A "counter-charge layer in generalized solvents" framework for electrical double layers in neat and hybrid ionic liquid electrolytes

Room-temperature ionic liquids (RTILs) have received significant attention as electrolytes due to a number of attractive properties such as their wide electrochemical windows. Since electrical double layers (EDLs) are the cornerstone for the applications of RTILs in electrochemical systems such as supercapacitors, it is important to develop an understanding of the structure-capacitance relationships for the EDLs of these systems. Here we present a theoretical framework termed "counter-charge layer in generalized solvents" (CGS) for describing the structure and capacitance of the EDLs in neat RTILs and in RTILs mixed with different mass fractions of organic solvents. Within this framework, an EDL is made up of a counter-charge layer exactly balancing the electrode charge, and of polarized generalized solvents (in the form of layers of ion pairs, each of which has a zero net charge but has a dipole moment--the ion pairs thus can be considered as a generalized solvent) consisting of all RTILs inside the system except the counter-ions in the counter-charge layer, together with solvent molecules if present. Several key features of the EDLs that originate from the strong ion-ion correlation in RTILs, e.g., overscreening of electrode charge and alternating layering of counter-ions and co-ions, are explicitly incorporated into this framework. We show that the dielectric screening in EDLs is governed predominantly by the polarization of generalized solvents (or ion pairs) in the EDL, and the capacitance of an EDL can be related to its microstructure with few a priori assumptions or simplifications. We use this framework to understand two interesting phenomena observed in molecular dynamics simulations of EDLs in a neat IL of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF(4)]) and in a mixture of [BMIM][BF(4)] and acetonitrile (ACN): (1) the capacitance of the EDLs in the [BMIM][BF(4)]/ACN mixture increases only slightly when the mass fraction of ACN in the mixture increases from zero to 50% although the dielectric constant of bulk ACN is more than two times higher than that of neat [BMIM][BF(4)]; (2) the capacitance of EDLs near negative electrodes (with BMIM(+) ion as the counter-ion) is smaller than that near positive electrodes (with BF(4)(-) as the counter-ion) although the closest approaches of both ions to the electrode surface are nearly identical.     

Characterization of phosphonium ionic liquids through a linear solvation energy relationship and their use as GLC stationary phases

In recent years, room temperature ionic liquids (RTILs) have proven to be of great interest to analytical chemists. One important development is the use of RTILs as highly thermally stable GLC stationary phases. To date, nearly all of the RTIL stationary phases have been nitrogen-based (ammonium, pyrrolidinium, imidazolium, etc.). In this work, eight new monocationic and three new dicationic phosphonium-based RTILs are used as gas–liquid chromatography (GLC) stationary phases. Inverse gas chromatography (GC) analyses are used to study the solvation properties of the phosphonium RTILs through a linear solvation energy model. This model describes the multiple solvation interactions that the phosphonium RTILs can undergo and is useful in understanding their properties. In addition, the phosphonium-based stationary phases are used to separate complex analyte mixtures by GLC. Results show that the small differences in the solvent properties of the phosphonium ILs compared with ammonium-based ILs will allow for different and unique separation selectivities. Also, the phosphonium-based stationary phases tend to be more thermally stable than nitrogen-based ILs, which is an advantage in many GC applications.     

Effect of Cosolvent on Bulk and Interfacial Characteristics of Imidazolium Based Room Temperature Ionic Liquids

Here we report a systematic study on electrical conductivity and surface tension of various concentrated solutions of imidazolium based room temperature ionic liquids (RTILs), viz. 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][ $\hbox {PF}_{6}$ ]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][ $\hbox {BF}_{4}$ ]) in the cosolvents methanol and acetonitrile at 298.15 K. The aim of the investigations was to explore the impact of cosolvents on bulk and interfacial characteristics of imidazolium based RTILs. It was observed that both methanol and acetonitrile mix non-ideally with and enhance the transport parameters of the imidazolium based RTILs. An interesting outcome of the presented work is that the investigated RTILs retain their inherent structural characteristics up to a high dilution limit with cosolvent, and this limit is higher in acetonitrile than in methanol as cosolvent. The findings establish that, in comparison to methanol, acetonitrile is a better cosolvent that can be used for enhancing the transport parameters of imidazolium based RTILs for electrochemical and other applications. The results are explained in light of structure-composition-property relations and ion-ion and ion-cosolvent interactions.     

