Morphology of α-Si3N4 in Fe–Si3N4 prepared via flash combustion

The state and formation mechanism ofα-Si3N4 in Fe–Si3N4 prepared by flash combustion were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate thatα-Si3N4 crystals exist only in the Fe–Si3N4 dense areas. When FeSi75 particles react with N2, which generates substantial heat, a large number of Si solid particles evaporate. The prod-uct between Si gas and N2 is a mixture ofα-Si3N4 andβ-Si3N4. At the later stage of the flash combustion process,α-Si3N4 crystals dissolve and reprecipitate asβ-Si3N4 and theβ-Si3N4 crystals grow outward from the dense areas in the product pool. As the temperature decreases, the α-Si3N4 crystals cool before transforming into β-Si3N4 crystals in the dense areas of Fe–Si3N4. The phase composition of flash-combustion-synthesized Fe–Si3N4 is controllable through manipulation of the gas-phase reaction in the early stage and theα→βtrans-formation in the later stage.     

PU与PVAc互穿网络聚合物的研究

研究了蓖麻油聚氨酯（ＰＵ）与聚醋酸乙烯酯（ＰＶＡｃ）在室温下生成的互穿网络聚合物（ＩＰＮ）。通过ＦＴ－ＩＲ和凝胶含量的测定,说明此种ＩＰＮ是接枝型ＩＰＮ。考察了该ＩＰＮ的各种组成对带锈铁板的附着力、柔韧性、冲击强度以及搭接剪切强度的影响。结果表明,当ＰＵ／ＰＶＡｃ＝５０／５０（ｗ／ｗ,质量比）时,ＩＰＮ的剪切强度最大,在此条件下合成的ＩＰＮ涂料是带锈铁板的良好涂料。     

Crystal structures of catalytic complexes of the oxidative DNA/RNA repair enzyme AlkB

Nucleic acid damage by environmental and endogenous alkylation reagents creates lesions that are both mutagenic and cytotoxic, with the latter effect accounting for their widespread use in clinical cancer chemotherapy. Escherichia coli AlkB and the homologous human proteins ABH2 and ABH3 (refs 5, 7) promiscuously repair DNA and RNA bases damaged by S(N)2 alkylation reagents, which attach hydrocarbons to endocyclic ring nitrogen atoms (N1 of adenine and guanine and N3 of thymine and cytosine). Although the role of AlkB in DNA repair has long been established based on phenotypic studies, its exact biochemical activity was only elucidated recently after sequence profile analysis revealed it to be a member of the Fe-oxoglutarate-dependent dioxygenase superfamily. These enzymes use an Fe(II) cofactor and 2-oxoglutarate co-substrate to oxidize organic substrates. AlkB hydroxylates an alkylated nucleotide base to produce an unstable product that releases an aldehyde to regenerate the unmodified base. Here we have determined crystal structures of substrate and product complexes of E. coli AlkB at resolutions from 1.8 to 2.3 A. Whereas the Fe-2-oxoglutarate dioxygenase core matches that in other superfamily members, a unique subdomain holds a methylated trinucleotide substrate into the active site through contacts to the polynucleotide backbone. Amide hydrogen exchange studies and crystallographic analyses suggest that this substrate-binding 'lid' is conformationally flexible, which may enable docking of diverse alkylated nucleotide substrates in optimal catalytic geometry. Different crystal structures show open and closed states of a tunnel putatively gating O2 diffusion into the active site. Exposing crystals of the anaerobic Michaelis complex to air yields slow but substantial oxidation of 2-oxoglutarate that is inefficiently coupled to nucleotide oxidation. These observations suggest that protein dynamics modulate redox chemistry and that a hypothesized migration of the reactive oxy-ferryl ligand on the catalytic Fe ion may be impeded when the protein is constrained in the crystal lattice.     

