton-pumping events.     

Dephosphorylation of the calcium pump coupled to counterion occlusion

P-type ATPases extract energy by hydrolysis of adenosine triphosphate (ATP) in two steps, formation and breakdown of a covalent phosphoenzyme intermediate. This process drives active transport and countertransport of the cation pumps. We have determined the crystal structure of rabbit sarcoplasmic reticulum Ca2+ adenosine triphosphatase in complex with aluminum fluoride, which mimics the transition state of hydrolysis of the counterion-bound (protonated) phosphoenzyme. On the basis of structural analysis and biochemical data, we find this form to represent an occluded state of the proton counterions. Hydrolysis is catalyzed by the conserved Thr-Gly-Glu-Ser motif, and it exploits an associative nucleophilic reaction mechanism of the same type as phosphoryl transfer from ATP. On this basis, we propose a general mechanism of occluded transition states of Ca2+ transport and H+ countertransport coupled to phosphorylation and dephosphorylation, respectively.     

不同形态磷在砂土中的移动性研究(英文)

预测土壤中磷的长期淋洗性需要了解土壤特性和不同形态磷的行为.本研究用模拟试验评估了不同磷负荷砂质土壤中不同形态磷的移动性.分别从浙江省衢州市和温州市采集具不同磷含量的蔬菜地土壤,每一地点分别采集2个深度的土壤(0～10 cm和10～30 cm),表层土壤(0～10 cm)通过添加不同量的磷酸盐、CaCO和无定形氧化铁,形成研究需要的不同磷含量和不同磷形态的系列土壤样品;淋洗柱长30 cm,由10 cm经培养处理的表层(0～10 cm)土壤和未经培养处理的亚表层土壤(10～30cm)构成,每一淋洗土柱连续经历12个循环的0.002 mol?L-1CaCl2溶液淋洗,收集的淋洗液用于分析钼酸反应总磷(TRP)、可溶态钼酸反应磷(DRP)和颗粒态钼酸反应磷(RPP);试验结束后鉴定土壤中水溶态磷、MehlichⅢ-P和磷的化学形态变化.结果表明:添加无定形氧化铁和碳酸钙可显著改变砂土中磷的形态,降低土壤磷的有效性;无定形态氧化铁在降低土壤磷有效性方面的作用大于碳酸钙;淋洗液中磷的形态主要为DRP,颗粒态磷占总磷的比例为1.2%～39.8%;TRP和DRP的损失与培养处理后表土中磷含量存在显著的相关.相关分析和淋洗试验后土壤中磷形态变化结果都表明:表土柱中淋移的磷主要来源于水溶性磷(H2O-P)和NaHCO3-P,与NaOH-P、HCl-P和残余磷的相关不明显;从表土淋失的磷有27.1%～54.2%被淋出土体,其余下移至10～30 cm土层中.研究结果还表明,添加无定形氧化铁可增加土柱中颗粒态磷的迁移.     

Solvent-free electrolytes with aqueous solution-like conductivities

Aqueous solutions are generally assumed to be superior electrolytic conductors because of the unique dielectric and fluid properties of water. We show that their conductivities can be matched by liquid electrolytes that contain no solvent. These are proton transfer salts that are liquid at ambient temperature. The high conductivities are due to the high fluidity and ionicity rather than some sort of Grotthus mechanism, although in certain cases a mobile proton population may make a non-negligible contribution. The highest conductivities have been obtained when both cations and anions contain protons. At 25 degrees C, values of >150 millisiemens per centimeter (mS x cm(-1)) appear possible; at 100 degrees C, 470 mS x cm(-1) has been measured. Because of the combination of high ionicity and proton exchange kinetics with low vapor pressure, the systems we describe also make excellent fuel cell electrolytes.     

Kinetic evidence for five-coordination in AlOH(aq)2+ ion

Trivalent aluminum ions are important in natural bodies of water, but the structure of their coordination shell is a complex unsolved problem. In strong acid (pH < 3.0), Al(III) exists almost entirely as the octahedral Al(H2O)6(3+) ion, whereas in basic conditions (pH > 7), a tetrahedral Al(OH)(4- structure prevails. In the biochemically and geochemically critical pH range of 4.3 to 7.0, the ion structures are less clear. Other hydrolytic species, such as AlOH(aq)2+, exist and are traditionally assumed to be hexacoordinate. We show, however, that the kinetics of proton and water exchange on aqueous Al(III), coupled with Car-Parrinello simulations, support a five-coordinate Al(H2O)4OH2+ ion as the predominant form of AlOH(aq)2+ under ambient conditions. This result contrasts Al(III) with other trivalent metal aqua ions, for which there is no evidence for stable pentacoordinate hydrolysis products.     

乙醇-水分子团簇ETHANOL-(WATER)_N(N=1～3)的理论研究

本文采用密度泛函理论(DFT)的B3LYP方法,在B3LYP/6-311++G(2d,2p)//B3LYP/6-311++G(d,p)基组水平上对乙醇-水分子团簇ethanol-(water)n(n=1~3)进行研究,对优化计算得到的各种稳定构型的结合能及结构参数进行分析。结果表明,对于乙醇-水异二聚体,水分子作为质子给体而乙醇分子作为质子受体的结构是最稳定的;对于乙醇-水异三聚体和异四聚体,每个分子即作为质子给体又作为质子受体的乙醇-水环状团簇构型最稳定;随着n值的增大,稳定性逐渐增强。     

α—蒎烯合成N—烷基—N—(α—龙脑烯基)乙酰胺类化合物及香气特征

以α-蒎烯为原料合成了系列新型的N-烷基-N-(α-龙脑烯基)乙酰胺类芳香化合物,并探索了氮原子上取代基的不同结构与产物香气间的构效关系。α-蒎烯经环氧化得到2,3-环氧蒎烷,再经催化异构化反应得到α-龙脑烯醛;α-龙脑烯醛与伯胺缩合、NaBH4选择性还原得到N-烷基-α-龙脑烯胺,再经乙酰化后得到N-烷基-N-(α-龙脑烯基)乙酰胺类化合物。采用1H-NMR、13C-NMR、FT-IR、MS等对合成酰胺类化合物进行了结构表征,对合成产物的香气特征进行了鉴定。结果表明:N-正丁基-N-(α-龙脑烯基)乙酰胺和N-叔丁基-N-(α-龙脑烯基)乙酰胺具有良好的香气特征,作为新型芳香化合物具有较好的开发价值。