Artificial ribonucleases 6. Ribonuclease activity of tetrapeptides based on amino acids involved in the catalytic site of RNase T1

Tetrapeptides based on amino acids involved in the catalytic site of RNase T1 were synthesized. These peptides interact with a 96-mer fragment of HIV-1 RNA, which results in phosphodiester bonds splitting. The efficacy of RNA cleavage depends on the mutual arrangement of oppositely charged amino acids (Glu and Arg or Lys) in a peptide. The introduction of an additional cationic fragment (based on bis-quaternary salts of 1,4-diazabicyclooctane) into an RNase mimetic leads to a considerable increase in the efficiency of RNA depolymerization. For Part 5, see Ref. 1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2596–2604, November, 2005.     

直接不对称催化Mannich反应

总结了近年来直接不对称Mannich反应的研究进展。对每一类催化剂的催化机 理加以阐述，讨论了其优缺点，讨论了其优缺点，并对其发展加以展望。     

4,5—环氧—2—戊烯醛多相催化加氢

研究了多相钯和镍催化剂上4,5-环氧-2-戊烯醛的催化加氢。发现钯催化剂上加氢产物为4,5-环氧戊醛(1)和2-羟基四氢吡喃(2),而镍催化剂上加氢产物为2和1,5-戊二醇(3)。1、2和3的最高收率分别为58.8%、62.0%和84.7%。讨论了不同催化剂对加氢产物组成的影响。     

固体酸催化条件下碳纳米管的形成

将正丁烯在不含金属微粒的催化剂上热解产生了碳纳米管．所用的催化剂是固体酸的氟促进的γ－Ａｌ２Ｏ３和分子筛型的ＨＺＳＭ－５．实验发现，这些固体酸催化剂热解产生碳纳米管所需的温度较低，碳纳米管的产生与催化剂的酸度和酸性位有一定的关联，而且所产生的碳纳米管的结构形态也比较独特．     

Studies on high chemical reactivity of nano-NaH

A comparison between the initial reaction rates of nanometric and commercial NaH has been studied in four test reactions: 1) hydrogenolysis of chlorobenzene; 2) selective reduction of cinnamaldehyde to cinnamyl alcohol; 3) metallation of dimethyl sulfoxide; and 4) catalytic hydrogenation of olefins. The experimental results indicate that when NaH is used as a chemical reagent in the first three reactions, the initial reaction rates of nano-NaH is 230, 120 and 110 times higher than those of the commercial ones respectively, and it is in agreement with the difference in specific surface areas between these two forms of NaH. When NaH is used as a catalyst component together with Cp₂TiCl₂ in the fourth reaction, catalyst with nano-NaH gives extremely high activity in the hydrogenation of olefins, while the one with commercial NaH gives no activity at all even if a large amount of the commercial NaH is used to make the total surface area equivalent to that of nano-NaH. Thus, it is evident that although large specific surface area is important for nano-NaH to be used as a catalyst component, high surface energy with surface defects seems to be more important. The large specific surface and the activated surface of nano-NaH with high surface energy should be the main factors for their extremely high chemical reactivity, while whether the former or the latter one plays a leading role depends on the type of reactions involved. __________ Translated from Chinese Journal of Applied Chemistry, 2007, 24(1): 21–24 [译自: 应用化学]     

Synthesis, Thermal, Electrical and Catalytic Studies of Some Transition Metal Polychelates of Bis-bidentate Schiff Base

