酶活性部位柔性的分形分析

引言蛋白质三维结构的研究一直是生物学上一个重要而复杂的问题。通过X晶体衍射和核磁共振技术,人们已经积累了大量的蛋白质结构数据,但进一步解析蛋白质结构与功能间的关系,尚存在一定难度。作为非线性科学分支的分形理论(fractaltheory),以其独特的研究方法揭示了自然界中非线性过程内在的随机性及其所具有的特殊规律性。虽然分形理论在20世纪70年代才首次提出[1],但     

The nature of the organoaluminum compound and the kinetic heterogeneity of active sites in lanthanide‐based diene polymerization

The influence of the organoaluminum compound on the kinetic heterogeneity of active sites in lanthanide‐based diene polymerization was investigated. It was found that the heterogeneity of investigated catalytic systems was shown in the existence of four types of active centers. They were formed at the beginning of the polymerization process and produced macromolecules with lengths that were definite for each type of active center. The nature of the organoaluminum compound greatly influenced the kinetic activity of the polymerization centers. A method for analyzing the curves' maximums of distribution on kinetic activity and the change in kinetic activity of every type of active centers is proposed. This method allows calculating the concentration values for each type of active center separately. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 674–685, 2003     

沥青岩中界面活性沥青质分子结构及其在矿物表面吸附特征

重质油固体系（如油砂、沥青岩、油页岩、重质油、油泥等）中因油-水-固三相复杂作用,导致分离困难。本文以印尼沥青岩重质油为例,针对重质组分中界面活性最强的界面活性沥青质的结构及其在矿物质表面吸附特性问题进行研究。通过凝胶渗透色谱、红外光谱仪、XPS等对界面活性沥青质的结构进行分析,提出其初步结构。以SiO₂为矿物固体模型,在甲苯溶剂环境中,采用QCM-D和AFM研究界面活性沥青质在固体表面的吸附特征,发现该类沥青质分子在SiO₂表面的吸附与普通沥青质分子存在较大差异,呈现多层吸附特征,符合Freundlich吸附模型。吸附膜存在较多高分散性团聚体,黏弹性较大,易于形成具有三维结构的强机械性界面膜。该结构和界面吸附特性可为揭示其在油水乳液稳定过程中的机理提供有利基础。     

Methanol: A “Smart” Chemical Probe Molecule

A novel chemisorption method was employed for the dissociative adsorption of methanol to surface methoxy intermediates in order to quantitatively determine the number of surface active sites on one-component metal oxide catalysts (MgO, CaO, SrO, BaO, Y₂O₃, La₂O₃, CeO₂, TiO₂, ZrO₂, HfO₂, V₂O₅, Nb₂O₅, Ta₂O₅, Cr₂O₃, MoO₃, WO₃, Mn₂O₃, Fe₂O₃, Co₃O₄, Rh₂O₃, NiO, PdO, PtO, CuO, Ag₂O, Au₂O₃, ZnO, Al₂O₃, Ga₂O₃, In₂O₃, SiO₂, GeO₂, SnO₂, P₂O₅, Sb₂O₃, Bi₂O₃, SeO₂ and TeO₂). The number of surface active sites for methanol dissociative adsorption corresponds to 3 mol/m² on average for many of the metal oxide catalysts. Furthermore, the methanol oxidation product distribution at low conversions reflects the nature of the surface active sites on metal oxides since redox sites yield H₂CO, acidic sites yield CH₃OCH₃ and basic sites yield CO₂. The distribution of the different types of surface active sites was found to vary widely for the different metal oxide catalysts. In addition, the commonality of the surface methoxy intermediate during dissociative chemisorption of methanol and methanol oxidation on oxide catalysts also allows for the quantitative determination of the turnover frequency (TOF) values. The TOF values for the various metal oxide catalysts were found to vary over seven orders of magnitude (10^–3 to 10⁴ s^–1). An inverse relationship (for metal oxide catalysts displaying high (>85%) selectivity to either redox or acidic products) was found between the methanol oxidation TOF values and the decomposition temperatures of the surface M–OCH₃ intermediates reflecting that the decomposition of the surface M–OCH₃ species is the rate-determining step during methanol oxidation over the metal oxide catalysts.     

