Exploration of Displacement Reaction/Sorption Strategies in Spectrometric Analysis

Abstract

Displacement reactions are very popular in nature, ranging from texbook knowledge of the Zn-CuSO₄ system to modern functional nucleic acid–involved metal ion displacement. Though synthetic chemistry harvests a lot from displacement reactions, analytical chemistry benefits greatly from various displacement reaction strategies, such as sensitivity improvement. In particular, the use of indicator displacement assay for new sensor development is of great interest worldwide. In this review, we summarize the advances in utilization of displacement reactions for improved spectrometric analysis. The main contents include displacement-based preconcentration schemes for trace metal analysis by analytical atomic spectrometry, indicator displacement assays focusing on the use of advanced nanomaterials, and displacement immunoassays using spectrometric measurements, with 117 references.     

Non-innocent probes in direct sonication: Metal assistance in oxidative radical CH functionalization

Direct sonication by means of ultrasound horns constitutes a widely used technique in chemical process technology. However, the direct contact between the metal probe and the reaction mixture does not always leave the chemical system unaffected. In this report, we study the tert-butyl hydroperoxide-mediated trifluoromethylation of heterocyclic structures, and the influence of sonication thereon. Metal leaching is observed during the process and further examined, showing that several metals can interfere significantly with the chemical reaction under study. Notably, vanadium metal was found to increase the reaction rate exceptionally well, rendering it a useful additive for this type of reactions. Ultimately, some mechanistic considerations are offered, to provide more insight into the nature of the catalytic effect of leached metals.     

Mechanism study of Single-Step synthesis of Fe(core)@Pt(shell) nanoparticles by sonochemistry

Transition metal (TM) core-platinum (Pt) shell nanoparticles (TM@Pt NPs) are attracting a great deal of attention as highly active and durable oxygen reduction reaction (ORR) electrocatalysts of fuel cells and metal-air batteries. However, most of the reported synthesis methods of TM@Pt NPs are multistep in nature, a significant disadvantage for real applications. In this regard, our group has reported a single-step method to synthesize TM@Pt NPs for TM = Mn, Fe, Co, and Ni by using sonochemistry, namely the UPS (ultrasound-assisted polyol synthesis) method. Previously, we proposed the mechanism of the formation of these TM@Pt NPs by UPS method, but rather in a rough sense. Some details are missing and the optimal conditions have not been established. In the present work, we performed detailed studies on the formation mechanism of UPS reaction by using Fe@Pt NPs as the model system. Effects of synthesis parameters such as the nature of metal precursor, conditions of ultrasound, and temperature profile as a function of reaction time were assessed, along with the analyses of intermediates during the UPS reaction. As results, we verified our previously proposed mechanism that, under appropriate conditions, Fe core is formed through the cavitation and implosion of the solvent, induced by the ultrasound, and the Pt shell is formed by the chemical reaction between Fe core and Pt reagent, independent from the direct effect of ultrasound. In addition, we established the optimal conditions to obtain a high purity Fe@Pt NPs in a high yield (>90% based on Pt), which may enable the increase of synthesis scale of Fe@Pt NPs, a necessary step for the real application of TM@Pt NPs.     

Recent developments in sonochemical polymerisation

High intensity ultrasound has been applied to two classes of step-growth polymerisation. The ring-opening polymerisation of cyclic lactones to polyesters was accelerated under 20 kHz ultrasound but, in the case of delta-valerolactone, sonication also promoted a depolymerisation reaction so that the molecular weight fell during later stages of the reaction. Sonication was also applied to the preparation of polyurethanes from a number of diisocyanates and diols. In all cases, the sonochemical reactions proceeded faster in the early stages and led to higher molecular weight polymers. The effect of changing the ultrasound intensity is discussed and some speculation as to the mechanisms of the reaction enhancements is given.     

