Mechanism of the rhodium porphyrin-catalyzed cyclopropanation of alkenes

The rhodium porphyrin-catalyzed cyclopropanation of alkenes by ethyl diazoacetate (EDA) is representative of a number of metal-mediated cyclopropanation reactions used widely in organic synthesis. The active intermediate in these reactions is thought to be a metal carbene complex, but evidence for the involvement of metal-olefin pi complexes has also been presented. Low-temperature infrared and nuclear magnetic resonance spectroscopies have been used to characterize a rhodium porphyrin-diazoalkyl adduct that results from the stoichiometric condensation of the catalyst and EDA. Optical spectroscopy suggests that this complex is the dominant steady-state species in the catalytic reaction. This compound decomposes thermally to provide cyclopropanes in the presence of styrene, suggesting that the carbene is indeed the active intermediate. Metal-alkene pi complexes have also been detected spectroscopically. Kinetic studies suggest that they mediate the rate of carbene formation from the diazoalkyl complex but are not attacked directly by EDA.     

Study by synchrotron radiation of the structure of a working catalyst at high temperatures and pressures

A relation among activity, composition, and structure was determined for a working catalyst by means of a stainless-steel reactor cell of novel design that permitted operation at temperatures and pressures similar to those in industrial reactors. Molybdenum K-edge x-ray absorption spectra were used to probe the structural environment of molybdenum in CoMoS/[unknown]-alumina catalysts while hydro-desulfurization of benzothiophene was proceeding at high temperature and pressure. For catalyst samples with different contents of cobalt, radial structure functions obtained from extended x-ray absorption fine structure data presented the same features as those obtained from the spectra of MoS(2)/[unknown]-alumina reference samples. Moreover, Mo-S and Mo-Mo coordination numbers were maximum for the sample with an atomic ratio of Co to (Co + Mo) of 0.33; this sample was also the most active catalyst tested.     

催化微波法合成氢化碱木质素

为了提高碱木质素的反应活性,以Pd/C为催化剂,采用微波法进行了碱木质素与H2的还原反应。运用1 H-NMR分析了碱木质素的结构变化,且利用凝胶渗透色谱（GPC）测定了碱木质素的分子量和分子量分布。结果表明:较佳的碱木质素加氢还原反应条件是负载量为3%的Pd/C催化剂用量为10%、温度为95℃、时间为30 min、氢气流速为20 mL/min。1 H-NMR分析显示:羰基和羧基含量减少,代表酚羟基和醇羟基的质子吸收增加。GPC分析显示:反应后碱木质素的分子量降低,而多分散性增大。元素分析显示:C和H含量在反应后都有所增加,而O含量则降低了,表明碱木质素发生了还原反应。与常规加热方式相比,微波法合成有利于提高酚羟基含量,缩短反应时间,而在提高碱木质素的总体反应活性方面没有表现出特殊的效应。      

A new redox cofactor in eukaryotic enzymes: 6-hydroxydopa at the active site of bovine serum amine oxidase

An active site, cofactor-containing peptide has been obtained in high yield from bovine serum amine oxidase. Sequencing of this pentapeptide indicates: Leu-Asn-X-Asp-Tyr. Analysis of the peptide by mass spectrometry, ultraviolet-visible spectroscopy, and proton nuclear magnetic resonance leads to the identification of X as 6-hydroxydopa. This result indicates that, contrary to previous proposals, pyrroloquinoline quinone is not the active site cofactor in mammalian copper amine oxidases. Although 6-hydroxydopa has been implicated in neurotoxicity, the data presented suggest that this compound has a functional role at an enzyme active site.     

Mn~（2＋）/UV催化O_3处理造纸废水的研究

以镁化合物、膨胀珍珠岩为原料,在室温条件下与水混合,干燥后即制得催化剂载体,通过表面负载MnSO4制备成一种新型Mn2＋催化剂。该催化剂平均密度为1.03 g/cm3,略大于水,可在反应器内很好流化。电镜扫描和能谱分析表明,Mn2＋在催化剂载体表面负载及催化性能稳定。对Mn2＋/UV催化O3处理造纸废水进行了试验研究,结果表明,对于COD为523 mg/L的造纸废水,在催化剂投加量为20 g、O3曝气量为60 ml/min、曝气时间为40 min、pH为7、紫外灯照射功率为30 W的最佳条件下,COD去除率可达到73%以上。     

Efficient dehydrogenation of formic acid using an iron catalyst

Hydrogen is one of the essential reactants in the chemical industry, though its generation from renewable sources and storage in a safe and reversible manner remain challenging. Formic acid (HCO(2)H or FA) is a promising source and storage material in this respect. Here, we present a highly active iron catalyst system for the liberation of H(2) from FA. Applying 0.005 mole percent of Fe(BF(4))(2)·6H(2)O and tris[(2-diphenylphosphino)ethyl]phosphine [P(CH(2)CH(2)PPh(2))(3), PP(3)] to a solution of FA in environmentally benign propylene carbonate, with no further additives or base, affords turnover frequencies up to 9425 per hour and a turnover number of more than 92,000 at 80°C. We used in situ nuclear magnetic resonance spectroscopy, kinetic studies, and density functional theory calculations to explain possible reaction mechanisms.     