En route to complete design of heterogeneous catalysts

Achieving complete control in the synthesis of the active center of a heterogeneous catalyst, which includes the active site, environment around the active site, and the access path is highly desirable but not attainable yet. However, there has been significant progress in recent years that permits a level of control of these properties that are unachievable before. Some illustrative examples are described to demonstrate this in the synthesis of active sites in metal and oxide catalysts and their surroundings. For the active site synthesis, examples include using polynuclear metal complexes as precursors, cluster beam deposition, and use of dendrimers to generate metallic active sites, protection of coordination unsaturation in the synthesis of oxide active sites, and employing silsesquioxane, and unit-by-unit approach. Exfoliation, use of inverse micelles, molecular and macromolecular templating as techniques to exert control of the environment of the active center are also discussed. The limitations of these synthetic methods and remaining challenges are examined.     

Combined Thermometric Analysis of a Series of Highly Dealuminated USY Zeolites

A transient reactor model was used to consolidate and quantify the data of ammonia adsorption microcalorimetry and single ammonia TPD runs, using several members of the commercial CBV series of dealuminated HY zeolites. The model accounts for the competitive re-adsorption of molecules desorbing from multiple sites, using the microcalorimetric data to constrain the desorption energy parameters to physically meaningful values. All TPD profiles were well represented by models consisting of only two or three distinct site types, even though the differential heat plots imply a continuous distribution of sites in the 160-80 kJ/mol range for all catalysts. Increasing dealumination severity is evidenced by a decrease in total site density for sites 100 kJ/mol. While there was no evidence of an enhancement of adsorption strength within the series studied, the range of site strengths available remained the same. There is correspondence between the density of adsites = 100 kJ/mol and the framework Al³⁺ concentration, although the ratio of these is less than one, even for Si/Al80. The inherent limits in using ammonia adsorption as an acidity probe are briefly mentioned.     

Kinetics-assisted identification and regulation of active sites for Pd-catalyzed propyne selective hydrogenation

Identification and regulation of active sites are significant for guiding the design and optimization of hydrogenation catalysts toward the target product but remain a great challenge. Herein, we demonstrate a kinetics-assisted identification method combined with theoretical calculations for identifying and further regulating the dominant active sites of Pd catalysts for propyne hydrogenation. Kinetics analysis and model calculations based on the cuboctahedron shape of Pd nanoparticles in the catalysts indicate the Pd(111) sites as the dominant active sites for the propyne conversion and propylene formation while the Pd(100) sites as those for the propane formation, which are further rationalized by theoretical calculations. Moreover, the Pd catalyst with electron-rich properties exhibits relatively higher activity and selectivity, guided by which the SiO₂ support with abundant electron-donating hydroxyl groups is employed to increase the Pd electron density. Such electronic regulation for the Pd catalyst clearly enhances the selective hydrogenation of propyne.     

The effect of boron incorporation on the structure and properties of glassy carbon

Boron was introduced into glassy carbon by chemical modification and by irradiating the precursor polymer with boron ions. Using chemical modification, a polymer with uniform distribution of boron in the bulk was obtained, whereas irradiation with B³⁺ produced a polymer with boron located in a narrow region under the surface. Following modification with boron, the samples were carbonized at 1273 K and examined using X-ray diffraction, Raman spectroscopy, temperature programmed desorption (TPD) and by hardness measurements. Structural analysis results suggest that boron is mostly substitutionally bonded in the glassy carbon structure regardless of the method used to introduce boron into the polymer precursor. Formation of crosslinks between glassy carbon ribbons during carbonization as a consequence of the recombination of ion beam induced changes in the polymer structure and a high concentration of boron in the subsurface layer is proposed to account for an increase of glassy carbon hardness. An increase in the total amount of surface oxygen groups was observed in the TPD spectra of both boron-modified samples due to an increase in the number of active sites. Results show that the nature of these sites is influenced by the initial distribution of boron in the polymer precursor.     

