Yuanchao Pei

Recovery of amino acids by imidazolium based ionic liquids from aqueous media

In this paper, imidazolium based ionic liquids [C4mim][PF6], [C6mim][PF6], [C6mim][BF4] and [C8mim][BF4] were used as alternative solvents for the recovery of some amino acids (L-tryptophan, L-phenylalanine, L-tyrosine, L-leucine and D-valine) from aqueous media. The experimental results shown that logarithm of partition coefficients, log (PIL/W), of the amino acids correlate well with the hydrophobicity of the amino acids, indicating the importance of the hydrophobic effect of amino acids as a driving force for their partition into a particular ionic liquid. The partition coefficients are found to be strongly affected by pH of aqueous phases and the water solubility in ionic liquids. They decrease steeply with increasing pH in the range of pH < pK1, but increase with increasing solubility of water in ionic liquid phases. The higher extraction degree at low pHs has been interpreted by the strong electrostatic interactions between cationic form of the amino acids and anion of the ionic liquids. The importance of anionic nature and the alkyl chain length on the cation of ionic liquids have also been examined. It is noted that ionic liquid with BF4− anion has much higher extraction efficiency for the amino acids than those with PF6− anion because of the stronger effective charge in BF4−. It seems likely that there is no correlation between the partition coefficients of the amino acids and the polarity of the ionic liquids. Preliminary results indicated that [C6mim][BF4] and [C8mim][BF4] ionic liquids may be adapted to liquid-liquid recovery process of some amino acids from aqueous media, and L-tryptophan can be effectively separated from fermentation broth in a multiple step process using [C6mim][BF4] as an extractant.

Design of environmentally friendly ionic liquid aqueous two-phase systems for the efficient and high activity extraction of proteins

Ionic liquids (ILs) have numerous applications in industrial processes as a benign alternative to conventional volatile organic solvents. However, many of them are toxic to organisms and are poorly biodegradable. In this work, a series of environmentally friendly cholinium ILs have been designed and synthesized. It was found that these ILs could form aqueous two-phase systems (ATPSs) with polypropylene glycol 400 (PPG400) which is thermo-sensitive, non-toxic and biodegradable. In order to understand the phase formation processes and possible application of these ATPSs for extraction/separation of proteins, the binodal curves and tie lines of these ATPSs were measured at 25 °C, and the effects of anionic structure of the ionic liquids, nature of the proteins and difference in the concentration of top- and bottom-phases on the partitioning behavior of some typical proteins were investigated systematically. It was shown that bovine serum albumin (BSA), trypsin, papain and lysozyme could be enriched effectively into the ionic liquid-rich phase of the ATPSs, and single-step extraction efficiency could be as high as 86.4–99.9% under the optimized conditions. Furthermore, enzyme activity of the native trypsin in water and in aqueous ionic liquid solutions was determined by using N-a-benzoyl-L-arginine ethyl ester as a substrate, and activity increases to about 127% was observed after 13 months storage. In addition, PPG400 has been recovered simply by heating and reused in the next extraction processes. This avoids the non-sustainable issue of highly salty water produced in the application of the polyethylene glycol (PEG) + salt and ionic liquid + salt ATPSs.

Partitioning behavior of amino acids in aqueous two-phase systems formed by imidazolium ionic liquid and dipotassium hydrogen phosphate.

Partition coefficients of amino acids, including glycine, alanine, 2-aminobutyric acid, valine, leucine, threonine, methinoine, tryptophan and tyrosine, in [C(n)mim]Br (n=4, 6, 8)+K(2)HPO(4) aqueous two-phase systems (ATPSs) have been determined, and the relative hydrophobicity of the equilibrium phases in the ionic liquids-based aqueous two-phase systems has been characterized by the Gibbs energies of transfer for methylene group from the bottom salt-rich phase to the top ionic liquid-rich phase. Based on these results, factors affecting the partitioning behavior of the amino acids have been investigated. It is shown that partition coefficients of the amino acids increase with the increase of hydrophobicity of the amino acids and the ionic liquids, solution pH value, tie-line length of the ATPSs and temperature of the systems. The possible driving forces and the thermodynamic parameters for the partitioning of amino acids in the ionic liquids-based ATPSs have also been discussed.

Partitioning Behavior of Wastewater Proteins in Some Ionic Liquids-Based Aqueous Two-Phase Systems

The recovery of wastewater proteins is gaining more attention in environmental protection. In the present work, phase diagram of the [Cnmim]X (n = 4, 6, 8; X = Cl and Br) + K2HPO4 aqueous two-phase systems have been determined, and the aqueous two-phase systems have been used to remove bovine serum albumin (BSA), lysozyme, and hemoglobin from the simulated wastewater. The influence of pH value, the composition of the aqueous two-phase systems, and the temperature of the systems on the partitioning of the proteins has been studied. It has been found that 76–100% of the proteins could be extracted into the ionic liquid-rich phase in a single step partition. The partition coefficients of lysozyme slightly increases but those of BSA and hemoglobin decrease with increasing tie line length (TLL). The higher extraction efficiency of the proteins is achieved at the pH value close to their isoelectric point and under higher temperatures. The results indicate that the IL-based aqueous two-phase systems have the potential for the separation of wastewater proteins.

Tunable LCST-type phase behavior of [FeCl4]−-based ionic liquids in water

In this work, 16 kinds of [FeCl4]--based magnetic ionic liquids (ILs) with different cation structures have been designed and synthesized, and their structures are characterized by IR and Raman spectroscopy. Then the lower critical solution temperature (LCST)-type phase behavior of these magnetic ILs in water is investigated as a function of concentration. It is shown that cation structure, alkyl chain length and molar ratio of FeCl3/chloride IL have a significant influence on the LCST of the mixtures. The phase separation temperature can be tuned efficiently by these factors. Meanwhile, the LCST-type phase separation process is also investigated by dynamic light scattering. The results support the mechanism that the hydrogen bonds of the [FeCl4]- anion with water have been gradually disrupted to form ILs aggregates with increasing temperature. In addition, the stability of the ILs in water is also examined in some details. These LCST-type phase separation systems may have potential applications in extraction and separation techniques at room temperature.