Analytical applications of room-temperature ionic liquids: a review of recent efforts

Room-temperature ionic liquids (RTILs) are solvents that may have great potential in chemical analysis. Recent surge in the number of publications/reports/books/monographs clearly indicate an increasing interest of scientific and engineering community toward these exciting and unique solvents. Consequently, a variety of analytical applications of RTILs have started to emerge. This review presents an account of some of the recent reports on RTILs in major subdisciplines of analytical chemistry. Specifically, recent literature representing the applications of RTILs in chromatography, extraction, electroanalytical chemistry, sensing, and spectrometry is reviewed. With a rapid growth in the number of publications on analytical applications of RTILs, it appears that in the near future these neoteric solvents are definitely going to be a permanent feature in analytical chemistry.     

Characterizing ionic liquids on the basis of multiple solvation interactions

Room-temperature ionic liquids (RTILs) are useful in many chemical applications. Recent publications have attempted to determine the polarity of RTILs using empirical solvent polarity scales. The results have indicated that most RTILs have similar polarities. Nevertheless, RTILs are capable of behaving quite differently when used as solvents in organic synthesis, matrixes in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, liquid-liquid extraction, and as stationary phases in gas chromatography. The work presented in this study uses a linear free energy approach to characterize 17 RTILs on the basis of their distinct multiple solvation interactions with probe solute molecules. This model provides data that can be used to help identify the interactions and properties that are important for specific chemical applications.     

室温离子液体在分离科学研究中的新进展

室温离子液体作为一种重要的绿色溶剂,由于在金属离子、小分子有机物的萃取分离,气体吸附分离以及作为液相和气相色谱固定相等许多分离过程中体现出高分离效率和高选择性的特点,正在成为分离科学研究的前沿领域.着重总结了从2003—2006年的室温离子液体在分离科学领域中的新进展,并对其应用领域和发展前景做了展望.提出进一步加强离子液体的功能化和固定化技术及其在分离科学中的应用基础研究,探索离子液体有效的回收和再循环利用的新方法,是离子液体今后在分离科学研究中的一系列重要内容.     

Understanding the wettability of nanometer-thick room temperature ionic liquids (RTILs) on solid surfaces

Many important applications of room temperature ionic liquids(RTILs), e.g., lubrication, energy storage and catalysis, involve RTILs confined to solid surfaces. In order to optimize the performance, it is critical to understand the wettability of nanometer-thick RTILs on solid surfaces. In this review, the recent progress in this filed is presented. First, the macroscopic wettability of RTILs on solids will be discussed briefly.Afterwards, the wetting of nanometer-thick RTILs will be discussed with the emphasis on RTIL/mica and RTIL/graphite interfaces since mica and graphite not only are mostly studied but also have important real-life applications. For RTIL/mica interface, the extended layering that promotes the wetting has been extensively reported and it is generally accepted that the electrostatic interaction at the RTIL/mica interface is the key. However, recent works from others and us highlight the unexpected effect of water:Water enables ion exchange between K+and the cations of RTILs on the mica surface and thus triggers the ordered packing of cations/anions in RTILs, resulting in extended layering. Different from mica, there is no electrical charge on the graphite surface. Interestingly, previous reports showed inconsistent results on the wettability of RTILs on graphite. Recent research from others and us suggested that π-π~+stacking between sp~2 carbon and the imidazoliumcation in the RTILs is the key to the extended layering and enhanced wettability of RTILs. Lastly, the future research directions will be briefly discussed.     

Transport properties of room-temperature ionic liquids from classical molecular dynamics

Room-temperature ionic liquids (RTILs) have attracted much attention in the scientific community in the past decade due their novel and highly customizable properties. Nonetheless, their high viscosities pose serious limitations to the use of RTILs in practical applications. To elucidate some of the physical aspects behind transport properties of RTILs, extensive classical molecular dynamics calculations are reported. Here, in particular, bulk viscosities and ionic conductivities of butyl-methyl-imidazole based RTILs are presented over a wide range of temperatures. The dependence of the properties of the liquids on simulation parameters, e.g., system-size effects or the choice of the interaction potential, is analyzed in detail.     

