超微NaY分子筛的合成(Ⅱ)──添加铝络合剂的影响

Na Y分子筛合成体系中添加铝的络合剂 (乙二胺四乙酸、柠檬酸和醋酸 ) ,可有效地减小分子筛的晶粒尺寸及增加分子筛的晶化速度和 Si O2 /Al2 O3物质的量比 .在添加柠檬酸的合成体系中 ,考察了柠檬酸的添加量对 Na Y分子筛晶化行为的影响 .发现存在着一个最佳的柠檬酸的添加量范围 ,即 n(柠檬酸 )∶ n(氧化铝 )≤ 2∶ 1 ,在此范围内 ,Na Y的晶化速率和硅铝比较高 ,而晶粒尺寸较小

Density functional calculations on the binding of dinitrogen to the FeFe cofactor in Fe-only nitrogenase: FeFeCo(mu(6)-N-2) as intermediate in nitrogen fixation

The geometries and stabilities of the FeFe cofactor at different oxidation states and its complexes with N-2 have been determined by density functional calculations. These calculations support an EPR-inactive resting state of the FeFe cofactor with four Fe2+ and four Fe3+ sites (4Fe(2+)4Fe(3+)). FeFeco(mu(6)-N-2) with a central dinitrogen ligand is predicted to be the most stable complex of the FeFe cofactor with N-2. It is easily formed by penetration of N-2 into the trigonal Fe-6 prism of the FeFe cofactor with an approximate barrier of 4 kcal mol(-1). The present DFT results suggest that an FeFeco(mu(6)-N-2) entity is a plausible intermediate in dinitrogen fixation by nitrogenase. CO is calculated to bind even more strongly than N-2 to the FeFe cofactor so that CO may inhibit the reduction of nitrogen by Fe-only nitrogenase

Catalytic site of nitrogenases and its chemical simulations

固氮酶是固氮微生物在常温常压下固氮成氨的催化剂,其催化机理和化学模拟一直是国际上长期致力研究的对象.钼铁蛋白高分辨1.0单晶X射线衍射分析表明,固氮酶催化活性中心铁钼辅基的结构为MO fE7S9C(r-HOMOCIT),其中,MO原子和3个u2-硫配体、1个组氨酸和1个高柠檬酸配位,形成八面体构型.高柠檬酸以α-烷氧基氧和α-羧基氧与钼螯合形成双齿配位,氨基酸残基上的组氨酸咪唑氮和半胱氨酸巯基与钼和铁单齿配位.在固氮酶铁钼辅基的生物合成过程中,高柠檬酸和咪唑侧基是在最后的合成步骤插入铁硫碳簇前驱体中,其中高柠檬酸和咪唑侧基有可能对质子传递以及稳定MO fE7S9C簇起到重要作用.本文从固氮酶铁钼辅基结构出发,结合最近本课题组从化学模拟出发,将固氮酶催化活性中心铁钼辅基结构修订为加氢新结构MO fE7S9C(r-HHOMOCIT)的研究,着重介绍了近年来国内外固氮酶活性中心、生物合成和催化作用机理的研究进展,并展望了固氮酶的研究前景.Nitrogenase catalyzes the reduction of dinitrogen to ammonia in the process of biological nitrogen fixation.In the past few decades, its catalytic mechanism and chemical simulation have been widely studied.The high resolution X-ray structural analysis of the Mo Fe protein in nitrogenase reveals the iron molybdenum cofactor(Fe Mo-co) as a cage structure, Mo Fe7S9C(R-homocit).The molybdenum atom is coordinated by three sulfur atoms, a nitrogen atom from histidine residue and two oxygen atoms from R-homocitrate.Recently, the model has been modified as a protonated structure of Mo Fe7S9C(R-Hhomocit).Homocitrate and imidazole sidechain may play important roles in delivering proton and stabilizing the Mo Fe7S9C cluster in the process of N2 reduction.However the mechanism of N2 reduction remains unclear.In this review, the chemistry of molybdenum with homocitrate and imidazole is discussed, including the iron molybdenum sulfur complexes, which will be helpful to understand the coordination environment of molybdenum atom in iron molybdenum cofactor.国家重点基础研究发展计划(2010CB126504); 国家自然科学基金(21073150)资