交联木薯淀粉微球对 Fe3的吸附研究

以木薯淀粉为原料,通过逆向悬浮聚合法合成交联木薯淀粉微球(CCSM),研究了合成的交联木薯淀粉微球对 Fe3+的吸附行为,利用红外光谱仪、X-射线衍射和热分析仪对木薯淀粉微球及其吸附产物进行了表征,研究其吸附机理.实验结果表明: CCSM 主要通过物理吸附、配位吸附方式来吸附 Fe3+;在 pH 值为4时交联木薯淀粉微球对 Fe3+吸附效果最好;在给定研究浓度范围内, CCSM 对 Fe3+的吸附等温线符合 Freundlich吸附等温方程     

Preparation of graphitic carbon nitride by electrodeposition

A new C-N compound b-C3N4 with the mechanicalproperties similar to those of diamond was predictedthrough the ab initio calculations of Liu and Cohen[1] in1989. The high hardness, high wear resistance, low coef-ficient of friction and wide energy gap make it attractive for industrial applications. With further theoretical work,five C3N4 structures, a-C3N4, b-C3N4, cubic (c-C3N4), pseudocubic (p-C3N4 ) and graphitic (g-C3N4), were pro-posed[2]. Many efforts have been made in attempts to s…     

La_(0.67)Sr_(0.33)Mn_(1-x)Fe_xO_3体系的正电子湮没研究

采用固相反应方法制备了名义成分为La0.67Sr0.33Mn1-xFexO3(0x0.2)的系列样品.利用X射线衍射、激光拉曼、正电子湮灭等实验手段并结合输运测量,对该系列样品进行了研究.结果表明,各样品均为正交钙钛矿结构;随着掺杂量的增加,样品的电阻率ρ急剧变大,绝缘体-金属转变峰随着掺杂浓度x的增加,峰值对应温度向低温区移动,这是由于样品内部晶体结构的变化所导致的.掺杂样品中缺陷及电子结构的变化与掺杂浓度密切相关,这主要是由于样品中的Mn3+被Fe3+所替代,部分Mn3+-O2-Mn4+铁磁双交换作用键被打断,样品中的铁磁与反铁磁作用的相互竞争以及样品内部电子局域化所形成的极化行为等因素的影响所导致的.     

环的交换性定理

本文证明了如下定理:定理1 环R有左单位元,N为R的幂零集元合,(?)x,y∈R,若x≡y((?)od N)就导致x,y与N中元可换或x~k=y~k,x~(k+1)=y~(k+1),其中k=k(x,y)>2,则N为R的理想;且当R/N的每一子环都幂等时,R为交换环.定理2 环R有左单位元且为2-扭自由,N为R的暴零元集合.若V~x,y∈R,x≡y(mod N)就导致x,y与N中元可换或x~k=y~k,x~(k+1)=y~(k+1),k=k(x,y)>2;或x~2=y~2,则N为R的理想,且当R/N的每一子环幂等时,R为交换环.     

苯甲酸与乙二胺反应的研究

在不同条件下考察了苯甲酸与乙二胺的反应 ,对反应产物、主要副产物及反应中间体进行了分离和鉴定 ,通过熔点测定、元素分析和红外光谱分析 ,确定了产物为 2 -苯基咪唑啉 ,主要副产物为二苯甲酰乙二胺 ,中间体之一为乙二胺与苯甲酸形成的双盐 .试验发现在不同溶剂中反应的产物和副产物的比例 ,产物纯度相差很大 .对反应机理及溶剂效应进行了讨论 .     

线性J-Armendariz环

如果对任意的f(x)=a₀+a₁x, g(x)=b₀+b₁x∈R［x］, f(x)g(x)=0蕴含所有a_ib_j∈J(R), 则环R称为线性J-Armendariz环(简称LJA环）. 其中: i,j∈{0,1}; J(R)是R的Jacobson根. 考虑LJA环的性质及与其他相关环类的关系, 给出了2-primal环的无限直积非2-primal环的简单例子, 并证明了Koethe猜想有肯定解当且仅当任意NI环的多项式环是LJA环.     

衬底偏压对γ′-Fe4N薄膜磁性的影响

采用直流磁控溅射方法, 以Ar/N₂（N₂/(Ar+N₂)=10％）为放电气体, 在Si(100)单晶衬底上获得了γ′-Fe₄N薄膜样品. 利用X射线衍射(XRD)和振动样品磁强计(VSM)研究衬底偏压对γ′-Fe₄N薄膜样品的影响. 结果表明, 随着衬底负偏压的增大, γ′-Fe₄N薄膜样品的晶胞参数减小, Fe和N的化合效率与样品的致密度提高, 表面缺陷减少, 矫顽力降低.      