Supercritical isopropanol as a reducing agent for inorganic oxides

Preparative methods for the reduction of simple and complex metal oxides by supercritical isopropanol (SCI) were developed. Procedures for effective work with SCI under usual laboratory conditions were suggested. Optimum reaction conditions (temperature and pressure) and reagent ratios for reactions between SCI and metal oxides were found. Disperse oxides coated by fine-dispersity metals that could be used as catalysts were prepared. Simple methods for obtaining metal nanoparticles by the reduction in situ of metal oxide nanoparticles stabilized in polyethylene and synthetic silica (opal) matrices with SCI were developed.     

Sonochemistry and sonoprocessing: the link,the trends and (probably) the future

Traditionally the community of scientists involved with ultrasound has been divided broadly into those who use it as a measurement device with no effect on the medium (high frequency low power ultrasound e.g. non-destructive testing) and those who use it to produce physical or chemical effects in a medium (higher power low frequency ultrasound e.g. sonochemistry). Divisions also exist within the broad spectrum of those involved with the latter. In the early days of sonochemistry this did not prove to be a major problem, the subject was new and the field was expanding within the chemistry community. However at a point some years ago Jean-Louis Luche made the very important observation that sonochemistry applications could be subdivided into reactions which were the result of "true" and "false" effects [Synthetic Organic Chemistry by J.-L. Luche, 1998, p. 376]. Essentially these terms referred to real chemical effects induced by cavitation and those effects that could be mainly ascribed to the mechanical impact of bubble collapse. These mechanical effects have not held the interest of synthetic chemists as much as the so-called true ones but nevertheless they are certainly important in areas such as processing. In this paper I will attempt to show that there are links that can be made across many of the ultrasound "disciplines" and that these links can only serve to strengthen research in the general area of power ultrasound. If research on power ultrasound is strong then research into "pure" sonochemistry will also flourish and "false" sonochemistry will be born again as a significant research area.     

Ultrasound-enhanced reactivity of calcium in the reduction of aromatic hydrocarbons

Reductions of aromatic hydrocarbons by calcium in ethylenediamine-n-alkylamine mixture were investigated under ultrasonic conditions. Using an ultrasonic probe, with naphthalene as test molecule, it has been demonstrated that under ultrasonic action the reactions proceed faster (x10) and require a lower metal quantity (0.5) than the reactions conducted with an efficient mechanical stirrer. In addition, at ambient temperature and depending on the specific alcohol addition, selective naphthalene reduction can be performed using ultrasound. 1,2-Dihydronaphthalene (88% yield) results from the reaction in the presence of 2-propanol, and 1,4,5,8-tetrahydronaphthalene (88% yield) is obtained with tert-butanol. Investigation of the metal surface points out the characteristics of the calcium ultrasonic activation. The procedure was efficiently tested with several aromatic hydrocarbons.     

Using sonochemistry for the fabrication of nanomaterials

One of the reasons for the huge interest in nanomaterials originated because of the prohibitive price that commercial companies have to pay for introducing new materials into the market. Nanotechnology enables these companies to obtain new properties using old and recognized materials by just reducing their particle size. For these known materials no government approval has to be obtained. Thus, the interest in nanomaterials has led to the development of many synthetic methods for their fabrication. Sonochemistry is one of the earliest techniques used to prepare nanosized compounds. Suslick, in his original work, sonicated Fe(CO)5 either as a neat liquid or in a decalin solution and obtained 10-20 nm size amorphous iron nanoparticles. A literature search that was conducted by crossing Sono* and Nanop* has found that this area is expanding almost exponentially. It started with two papers published in 1994, two in 1995, and increased to 59 papers in 2002. A few authors have already reviewed the fields of Sono and Nano. It should be mentioned that in 1996, Suslick et al. published an early review on the nanostructured materials generated by ultrasound radiation. Suslick and Price have also reviewed the application of ultrasound to materials science. This review dealt with nanomaterials, but was not directed specifically to this topic. The review concentrated only on the sonochemistry of transition metal carbonyls and catalytic reactions that involve the nanoparticles resulting from their sonochemical decomposition. Grieser and Ashokkumar have also written a review on a similar topic. A former coworker, Zhu, has recently submitted for publication a review article entitled "Novel Methods for Chemical Preparation of Metal Chalcogenide Nanoparticles" in which he reviews three synthetic methods (sonochemistry, sonoelectrochemistry, and microwave heating) and their application in the synthesis of nanosized metal chalcogenides. Although still unpublished, I myself have recently written a review discussing novel methods (sonochemistry, microwave heating, and sonoelectrochemistry) for making nanosized materials. The current review will: (1) Present the four main advantages that sonochemistry has over other methods related to materials science and nanochemistry; (2) concentrate on the more recent (2003) literature that was not reviewed in the previously-mentioned reviews, and (3) focus on a specific question, such as what is the typical shape of products obtained in sonochemistry? This review will not survey the literature related to sonoelectrochemistry.     