Room Temperature Ionic Liquids: Their Cohesive Energies,Solubility Parameters and Solubilities in Them

The cohesive energies of room temperature ionic liquids, RTILs, at the reference temperature T _ref = 298.15 K have been obtained from their molar enthalpies of vaporization. They are ce(298) = ?_v H°(298) ? 298.15R, on regarding the vapors as single ion-paired molecules. The cohesive energy densities, ced = ce/V = δ _H ² are the squares of the (Hildebrand) solubility parameters of the RTIL, which are presented for many RTILs. The solubilities of a variety of solutes in RTILs are discussed in relation to the solubility parameters. It turned out that the δ _H values of RTILs, obtained from the enthalpies of vaporization, may be used for empirical correlations, but are not able to predict the solubilities of solutes in RTILs.     

离子液体在无机纳米材料合成上的应用

室温离子液体作为一种新型的绿色环保溶剂,在无机纳米材料合成中的应用引起越来越多研究者的注意。目前,已经利用室温离子液体合成出了纳米多孔材料、纳米粒子和中空球、一维纳米材料等。与传统的溶剂相比,离子液体在合成过程中体现出了很多优势,且合成的产物也不同,为无机纳米材料的合成开辟了一条新途径。本文就近年来国内外相关研究进展,对离子液体在无机纳米材料合成中的应用进行综述。     

Effects of room-temperature ionic liquids on the chemical vapor generation of gold: Mechanism and analytical application

To get insight into the mechanism of the effect of room-temperature ionic liquids (RTILs) on the chemical vapor generation (CVG) of noble metals, gold was taken as a model element, and eight RTILs were examined. All the RTILs resulted in 3-24 times improvement in sensitivity for Au, depending on their nature. For the RTILs with identical anion, the RTILs with the cations of short chain exhibited better enhancement effect than those with long alkyl chain length or complex branch chain. For the RTILs with identical cation, the RTILs with Br⁻ gave the best enhancement effect. The formation of ion pairs between the cation of RTILs and the anion species of gold via electrostatic interaction, and/or the substitution of the Cl⁻ in the anion species of gold by the anion of RTILs likely enabled a more effective CVG reaction to occur. The RTILs also facilitated the generation of small bubbles and provided an electrostatic stabilization to protect the unstable volatile gold species and to help fast isolation of volatile gold species from the reaction mixture. 1-Butyl-3-methylimidazolium tetrafluoroborate [C₄mim]Br gave the best improvement in the sensitivity (24 times) among the RTILs studied, and also reduced the interferences from common transition and other noble metals. Based on the enhancement effect of [C₄mim]Br, a novel flow injection-CVG-atomic fluorescence spectrometric method with a detection limit (3s) of 1.9 μg L⁻¹ and a precision of 3.1% (50 μg L⁻¹, RSD, n = 11) was developed for the determination of trace gold in geological samples.     

Organocatalysts for the controlled "immortal" ring-opening polymerization of six-membered-ring cyclic carbonates: a metal-free, green process

Six-membered cyclic carbonates, namely trimethylene carbonate (TMC), 3,3-dimethoxytrimethylene carbonate (DMTMC) and 3-benzyloxytrimethylene carbonate (BTMC), undergo controlled "immortal" ring-opening polymerization (iROP) under mild conditions (bulk, 60-150 °C), by using organocatalysts, including an amine [4-N,N-dimethylaminopyridine (DMAP)], a guanidine [1,5,7-triazabicyclo-[4.4.0]dec-5-ene (TBD)], or a phosphazene [2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP)], in the presence of an alcohol [benzyl alcohol (BnOH), 1,3-propanediol (PPD), glycerol (GLY)] that acts as both a co-initiator and a chain-transfer agent. Remarkably, such organocatalysts remain highly active in the iROP of technical-grade, unpurified TMC. Under optimized conditions, as much as 100,000 equivalents of TMC were fully converted by as little as 10 ppm of BEMP with the simultaneous growth of as many as 200 polymer chains, allowing the preparation of high molar mass poly(trimethylene carbonate)s (up to 45,800 g mol(-1)). These catalyst systems enable among the highest activities (TOF=55,800 h(-1)) and productivities (TON=95,000) ever reported for the ROP of TMC.     

