Ternary Deep Eutectic Solvent Research Articles

Electrodeposition of Silver in a Ternary Deep Eutectic Solvent and the Electrochemical Sensing Ability of the Ag-Modified Electrode for Nitrofurazone.

The determination of nitrofurazone (NFZ) has received substantial attention because it is a kind of antibiotic drug. Herein, a rapid and low-cost electrochemical sensor for the analysis of NFZ is reported. The method uses Ag-modified electrodes in which different surfactants, hexadecyltrimethylammonium bromide and sodium dodecyl sulfate, in a ternary choline chloride-urea-glycerol deep eutectic solvent were deposited. The physical properties of the solutions with various surfactants are investigated by a conductivity meter, viscometer, and tensiometer. The morphologies and crystallinity of the Ag-modified electrodes were characterized by using scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction. Electrochemical impedance spectroscopy and CV analyses indicate that the as-prepared Ag-SDS electrode exhibited better performance as a NFZ sensor. The dynamic linear range of NFZ is 0.66-930 μM with a corresponding detection limit of 0.37 μM. The proposed electrochemical sensor was applied to detect NFZ in the aquaculture water sample, and the results showed good recovery in the range from 100.28 to 102.65%.

Application of natural deep eutectic solvents-based in-syringe dispersive liquid-liquid microextraction for the extraction of five acaricides in egg samples

ABSTRACT An efficient sample preparation method has been developed for the simultaneous analysis of amitraz, fipronil, fipronil sulfone, carbaryl and cypermethrin in egg based on in-syringe dispersive liquid-liquid microextraction. In this process, the sample is transferred into a glass test tube and suitable volumes of zinc acetate solution and choline chloride-ascorbic acid deep eutectic solvent are added to the tube and the mixture is sonicated. After centrifugation, the separated phase is mixed with deionised water to decrease its viscosity. Then, it is mixed with a ternary deep eutectic solvent (choline chloride-acetic acid-n-octanol) and dispersed into deionised water filled into barrel of a syringe.The method has low limits of detection (0.70–2.4 ng g−1) and quantification (2.3–8.0 ng g–1), good linearity (r2 ≥ 0.9968), and satisfactory repeatability (relative standard deviation ≤ 11% for intra–(n = 6) and inter-day (n = 5) precisions). Finally, the proposed method was applied on different egg samples and cypermethrin and fipronil sulfone were found in three of them.

A green air assisted-dispersive liquid-liquid microextraction based on solidification of a novel low viscous ternary deep eutectic solvent for the enrichment of endocrine disrupting compounds from water.

A green air-assisted dispersive liquid-liquid microextraction based on floating organic droplet solidification (DLLME-SFOD) was introduced for the enrichment of five endocrine disrupting compounds (EDCs) from water using a ternary deep eutectic solvent (TDES) as an extracting solvent prior to their determination by HPLC-PDA. The eutectic solvents were synthesized by combining various fatty acids which can concurrently act as both hydrogen bond acceptors (HBA) and hydrogen bond donors (HBD). Adding a third component to classical two-component eutectic solvents allows to purposefully control density, melting point, and viscosity of the synthesized solvents. Ternary and binary eutectic solvents with C9 acid provided excellent extraction efficiency in comparison with other eutectic solvents with C8 acid, while ternary solvents provided superior extraction efficiency to binary ones. Different variables that could influence the microextraction efficiency were optimized applying central composite face-centered design (CCF). At the optimum conditions, the method had low detection limits ranging from 0.96-2.30 µg/L with a preconcentration up to 134-folds. The method showed good linearity from the linear regression with an excellent correlation coefficient (r2 > 0.999). A good inter- and intraday precision (%RSD < 7%) and%recovery > 90% were achieved proving the method high precision and accuracy. Furthermore, the potential of using the TDES for determining the EDCs from five real water samples was proved through the higher extraction efficiency of the EDCs (90.06-104.43%) with results uncertainty < 20% for most of the compounds. Finally, the method greenness was evaluated by Raynie pictogram, analytical eco-scale, and Green Analytical Procedure Index (GAPI) approaches which confirm the superior eco-friendship of our method in comparison with other reported methods.

