Determination of small quantities of xanthate

A new spectrophotometric method for the determination of very small amounts of xanthate in solutions, particularly cyanide solutions from gold-extraction plants, is described. It is based on the formation and extraction of copper(II) xanthate. The coefficient of variation is 1.0% at the 40-ppm level and 3.4% at the 4-ppm level and the lower limit of determination is approximately 0.5 ppm. Copper(II) xanthate normally decomposes into copper(I) xanthate and dixanthogen, but in the proposed method the decomposition is delayed.     

霍尔效应

1879年,二十四岁的霍尔在研究载流导体在磁场中所受的力的性质时,发现了一种电磁效应,即如果在电流的垂直方向加以磁场,则在同电流和磁场都垂直的方向上将建立一个电场。这个效应后来被称为霍尔效应。从那时到现在,一百年过去了,霍尔效应以及利用这个     

塞曼效应

塞曼效应是继法拉第效应(1845年)和克尔效应(1888年)之后发现的第三个磁光效应(1896年)。这是光源在磁场的作用下其线光谱发生分裂的现象,它对于光的辐射机理提供了极好的保证,由于及时得到洛仑兹理论的解释而受到重视,被誉为继X光(1895年)之后物理学最重要的发现之一。1902年,塞曼(Pieter Zeeman,1865—1943)因这一发现与洛仑兹(H.A.Lorentz,1853—1928)共获诺贝尔物理奖。     

迈克耳孙——莫雷实验的前前后后

迈克耳孙——莫雷实验是由经典物理学过渡到近代物理学的一个重要的“指路牌”。本文拟对这个著名实验的历史背景和发展过程,作一点介绍。 (一)迈克耳孙为什么要做以太漂移实验? 十九世纪,光的波动说获得很大成功,以太的观念也就取得了统治地位。当时的科学界普遍认为,光既然是波,如果不通过某种介质传播,是不可想象的。人们根据所知事实,给以太作出这样那样的假定,例如假定它是充满一切空间(包括物体内部)的某种绝对静止、极其稀薄的刚性介质。十九世纪后半世纪,麦克斯韦(J.C.Maxwell,1831—1879)的电磁场理论(1864年)证明光是电磁波,但…     

Chromium(III) octaethylporphyrinato tetracarbonylcobaltate: a highly active, selective, and versatile catalyst for epoxide carbonylation

The development of a highly active and selective porphyrin-based epoxide carbonylation catalyst, [(OEP)Cr(THF)2][Co(CO)4] (1; OEP = octaethylporphyrinato; THF = tetrahydrofuran), is detailed. Complex 1 is a separated ion pair composed of a tetracarbonylcobaltate anion and an octahedral chromium porphyrin complex axially ligated by two THF ligands. Regarding the carbonylation of epoxides to beta-lactones, catalyst 1 exhibits excellent turnover numbers (up to 10,000) and turnover frequencies (up to 1670 h(-1)), with regioselective carbonyl insertion occurring between the oxygen and the sterically less hindered carbon of the epoxide substrate. Complex 1 is highly tolerant of nonprotic functional groups, carbonylating an array of aliphatic and cycloaliphatic epoxides, as well as epoxides with pendant ethers, esters, and amides. With careful control of reaction conditions in the carbonylation of glycidyl esters, the exclusive production of either the beta- or gamma-lactone isomer was achieved. Through analysis of reaction stereochemistry, a mechanism for the formation of gamma-lactone products was proposed. Overall, a broad array of synthetically useful lactones has been synthesized in a rapid and selective fashion by catalytic carbonylation using [(OEP)Cr(THF)2][Co(CO)4].     

Synthesis and characterization of the first trimetallic nitride templated pyrrolidino endohedral metallofullerenes

New pyrrolidino derivatives of both diamagnetic and paramagnetic trimetallic nitride templated endohedral metallofullerenes were synthesized by the Prato reaction, isolated and characterized by means of MALDI-TOF MS, NMR and UV-vis spectroscopies.     

An unprecedented fivefold interpenetrated lvt network containing the exceptional racemic motifs originated from nine interwoven helices

An unprecedented fivefold interpenetrated lvt network, containing the rare racemic motifs originated from nine interwoven helices, is reported, which represents the highest degree of interpenetration presently known for 3D nets containing only planar four-coordinate nodes.     

Duplex strand formation using alternating copolymers

The regular arrangement of complementary diaminopyridine-thymine (DAP-THY) on alternating copolymers permits cooperative binding events and the effective formation of well-controlled micrometre-scale aggregates.     

Two-dimensional double metal cyanide complexes: highly active catalysts for the homopolymerization of propylene oxide and copolymerization of propylene oxide and carbon dioxide

The synthesis of two-dimensional double metal cyanide complexes of the formula Co(H2O)2[M(CN)4].4H2O (M=Ni, Pd or Pt) and the X-ray crystal structure of Co(H2O)2[Pd(CN)4].4H2O are presented. The anhydrous forms of these complexes were found to be effective catalyst precursors for the homopolymerization of propylene oxide as well as the random copolymerization of propylene oxide and carbon dioxide to produce poly(propylene oxide-co-propylene carbonate) with no propylene carbonate byproduct. A detailed copolymer microstructure is proposed.