Calculation of the probability for ionic association and dissociation reactions by molecular dynamics and umbrella sampling

Investigating chemical reactions by computational techniques and finding new ways to study these reactions is an important necessity in the fields of chemistry, chemical engineering and biology. In this study, we have presented a new procedure for studying the interactions between divalent metal ions and carboxylates by using umbrella sampling. In some cases, it is more convenient to use variable coordinate reaction probabilities instead of potential energy or free energy curves, which in general are more widely used and available in the literature. Particularly, for practical purposes in building multi-scale models it could be more convenient to use the probability of reaction as a function of the separation distance between two carboxylate moieties when they are simultaneously associated to a metal ion. In this work, we have modelled the interactions between two carboxylates (propanoate ions) and divalent metal ions (calcium or magnesium) in order to obtain the probability of reaction as a function of the separation distance between the two carboxylates. By calculating the probability, it also became apparent that in the system containing calcium, the carboxylates have higher probability of reaction compared to the system containing magnesium. Furthermore, the presented probability could be also used for other multi-scale modelling purposes where these interactions are of main importance. The proposed procedure could also have application in other systems of interest.     

Real time chemical dynamics at surfaces

It is a major goal in surface science to make movies of molecules on surfaces, in which the reaction of the molecules on the surface can be followed on a femtosecond time scale, with sub-nanometer resolution. By moving the actors (the molecules) to precisely determined positions on the stage (the surface) at some well-defined moment in time, and subsequently making a space- and time-resolved documentary of what happens next, we would be able to understand the reactive interactions between molecules on surfaces in the greatest possible detail. This would enable us to set the stage and bring together the actors in such a way as to produce the chemical outcomes our society needs, by improving existing catalysts and designing novel catalysts, and by engineering novel reactions on surfaces. Any future director of such movies needs to know which techniques (i.e., which theoretical and experimental methods) hold promise for movie making, what has been done with these techniques, and what can be done with appropriate extensions. The methods we discuss are: (i) the time-dependent wave packet method, which is a theoretical method for simulating molecule–surface reactions with sub-nanometer resolution on a femtosecond time scale, (ii) molecular beam experiments, which allow detailed investigation of the molecule–surface interaction at a molecular level, and (iii) time-resolved laser pump–probe experiments, which allow reactions to be studied with femtosecond resolution. In particular, we discuss (i) theoretical studies of the dissociation reaction of hydrogen on metal surfaces, the reactive system presently understood at the greatest level of detail, (ii) the reactive and non-reactive scattering of heavy diatomics (NO,CO) from metal surfaces, and (iii) the competition between reaction of coadsorbed CO with O and desorption of CO, again on a metal surface. We examine possibilities to extend these methods to make movies at the desired level of detail. We also discuss which reactions are likely to provide good material for plots of movies that will be exciting for future generations of surface scientists.     