Novel low viscous hydrophobic deep eutectic solvents liquid-liquid microextraction combined with acid base induction for the determination of phthalate esters in the packed milk samples

A quick and simple sample extraction method was demonstrated for the liquid-liquid microextraction of seven phthalate acid esters (PAEs) using acid-base induced deep eutectic solvent (DES) with vortex-mixing assistance. The binary and ternary DESs were prepared by a range of fatty acids (C8-C12) and menthol, which ones act as hydrogen bond donors and acceptors respectively. Fatty acids and menthol served as an extraction solvent and a pH-dependent phase based on the acid-base reaction caused by the adjustment of the pH of the solution. Additionally, the extraction efficiency of the deep eutectic solvent (DES) was improved by adding the emulsifier sodium hydroxide. Hydrochloric acid was used as a phase separation agent. Additionally, the key parameters were optimized through orthogonal array experimental design and statistical analysis. Under the optimal extraction conditions, good linearity of the method was obtained in the concentration range from 1 to100 μg mL−1 for phthalate esters, and preconcentration was completed within 5 min. The limits of detection (LODs) was 1.06–4.55 ng mL−1, respectively. The spiked recovery values of actual samples were in the range of 83.9%–107.0% with relative standard deviations (RSDs) of 1.63–4.44%. The quantification limits of the seven phthalates were 3.20 to 13.61 ng mL−1. Thus, the overall experimental results revealed the promise of deep eutectic solvent (DES) for support in determining phthalate acid esters (PAEs). Therefore, this method could be used for the determination of seven phthalate acid esters in packaged milk samples.

Ternary deep eutectic solvent modified cadmium selenide quantum dots as a selective fluorescent probe for sensing of uranyl ions in water samples

A single step hydrothermal approach for the synthesis of CdSe QDs using green precursor materials with the assistance of urea-thioglycolic acid-choline chloride ternary deep eutectic solvent (TDES-CdSe QDs) in an aqueous solution is reported. The fluorescent TDES-CdSe QDs probe was successfully applied to the fast and selective detection of uranyl ions. It was found that the fluorescence emission of the probe was dramatically quenched by uranyl ions, while other ions had no significant influence on the fluorescence intensity of the DES-CdSe QDs. The nanoprobe was systematically characterized by FTIR, XRD, TEM and EDX analysis. Some key factors affecting the performance of TDES-CdSe QDs probe were optimized using response surface methodology based on face centered central composite design. Under the optimal conditions, the DES-CdSe QDs probe provided a linear response to uranyl ions in the concentration range from 10 to 500 nM with a limit of detection 5.7 nM. The relative standard deviation (RSD%) of the developed method for five replicate determinations of uranyl ions at 100 nM was estimated to be 1.9%. In addition, the proposed method was successfully explored to the uranyl ions quantitation in environmentally water samples and desirable results were achieved.

Combined magnetic molecularly imprinted polymers with a ternary deep eutectic solvent to purify baicalein from the Scutellaria baicalensis Georgi by magnetic separation

A ternary deep eutectic solvent (DES) was applied as a novel functional monomer for synthesis of molecularly imprinted polymers (MIPs) to separate baicalein from the Scutellaria baicalensis Georgi (S. baicalensis). For rapid separation from the complex systems, modified Fe3O4 particles were used as the magnetic cores to prepare magnetic deep eutectic solvent molecularly imprinted polymers (DES-MMIPs). The prepared DES-MMIPs were characterized by scanning electron microscopy, transmission electron microscopy, dynamic light scattering, Fourier transform infrared spectra, x-ray diffraction, thermal gravimetric analysis, vibrating sample magnetometer and BET analysis. Moreover, the adsorption capability and selectivity of DES-MMIPs to baicalein were investigated systematically. The results of adsorption experiments demonstrated that DES-MMIPs showed excellent binding capacity to baicalein and the selectivity of DES-MMIPs to baicalein was much higher than that of structure analogues (quercetin, hesperetin and keampferol). Finally, DES-MMIPs were applied in selective extraction of baicalein in the S. baicalensis by magnetic separation. The analysis was conducted by high performance liquid chromatography. The recoveries of baicalein in the S. baicalensis ranged from 91.6% to 99.3%. It had been proven that the DES-MMIPs were an innovative and effective adsorbent for selective recognition and separation of baicalein in complex systems.

