络合型催化剂丙烯聚合动力学研究

本工作对络合型(Solvay型)TiCl_3催化剂—(C_2H_5)_2AlCl体系丙烯聚合进行了活性中心浓度C_p、链增长速率常数k_p和链增长活化能E_p等的测定,并与常规TiCl_3·0.33AlCl_3进行了比较,C_p以动力学方法求取,数均分子量以粘度法测定经分子量分布校正,结果表明,络合型催化剂活性比常规催化剂高,不仅是由于C_p增高,在更大程度上是由于k_p提高。     

OSW saponins: facile synthesis toward a new type of structures with potent antitumor activities

[reaction: see text] OSW saponins, featuring a 16beta,17alpha-dihydroxycholest-22-one aglycon and an acylated beta-D-xylopyranosyl-(1-->3)-alpha-L-arabinopyranosyl residue attached to the 16-hydroxyl group, have recently been discovered from a group of lily plants, which show potent antitumor activities with a novel mechanism of action. This paper describes an aldol approach to the stereoselective construction of the 16alpha,17alpha-dihydroxycholest-22-one structure from 16alpha-hydroxy-5-androsten-17-ones and propionates. Elaboration of the aldol adducts toward OSW-1, involving installation of the isoamyl ketone side chain, inversion of the 16-hydroxyl configuration, and selective protection of the C22-oxy function, has been explored and accomplished. In particular, the present route was found convenient for the synthesis of OSW saponin analogues with a C22-ester side chain. Thus, the 23-oxa-analogue of OSW-1 (40) was prepared starting from the industrial dehydroisoandrosterone (1) in a linear eight-step sequence and in 26% overall yield. Analogues with a variety of modified side chains were prepared, via aldol condensation with propionates of varying length, thiopropionate, and acetate (for preparation of 68-75) or via aminolysis of the 22,16-lactone 26 (for preparation of the 23-N-analogues). Cross metathesis (CM) reaction was also found feasible for modification at the final stage from C22-allyl ester 70. Valuable structure-activity relationships (SAR), together with the practical synthetic approach, have thus been provided to set a new stage for further studies on this new type of antitumor structures.     

Detailed Structural Characterizations of SBA‐15 and MCM‐41 Mesoporous Silicas on a High‐Resolution Transmission Electron Microscope

Using high‐resolution transmission electronic micrograph (HR‐TEM) observation, one can clearly see the pore geometry of the MCM‐41 and SBA‐15 mesoporous silicas to determine that their pore shapes are hexagonal and round, respectively. With the perpendicular orientations of the nanochannels to the electron beam, parallel line images of the (100) and (110) repeating spacings were observed. In the SBA‐15 mesoporous silicas, there are byproducts of the granular silica and disordered mesostructures, attributed to the weak hydrogen interactions between Pluronic 123 blockcopolymer and the silica species. There are also many different and significant +π disclination defects in SBA‐15 and MCM‐41 surfactant‐silica composites. The SBA‐15 with a thicker silica wall is more stable under irradiation by high‐energy electron beams compared to MCM‐41, which has thinner wall thickness. Some carbon nanostructure impurities were found in some carbon films on the metal grids.     

Ab initio studies on the thermolysis of azetidine

The reaction mechanism of the thermolysis of azetidine to form ethylene and methylen-imine has been studied by ab initio SCF MO method at STO--3G and 3-21G levels. Two possible step-wise pathways are explored. One is the breaking of C--C bond as the first step, while the other is thebreaking of C--N bond. All the stationary points on the potential energy surface (PES) are fully optimiz-ed. MP2 / 3-21G single point calculations on all stationary points and MCSCF / STO-3G computationsfor some stationary points are also carried out. The calculations indicate that azetidine decomposesvia biradicaloid intermediates and the cleavage of C--N bond is preferable to that of C--C bond.     