Selective electrodes for [PF6]− and [BF4]− anions based on the associates formed by ionic liquid and cationic dyes

The feasibility of the newly synthesized ionic associates L1 and L2 formed by ionic liquid [C4mim][PF6] and cationic dyes (malachite green and methylene blue) has been tested as a novel ionophore for the preparation of anion-selective polymeric membrane electrodes. The electrode exhibits Nernstian response and enhanced potentiometric selectivity towards [PF6](-) compared to many other anions. The influence of some experimental parameters such as membrane composition, nature of plasticizer and amount of additive on the potential response of the [PF6](-) sensor are investigated. Under the optimized conditions, the response slopes of the membrane electrodes towards [PF6](-) are 59.7±0.5 and 58.1±0.5 mV/decade based on ionophore L1 and L2, respectively, in 1.0×10(-5)-1.0×10(-1) or 1.0×10(-6)-1.0×10(-1) mol/L concentration range. Interestingly, the optimized electrodes based on ionophores L1 and L2 also exhibit Nernstian response characteristics (60.3±0.5 and 56.0±0.5 mV/decade) for tetrafluoroborate anion [BF4](-) in a wide concentration range. Thus, the proposed sensor has been used for the determination of [PF6](-) and [BF4](-) in aqueous ionic liquids samples and the solubility of the [PF6](-) and [BF4](-) based ionic liquids in water. The satisfactory results are obtained.

Equilibrium Partitioning of Phenols and Phenyl Amines between [BF4]- Based Ionic Liquids and Aqueous Solution

In this paper, ionic liquids [C6mim][BF4] and [C8mim][BF4] have been used, for the first time, as alternative solvents for the extraction of organic pollutants such as phenols and phenyl amines from aqueous solution. The experimental results shown that partition coefficients of these compounds were strongly affected by pH of aqueous phase, and the molecular forms of these solutes were found to be efficiently extracted by the ionic liquids. This suggested that the partitioning of the phenols and phenyl amines was driven mainly by the dispersion interactions between the molecular forms of the solutes and cation of the ionic liquids and the hydrogen bonding interactions between the solutes and anion of the ionic liquids. Thermodynamic properties have also been determined for representative extraction processes. It is shown that the partitioning process is exothermic in nature and controlled by enthalpy term. Preliminary recovery experiments suggest that [C8mim][BF4] ionic liquid may be adapted to removal organic pollutants from aqueous solution with good recycling.

Partition Behavior of Drug Molecules in Cholinium-Based Ionic Liquids

In this paper, a series of ionic liquids (ILs) contains cholinium as cations were prepared. These ILs were used as extractants to separate some model drug molecules. The partition coefficients of these drug molecules between ILs and aqueous solutions were determined. Furthermore, the influence of different extraction parameters was investigated: volume ratio, equilibrium time, pH values, temperature, and ILs structure. It is shown that these ILs are highly effective materials for the extraction of drug molecules. The results imply that these ILs may have potential in drug extraction or separation as a new type of media.

Solvation of the Ionic Liquid [C4mim][PF6] in Aqueous Ethanol Solutions from Molar Volume, Viscosity and Conductivity Measurements

Abstract Standard partial molar volumes V2,Φ0, viscosity B-coefficients and molar conductivities λm for the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6] in aqueous ethanol solutions (xethanol = 0.5∼0.9) have been determined from density, viscosity and conductivity measurements at 298.15 K. It is shown that values of V2,Φ0 decrease, while those of viscosity B-coefficients increase with increasing mole fraction of ethanol in the solvents. The molar conductivities of the ionic liquid are found to be decreased with increase of both the ionic liquid concentration and the ethanol content in the systems. Experimental results have been discussed in terms of the ionic liquid–solvent interactions and the ion associations of the ionic liquid in aqueous ethanol solutions.

A green separation strategy for neodymium (III) from cobalt (II) and nickel (II) using an ionic liquid-based aqueous two-phase system

It is significant to develop sustainable strategies for the selective separation of rare earth from transition metals from fundamental and practical viewpoint. In this work, an environmentally friendly solvent extraction approach has been developed to selectively separate neodymium (III) from cobalt (II) and nickel (II) by using an ionic liquid-based aqueous two phase system (IL-ATPS). For this purpose, a hydrophilic ionic liquid (IL) tetrabutylphosphonate nitrate ([P4444][NO3]) was prepared and used for the formation of an ATPS with NaNO3. Binodal curves of the ATPSs have been determined for the design of extraction process. The extraction parameters such as contact time, aqueous phase pH, content of phase-formation components of NaNO3 and the ionic liquid have been investigated systematically. It is shown that under optimal conditions, the extraction efficiency of neodymium (III) is as high as 99.7%, and neodymium (III) can be selectively separated from cobalt (II) and nickel (II) with a separation factor of 103. After extraction, neodymium (III) can be stripped from the IL-rich phase by using dilute aqueous sodium oxalate, and the ILs can be quantitatively recovered and reused in the next extraction process. Since [P4444][NO3] works as one of the components of the ATPS and the extractant for the neodymium, no organic diluent, extra etractant and fluorinated ILs are used in the separation process. Thus, the strategy described here shows potential in green separation of neodymium from cobalt and nickel by using simple IL-based aqueous two-phase system.