New innovations in ionic liquid–based miniaturised amperometric gas sensors

Gas detection is an essential part of everyday life; for some applications, using sensors for toxic and hazardous gases can literally mean the difference between life and death. In this minireview, recent progress in amperometric gas sensing using miniaturised electrodes and devices is described. The focus is on the use of nonvolatile room-temperature ionic liquids (RTILs) as electrolytes, which possess inherent advantages such as wide electrochemical windows, high thermal and chemical stability, intrinsic conductivity and good solvating properties. Various different gases, electrodes and RTILs have been investigated in the strive towards new materials for improved gas sensors. The most recent developments using porous membrane electrodes, planar devices (e.g. screen-printed, thin-film, microarray and interdigitated electrodes) and the modification of these surfaces for improved sensitivity are described. RTILs have great potential to be used as electrolytes in amperometric gas sensors, with improved lifespan of the sensor in hot/dry environments and allowing miniaturisation of devices. However, it is clear that more understanding of their long-term operation and utility in real environments (e.g. background air, varying temperatures and humidity levels) is needed before their realisation in successful commercial devices.     

Evolution of pyrrolidine-type asymmetric organocatalysts by "click" chemistry

Click chemistry has been employed to construct a library of the pyrrolidine-type asymmetric organocatalysts. The clicked organocatalysts were evaluated in asymmetric Michael addition of ketones to nitroolefins, showing good catalytic activity and stereoselectivity (up to 100% yield, syn:anti = 99:1, 96% ee).     

Bifunctional iminophosphorane superbases: Potent organocatalysts for enantio- and diastereoselective Michael addition reactions

Bifunctional iminophosphorane (BIMP) organocatalysts catalyze the enantio- and diastereoselective Michael additions of high pK_a cyclic malonamate ester pro-nucleophiles to nitroalkenes with reactivity profiles of up to 3 orders of magnitude greater than tertiary amine bifunctional Brønsted base/(thio)urea organocatalysts. The unrivalled performance of the BIMPs allows reaction times of challenging reactions to be slashed from weeks to minutes and has enabled new flow chemistry applications using polystyrene-supported versions contained within a flow reactor.     

高效多羟胺有机催化剂选择性催化分子氧氧化研究进展

基于氧气(空气)为氧源的选择性催化分子氧氧化技术在制备含氧精细化学品或食品添加剂与医药等的重要中间体方面一直受到科学界的广泛关注.由于碳氢化合物中碳氢键的反应惰性和分子氧的自旋禁阻作用,设计与开发高效催化剂或催化体系以实现碳氢化合物的选择性氧化是当前催化氧化领域的研究热点.在已发展的过渡金属盐、仿生催化剂、有机催化剂、酶、碳材料和卤化物等众多催化剂中,以N-羟基邻苯二甲酰亚胺(NHPI)为代表的羟胺有机催化剂由于在温和条件下的卓越催化性能而备受瞩目.尽管基于羟胺有机催化剂的催化体系具有良好的工业应用前景,但仍存在催化剂高温易分解、使用量较大和可回收性较差等缺点.近年来,许多实验与理论工作围绕改进这些缺点展开,设计了一系列羟胺有机催化剂及其协同催化体系,如在NHPI结构中修饰疏水链基团、吸电子基团、N-烷氧基团和离子液体,或固载金属-有机框架材料、无机物和聚合物,或组合光催化剂.尽管已有大量综述总结了相关研究进展,但尚未见到有关近年来发展的多羟胺有机催化剂及其高效催化氧化性能的综述报道.本文综述了近15年来多羟胺有机催化剂选择性催化分子氧氧化碳氢化合物的研究进展.首先,简要概述了N,N-二羟基邻苯二甲酰亚胺(NDHPI)和N,N',N"-三羟基异氰基尿酸(THICA)两种多羟胺有机催化剂的合成方法,系统介绍了它们在各类碳氢化合物氧化中的高效催化性能,并与普遍应用的NHPI的催化性能进行对比.由于NDHPI与THICA具有多羟胺的独特结构,它们只需要比NHPI更少的用量便可获得比NHPI更高的催化氧化效率,可以直接利用高压空气实现对碳氢化合物的选择性催化氧化,并且在较高温度下依然具有较好的催化效果.在此基础上,介绍了联系实验与理论之间的重要工作,总结了多羟胺有机催化剂的合理设计策略.理论计算研究揭示了NDHPI与THICA的催化性能优于NHPI的主要原因是具有类似于吸电子效应的多羟胺与多氮氧自由基结构能显著增强催化剂的夺氢活性.通过对NDHPI结构的进一步修饰和夺氢活性研究,提出了该类催化剂的合理设计策略:在芳环体系中增加共轭的羟胺基团数量,或在NDHPI苯环中掺杂N原子或引入离子对基团都能提高催化剂的夺氢活性;增大芳环共轭体系对催化剂的夺氢活性影响较小,但该活性仍高于NHPI.这也为基于碳材料的非均相共轭多羟胺有机催化剂的开发提供了理论依据.最后,结合羟胺有机催化剂的发展现状和上述设计策略,设计了基于金属卟啉/席夫碱等仿生催化剂、(含离子对结构)聚合物、非均相碳材料和多N-烷氧基团等几种具有潜在发展前景的模型多羟胺有机催化剂,分别讨论了这些催化剂的优点和局限性,并展望了多羟胺有机催化剂的可能应用及其在催化氧化过程中仍需系统研究的方向.     