Polychelates of Mn（Ⅱ）, Fe（Ⅱ）, Co（Ⅱ）, Ni（Ⅱ）, Cu（Ⅱ）, Zn（Ⅱ） and Cd（Ⅱ） with the bis salen-type ligand derived from 4,4＇-bis[（salicylaldehyde-5）azo]biphenyl and 1,4-diaminobutane have been synthesized. All the polychelalls have been characllrized by elemental analysis, magnetic susceptibility measurements, IR, electronic spectra and thennogravirncuic studies. All the complexes isolated in solid stall are dark coloured and insoluble in water and common organic solvents. The ligand behaves as a bis-bidentall molecule coordinating through the phenolic oxygen and azomethine nitrogen atoms. The thermal decomposition of these metal complexes was investigated by thermogravimetric analysis and data have been analyzed for kinetic parameters using Broido equation. The solid-state electrical conductivity of the ligand and its polychelalls in the form of compressed pellet was studied in the temperaturc range from 313 to 413 K All the polychelalls were found to show semiconducting nature. The Mn（Ⅱ）, Fe（Ⅱ）, Co（Ⅱ） and Ni（Ⅱ） polychelalls have been assessed for the catalytic epoxidation of styrene.     

漆酚缩甲醛镧配合物的制备、结构及性能

利用漆酚缩甲醛(PUF)和三氯化镧在非水热溶剂中反应制得漆酚缩甲醛镧配合物(PUFLa)，IR、XPS和TG表征结果表明：三氯化镧中La^3 与漆酚缩甲醛中酚羟基上的氧形成了配位键；在La^3 的作用下，PUF上的侧链进一步交联聚合。PUFLa在亚硫酸钠水溶液中能引发催化甲基丙烯酸甲酯聚合。通过正交实验设计考察了PUFLa用量、反应温度、反应时间、单体甲基丙烯酸甲酯用量和亚硫酸钠浓度对单体转化率的影响。结果表明。反应温度和反应时间是影响单体转化率的主要因素。PUFLa还具有良好的耐热性和抗溶剂性。     

Synthesis and Thermal Decomposition of Mn-Al Layered Double Hydroxides

In this paper, the synthesis and thermal decomposition behavior of hydrotalcite-like Mn-Al layered double hydroxide (LDH) have been investigated. First, the Mn-Al LDH was synthesized by the coprecipitation method using various anions such as Cl⁻, CO²⁻₃, NO⁻₃, SO²⁻₄ or dicarboxylic acids (DCA). The single phase of the Mn-Al LDH was obtained when Cl⁻, NO⁻₃ or DCA was used as a guest anion. In the case of CO²⁻₃ or SO²⁻₄, the solid products included MnCO₃ or shigaite as a by-product. The crystallinity of the Cl/Mn-Al LDH was greatly influenced by a drying temperature and that the crystallinity of the Cl/Mn-Al LDH dried at room temperature was found to rise about 6 times in comparison with that dried at 333 K. The DCA/Mn-Al LDH was found to have an expanding LDH structure, supporting that the LDH basal layers were bridged by the intercalated DCA anion. Then, the thermal decomposition of the DCA/Mn-Al LDH has been examined, and the intercalated DCA was found to be decomposed at lower temperature than DCA itself. The oxidation number of Mn ion rose with increasing the heat treatment temperature and was +2.70 with crystallizing Mn₃O₄ after being heated at 973 K. The thermal decomposition of guest DCA was thought to be accelerated by the strong catalytic action of Mn ion in the host hydroxide basal layers.     

Routine catalytic determination of trace amounts of cobalt in small urine samples

The oxidation of catechol by hydrogen peroxide, catalyzed by cobalt(II), is a highly sensitive and selective reaction. It makes it possible to analyze a small sample of urine (5.0 ml) for cobalt without the need for isolation of the analyte from the matrix. The sample is dried and dry-ashed according to a temperature programme, and the residue is dissolved in hydrochloric acid. After filtration of the solution, acetate buffer and sodium citrate are added and cobalt is determined catalytically in an aliquot of the solution, by the standard-addition method.     

A generic approach for the catalytic reduction of nitriles

The scope of nickel boride mediated reduction of nitriles has been extended further to allow the preparation of Boc protected amines via a mild catalytic process. It is noteworthy that the toxicity of this procedure is greatly reduced due to its catalytic nature in nickel(II) chloride used in combination with excess sodium borohydride. The protocol is marked by its resilience towards air and moisture and hence an easy and general practical protocol.