Acid function of Al‐MCM‐41 supported platinum catalysts in hydrogenation of benzene, toluene o‐xylene

A series of Al‐MCM‐41 mesoporous materials with different Si/Al ratios are synthesized. The acidities of catalysts are measured by the temperature‐programmed desorption of ammonia (NH₃‐TPD) and IR spectra of pyridine. Their catalytic activities for hydrogenation of benzene, toluene and o‐xylene are investigated on a pulse reactor system. NH₃‐TPD and IR results show that only weak and medium acid sites could be observed on the catalysts, and the number of total acid sites decreases obviously with the increase of the Si/Al ratio whereas the medium acid sites are somewhat constant. The introduction of platinum onto Al‐MCM‐41 material decreases the total acid number by a small amount. The hydrogenation activities of the 1% Pt/HAl‐MCM‐41 catalysts are found to correspond well with the ratio of medium acid sites to total acid sites in the employed catalysts. It is proposed that, in addition to metal sites, the acid sites in the metal–acid interfacial regions are also the active sites for hydrogenation and the medium acid sites play important roles in the reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization and NO decomposition activity of Cu-MFI zeolite in relation to redox behavior

The redox behavior and states of Cu ions in Cu ion-exchanged MFI (Cu(n)-MFI, n: exchange level) have been investigated by means of temperature-programmed desorption (TPD) of oxygen, diffuse reflectance (DR) UV–VIS spectroscopy and Cu⁺ photoluminescence (PL) spectroscopy. TPD chromatograms of oxygen from Cu(n)-MFI were characterized by the appearance of three desorption peaks: (below 200°C), β (300–500°C) and γ (above 500°C). It has been suggested that and β oxygen are extra-lattice oxygen adsorbed on Cu ions, while γ oxygen is lattice oxygen coordinated to Cu ions. The Cu⁺ emission was tremendously reduced once the catalyst contacted with O₂ and NO at elevated temperatures such as 500°C, and it was almost invisible under the working state of the catalyst, suggesting that PL-active Cu⁺ ions are not real active sites under the working state. The desorption of β oxygen was intimately related to the creation of active centers for the NO decomposition reaction. DR measurements showed that the desorption of β oxygen caused tetragonal Cu²⁺ to decrease and trigonal Cu²⁺ to increase simultaneously. It has been proposed that both Cu²⁺ and Cu⁺ are involved in the NO decomposition catalysis over Cu-MFI under the working state.     

CaO对汞的选择性吸附及SO2毒化特性

利用Ca（NO₃）₂作为前体,SiO₂为载体,制备了一种担载型CaO吸附剂,在固定床实验装置上分别研究了该吸附剂对元素汞（Hg⁰）和氯化汞（HgCl₂）等不同形态汞的选择性吸附性能,以及SO₂对CaO吸附剂汞形态吸附过程的影响,同时结合程序升温脱附和原位红外漫反射表征技术,深入探究了CaO的选择性吸附机理及SO₂毒化机制。汞形态吸附实验结果表明,在纯N₂气氛和掺杂SO₂气氛下,CaO对Hg⁰均保持了接近100%的穿透率,而对HgCl₂在两种气氛下则分别表现出66.0%和60.3%的吸附效率,说明SO₂与HgCl₂在CaO表面存在竞争吸附关系;吸附实验前后CaO的表征结果显示,与Hg⁰相比,HgCl₂更易与CaO表面各碱性位形成单配位、双配位等多种吸附构型,SO₂与HgCl₂在易形成单配位的活性位上形成竞争吸附关系,进而在一定程度上降低了CaO对HgCl₂的吸附效率。     

Multiple active site Monte Carlo model for heterogeneous Ziegler‐Natta propylene polymerization