A Facile Preparation of New Chiral Diamines/Amino-acids (Alcohols) Derived from L-Proline

Living systems use enzymes to catalyze stereoselective reactions with very high fidelity. Since proline was demonstrated as the simplest "enzyme" that mimics type Ⅰ aldolase to catalyze aldol reaction,[1～3] it has attracted much attention in chemistry and other relative fields to design and synthesize highly efficient chemzyme or organocatalysts that can activate normally unreactive substances to useful asymmetric catalytic transformations.     

有机小分子催化的不对称Strecker反应研究进展

有机小分子催化的不对称合成反应是目前研究最为活跃的领域之一. 不对称Strecker反应是合成光学活性α-氨基酸衍生物的有效手段. 目前报道的催化不对称Strecker反应的有机催化剂主要有手性胍类、手性(硫)脲衍生物、氮-氧偶极化合物、手性Brønsted酸等, 取得了良好的催化活性和对映选择性. 对各类有机小分子催化剂在有机催化不对称Strecker反应中的应用研究进展, 以及催化剂结构与反应条件对催化活性和不对称诱导作用的影响进行了简要评述.     

Highly diastereo- and enantioselective direct aldol reactions promoted by water-compatible organocatalysts bearing a pyrrolidinyl-camphor structural scaffold

Efficient synthetic routes have been developed for the synthesis of a series of pyrrolidinyl-camphor containing organocatalysts (1-10). Structural modifications were made by varying the stereo- and electronic properties of the camphor scaffold and the aromatic substituents. These readily tunable and amphiphilic organocatalysts were evaluated for the direct asymmetric aldol reaction of various aromatic aldehydes and cyclohexanone either in organic solvents or in the presence of water. The aldol reaction proceeded smoothly with excellent chemical yields (up to 99%), enantioselectivities (up to 99% ee), and anti-diastereoselectivities (up to 99:1) with a catalytical amount of the bifunctional organocatalysts (20 mol %) under optimal reaction conditions. Mechanistic transition models are proposed and the stereochemical bias of the asymmetric aldol reaction is presented.     

Strategies for "wiring" redox-active proteins to electrodes and applications in biosensors, biofuel cells, and nanotechnology

In this tutorial review the basic approaches to establish electrochemical communication between redox-active proteins and electrodes are elucidated and examples for applications in electrochemical biosensors, biofuel cells and nanotechnology are presented. The early stage of protein electrochemistry is described giving a short overview over electron transfer (ET) between electrodes and proteins, followed by a brief introduction into experimental procedures for studying proteins at electrodes and possible applications arising thereof. The article starts with discussing the electrochemistry of cytochrome c, the first redox-active protein, for which direct reversible ET was obtained, under diffusion controlled conditions and after adsorption to electrodes. Next, examples for the electrochemical study of redox enzymes adsorbed on electrodes and modes of immobilization are discussed. Shortly the experimental approach for investigating redox-active proteins adsorbed on electrodes is outlined. Possible applications of redox enzymes in electrochemical biosensors and biofuel cells working by direct ET (DET) and mediated ET (MET) are presented. Furthermore, the reconstitution of redox active proteins at electrodes using molecular wire-like units in order to "wire" the proteins to the electrode surface and possible applications in nanotechnology are discussed.