Synthesis of Ultrafine Zeolite NaY(Ⅰ) Effect of Light Rare Earth Ions Additive

联系人简介: 晁自胜( 1967 年出生) , 男, 博士, 副教授, 从事分子筛合成及多相催化研究.[中文文摘]导向剂的陈化时间和反应胶的晶化温度可以影响 Na Y分子筛的晶化行为 .随导向剂陈化时间的增加 ,Na Y分子筛的晶化速度加快 ,晶粒尺寸减小 ;随晶化温度的升高 ,Na Y分子筛的晶化速度加快 ,但晶粒尺寸增加 .而向合成体系中添加轻稀土离子 (L n3+)对 Na Y分子筛的晶化行为影响更为明显 .与未添加稀土离子时相比较 ,在一定的稀土离子添加量范围内 [n(L n3+) / n(Al3+) 5. 7) and the shortest cr ystallizat io n t ime( < 36 h) . T he role of the added Ln3+ ions was proposed to be that there formed the micro-cry stalline Ln( OH) 3 under the synthesis condit ions, w hich may present addit ional area to init iate the nucleat io n of zeolite NaY.中国石化集团公司科技开发项目!(批准号 :X5980 10 )资助

Enzymatic and catalytic reduction of dinitrogen to ammonia: Density functional theory characterization of alternative molybdenum active sites

We used density functional calculations to model dinitrogen reduction by a FeMo cofactor containing a central nitrogen atom and by a Mo-based catalyst. Plausible intermediates, reaction pathways, and relative energetics in the enzymatic and catalytic reduction of N-2 to ammonia at a single Mo center are explored. Calculations indicate that the binding of N-2, to the Mo atom and the subsequent multiple proton-electron transfer to dinitrogen and its protonated species involved in the conversion of N-2, are feasible energetically. In the reduction of N-2, the Mo atom experiences a cycled oxidation state from Mo(IV) to Mo(VI) by nitrogenase and from Mo(III) to Mo(VI) by the molybdenum catalyst, respectively, tuning the gradual reduction of N-2. Such a wide range of oxidation states exhibited by the Mo center is crucial for the gradual reduction process via successive proton-electron transfer. Present results suggest that the Mo atom in the N-centered FeMo cofactor is a likely alternative active site for dinitrogen binding and reduction under mild conditions once there is an empty site available at the Mo site. (c) 2005 Wiley Periodicals, Inc

Synthesis of ultrafine zeolite NaY(I) - Effect of light rare earth ions additive

Ultrafine zeolite NaY was hydrothermally crystallized with silica sol and Al-2(SO4)(2) as source materials via optimizing synthesis conditions and adding light rare earth ions (Ln(3+)) to the synthesis batch. The crystallization performance of NaY could be affected by the aging time of nucleation Si-Al gel and the crystallization temperature of reaction Si-Al gel. With increasing the aging time (2-7 d) of nucleation gel, the crystallization rate of zeolite NaY increased whereas the average crystal size of zeolite NaY decreased. When elevating the crystallization temperature (363-383 K) of reaction gel, both the crystallization rate and the average crystal size of zeolite NaY increased. Nevertheless, the crystallization performance of zeolite NaY was more remarkably affected by the addition of Ln(3+) ions in the synthesis batch. The crystallization rate and the n (SiO2)/n(Al2O3) ratio obviously increased while the average crystal size greatly reduced when zeolite NaY was crystallized in the presence of Ln(3+) ions, comparing with that in the absence of Ln(3+) ions, It was found that, with the amount of the added Ln(3+) ions increasing, the average crystal size of zeolite NaY decreased followed by increasing, while the crystallization rate and the SiO2/Al2O3 ratio in framework changed in the opposite direction. The optimal amount of Ln(3+) additive appears to be in the range of n(Ln(3+)) : n(Al3+) = 0.05 : 1-0.1 : 1 in mole. In the case, the as-synthesized NaY zeolites had the smallest average crystal sizes (5.7) and the shortest crystallization time (<36 h), The role of the added Ln(3+) ions was proposed to be that there formed the micro-crystalline Ln(OH)(3) under the synthesis conditions, which may present additional area to initiate the nucleation of zeolite NaY