Techniques for measuring surface forces

The forces acting between colloidal particles and between surfaces are of utmost importance for determining the behaviour of dispersed systems and adhesion phenomena. Several techniques are now available for direct measurement of these surface forces. In this review we focus on some of these methods. Two techniques for measuring forces between macroscopic solid surfaces; the interferometric surface force apparatus, known as the SFA, and a novel instrument which is based on a bimorph force sensor, the so-called MASIF, are described in some detail. Forces between a macroscopic surface and a particle can be measured with the atomic force microscope (AFM) using a colloidal probe, or by employing total internal reflection microscipy (TIRM) to monitor the position of a colloidal particle trapped by a laser beam. We also describe two different techniques that can be used for measuring forces between “soft” interfaces, the thin film balance (TFB) for single foam, emulsion and solid/fluid/fluid films, and osmotic stress methods, commonly used for studying interactions in liquid crystalline surfactant phases or in concentrated dispersions. The advantages and limitations of each of these techniques are discussed and typical results are presented.     

Galvanic Stripping - A Simple and Versatile Approach to Trace Analysis

Abstract

A rapid, simple and versatile analytical technique based on galvanio stripping has been proposed. In this technique, metal ions are preconcentrated onto a mercury film coated glassy carbon electrode (MFGCE). The amal-gamated metals are re-oxidized by galvanic stripping without the aid of any external electrical field or oxidant in solution. The development and relative advantages that can acorue by the utilization of this technique are discussed.     

仲醇的氧化动力学拆分

光学活性仲醇是非常重要的合成多种具有药物和生物活性化合物的原料和关键中间体,它们可通过外消旋仲醇的氧化动力学拆分获得。本文按氧化剂和手性催化剂的类别分类综述了近年来通过氧化动力学拆分获得光学活性仲醇方法的进展,并对一些方法的机理进行了描述。对以(-)-金雀花碱-钯(Ⅱ)、金雀花碱类似物-钯(Ⅱ)、N-杂环卡宾(NHC)-钯(Ⅱ)、手性双官能团-铱配合物以及手性(ON)-钌(salen)配合物催化的分子氧为氧化剂的仲醇的氧化动力学拆分进行了充分讨论。此外,还讨论了手性salen-锰(Ⅲ)催化二乙酰基碘苯以及通过不对称氢转移的方法对仲醇的氧化动力拆分。可以发现,(-)-金雀花碱-钯(Ⅱ)-分子氧体系在目前所有仲醇氧化动力学拆分体系中表现最佳。用于仲醇氧化动力学拆分的高效体系仍有待进一步开发。     

The capacity and mechanisms of various oxidants on regulating the redox function of ZVI

It is well known that zero-valent iron(ZVI) could catalyze the oxidation of various oxidants to realize the rapid oxidation removal of pollutants. However, in this study, we found that the addition of different oxidants could regulate the redox function of ZVI system. In three different co-treatment systems, the effects of different oxidizers(peroxymonosulfate(PMS), persulfate(PDS), hydrogen peroxide(H_2O_2))dosages on the ratios of oxidative degradation rate and reductive degradation rate of p-nitrophenol(PNP)were studied. The effect of the H~+ released from oxidizers and the generated reactive oxygen species(ROS) in ZVI/PMS, ZVI/PDS, ZVI/H_2O_2 systems were detailed discussed. Especially, the contribution of generated ROS for reductive degradation of PNP was quantified in the ZVI/H_2O_2 system. Based on the results of TOC removal, UV–vis absorption spectra, and intermediates concentration curves, it was found that the degradation of PNP changed from reduction to oxidation with the increase of oxidant proportion.When the molar ratio of ZVI to oxidizer equal to 100, PNP was mainly degraded by reduction accompanied by slight oxidation. Combined with the results of SEM-EDS and XPS, it was confirmed that the enhanced degradation of PNP under the addition of oxidant was mainly related to the generated ROS,the additional H~+, and the corrosion products of ZVI.     