Sonochemical effects on free phenolic acids under ultrasound treatment in a model system

Sonochemical effects on seven free phenolic acids under ultrasound treatment in a model system have been investigated. The degradation products have also been tentatively identified by FTIR and HPLC-UV-ESIMS. Five phenolic acids (protocatechuic acid, p-hydroxybenzoic acid, vanillic acid, p-coumaric acid, and ferulic acid) proved to be stable, while two others (caffeic acid and sinapic acid) were degraded under ultrasound treatment. The nature of the solvent and the temperature has been identified as important factors in determining the degradation reaction. Liquid height, ultrasonic intensity, and duty cycle of the ultrasound exposure affected only the degradation rate and did not change the nature of the degradation. The degradation rates of caffeic acid and sinapic acid decreased with increasing temperature. The degradation kinetics of these two acids under ultrasound conformed to zeroth-order reactions at ?5 to 25 °C. Both decomposition and polymerization reactions occurred when caffeic acid and sinapic acid were subjected to ultrasound. Degradation products, such as the corresponding decarboxylation products and their dimers, have been tentatively identified.     

Comparison of the electrochemical behaviour of SnO2 and PbO2 negative electrodes for lithium ion batteries

In this paper we report our structural and electrochemical investigations of tin dioxide and lead dioxide electrodes in order to highlight the difference observed between them. The electrochemical reactions of these two oxides are known: the reduction of the metal oxide and the reversible formation/decomposition of the lithium-metal alloys. The reversible capacity of these systems is based on the alloy formation. The first reaction is supposedly irreversible (formation of Li₂O), but the X-ray diffraction analysis and especially¹¹⁹Sn Mössbauer spectrometry show a possible re-oxidation of the metal particles in the case of tin dioxide electrodes. However, this reaction is not fully reversible and occurs at a high potential vs. Li. For lead dioxide electrodes, the re-oxidation of the metal particles seems more difficult in spite of the similar structure of both oxides.     

Effect of surface acoustic waves on activity in heterogeneous catalysis

A synopsis of the recent developments in acoustically influencing and controlling gas-surface interactions is presented. The cleaning effect of ultrasound and its surface activation play an important role for the sonochemical enhancement of reactivity in chemical processes involving solid and liquid phases. So far, there have only been a few studies on the effects of surface acoustic waves on surface chemical reactions under high-vacuum conditions by the application of piezoelectric surface acoustic wave transducers. Very recently, metal films deposited between InterDigital Transducer (IDT) electrodes on a LiNbO₃ substrate have shown a significant inerease in catalytic activity during surface acoustic excitation and Edge-Bonded Transducers (EBT) with a metal single crystal as a substrate have been used to acoustically influence the rate in the oscillatory reaction for CO oxidation. Tunable narrowband surface acoustic excitation is anticipated to be an efficient route to control catalytic processes, and in our work this approach is being used to investigate the physical basis of this process.     

Greener organic synthetic methods: Sonochemistry and heterogeneous catalysis promoted multicomponent reactions

Ultrasound is an essential technique to improve organic synthesis from the point of view of green chemistry, as it can promote better yields and selectivities, in addition to shorter reaction times when compared to the conventional methods. Heterogeneous catalysis is another pillar of sustainable chemistry being the recycling and reuse of the catalysts one of its great advantage. In the other hand, multicomponent reactions provide the synthesis of structurally diverse compounds, in a one-pot fashion, without isolation and purification of intermediates. Thus, the combination of these protocols has proved to be a powerful tool to obtain biologically active organic compounds with lower costs, time and energy consumption. Herein, we provide a comprehensive overview of advances on methods of organic synthesis that have been reported over the past ten years with focus on ultrasound-assisted multicomponent reactions under heterogeneous catalysis. In particular, we present pharmacologically important N- and O-heterocyclic compounds, considering their synthetic methods using green solvents, and catalyst recycling.     

