CuO/CeO2催化剂的催化氧化性能及其表征

用CO流动反应法 ,程序升温还原 (TPR) ,光电子能谱 (XPS)和X射线衍射Rietveld分析等技术研究了CuO ,CeO2 及CuO/CeO2 各组分催化剂。结果表明 :单组分的CuO和CeO2 对CO的氧化活性较低 ,但CuO与CeO2 形成复合氧化物后 ,其CO氧化活性明显提高 ,这可能与铜物种在CeO2 表面的价态 (Cu2 + 和Cu+ ) ,分散状态和还原性能有关。CuO在CeO2 上的负载量对铜物种在CeO2 表面形成的价态 (Cu2 + 和Cu+ )至关重要 ,CuO的负载量为 1 0 %时 ,XPS检测不到Cu2p3/2 (eV)结合能 ;当CuO的负载量为 5 0 %时 ,CuO主要以Cu2 + 和Cu+ 形式存在 ,而负载量大于 5 0 %时 ,CuO则以Cu2 + 形式存在。由于形成了CuO/CeO2 复合氧化物 ,使离子半径小于Ce4 + 的CuO进入了CeO2 晶格 ;当CuO的负载量达到 5 0 %时 ,CuO的晶粒尺寸值为最小 ( 6 1nm) ,而晶格畸变值为最大 ( 2 86× 10 - 3) ,此时 ,催化剂具有较高的表面能和最佳的CO氧化活性     

Lipophilicity in PK design: methyl, ethyl, futile

Lipophilicity, often expressed as distribution coefficients (log D) in octanol/water, is an important physicochemical parameter influencing processes such as oral absorption, brain uptake and various pharmacokinetic (PK) properties. Increasing log D values increases oral absorption, plasma protein binding and volume of distribution. However, more lipophilic compounds also become more vulnerable to P450 metabolism, leading to higher clearance. Molecular size and hydrogen bonding capacity are two other properties often considered as important for membrane permeation and pharmacokinetics. Interrelationships among these physicochemical properties are discussed. Increasing size (molecular weight) often gives higher potency, but inevitably also leads to either higher lipophilicity, and hence poorer dissolution/solubility, or to more hydrogen bonding capacity, which limits oral absorption. Differences in optimal properties between gastrointestinal absorption and uptake into the brain are addressed. Special attention is given to the desired lipophilicity of CNS drugs. In examples using -blockers, Ca channel antagonists and peptidic renin inhibitors we will demonstrate how potency and pharmacokinetic properties need to be balanced.     

Co—Mo／MgO—Al2O3水煤气耐硫变换催化剂失活的研究

利用Ｘ－射线衍射，扫描电镜，拉曼光谱，等离子发射光谱和比表面测定等方法研究了不同状态下失活及新鲜催化剂的结构，杂种类及含量。结果表明，超温使催化剂晶化明显，制备方法对催化剂结构有直接影响，再生使其强度降低，条形催化剂比较容易粉化，无机杂质是次要的失活原因。     

SEC–MALLS analysis of cellulose using LiCl/1,3-dimethyl-2-imidazolidinone as an eluent

The lithium chloride/1,3-dimethyl-2-imidazolidinone (LiCl/DMI) solvent system for cellulose was adopted as a mobile phase of size-exclusion chromatographic (SEC) analysis of cellulose, and the applicability of this system was examined using multi-angle laser light scattering and ¹³C-NMR analysis. The results indicate that 8% (w/v) LiCl/DMI ID a true solvent for cellulose, and that cellulose molecules dissolving ID 1% (w/v) LiCl/DMI are separated orderly depending on their molecular mass (MM) or root-mean-square (RMS) radius by the SEC system. Practically, no aggregates were detected ID the dilute cellulose/LiCl/DMI solutions. Furthermore, high stability of cellulose/LiCl/DMI solutions has been demonstrated; only a few percent of decline ID average MM was observed even after storage for 6 months at room temperature. Relationships between RMS radius and MM for hardwood bleached kraft pulp ID 1% LiCl/DMI was estimated as the following equation: _g^0.59, corresponding to a Mark–Houwink–Sakurada exponent of 0.77.     

Inclusion complexes of proteins: Interaction of cyclodextrins with peptides containing aromatic amino acids studied by competitive spectrophotometry

The stability constants were measured of inclusion complexes formed from aromatic amino acids and their oligopeptides with - and-cyclodextrin, hydroxypropyl-cyclodextrin, and partially methylated-cyclodextrin. The method of competitive spectrophotometry withp-nitrophenol as a competing reagent was used, and measurements were made at pH 7.4-Cyclodextrin formed complexes of higher stability than the other hosts. The stability of complexes of oligopeptides containing L-phenylalanine was invariably higher than that of L-phenylalanine itself. A model for interaction of proteins with cyclodextrins is proposed, in which the most stable complexes are formed when the native functional form of proteins is unfolded and the nonpolar residues that are buried inside the structure are exposed to water. The complexation of the unfolded structure favors its formation; thus thermal denaturation of proteins is easier in the presence of cyclodextrins. On the other hand, this complexation prevents the intermolecular association of unfolded structures by noncovalent hydrophobic bonding between the exposed nonpolar residues; furthermore, the unfolded complexed forms may revert to the native functional form. This prevention of intermolecular association may explain the stabilizing effect of cyclodextrins on solutions of proteins: a return to the native form is achieved more easily from the complexed, unfolded form than from the unfolded, aggregated forms.Dedicated to Professor József Szejtli.     