间位苯基桥联的锰（Ⅲ）双咔咯的合成、表征及催化氧化性质

通过间苯二甲醛与5-氟苯基二吡咯甲烷反应合成了一种新的间位苯基桥联的双咔咯1,并利用锰盐与自由咔咯反应制备了其锰的金属配合物2。采用紫外、质谱、核磁、XPS等手段对化合物进行了表征。以苯乙烯为底物考察了锰双咔咯2的催化氧化性质,探讨了时间、溶剂、氧源、轴向配体对催化反应的影响。结果表明以亚碘酰苯和间氯过氧苯甲酸为氧源时催化的主要产物为环氧苯乙烷,而以双氧水和叔丁基过氧化氢为氧源时则主要产物为苯甲醛;在极性溶剂中的催化氧化产率较高。轴向配体对催化氧化有促进作用,不同轴向配体对催化反应产率提高的顺序是：1-甲基咪唑 >吡啶 >咪唑。     

间位苯基桥联的锰(Ⅲ)双咔咯的合成、表征及催化氧化性质(英文)

通过间苯二甲醛与5-氟苯基二吡咯甲烷反应合成了一种新的间位苯基桥联的双咔咯1,并利用锰盐与自由咔咯反应制备了其锰的金属配合物2。采用紫外、质谱、核磁、XPS等手段对化合物进行了表征。以苯乙烯为底物考察了锰双咔咯2的催化氧化性质,探讨了时间、溶剂、氧源、轴向配体对催化反应的影响。结果表明以亚碘酰苯和间氯过氧苯甲酸为氧源时催化的主要产物为环氧苯乙烷,而以双氧水和叔丁基过氧化氢为氧源时则主要产物为苯甲醛;在极性溶剂中的催化氧化产率较高。轴向配体对催化氧化有促进作用,不同轴向配体对催化反应产率提高的顺序是:1-甲基咪唑吡啶咪唑。     

Quantitative Analysis of Mixed Polymer Systems by the Use of Gel Permeation Chromatography

Abstract

The use of gel permeation chromatography for the quantitative analysis of composition in mixed polymer systems is presented. The advantages of this method in determining the compositions of conjugate phases in polymer 1-polymer 2-solvent systems is discussed with typical examples.     

New Analytical Techniques for the Detection of BSE and other TSEs

Abstract

This review discusses new methods for detecting BSE and other TSE prions. A number of different analytical techniques have been applied in the past few years. New immunoassays (as well as new antibodies), an improved Western blot, CE-based methods, and a Raman-based method are some of the analytical techniques reviewed. In addition, methods to increase the concentration of prions and some cautionary notes are presented in this review.     

烯丙位氧化的几种方法

综述了近年来烯丙位氧化的研究进展，详细讨论了过渡金属及其络合物、硒化 合物在烯丙位氧化中的应用，并简述了丁基锂方法、固相催化方法、生物氧化方法 和次氯酸钠氧化方法在烯丙位氧化中的应用．     

Professor Eduardo F. A. Neves (1933–2006)

Abstract

The present note deals with the optimization of the combustion of organic materials to CO₂ in Pyrex and quartz tubes. The influence of temperature and oxidant on the combustion yield was investigated. Different physical forms of CuO and a CuO/MnO₂-mixture were used as oxidants. Possible isotopic effects during combustion were tested by gas isotope ratio mass spectrometry (GIRMS) of the CO₂. Excellent results were obtained for combustion in Pyrex at 530 °C using CuO rods mixed with 20% MnO₂ as oxidant. The stable isotope results for CO₂ prepared with this method were accurate and showed a very good precision of 0.030 %. Applications for which quantitative combustion is a necessity, we suggest the use of CuO powder (< 100 μm) as oxidant and a combustion temperature of 850 °C.     

