Electroanalysis of Neutral Precursors in Protic Ionic Liquids and Synthesis of High-Ionicity Ionic Liquids

Phenylpropyl Guanidinium Magnetic Ionic Liquid for Green and Selective Extraction of RNA

A phenylpropyl guanidinium magnetic ionic liquid (PGMIL) was designed and prepared to extract RNA from complex samples. The properties of PGMIL were characterized by a vibrating sample magnetometer, Fourier transform infrared spectrometer, thermogravimetric analyzer, transmission electron microscope, and scanning electron microscope. Through single-factor analysis, the factors affecting the RNA extraction process, such as PGMIL volume, temperature, extraction time, and pH, were systematically investigated. The ability of PGMIL to selectively extract RNA was investigated by a NanoDrop. Under the optimized conditions, the extraction efficiency of RNA can reach 81.9 ± 1.9%. The proposed extraction method has been demonstrated with the extraction of RNA from a series of complex sample matrices, including a metal ion mixture and medicinal yeast. After extraction, the retained RNA could be readily recovered by simply using Tris-HCl buffer, with a recovery rate of 68.11 ± 2.45%. Regeneration studies have shown that the extraction efficiency of PGMIL did not change significantly after using 4 times. This study provides a green, rapid, and environmental friendly extraction method for the selective extraction of RNA.

Electrochemical Stability of Zinc and Copper Surfaces in Protic Ionic Liquids

Ionic liquids are versatile solvents that can be tailored through modification of the cation and anion species. Relatively little is known about the corrosive properties of protic ionic liquids. In this study, we have explored the corrosion of both zinc and copper within a series of protic ionic liquids consisting of alkylammonium or alkanolammonium cations paired with nitrate or carboxylate anions along with three aprotic imidazolium ionic liquids for comparison. Electrochemical studies revealed that the presence of either carboxylate anions or alkanolammonium cations tend to induce a cathodic shift in the corrosion potential. The effect in copper was similar in magnitude for both cations and anions, while the anion effect was slightly more pronounced than that of the cation in the case of zinc. For copper, the presence of carboxylate anions or alkanolammonium cations led to a notable decrease in corrosion current, whereas an increase was typically observed for zinc. The ionic liquid-metal surface interactions were further explored for select protic ionic liquids on copper using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to characterize the interface. From these studies, the oxide species formed on the surface were identified, and copper speciation at the surface linked to ionic liquid and potential dependent surface passivation. Density functional theory and ab initio molecular dynamics simulations revealed that the ethanolammonium cation was more strongly bound to the copper surface than the ethylammonium counterpart. In addition, the nitrate anion was more tightly bound than the formate anion. These likely lead to competing effects on the process of corrosion: the tightly bound cations act as a source of passivation, whereas the tightly bound anions facilitate the electrodissolution of the copper.

Guanidinium Hydrophobic Magnetic Ionic Liquid-Based Dispersive Droplet Extraction for the Selective Extraction of DNA

Six hydrophobic magnetic guanidinium ionic liquids (HMILs) were designed and prepared for the extraction of DNA. The physical and thermal properties of the HMILs were characterized using vibrating sample magnetometry, density meter, rotational rheometer, Karl Fischer moisture, Fourier transform infrared spectrometry, and thermogravimetric analysis. Single-stranded DNA and duplex DNA extracted by HMILs can be rapidly collected by a magnet. Three assisted extraction methods, including vortex extraction, mechanical shaking extraction, and ultrasonic extraction, were introduced to extract DNA with HMILs and the extraction efficiencies were evaluated using NanoDrop. Influencing factors of the DNA extraction were comprehensively evaluated, involving the HMIL volume, extraction time, pH, and extraction temperature. The HMIL-based extraction method can well extract DNA from complex matrices and Escherichia coli cell lysates.

Insights on the catalytic behaviour of sulfonic acid-functionalized ionic liquids (ILs) in transesterification reactions - voltammetric characterization of sulfonic task-specific ILs with bisulfate anions

This work shows for the first time the link between the amount of free sulfuric acid (as detected by cyclic voltammetry) and the activity of sulfonic-acid-functionalized ionic liquids (ILs) as acid catalysts for a transesterification reaction, and demonstrates that sulfonic acid groups, while are not directly involved in the catalysis, release the free acid during the reaction. Two imidazolic ILs with bisulfate as the counterion and their corresponding task-specific ILs (TSILs) that resulted from the addition of a sulfonic acid group inside the imidazolic-base structure were studied. The outstanding catalytic activity at room temperature of the TSILs 1-(4-sulfonic acid)-butyl-3-methylimidazolium bisulfate ([bsmim]HSO4) and 1-(4-sulfonic acid)-butyl-imidazolium bisulfate ([bsHim]HSO4) for the transesterification of p-nitrophenyl acetate with methanol was associated to the significant amounts of free sulfuric acid in equilibria with the ionic pairs. It was concluded that these TSILs function as reservoirs for releasing the free acid, which is the actual acid catalyst. In contrast, the corresponding non-sulfonic ILs supply very little amounts of free acid and consequently present low catalytic activities at room temperature, which in fact can be improved by increasing the reaction temperature up to 100 °C.