Multifunctional ternary deep eutectic solvent-based membranes for the cost-effective ethylene/ethane separation

Membrane technology is a forward-looking approach for gas separation, while the implementation of membrane with high performance for ethylene/ethane separation still challenges the world. Herein, a multifunctional ternary deep eutectic solvent (DES)-based membrane was constructed for the cost-effective ethylene/ethane separation. The incorporation of a sweetener (Al(NO3)3) with the AgNO3/methylacetamide (NMA) mixture to form a ternary DES not only significantly promoted the ethylene/ethane selectivity but also enhanced the long-term stability of resultant membranes, which killed two birds with one stone. Various spectroscopic characterization and quantum mechanical calculations revealed that the complexing interaction between Ag+ and NMA and the complexing interaction between Al3+ and NO3− weakened the electrostatic interaction between Ag+ and NO3−, and improved the interaction energy between ethylene molecule and Ag+ carrier. By the synergy effects of two different complexing interactions, the ternary DES-based membranes exhibited high ethylene permeability, ethylene/ethane selectivity and stability, outperforming majority of the previously published data. Therefore, the membranes proved the grand potential for ethylene/ethane separation, and this work will shed light on the design of multifunctional liquid membranes for precise molecular separation.

Homogenous liquid–liquid extraction followed by dispersive liquid–liquid microextraction for the extraction of some antibiotics from milk samples before their determination by HPLC

In current study, an efficient sample pretreatment method based on combination of salt induced–homogenous liquid–liquid extraction and ternary deep eutectic solvent–based dispersive liquid–liquid microextraction has been developed for the extraction of some antibiotics (oxytetracycline, doxycycline, penicillin G, and chloramphenicol) from milk samples before their analysis with high performance liquid chromatography. In this process, acetonitrile which acts as proteins precipitation agent and extraction/dispersive solvent, simultaneously, is added to the sample containing the analytes. After centrifugation, a homogenous solution (aqueous phase + acetonitrile) is formed upper the precipitated proteins of milk. This solution is passed through a barrel filled with solid sodium sulfate. By doing so, phase separation is occurred and the analytes are extracted into the separated acetonitrile phase which is subsequently taken, mixed with a newly synthesized water–immiscible deep eutectic solvent (phosphocholine chloride:dichloroacetic acid:dodecanoic acid) at μL–level, and hastily injected into deionized water placed into a test tube. After centrifugation, an aliquat of the sedimented phase is removed and injected into the separation system. The method was validated it was found that it had high extraction recoveries (65–81%) and enrichment factors (455–567), low limits of detection (2.0–2.8 μg L−1) and quantification (6.5–9.3 μg L–1), and satisfactory repeatability (relative standard deviation ≤ 8.0%). Finally, the introduced method was utilized in analysis of the studied antibiotics in packed milk samples marketed in Tabriz, Iran.

Preparation of a ternary deep eutectic solvent as extraction solvent for dispersive liquid-liquid microextraction of nitrophenols in water samples

A dispersive liquid-liquid microextraction (DLLME) was developed for extraction of 4-nitrophenol (4-NP) and 2,4-dinitrophenol (2,4-DNP) in water samples by using a novel ternary hydrophobic deep eutectic solvent (DES) before high performance liquid chromatography determination. Preparation of the DES was done by mixing tetrabutylammonium bromide as acceptor of hydrogen bond and thymol and octanoic acid as donor of hydrogen bondat 60 °C for 5 min. Affecting parameters on extraction were evaluated and optimized. In optimal conditions, calibration curves were linear in the range of 1.0−500 μg L −1 (R 2 ≥ 0.99). The limit of detection (LOD) and limit of quantification (LOQ) was 0.2 and 0.6 μg L −1 for 4-NP and 0.3 and 0.9 μg L -1 for 2,4-DNP. The intra-day (n = 6) and inter-day (n = 3) precisions at concentration levels of 5.0 and 50 μg L −1 were less than 4.0 % expressed as relative standard deviation. Preconcentration factor was 200 and 180 for 4-NP and 2,4-DNP, respectively. Finally, applicability of the suggested procedure was investigated via analysis of water samples from different origin (tap, lake and fish pond). Recoveries obtained were acceptable (between 92.5 and 98.7 %).