Watching DNA polymerase η make a phosphodiester bond

DNA synthesis has been extensively studied, but the chemical reaction itself has not been visualized. Here we follow the course of phosphodiester bond formation using time-resolved X-ray crystallography. Native human DNA polymerase η, DNA and dATP were co-crystallized at pH?6.0 without Mg(2+). The polymerization reaction was initiated by exposing crystals to 1?mM Mg(2+) at pH?7.0, and stopped by freezing at desired time points for structural analysis. The substrates and two Mg(2+) ions are aligned within 40?s, but the bond formation is not evident until 80 s. From 80 to 300?s structures show a mixture of decreasing substrate and increasing product of the nucleotidyl-transfer reaction. Transient electron densities indicate that deprotonation and an accompanying C2'-endo to C3'-endo conversion of the nucleophile 3'-OH are rate limiting. A third Mg(2+) ion, which arrives with the new bond and stabilizes the intermediate state, may be an unappreciated feature of the two-metal-ion mechanism.     

分步法合成SA-IP-P(AA/AM)互穿网络高吸水性树脂及其性能研究

以淀粉接枝丙烯酸共聚物SA为互穿物,以丙烯酸(AA)、丙烯酰胺(AM)为聚合单体,N,N’-亚甲基双丙烯酰胺(NMBA)为交联剂,采用(NH4)2S2O8-NaHSO3氧化还原引发体系,通过分步法制备SA-IP-P(AA/AM)互穿网络高吸水性树脂。其适宜反应条件为:w(丙烯酰胺/丙烯酸)=0.4;丙烯酸中和度85%;引发剂用量0.32%;交联剂用量0.035%;SA用量8%.在此条件下合成的SA-IP-P(AA/AM)树脂吸去离子倍率和吸0.9%NaCl盐水倍率分别可达到1 480 g.g-1和120 g.g-1.通过红外光谱、扫描电镜、透射电镜和X射线衍射等测试研究了产物中互穿聚合物网络结构,结果显示在保持已有树脂优良性能的基础上,进一步改善了高吸水树脂的保水性能、耐盐性和对环境中水分的应答性.     

Multiphoton ionization of pyrrole-water mixed clusters

Multiphoton ionization of the hydrogen-bonded pyrrole-water clusters ( C4H5 N)n H2O)m is studied with a reflectron?time of flight mass spectrometer at 355 nm. With increasing partial concentration of pyrrole in a gas mixture source, a series of poly-pyrrole-water binary-mixed cluster ions can be observed, including unprotonated cluster ions [(C4H5N)x (H2O)y]* , protonated cluster ions [(C4H5N)x (H2O)yH]* and dehydrogenated cluster ions [ ( C4 H4 N) ( C4 H5 N) x ( H2O) y ] + . Ab initio calculations of their structures, bond strengths, charge distributions and re action energies are carried out. Stable structures of these clusters are obtained from the calculations. A probable forma tion mechanism of the cluster ions [(C4H5N)x(H2O)y] + , [(C4H5N)x (H2O)y]H+ and [(C4H4N) (C4H5N)x (H2O)y]-is supposed to be the ionization of clusters followed by dissociation.     

N,N’-二乙氧羰基-N”,N’”-(1,6-亚己基)双硫脲的合成、结构表征及其与金属离子的作用

由氯甲酸乙酯和硫氰酸钠经亲核取代反应和异构化合成N-乙氧羰基异硫氰酸酯中间体,再将该中间体与1,6-己二胺经亲核加成反应,合成N,N’-二乙氧羰基-N”,N””-(1,6-亚己基)双硫脲.对其进行元素分析、红外光谱、核磁共振氢谱及碳谱分析.将所得产物配成溶液,分别与Cu2+,Ni2+和Fe3+溶液混合,用紫外可见分光光度计测定产物溶液吸光度的变化,对产物与Cu2+离子的沉淀产物进行红外光谱检测,对比产物与其Cu2+络合物的红外光谱.研究结果表明:具有新型结构的双硫脲可分别与此3种离子发生反应,并表现出对Fe3+的较强选择性.产物与Cu2+生成的络合物为环状螯合物.     