In this study, the kinetics of propylene polymerization catalyzed with the fourth heterogeneous Ziegler‐Natta catalyst is studied. More than one type of active site is present in the propylene polymerization based on an analysis of the GPC curves. A multiple active site kinetic model (MSmodel) is proposed by using Monte Carlo technique. Good agreements in the polymerization kinetics are achieved for fitting the kinetic profiles with the MSmodel. In addition, the MSmodel is used to describe the dynamic evolutions of the active sites and their effects on the propylene polymerization. The simulated results indicate that different types of active sites have different polymerization kinetics and the site type can affect the propylene polymerization kinetics. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

紫外分光光度法测定中药中黄嘌呤氧化酶抑制活性研究

黄嘌呤氧化酶(XOD)抑制剂是一类重要的抗痛风药物。寻求具有强XOD抑制活性的天然药物及其活性成分具有重要意义。采用紫外分光光度法对一系列中药中XOD抑制活性进行了直接测定。考察了抑制活性最强药物各部分的活性,并对其主要活性部位分离出了一个活性成分,最后采用IR、MS1、H NMR和13C NMR分析手段对其进行了鉴定。结果表明,丹皮具有最强XOD抑制活性,乙酸乙酯部分为其主要活性部位,没食子酸为其活性成分之一。     

TPD study for direct synthesis of methylchlorosilanes

Temperature programmed desorption (TPD) was performed to obtain information about the role of silicon, catalyst (copper), and promoters (zinc and tin), and to characterize the active sites for the formation of silanes. Use of infrared spectroscopy allowed rapid analysis of the gas-phase product composition. During TPD where methyl chloride was used as an adsorbate, methyl chloride (MeCl), hydrogen chloride (HC1), methane (CH₄) and silanes were produced from contact masses. Although dimethyldichlorosilane (DMDC), methyltrichlorosilane (MTCS), methyltrichlorosilane (MTCS), trimethylchlorosilane (TMCS) and dimethylchlorosilane (DMCS) were produced during the direct reaction, tetrachlorosilane (QCS), trichlorosilane (TCS), methyltrichlorosilane (MTCS), and methyldichlorosilane (MDCS) were the major silanes observed during the TPD. Zinc promotion to silicon-copper contact mass (CuSi mass) increased the production of TCS, while tin promotion decreased the production of silanes having H atom, and increased the production of MTCS. Copromotion of 0.5 wt% zinc and 0.2 wt% tin increased the MTCS production further; however, the copromotion of zinc (0.5 wt%) and tin containing a small amount of tin (0.01 wt%) produced QCS as a major silane product. The silicon sites having two or three surface species such as CH₃, Cl and H were proposed as the active sites responsible for the formation of silanes, and the silicon sites of = SiCl₂ and =Si(CH₃)Cl were the most abundant under the steady state condition.     

氮掺杂碳材料的制备及其化学活性位点研究

为了找出比较优异的非铂电极材料,并分析得出其最佳活性位点,分别从氮掺杂碳和碳载过渡金属氮材料催化剂在阴极催化的两个方向进行了探究。现如今通过X射线光电子能谱分析(XPS)可以检测出吡啶型氮、吡咯型氮和石墨型氮三种主要的氮掺杂活性位点。氮掺杂碳(G-N),氮掺杂碳纳米管(NCNT)以及氮掺杂石墨烯-氮掺杂碳纳米管(N-GO1@CNTs2)三种典型的氮掺杂碳材料进行分析。由此可见碳载过渡金属氮催化剂材料的催化活性位点很有可能主要是氮化金属化合物起作用。     

选择性絮凝的方法及其机理(II)

对选择性絮凝的现有方法按照其特点进行了系统的分类,从吸附角度和动力角度两个大方面考虑选择性絮凝的方法。吸附角度又包括增减颗粒上的活性质点数、絮凝剂分子量、絮凝剂用量、分子识别和絮凝剂形态五个方面。文中的分类方式基本涵盖了所有的选择性絮凝方法,并对选择性絮凝方法的机理和分类规律进行了阐述。这里着重介绍除增减颗粒活性质点数外的其他方法,同时,根据选择性絮凝分类方法的规律,首次提出了几种新方法并进行了探索性论述,如用合适的剪切力提高絮凝的选择性等。     