Efficient removal of lignin from vegetable wastes by ultrasonic and microwave-assisted treatment with ternary deep eutectic solvent

A low-cost and green biorefinery will increase the economy and revenue from cellulose food waste biomass. Ultrasound and microwave-assisted Ternary deep eutectic solvents (TDES) pretreatment were developed to deconstruct the recalcitrant structure of garlic skin (GS) and green onion root (GOR) for further lignocellulose fractionation and cellulose enzymatic hydrolysis. In this study, the TDES consists of choline chloride (ChCl) as hydrogen bond acceptor, glycerin, oxalic acid, urea and metal chloride as hydrogen bond donor. The results showed that ultrasound (room temperature, 30 min) and microwave (80 °C, 20 min)-assisted TDES pretreatment resulted in notable removal of lignin. Under the optimum conditions (ultrasound frequency: 20+28+40 kHz; TDES: ChCl-Gly-AlCl3·6H2O (1:2:0.2); heating method: ultrasound microwave), the lignin removal rate of GS and GOR reached 90.14 and 92.34 %, respectively. Simultaneously, the cellulose content of GS and GOR was increased by 48.52 and 50.28 %, respectively, which was significantly enhanced by 1.94 and 1.45 times, respectively, compared to that of the original biomass without pretreatment. Besides, the content of the reducing sugar in the enzymatic hydrolysate of GS and GOR was 2.63 and 3.11 %, respectively. All these structural characteristics (FT-IR, XRD and SEM) confirmed the efficient fractionation of GS and GOR by ultrasonic and microwave pretreatment. Overall, this work demonstrated a novel and high-performance pretreatment method for eff ;ective lignocellulose deconstruction and cellulose digestibility.

Impregnating deep eutectic solvent choline chloride:urea:polyethyleneimine onto mesoporous silica gel for carbon dioxide capture

Development of green sorbents to capture carbon dioxide (CO2) whilst minimising their environmental impacts has gained interest among scientists. Deep eutectic solvent has been proposed as a promising green solvent for CO2 separation. In this study, a solid composite adsorbent based on mesoporous silica-gel (SG200) and deep eutectic solvent (DES) mixture of choline chloride:urea:polyethyleneimine (ChCl:U:PEI) was prepared by wet impregnation technique. The surface chemistry, thermal stability, surface porosity, CO2 adsorption capacity, and the effect of temperature on CO2 uptake by the adsorbents were studied. The highest CO2 adsorption of 51 mg/g at 25 °C and 1 bar was achieved by adsorbent with 25%ChCl:U:PEI loading, followed by 22%PEI (48 mg/g) and 24%ChCl:PEI (43 mg/g) loadings. Increased temperature was found to reduce the CO2 adsorption capacity. In addition, results from X-ray photoelectron spectroscopy (XPS) revealed the presence of cabamate ion after CO2 adsorption. This study revealed that the ternary DES, ChCl:U:PEI impregnated onto mesoporous silica sorbent has a promising potential to capture CO2.

Doxorubicin Loading on Functional Graphene as a Promising Nanocarrier Using Ternary Deep Eutectic Solvent Systems

The application of graphene in the field of drug delivery has attracted massive interest among researchers. However, the high toxicity of graphene has been a drawback for its use in drug delivery. Therefore, to enhance the biocompatibility of graphene, a new route was developed using ternary natural deep eutectic solvents (DESs) as functionalizing agents, which have the capability to incorporate various functional groups and surface modifications. Physicochemical characterization analyses, including field emission scanning electron microscope, fourier-transform infrared spectroscopy, Raman spectroscopy, Brunauer−Emmett−Teller, X-ray diffraction, and energy dispersive X-ray, were used to verify the surface modifications introduced by the functionalization process. Doxorubicin was loaded onto the DES-functionalized graphene. The results exhibited significantly improved drug entrapment efficiency (EE) and drug loading capacity (DLC) compared with pristine graphene and oxidized graphene. Compared with unfunctionalized graphene, functionalization with DES choline chloride (ChCl):sucrose:water (4:1:4) resulted in the highest drug loading capacity (EE of 51.84% and DLC of 25.92%) followed by DES ChCl:glycerol:water (1:2:1) (EE of 51.04% and DLC of 25.52%). Following doxorubicin loading, graphene damaged human breast cancer cell line (MCF-7) through the generation of intracellular reactive oxygen species (>95%) and cell cycle disruption by increase in the cell population at S phase and G2/M phase. Thus, DESs represent promising green functionalizing agents for nanodrug carriers. To the best of our knowledge, this is the first time that DES-functionalized graphene has been used as a nanocarrier for doxorubicin, illustrating the potential application of DESs as functionalizing agents in drug delivery systems.