Structure and conformational features of tetrahydrothienothiepinoisoxazole as a novel heterocyclic system

The crystal and molecular structure of a novel heterocyclic system, 8-methyl-3,3a,4,5-tetrahydrothieno[3,2:6,7]thiepino[4,5-c]isoxazole, has been determined by X-ray analysis. The seven-membered ring has the boat conformation (B), while the isoxazoline cycle has the flat chair conformation (₃E). There are strong steric strains between the vicinal protons at the C(3a), C(3), and C(4) atoms.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1795–1797, October, 1994.     

Preparation and characterization of high-specific-surface-area activated carbons from K2CO3-treated waste polyurethane

An activated carbon with high specific surface area was prepared from polyurethane foam by chemical activation with K2CO3 and the influences of carbonization temperature and impregnation ratio on the pore structure of the prepared activated carbon were investigated. It was found that the specific surface area of the activated carbon was at a maximum value (about 2800 m(2)/g) at a carbonization temperature of 1073 K and at an impregnation ratio of 1.0. It was concluded that the polyurethane foam structure was modified during impregnation by K2CO3, K2CO3 promoted charring during carbonization, and then the weight loss behavior was changed below 700 and above 1000 K, carbon in the char was consumed by K2CO3 reduction, and this led to the high specific surface area. The prepared activated carbon had a very sharp micropore size distribution, compared with the commercial activated carbon having high specific surface area. The amounts of three organic vapors (benzene, acetone, and octane) adsorbed on the prepared activated carbons was much larger than those on the traditional coconut shell AC and the same as those on the commercial activated carbon except for octane. We surmised that the high specific surface area was due to the modification of the carbonization behavior of polyurethane foam by K2CO3.     

Uniform Rice-like CdS Particles Prepared from Water-in-oil Microemulsions

IntroductionNano-sized semiconductors are of great interestdue to their special optical and electronic proper-ties[1,2].As one of the mostimportantⅡ—Ⅵsemicon-ductors,CdS has importantapplications in many fields,such as the solar cell field,non linear o…     

MONTE CARLO SIMULATION OF TRIBLOCK COPOLYMER/HOMOPOLYMER BLEND FILMS

1. INTRODUCTION The extensive applications of block copolymer have been studied in detail due to their special molecular architecture and characteristic [1,2]. Recently, many studies including theoretical analysis and experimental techniques have addressed the polymer blend system of diblock copolymer/homopolymer [3~9]. An early investigation presented a quantitative analysis of homopolymer distributions in well-ordered copolymer microdomains through mixing polystyrene (PS) or poly methyl…     

Different catalysis role of in‐loop and out‐of‐loop waters in assisting HNS/HSN proton transfer isomerizations: Bridging vs. surrounding effect

In this work, a density function theory (DFT) study is presented for the HNS/HSN isomerization assisted by 1–4 water molecules on the singlet state potential energy surface (PES). Two modes are considered to model the catalytic effect of these water molecules: (i) water molecule(s) participate directly in forming a proton transfer loop with HNS/HSN species, and (ii) water molecules are out of loop (referred to as out‐of‐loop waters) to assist the proton transfer. In the first mode, for the monohydration mechanism, the heat of reaction is 21.55 kcal · mol^?1 at the B3LYP/6‐311++G** level. The corresponding forward/backward barrier lowerings are obtained as 24.41/24.32 kcal · mol^?1 compared with the no‐water‐assisting isomerization barrier T (65.52/43.87 kcal · mol^?1). But when adding one water molecule on the HNS, there is another special proton‐transfer isomerization pathway with a transition state 10T′ in which the water is out of the proton transfer loop. The corresponding forward/backward barriers are 65.89/65.89 kcal · mol^?1. Clearly, this process is more difficult to follow than the R–T–P process. For the two‐water‐assisting mechanism, the heat of reaction is 19.61 kcal · mol^?1, and the forward/backward barriers are 32.27/12.66 kcal · mol^?1, decreased by 33.25/31.21 kcal · mol^?1 compared with T. For trihydration and tetrahydration, the forward/backward barriers decrease as 32.00/12.60 (30T) and 37.38/17.26 (40T) kcal · mol^?1, and the heat of reaction decreases by 19.39 and 19.23 kcal · mol^?1, compared with T, respectively. But, when four water molecules are involved in the reactant loop, the corresponding energy aspects increase compared with those of the trihydration. The forward/backward barriers are increased by 5.38 and 4.66 kcal · mol^?1 than the trihydration situation. In the second mode, the outer‐sphere water effect from the other water molecules directly H‐bonded to the loop is considered. When one to three water molecules attach to the looped water in one‐water in‐loop‐assisting proton transfer isomerization, their effects on the three energies are small, and the deviations are not more than 3 kcal · mol^?1 compared with the original monohydration‐assisting case. When adding one or two water molecules on the dihydration‐assisting mechanism, and increasing one water molecule on the trihydration, the corresponding energies also are not obviously changed. The results indicate that the forward/backward barriers for the three in‐loop water‐assisting case are the lowest, and the surrounding water molecules (out‐of‐loop) yield only a small effect. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006