稀土元素对甲硫醇催化分解活性位点的调控作用

采用等体积浸渍法制备La、Ce改性的MCM-41催化剂,考察不同稀土金属元素对甲硫醇催化分解活性位点的调控作用。采用N_2吸附-脱附、XRD、XPS、H_2-TPR和NH_3/CO_2-TPD等对La、Ce改性催化剂进行物理化学性能测试,确定稀土元素La、Ce在催化剂中存在的形态和作用。研究表明,甲硫醇催化分解存在两步反应,低温条件下甲硫醇催化分解生成甲硫醚中间体,高温条件下甲硫醚进一步催化分解生成硫化氢和甲烷等小分子产物。对于10%Ce/MCM-41催化剂,表面活性氧是甲硫醇催化分解的低温活性中心,强酸性位点是甲硫醇催化分解的高温活性中心,二者在反应中起协同催化作用,而对于10%La/MCM-41催化剂,强酸性位点是甲硫醇催化分解的活性中心。     

选择性絮凝的方法及其机理(I)——增加或减少颗粒上的活性质点数法

选择性絮凝现有方法的分类可从吸附角度和动力角度两个大方面考虑。着重介绍从吸附角度考虑的增减颗粒上的活性质点数的方法,它包括选择合适的絮凝剂官能团、改变颗粒表面电位法、使用选择性分散剂法和近年来开发的SBA(质点阻塞剂)法等一些常用的方法。也对选择性絮凝方法的机理和分类规律进行了阐述。     

Simultaneous characterization of acidic and basic properties of solid catalysts by a new TPD method and their correlation to reaction rates

We propose a new TPD method for simultaneously characterizing the acidic and basic properties of solid catalysts by utilizing the co-adsorption of NH₃ and CO₂ on catalysts. First CO₂ was adsorbed on the catalyst sample; then NH₃ was adsorbed on it. Another adsorption sequence of NH₃ and CO₂, and CO₂ and NH₃ single adsorptions were also conducted. The TPD measurements were carried out by heating the catalyst sample from 373 to 773 K at a heating rate of 2.5 K min⁻¹ in a helium stream under a total pressure of 1.3 kPa. In solid acid catalysts, there is little difference in the NH₃-TPD spectra between single and co-adsorption systems. This results from the absence of any induction effect between the acid and base sites, because the number of base sites in the solid acid catalyst is very small. In contrast, in a solid acid–base catalyst of alumina, a remarkable difference in the NH₃-TPD spectra was observed between single adsorption and co-adsorption systems. The difference in the TPD spectra between single and co-adsorption systems was ascribed to a strong induction effect appearing on the acid and base sites, which was proved by an in situ IR measurement. The validity of the TPD method was examined by correlating the number of the strong acid sites to catalytic activities of dehydrolysis of ethanol over solid acid and solid acid–base catalysts. In solid acid–base catalysts, the number of strong acid sites was calculated from the activation energy distribution for the desorption of NH₃ in a co-adsorption system because of the strong induction effect. A proportional relationship between the intrinsic reaction rate constant, which is based on the concentration of ethanol within the catalyst, and the number of strong acid sites could be obtained, regardless of the catalysts or their types or pore structure.     

活性C-SiO_2吸附材料的制备及对酚类物质的吸附

用四氯化硅及与适量的氧化钙、氧化铝、磷酸钙化学试剂的组合产生活化剂及一些含碳的废弃物用于制备活性炭—二氧化硅吸附材料,用分光光度法研究对不同酚类物质的吸附。本法制备的吸附材料对酚类的吸附率有的高达96%以上。不加入碱性氧化物及盐类(磷酸钙)用四氯化硅水解液浸泡木屑进行碳化与活化吸附效果更佳。