Highly Stable Dispersion of Carbon Nanotubes in Deep Eutectic Solvent for the Preparation of CNT‐Embedded Carbon Xerogels for Supercapacitors

AbstractThe current study reports a kind of ternary deep eutectic solvent (DES) based on choline chloride, urea, and glycerol for the dispersion of multi‐walled carbon nanotubes (MWCNT) in the presence of surfactant. MWCNT‐embedded organic gels were subsequently prepared from the polymerization of resorcinol and formaldehyde in the obtained MWCNT‐dispersed DES. It has been demonstrated that the as‐prepared DES is excellent in dispersing and stabilizing the MWCNT, and thus allows the in situ synthesis of MWCNT functionalized resorcinol‐formaldehyde xerogels with no visible phase‐separation during the long sol‐gel process. After ambient drying and carbonization, MWCNTs can be well dispersed within the carbon xerogel matrix. The obtained carbon material possesses increased electrical conductivity while preserves the well‐developed porous structure. When used as electrodes in supercapacitors, it exhibits enhanced capacitance as well as rate performance. The specific capacitance at 0.5 A g−1 was 228 F g−1, 22 % more capacitance than that of the pristine carbon xerogel. More remarkably, it provides the electrodes with more than 200 % enhancement in capacitance when compared with that of the MWCNT‐embedded carbon xerogel prepared in aqueous solvent under the same conditions.

Development of an air-assisted liquid-liquid microextraction method based on a ternary solidified deep eutectic solvent in extraction and preconcentration of Cd(II) and Zn(II) ions

ABSTRACT A green, simple, rapid, and efficient ligandless air-assisted liquid-liquid microextraction procedure based on solidification of a ternary deep eutectic solvent was developed for the extraction of trace amounts of cadmium(II) and zinc(II) ions in aqueous samples prior to their determination by flame atomic absorption spectrometry. For this purpose, the deep eutectic solvent is formed by mixing sorbitol, menthol, and mandelic acid at a suitable mole ratio and after heating for a short time, a deep eutectic solvent with low density compared to water is synthesised. The synthesised solvent is used as a chelating agent and also as an extraction solvent. Under the optimum experimental conditions, the linear ranges were obtained in the ranges of 0.5–12.5 and 0.5–10.0 µg L−1 for Zn(II) and Cd(II), respectively. The relative standard deviations (n = 6, C = 2.5 µg L−1 of each cation) were 4.2% and 3.4%, for Cd(II) and Zn(II), respectively. Moreover, the obtained detection limits were 0.15 and 0.12 µg L−1 for Cd(II) and Zn(II), respectively. The accuracy of the developed method was studied by analysing SPS-WW2 Batch 108 water as a certified reference material. Finally, the proposed method was successfully applied in the determination of Cd(II) and Zn(II) ions in water and fruit juice samples. Abbreviations: AALLME: Air-assisted liquid-liquid microextraction; ER: Extraction recovery; FAAS: Flame atomic absorption spectrometry; LOD: Limit of detection; LOQ: Limit of quantification; RSD: Relative standard deviation

Development of a dispersive liquid-liquid microextraction method based on a ternary deep eutectic solvent as chelating agent and extraction solvent for preconcentration of heavy metals from milk samples

A simple, green, rapid, and efficient ligandless dispersive liquid-liquid microextraction procedure based on solidification of a ternary deep eutectic solvent has been proposed for the extraction of trace amounts of Cd(II), Cu(II), and Pb(II) ions in milk samples prior to their determination by flame atomic absorption spectrometry. Initially, a suitable mole ratio of sorbitol, menthol, and mandelic acid are mixed in a test tube, and after heating, a deep eutectic solvent with low density compared to water is formed. The synthesized solvent is used as a chelating agent and an extraction solvent in the extraction of some heavy metal ions from milk samples. The influence of several effective parameters on the responses and extraction recoveries of the analytes was investigated. Under the optimum experimental conditions, the linear ranges were in the ranges of 1.0–40 μg L−1 for Cd(II) and Pb(II), and 1.0–25 μg L−1 for Cu(II). The obtained relative standard deviations (n = 6, C = 2.5 μg L−1 of each cation) and detection limits were in the ranges of 3.4–4.1% and 0.38–0.42 μg L−1, respectively. Finally, the developed method was successfully applied for the determination of Cd(II), Cu(II), and Pb(II) ions in different milk samples.