Three-dimensional effects on the linear adiabatic molecular wavefunctions in the H + H2 system

The adiabatic molecular wavefunctions in the H + H₂ system are obtained in one dimension by solving the double-well potential problem. In three dimensions, the corresponding linear adiabatic molecular wavefunctions are obtained. A comparison between these wavefunctions clearly suggests that the probability of reaction is smaller in three dimensions.     

Polyketide chain length control by chain length factor

Bacterial aromatic polyketides are pharmacologically important natural products. A critical parameter that dictates product structure is the carbon chain length of the polyketide backbone. Systematic manipulation of polyketide chain length represents a major unmet challenge in natural product biosynthesis. Polyketide chain elongation is catalyzed by a heterodimeric ketosynthase. In contrast to homodimeric ketosynthases found in fatty acid synthases, the active site cysteine is absent from the one subunit of this heterodimer. The precise role of this catalytically silent subunit has been debated over the past decade. We demonstrate here that this subunit is the primary determinant of polyketide chain length, thereby validating its designation as chain length factor. Using structure-based mutagenesis, we identified key residues in the chain length factor that could be manipulated to convert an octaketide synthase into a decaketide synthase and vice versa. These results should lead to novel strategies for the engineered biosynthesis of hitherto unidentified polyketide scaffolds.     

Separation of Sulfonylurea Herbicides and Determination of Bensulfuron-methyl Residues in Tapwater by HPTLC

JPC – Journal of Planar Chromatography – Modern TLC - In this work we have studied the separation of a mixture of the sulfonylurea herbicides (metsulfuron-methyl, chlorsulfuron,...     

甲烷氧化偶联催化反应的特征

应用程序升温反应（ＴＰＲ）及质谱分析表征了ＣａＯ，Ｓｍ２Ｏ３，０．５－１０％Ｓｍ／ＣａＯ催化剂上的甲烷氧化偶联反应特性。谱图分析表明，在４００－１０００℃范围内，甲烷氧化偶联反应产物的变化呈现三个反应温度区域：（１）完全氧化区，反应主要为ＣＨ３·在催化剂表面完全氧化形成ＣＯｘ和Ｈ２：（２）偶联区，主要为ＣＨ３·的氧化和偶联竞争反应，Ｈ２谱线出现明显的低温峰；（３）氧耗尽区，反应为高温气相反应，产物     

Toward the most versatile fluorophore: Direct functionalization of BODIPY dyes via regioselective C—H bond activation

BODIPY dyes are privileged fluorophores that are now widely used in highly diverse research fields. An overview of BODIPY dyes and a summarization of the different synthetic methodologies reported for direct C-H functionalization of the BODIPY framework have been provided.     

MECHANICAL PERTURBATION INDUCED MOLECULAR ALIGNMENTS IN A SIDE-CHAIN LIQUID CRYSTALLINE POLYACETYLENE, POLY{10-[4-(4''-METHOXYPHENOXY-CARBOML)PHENOXYCARBONYL]-1-DECYNE}*

A new liquid crystalline polyacetylene containing a phenyl benzoate mesogen (5) is synthesized,whose mesomorphic properties are found to be easily "tunab1e" by simple mechanical perturbation. Thepolymerization of 10- [ 4 - (4' -methoxyphenoxycarbonyl )phenoxycarbonyl] - 1 -decyne (4 ) in itiated by theWCl_6-Ph_4Sn/dioxane complex yields polymer 5 with a M_w of 28400. The molecular structure of 5 ischaracterized by NMR, IR, and UV spectroscopy and its liquid crystalline behavior is investigated by DSC,POM, and XRD analysis. Upon mechanical perturbation, 5 exhibits unusual agitation-induced high-strengthdisclinations, shear-induced inversion walls, and solidification-induced banded textures. Such phenomenahave been observed in the main-chain liquid crystalline polymers with rigid backbones, but have seldom beenreported for the side-chain liquid crystalline polymers with flexible backbones, suggesting that the rigidpolyacetylene backbone of 5 plays a constructive role in inducing the novel molecular alignments.