Kinetics and mechanisms of decomposition reaction of hydrogen peroxide in presence of metal complexes

Hydrogen peroxide was discovered in 1818 and has been used in bleaching for over a century [ 1 ]. H₂O₂ on its own is a relatively weak oxidant under mild conditions: It can achieve some oxidations unaided, but for the majority of applications it requires activation in one way or another. Some activation methods, e.g., Fenton's reagent, are almost as old [ 2 ]. However, by far the bulk of useful chemistry has been discovered in the last 50 years, and many catalytic methods are much more recent. Although the decomposition of hydrogen peroxide is often employed as a standard reaction to determine the catalytic activity of metal complexes and metal oxides [ 3 , 4 ], it has recently been extensively used in intrinsically clean processes and in end‐of‐pipe treatment of effluent of chemical industries [ 5 , 6 ]. Furthermore, the adoption of H₂O₂ as an alternative of current industrial oxidation processes offer environmental advantages, some of which are (1) replacement of stoichiometric metal oxidants, (2) replacement of halogens, (3) replacement or reduction of solvent usage, and (4) avoidance of salt by‐products. On the other hand, wasteful decomposition of hydrogen peroxide due to trace transition metals in wash water in the fabric bleach industry, was also recognized [ 7 ]. The low intrinsic reactivity of H₂O₂ is actually an advantage, in that a method can be chosen which selectively activates it to perform a given oxidation. There are three main active oxidants derived from hydrogen peroxide, depending on the nature of the activator; they are (1) inorganic oxidant systems, (2) active oxygen species, and (3) per oxygen intermediates. Two general types of mechanisms have been postulated for the decomposition of hydrogen peroxide in the presence of transition metal complexes. The first is the radical mechanism (outer sphere), which was proposed by Haber and Weiss for the Fe(III)‐H₂O₂ system [ 8 ]. The key features of this mechanism were the discrete formation of hydroxyl and hydroperoxy radicals, which can form a redox cycle with the Fe(II)/Fe(III) couple. The second is the peroxide complex mechanism, which was proposed by Kremer and Stein [ 9 ]. The significant difference in the peroxide complex mechanism is the two‐electron oxidation of Fe(III) to Fe(V) with the resulting breaking of the peroxide oxygen‐oxygen bond. It is our intention in this article to briefly summarize the kinetics as well as the mechanisms of the decomposition of hydrogen peroxide, homogeneously and heterogeneously, in the presence of transition metal complexes. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 643–666, 2000     

The role of non-linear electron spin resonance spectroscopies Perspectives in microscopic studies of liquid-crystalline polymers

Abstract

The advantages and the limits of electron spin resonance applied to the study of microscopic interactions in liquid crystalline polymers are discussed. Difficulties of current E.S.R. techniques in studying the very slow molecular dynamics suggest the search for novel techniques. Two non-linear C.W. E.S.R. techniques are described; multiple irradiation schemes are studied in a unified theoretical treatment. These methods give direct measurements of the longitudinal relaxation dynamics and are completely independent of the inhomogeneous broadening of the spectral lines. Their capabilities for investigating ultra-slow relaxation rates are evidenced.     

Efficient gold and silver electrodes for surface enchanced raman spectral studies of electrochemical systems: The behaviour of pyridine and naphthalene adsorbed on roughened gold electrodes

A method is described whereby surface enhanced Raman (SER) active electrode surfaces of gold and silver may be made without recourse to the oxidation—reduction techniques which have been used hitherto. This method involves electroplating at low current density from dilute (< 10^?2M) solutions of a suitable salt or complex in the absence of supporting electrolyte.Scanning electron microscopy shows the surfaces to consist of small spherical particles of fairly constant diameter packed together on the electrode. The sphere diameters are typically 70 nm (gold) and 180 nm (silver) for electrodes prepared in this manner. These electrodes exhibit intense SER scattering and have advantages over oxidation—reduction roughened electrodes. As examples of their utility some results are presented relating to the gold/pyridine and gold/naphthalene systems and these are discussed in relation to results obtained by other workers in similar systems using different methods, i.e., ellipsometry and differential capacitance variation.     