Understanding the Role of Protic Ionic Liquids (PILs) in Reactive Systems: Rational Selection of PILs for the Design of Green Synthesis Strategies for Allylic Amines and β-Amino Esters

The reactive behaviour of protic ionic liquids (PILs) has been shown to be governed not only by their chemical structures but also by their global compositions, which include the presence of free acids and bases at equilibrium with ionic pairs. Six PILs composed of primary, secondary, or tertiary alkyl ammonium cations with two couterions, nitrate or acetate, were tested in model reactions with unsaturated substrates. The free species that were naturally present in these liquids were identified by cyclic voltammetry. Only tributylammonium nitrate was found to be mostly composed just of the ionic pair; the other five PILs also contain variable amounts of free acid and amine. In reactive systems, these free species determine the products of the reaction. In particular, allylic amines and β-amino esters were obtained in good yields (91 and 75 %, respectively) by reaction of conjugated dienes and acrylates in the presence of PILs. By taking into account the actual composition of each PIL, it was possible to direct the reaction path towards a specific product with good yields, to ensure acid catalysis, to avoid polymerization of the substrate, and to promote phase transfer of products. These results establish some useful guidelines for the rational design of new PIL-based one-step synthetic strategies.

Key factor governing the physicochemical properties and extent of proton transfer in protic ionic liquids: ΔpKa or chemical structure?

A series of protic ionic liquids (PILs) are prepared by neutralisation of bis(trifluoromethanesulfonyl)amide acid (H[NTf₂]) with various amines, and the properties (especially thermal stability and ionicity) are compared with those of PILs from 1,8-diazabicyclo[5.4.0]-7-undecene (DBU) and various acids.

Engineering the Interface of Carbon Electrocatalysts at the Triple Point for Enhanced Oxygen Reduction Reaction

The aqueous oxygen reduction reaction (ORR) has recently received increased attention due to its critical role in clean and sustainable energy-generation technologies, such as proton exchange membranes (PEM) fuel cells, alkaline fuel cells and Zn-air batteries. The sluggish kinetics associated with ORR result from multistep electron-transfer process. The slow kinetics are partially related to the O₂ adsorption process onto the catalyst, which happens at the triple-phase boundary (TPB) of the electrocatalyst-electrolyte-oxygen interface. Hence, tremendous efforts have been devoted to improving the intrinsic properties of electrocatalysts such as active sites, electrical conductivity and porosity. Engineering the electrocatalyst's interfacial properties is another critical issue in ORR, however less described in the literature. The surface of the catalyst provides the microenvironment for the triple boundary interface reaction, which directly influences its electrocatalytic activity and the kinetics. This Minireview is a summary of the existing literature on manipulating the interfacial surface of non-precious metal catalysts at the triple point between the solid catalyst, the aqueous electrolyte and the O₂ gas with the aim of improving the ORR efficiency. Various approaches towards improving the wettability and nanostructuring the catalyst surface to boost the activity of the surface-active sites and provide improved stability are discussed.

Voltammetric Perspectives on the Acidity Scale and H+/H2 Process in Ionic Liquid Media

Nonhaloaluminate ionic liquids (ILs) have received considerable attention as alternatives to molecular solvents in diverse applications spanning the fields of physical, chemical, and biological science. One important and often overlooked aspect of the implementation of these designer solvents is how the properties of the IL formulation affect (electro)chemical reactivity. This aspect is emphasized herein, where recent (voltammetric) studies on the energetics of proton (H⁺) transfer and electrode reaction mechanisms of the H⁺/H₂ process in IL media are highlighted and discussed. The energetics of proton transfer, quantified using the p K_a (minus logarithm of acidity equilibrium constant, K_a) formalism, is strongly governed by the constituent IL anion, and to a lesser extent, the IL cation. The H⁺/H₂ process, a model inner-sphere reaction, also displays electrochemical characteristics that are strongly IL-dependent. Overall, these studies highlight the need to carry out systematic investigations to resolve IL structure and function relationships in order to realize the potential of these diverse and versatile solvents.