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。     

Delta-1-tetrahydrocannabinol: structure of a major metabolite

triangle up(1)-Tetrahydrocannabinol, the major psychotomimetically active compound of Cannabis, was metabolized in vitro by the 10, OOOg supernatant from rabbit liver. By mass and nuclear magnetic resonance spectrometry, the major metabolite was identified as 7-hydroxy-triangle up(1)-tetrahydrocannabinol. The latter compound of Cannabis, was metabolized in vitro by the 10,OOOg supernatant from     

Observation of 239Pu nuclear magnetic resonance

In principle, the spin-? plutonium-239 ((239)Pu) nucleus should be active in nuclear magnetic resonance spectroscopy. However, its signal has eluded detection for the past 50 years. Here, we report observation of a (239)Pu resonance from a solid sample of plutonium dioxide (PuO(2)) subjected to a wide scan of external magnetic field values (3 to 8 tesla) at a temperature of 4 kelvin. By mapping the external field dependence of the measured resonance frequency, we determined the nuclear gyromagnetic ratio (239)γ(n)(PuO(2))/2π to be 2.856 ± 0.001 megahertz per tesla (MHz/T). Assuming a free-ion value for the Pu(4+) hyperfine coupling constant, we estimated a bare (239)γ(n)/2π value of ~2.29 MHz/T, corresponding to a nuclear magnetic moment of μ(n) ≈ 0.15μ(N) (where μ(N) is the nuclear magneton).     

Two-state allosteric behavior in a single-domain signaling protein

Protein actions are usually discussed in terms of static structures, but function requires motion. We find a strong correlation between phosphorylation-driven activation of the signaling protein NtrC and microsecond time-scale backbone dynamics. Using nuclear magnetic resonance relaxation, we characterized the motions of NtrC in three functional states: unphosphorylated (inactive), phosphorylated (active), and a partially active mutant. These dynamics are indicative of exchange between inactive and active conformations. Both states are populated in unphosphorylated NtrC, and phosphorylation shifts the equilibrium toward the active species. These results support a dynamic population shift between two preexisting conformations as the underlying mechanism of activation.     

A thermally re-mendable cross-linked polymeric material

We have developed a transparent organic polymeric material that can repeatedly mend or "re-mend" itself under mild conditions. The material is a tough solid at room temperature and below with mechanical properties equaling those of commercial epoxy resins. At temperatures above 120 degrees C, approximately 30% (as determined by solid-state nuclear magnetic resonance spectroscopy) of "intermonomer" linkages disconnect but then reconnect upon cooling, This process is fully reversible and can be used to restore a fractured part of the polymer multiple times, and it does not require additional ingredients such as a catalyst, additional monomer, or special surface treatment of the fractured interface.     

玫瑰花中抗补体活性成分研究

[目的]分离鉴定玫瑰（Rosa rugosa）花中的抗补体活性成分。[方法]在活性筛选指导下,并用多种色谱方法进行分离纯化,并用核磁共振、质谱数据与文献数据对比鉴定化合物结构。[结果]从活性部位中分离出3个黄酮类化合物,分别为木犀草素（1）、槲皮素（2）和山柰酚（3）。[结论]玫瑰花提取物有体外抗补体作用,其中黄酮类化合物是其活性成分。     

甲硝唑半抗原及全抗原合成与鉴定

在微波加热条件下,将甲硝唑与琥珀酸酐反应,合成半抗原甲硝唑半琥珀酸酯,氢核磁共振、电喷雾质谱、红外光谱方法的鉴定结果表明,目标半抗原合成成功;通过活泼酯法将半抗原与载体蛋白偶联制备甲硝唑全抗原,紫外光谱法鉴定结果表明,全抗原合成成功.     