Conformational Transmission in 5′-PV and 5′-PV TBP Phosphorylated Nucleosides. Implications For DNA Structure and Dynamics

Abstract

Specific conformational changes in DNA and RNA can be induced via a transient pentacoordination of the phosphorus atoms in the helix backbone. The details of this conformational transmission mechanism are discussed briefly, using experimental data that were obtained with a set of 5′-pIV and 5′-pV phosphorylated tetrahydrofurfuryl systems. A conformational study on the more realistic model system, the dinucleotide 2 in which a stabilized pentacoordinated phosphorus forms the internucleoside linkage, is presented. Furthermore, it has been found that methylation of the phosphate groups in d(T_pT_pT_pT_pT_pT) results in the formation of a non-Watson & Crick type parallel duplex DNA structure, in which the two strands are joined via hydrogen bonding between the thymidine bases. Various physico-chemical techniques (e.g. NMR methods and UV hyperchromicity) were used to elucidate the structural details of the parallel duplex. Characteristic properties (parallellity, slimness, symmetry) are presented.     

Amperometric biosensors employing an insoluble oxidant as an interference-removing agent

A strong oxidant membrane is introduced to amperometric biosensors in order to solve the problem associated with interference from readily oxidizable species. The proposed biosensors are in planar format, and are composed of four components, i.e. a base amperometric transducer, an enzyme layer, a protecting membrane, and an oxidant membrane. In this sensor format, interfering species are removed by an oxidation reaction during their diffusion through the oxidant membrane. The oxidant membrane is introduced by dispensing a mixture of an oxidant and a polymer matrix as dissolved in an organic solvent, and thus, could be easily adapted to mass fabrication of miniature biosensors. In this work, several different reagents are examined as oxidants: BaO₂, CeO₂, MnO₂ and PbO₂. Of these, PbO₂ is shown to yield biosensors with the best performance, in terms of reducing interfering signals. Two different matrix systems are devised for use in formulating oxidant membranes: hydrophilic polyurethane (HPU) and cellulose acetate incorporating poly(ethylene glycol) (CA/PEG). While the CA/PEG-type sensor displays better sensitivity and faster response behavior, the HPU-type is shown to exhibit more pronounced interference-removing ability. The analytical utility of the proposed oxidant membrane is demonstrated by fabricating amperometric glucose and creatinine sensors as the model biosensor systems, and by investigating their response characteristics.     

硒催化的乙二胺、乙醇胺和环胺的氧化羰基化反应

研究了以硒粉作催化剂,一氧化碳为羰基化试剂的乙二胺、乙醇胺和一些环胺的羰基化反应,考察了氧化剂对反应的影响。发现氧气是该反应较好的氧化剂,而没有氧化剂存在时,几乎没有羰基化反应发生。在硒／氧化剂体系存在下,乙二胺和乙醇胺这样一些分子内具有相邻两个亲基团物质的羰基化反应易趋向于分子内羰基化形成较为稳定的五元环产物,产率和选择性较高;而环胺如哌啶和吗啡啉的羰基化可生成相应的四取代脲产物。对反应机理进行     

A tutorial comparison of the NMRIT and LAOCOON approaches for analyses of complex solution‐phase nuclear magnetic resonance spectra

For spin ½ nuclei the two most frequently used iterative approaches for determinations of NMR chemical shifts (h_i) and coupling constants (J_i), NMRIT and LAOCOON, are discussed. When multiple pulse techniques for extraction of these parameters fail or lead to complicated spectra in the cases of very strongly coupled spin systems and systems involving magnetically nonequivalent, chemical shift equivalent nuclei, recourse to these iterative methods is necessary. The former approach employs the energy levels derived from the observed transition frequencies, whereas the latter approach uses the observed transition frequencies. Derivations of the general iterative equations for both approaches are given, along with the specific equations for the ABC spin system. The matrix nature of the derivation of these equations is stressed. Also discussed is the modified NMRIT program, NMRENIT, which has major advantages over the former in cases with symmetry and in cases where not enough lines can be assigned to link all the energy levels. The advantages of the latter program over LAOCOON in certain cases are discussed. Some general advice on the use of both approaches is presented. The Hoffman energy level approach is also discussed and it is shown that it yields the same iterative equations as the LAOCOON approach. Copyright © 2002 John Wiley & Sons, Ltd.