C-S Activation of CS2 by Nb+ in Gas Phase

以Nb⁺与CS₂反应作为第二前过渡金属离子与CS₂反应生成金属硫化物离子和CS的范例体系. 采用密度泛函UB3LYP方法,对于Nb⁺采用Stuttgart赝势基组,对于C和S采用6-311＋G(2d)基组,计算研究了Nb⁺在基态和激发态时与CS_{2气相反应的机理. 全参数优化了反应势能面上各驻点的几何构型,并且用频率分析方法和内禀反应坐标方法对过渡态进行了验证. 结果表明Nb⁺与CS2的反应是插入-消去反应,在反应过程中会发生系间窜越,并且找到了两个势能面的能量最低交叉点.}     

Sonochemical cycloadditions in ionic liquids. Lessons from model cases involving common dienes and carbonyl dienophiles

This contribution describes a series of sonochemical cycloadditions involving either cyclopentadiene or 1,3-cyclohexadiene with carbonyl dienophiles in an imidazolium-based ionic liquid as reaction medium. In general, ultrasound does effectively improve these processes in terms of higher yields and/or shorter reaction times when compared with the corresponding silent reactions. Stereoselectivities, however, remain practically unaffected by sonication. The role of ionic liquids under ultrasonic activation is also discussed.     

超声辐照对酶促反应影响的研究进展

综述了超声辐照对于酶活性和酶催化反应的影响,以及各种超声参数对反应的影响,并展望了超声辐照在酶促反应中的应用前景。     

Reactions of oxygen-containing molecules on transition metal carbides: Surface science insight into potential applications in catalysis and electrocatalysis

Historically the interest in the catalytic properties of transition metal carbides (TMC) has been inspired by their “Pt-like” properties in the transformation reactions of hydrocarbon molecules. Recent studies, however, have revealed that the reaction pathways of oxygen-containing molecules are significantly different between TMCs and Pt-group metals. Nonetheless, TMCs demonstrate intriguing catalytic properties toward oxygen-containing molecules, either as the catalyst or as the catalytically active substrate to support metal catalysts, in several important catalytic and electrocatalytic applications, including water electrolysis, alcohol electrooxidation, biomass conversion, and water gas shift reactions. In the current review we provide a summary of theoretical and experimental studies of the interaction of TMC surfaces with oxygen-containing molecules, including both inorganic (O₂, H₂O, CO and CO₂) and organic (alcohols, aldehydes, acids and esters) molecules. We will discuss the general trends in the reaction pathways, as well as future research opportunities in surface science studies that would facilitate the utilization of TMCs as catalysts and electrocatalysts.     

Ethoxylation of p-chloronitrobenzene using phase-transfer catalysts by ultrasound irradiation: a kinetic study

Ethoxy-4-nitrobenzene was synthesized by the reaction of 4-chloronitrobenzene with potassium ethoxide in a homogeneous system using benzyltriethylammonium chloride (QCl) as a phase-transfer catalyst at 50 degrees C under ultrasound irradiation conditions. The use of phase-transfer catalysts and ultrasound has been compared and demonstrated in this nucleophilic substitution reactions. The kinetics of the reaction depends on the effect of amount of catalyst, quaternary ammonium salts, agitation speed, amount of potassium hydroxide, amount of ethanol, temperature and the frequency of the ultrasound waves on the conversion of the reaction.     

Influence of ultrasound on mixing on the molecular scale for water and viscous liquids

Micromixing has a decisive action on the yield of fast reactions such as combustions, polymerizations, neutralizations and precipitations. The aim of this study was to test the possible effect of ultrasound on micromixing, through the phenomenon of acoustic cavitation. To evaluate the local state of micromixing, we used a system of parallel competing reactions involving the Dushman reaction between iodide and iodate, coupled with a neutralization. At first, we studied the effects of the acoustic frequency on micromixing (20-540-1000 kHz). It was found that micromixing through acoustic cavitation and acoustic streaming was more important at 20 kHz than at 540 kHz or 1 MHz. At high and low frequency, it was shown that the injection must be located near the ultrasonic emitter. The influence of the acoustic intensity proved to be predominant mostly for low intensities; for an acoustic intensity of 10 W cm(-2), a characteristic micromixing time of about 0.015 s has been obtained. Viscous media have been studied and experiments showed that micromixing is more difficult to achieve than in aqueous media, but that ultrasound may be as effective as classic stirring.