基于催化应用调控氧化铈纳米材料的形貌

催化剂的设计、合成和结构调控是获得优异性能的关键.传统的策略主要是尽量减小催化剂颗粒尺寸以增加活性中心的数目,即尺寸效应.近年来,材料科学的快速发展使得在纳米尺度上调变催化剂的尺寸和形貌成为可能,特别是通过形貌调控可暴露更多的高活性晶面,大幅度提高催化性能,即纳米催化中的形貌效应.因此,调节催化剂的尺寸与形貌可以单独或协同优化材料的性能.氧化铈作为催化剂的重要组分与结构、电子促进剂被广泛应用于多相催化剂体系.本文总结了近期氧化铈材料形貌可控合成的进展,包括主要的合成策略和表征方法; 进而分析了氧化铈和金-氧化铈催化材料的形貌效应,指出金-氧化铈之间独特的相互作用与载体形貌密切相关; 阐述了氧化铈纳米材料因暴露晶面的差异而获得不同催化性能的化学机制.     

冷冻干燥中升华界面移动的微CT实验研究

采用微CT扫描仪的扫描成像,图像重构及灰度值分析技术对不同厚度苹果片冷冻干燥的升华过程进行实验观察,分析了界面的移动特性.结果表明,对于单面传导加热的升华干燥过程,物料升华不仅在顶面进行,与搁板接触的底面以及侧面也会有水蒸气逸出.厚物料在升华过程中有一个明显的球形冻结区,升华界面呈三维模式逐渐向物料几何中心收缩.无论物料厚薄,刚开始升华干燥速率比较快,随着干燥层的增厚,升华过程的热质阻力增大,升华速率减慢.     

Axially chiral directly beta,beta-linked bisporphyrins: synthesis and stereostructure

[reaction: see text] A novel type of "superbiaryl", the first porphyrin dimers with an intrinsically chiral structure, has been prepared. The atropo-enantiomers were configurationally assigned by HPLC-CD combined with quantum chemical CD calculations.     

2-羟基-1-萘甲醛缩氨基胍铜配合物的合成及表征

铜是生物体内必需的微量元素,是一些重要酶的活性中心,其配合物不仅在生命体系有着特殊的生物活性[1],而且由于具有特殊的磁学、电学、光学等性质而在材料、催化等许多领域中表现出潜在应用价值,因而成为人们关注的热点课题之一[2],为此我们合成了2-羟基-1-萘甲醛缩氨基胍铜配合物,并对此配合物进行了一系列表征.     

一维链状配位聚合物[Cd{5-(NO2)sal}2(2,2'-bipy)]n的合成与晶体结构

A coordination polymer of [Cd{5-(NO2)sal}2(2,2'-bipy)]n (5-(NO2)sal=5-nitrosalicylate, 2,2'-bipy=2,2'-bipyridine) was synthesized by hydrothermal reaction and characterized by elemental analysis, IR and X-raydiffraction single crystal structure analysis. The title complex crystallizes in monoelinic with space group C2/c, a=2.730 8(16) nm, b=1.272 3(5) nm, c=0.674 5(3) nm,β=96.73(2)°, V=2.327(2) nm3, Z=4, R=0.022 2, wR=0.057.The 5-nitrosalicylate anions doubly bridge the Cd(Ⅱ) atoms to form one-dimensional polymeric chain with therepeated eight-membered ring units (Cd-O-C-O)2. The crystal structure is stabilized by intra- and interchainhydrogen bonds interactions.     

二氧化碳速冻喷射器的优化设计及实验研究

本文在文献［３］的基础上作了优化计算的改进,利用气固两相流［１］和系统的优化计算模型编制程序,从最佳面积比、喷射个数和套筒尺寸之间的紧密联系出发,获得了优化设计速冻喷射系统的方法,用于设计速冻系统的套筒、喷嘴的结构尺寸。本文还将理论计算结果与试验数据进行比较,获得了满意的结果。     

超声溶栓

超声溶栓长期为人们所重点研究。本文对超声溶栓技术进行了综述,着重介绍和分析了其发展历史、溶栓机理、技术特点和研究现状,最后对以后的研究工作提出了一些看法。     

Structure and biosynthesis of the marine streptomycete ansamycin ansalactam A and its distinctive branched chain polyketide extender unit

Reported is the structure and biosynthesis of ansalactam A, an ansamycin class polyketide produced by an unusual modification of the polyketide pathway. This new metabolite, produced by a marine sediment-derived bacterium of the genus Streptomyces , possesses a novel spiro γ-lactam moiety and a distinctive isobutyryl polyketide fragment observed for the first time in this class of natural products. The structure of ansalactam A was defined by spectroscopic methods including X-ray crystallographic analysis. Biosynthetic studies with stable isotopes further led to the discovery of a new, branched chain polyketide synthase extender unit derived from (E)-4-methyl-2-pentenoic acid for polyketide assembly observed for the first time in this class of natural products.