Synthesis of hierarchical porous BCN using ternary deep eutectic solvent as precursor and template for aerobic oxidative desulfurization

Abstract Boron carbon nitride (BCN) has exhibited superior aerobic catalytic performance in oxidation reactions. Herein, the hierarchical porous BCN catalyst was synthesized using a ternary deep eutectic solvent (DES) composed of boric acid, urea and choline chloride as the precursor and template. The as-prepared BCN exhibited impressive catalytic performance in oxidative desulfurization of fuel. Under the optimized conditions, the BCN catalyst can reach 98.4% sulfur removal in 4 h and recycle 5 times with a little activity decrease. Experimental results revealed that the excellent catalytic activity was found to be originated from an improved electron delocalization. Combined with the density functional theory (DFT), the improved electron delocalization increased the electronic density of the BCN, promoting the activation of dioxygen. This strategy provides a novel approach for the design of high-performance catalyst in oxidative desulfurization.

Ternary Deep Eutectic Solvent Behavior of Water and Urea?Choline Chloride Mixtures.

Deep eutectic solvents (DESs) have potential as designer media whose physical, chemical, electrochemical, and spectroscopic properties are easily and broadly tuned. Due to the ubiquity of water and the hygroscopic nature of many DES components, it is important to understand how water affects DESs both on the nanoscale and in the bulk. Here, we present a study of the physical properties of DES/water mixtures. We found that water appears to form a ternary DES when mixed with 2:1 urea/ChCl.

One-step electrodeposited Ni-graphene composite coating with excellent tribological properties

How to solve the agglomeration of graphene in the plating bath is an essential challenge to synthesize graphene reinforced composite coatings by electrodeposition. In this paper, the exfoliated graphene (EG) from the graphite electrode was electrodeposited into the composite coating by simultaneously exfoliation and deposition in a ternary deep eutectic solvent. The preparation method is not only simple, but also effective in, and reducing the agglomeration of graphene. The collected EG was characterized by TEM, SEM, and Raman. The results show that few-layers EG is transparent. XRD, SEM, and EDS were used to examine the nickel-graphene composite coating. The results show that the graphene uniformly disperses in the composite coating. The Ni grains are refined, and the crystal plane orientation does not change. Compared with the pure Ni coating, the hardness and wear resistance of the Ni-graphene coating are significantly improved.

New insight into experimental and computational studies of Choline chloride-based ‘green’ ternary deep eutectic solvent (TDES)

In this study, we have examined the influence of ternary component (n-butanol, iso-butanol, and butandiol) as hydrogen bond donor (HBD) on binary Deep eutectic solvents (BDES) as hydrogen bond acceptor (HBA) which is composed of Choline chloride (ChCl) and Malonic acid (MA) in equimolar ratio (1:1) also called as maline to understand the hydrogen bonding interactions involved therein. The physicochemical properties of such as density, sound velocity, refractive index, conductivity, and viscosity of maline and TDES were evaluated at 303.15 K. Fourier-transform infrared spectroscopy (FT-IR) validated the molecular structures of the components and the involvement of extensive hydrogen bonding. Here the combination of maline (ChCl: MA) with the mentioned alcohols was simulated using Gauss View 5.0.9 package. Study showed that maline and butandiol exhibited a well-established and high relative hydrogen bond networks between them leading to a larger melting point depression in comparison to n-butanol and iso-butanol. Such a response could be related to the stable homogeneous system formed by butandiol and not by n-butanol and iso-butanol. These findings are further supported and significantly validated by the evaluation of Total energy (T.E) which accounts for the involvement of molecular orbitals. Additionally, the 3D-molecular electrostatic potential (3D-MEP) description was performed to predict the coordination of electrophilic and nucleophilic sites between the HBA and HBD.

Boric acid-based ternary deep eutectic solvent for extraction and oxidative desulfurization of diesel fuel

Ternary deep eutectic solvents were used for ODS of fuels (DESs) for the first time although most research continues to be focused on binary DESs.