石榴皮提取物绿色合成纳米零价铁及合成机理探究

以石榴皮提取物为还原剂和稳定剂，绿色合成了纳米零价铁(GS-nZVI)。通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)、热重分析(TGA)等表征手段对GS-nZVI的物理化学性质进行了表征，结合粒径、Zeta电位测试结果和化学平衡基本原理，讨论了合成条件(如反应时间、铁盐浓度、提取物多酚的质量浓度)对GS-nZVI粒径和产率的影响，并提出了可能的合成机理。结果表明:石榴皮提取物合成的GS-nZVI呈无定型结构，提取物中多酚类物质不仅能把亚铁盐(Fe2+)还原为零价铁(Fe0)，而且可作为稳定剂包覆在GS-nZVI表面，提高纳米粒子分散性。反应时间为120 min，Fe2+浓度为0.05 mol/L，多酚的质量浓度为15 mg/mL时合成的GS-nZVI粒径、产率综合结果最优，其产率为24.45%、粒径分布主要集中在213 nm。     

Ethylene oligomerization by novel iron(Ⅱ) diimine complexes/MAO

Two novel Fe(Ⅱ) diimine complexes have been synthesized. In combination with MAO, they generate active catalytic systems that oligomerize ethylene with both high catalytic activity and high selectivity for α-olefins. The effects of substituents on the aryl ring, reaction temperatures and molar ratios of Al/Fe on catalytic activity and product distribution are studied.     

γ′-Fe4N薄膜的制备及其磁性

采用直流磁控溅射方法, 以Ar/N₂为放电气体（N₂/(Ar+N₂)=10％）, 在玻璃和NaCl(100)单晶片上分别沉积获得Fe-N薄膜样品. 利用X射线衍射(XRD)、 原子力显微镜(AFM)和超导量子干涉仪(SQUID)对样品的结构、 形貌和磁性能进行分析, 研究基片和基片温度等条件对薄膜的影响. 结果表明, 以NaCl单晶为基片获得单相γ′-Fe₄N薄膜, 与玻璃基片相比可降低其生成的基片温度并可扩大形成温度的范围, 且比饱和磁化强度略有增大.      

C3H7/NH2/Fe+体系反应活性的密度泛函研究

采用B3LYP密度泛函理论对C3H7/NH2／Fe^＋体系生成乙烯和丙烯的反应路径进行了研究。在B3LYP／6-31＋G＊＊水平上，优化了4重态势能面上的极小值和过渡态的几何构型，计算了它们的能量和频率等参数，得到了该反应的势能面以及反应基元过程的详细信息。     

γ′-（Fe1-xNix)4N薄膜结构及其磁学性能

采用直流磁控溅射方法, 在Si(100)单晶衬底上制备不同质量分数Ni掺杂的γ′-（Fe_1-xNi_x)₄N纳米晶薄膜样品,  并利用能谱分析、 X射线衍射(XRD)、 扫描电子显微镜(SEM)和振动样品磁强计(VSM)测试分析样品中Fe与Ni的原子比、 结构、 形貌及磁学性能. 结果表明, 在样品中掺杂Ni可提高材料的结构稳定性, 优化材料的软铁磁性能.     

Gas-phase production and photoelectron spectroscopy of the smallest fullerene, C20

Fullerenes are graphitic cage structures incorporating exactly twelve pentagons. The smallest possible fullerene is thus C20, which consists solely of pentagons. But the extreme curvature and reactivity of this structure have led to doubts about its existence and stability. Although theoretical calculations have identified, besides this cage, a bowl and a monocyclic ring isomer as low-energy members of the C20 cluster family, only ring isomers of C20 have been observed so far. Here we show that the cage-structured fullerene C20 can be produced from its perhydrogenated form (dodecahedrane C20H20) by replacing the hydrogen atoms with relatively weakly bound bromine atoms, followed by gas-phase debromination. For comparison we have also produced the bowl isomer of C20 using the same procedure. We characterize the generated C20 clusters using mass-selective anion photoelectron spectroscopy; the observed electron affinities and vibrational structures of these two C20 isomers differ significantly from each other, as well as from those of the known monocyclic isomer. We expect that these unique C20 species will serve as a benchmark test for further theoretical studies.