Intermetallic Compounds of the Type MNi5 as Methanation Catalysts

Catalytic reactions of carbon monoxide with hydrogen have been studied in which intermetallic compounds of the formula MNi(5) (where M is thorium, uranium, or zirconium) have been used as the catalysts. The materials perform effectively as methanation catalysts; ThNi(5) has a specific activity exceeding that of a typical commercial oxide-supported methanation catalyst by a factor of about 5. This material also shows superior resistance to hydrogen sulfide poisoning. Nickel, formed as a decomposition product of the MNi(5) intermetallic compound, is probably the active species, but its properties are influenced by the nature of M in the precursor MNi(5) system.     

Radiation damage, at high temperatures

The successful development of nuclear power reactors that are economically competitive with other sources of energy has led us to believe that more economical reactors will be developed. But, in developing the next generation of reactors, a new set of problems must be overcome. One of the most important of these is that of the embrittlement of the structural materials at high temperatures as a result of the intense neutron fields in these advanced systems. The radiation-induced embrittlement at high temperatures is probably associated with helium produced in the materials due to (n,alpha) reactions with the metal, and in some alloys radiation-induced precipitation of compounds within the alloy may also play a role. We believe that the most serious longterm problem is the generation of helium. Our current understanding of the mechanism by which this radiation damage is produced has allowed us to effect some improvement in the behavior of conventionally produced structural alloys, through minor modifications of the normal working and annealing processes used in their manufacture. However, we may find that new alloys will have to be developed to withstand the service conditions in future nuclear power reactors.     

Chemical identification of a tumor-derived angiogenic factor

Neoplasms produce substances that induce blood vessel formation (angiogenesis). Fractions from ethanol extracts of the Walker 256 carcinoma were isolated by silica column chromatography and C18 reversed-phase high-performance liquid chromatography. Two of the isolated fractions induced neovascularization when tested in the rabbit corneal micropocket assay. One of the fractions was identified as nicotinamide by desorption-electron impact mass spectrometry, nuclear magnetic resonance spectroscopy, and gas chromatography-mass spectrometry. The second active fraction contained nicotinamide as part of a more complex, as yet unidentified, molecular arrangement. Microgram quantities of commercial nicotinamide induced neovascularization in the corneal micropocket assay and in the chick chorioallantoic membrane assay.     

Functional neuroimaging of speech perception in infants

Human infants begin to acquire their native language in the first months of life. To determine which brain regions support language processing at this young age, we measured with functional magnetic resonance imaging the brain activity evoked by normal and reversed speech in awake and sleeping 3-month-old infants. Left-lateralized brain regions similar to those of adults, including the superior temporal and angular gyri, were already active in infants. Additional activation in right prefrontal cortex was seen only in awake infants processing normal speech. Thus, precursors of adult cortical language areas are already active in infants, well before the onset of speech production.     

Noncovalent binding of a spin-labeled inhibitor to ribonuclease

The stable free radical 2,2,6, 6-tetramethyl-4-hydroxypiperidin-1-oxyl monophosphate has been synthesized; it binds to ribonuclease. The selective changes in the nuclear magnetic resonance spectrum of the enzyme produced by the free radical make it possible to define qualitatively the region of the enzyme to which it binds. The radical appears to occupy a site similar to that to which inorganic phosphate binds which is close to or within the active site of the enzyme.     

Dynamics of the hippocampus during encoding and retrieval of face-name pairs

The medial temporal lobe (MTL) is critical in forming new memories, but how subregions within the MTL carry out encoding and retrieval processes in humans is unknown. Using new high-resolution functional magnetic resonance imaging (fMRI) acquisition and analysis methods, we identified mnemonic properties of different subregions within the hippocampal circuitry as human subjects learned to associate names with faces. The cornu ammonis (CA) fields 2 and 3 and the dentate gyrus were active relative to baseline only during encoding, and this activity decreased as associations were learned. Activity in the subiculum showed the same temporal decline, but primarily during retrieval. Our results demonstrate that subdivisions within the hippocampus make distinct contributions to new memory formation.     

Heterogeneous atmospheric aerosol production by acid-catalyzed particle-phase reactions

According to evidence from our laboratory, acidic surfaces on atmospheric aerosols lead to potentially multifold increases in secondary organic aerosol (SOA) mass. Experimental observations using a multichannel flow reactor, Teflon (polytetrafluoroethylene) film bag batch reactors, and outdoor Teflon-film smog chambers strongly confirm that inorganic acids, such as sulfuric acid, catalyze particle-phase heterogeneous reactions of atmospheric organic carbonyl species. The net result is a large increase in SOA mass and stabilized organic layers as particles age. If acid-catalyzed heterogeneous reactions of SOA products are included in current models, the predicted SOA formation will be much greater and could have a much larger impact on climate forcing effects than we now predict.