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DOI: 10.1039/D2GC00906D (Tutorial Review) Green Chem., 2022, 24, 5035-5045

Supramolecular deep eutectic solvents and their applications

Patrycja Janicka a, Massoud Kaykhaii ab, Justyna Płotka-Wasylka cd and Jacek Gębicki *a
aGdansk University of Technology, Faculty of Chemistry, Department of Process Engineering and Chemical Technology, 80–233 Gdansk, G. Narutowicza St. 11/12, Poland. E-mail: jacek.gebicki@pg.edu.pl
bDepartment of Chemistry, Faculty of Sciences, University of Sistan and Baluchestan, Zahedan 98135-674, Iran
cGdansk University of Technology, Faculty of Chemistry, Department of Analytical Chemistry, 80–233 Gdansk, G. Narutowicza St. 11/12, Poland
dBioTechMed Center, 80–233 Gdansk, G. Narutowicza St. 11/12, Poland

Received 8th March 2022 , Accepted 13th May 2022

First published on 16th May 2022

Abstract

In recent years, the growing awareness of the harmfulness of chemicals to the environment has resulted in the development of green and sustainable technologies. The compromise between economy and environmental requirements is based on the development of new efficient and green solutions. Supramolecular deep eutectic solvents (SUPRADESs), a new deep eutectic solvent (DES) subclass characterized by inclusion properties, are a fresh discovery that could have a significant impact on the development of green chemistry. SUPRADESs known in the literature consist of green ingredients, their physicochemical properties are similar to those of conventional DESs, and their supramolecular nature allows for selective binding of numerous chemical compounds – for many applications SUPRADESs show much higher efficiency compared with DESs. Because of the inclusion of cyclodextrins in their structure, these solvents are able to bind to many compounds through the formation of hydrogen bonds (typical of DESs) and at the same time interact with them in a host–guest mechanism. The combination of the environmentally friendly properties of DESs with those of cyclodextrins could be a breakthrough in the context of green chemistry. This review paper summarizes the available knowledge about SUPRADESs – their composition, physicochemical properties, applications and perspectives. SUPRADESs described in the work are fully green, non-toxic, and biodegradable solvents which are capable of efficiently absorbing many substances. So far, few SUPRADESs are known, but some of them are classified as low melting mixtures (LMM). It is very important to systematize the data available on these green solvents and properly classify them. We hope that identifying their potential and green characteristics will support further promising discoveries.

1. Introduction

In the manufacturing industries, such as production of cosmetics, degreasing agents, paints and pharmaceuticals, application of toxic and volatile organic solvents is very common. Many of these solvents are irritating, carcinogenic and mutagenic, and adversely affect water, soil and air.1 The most commonly used organic solvents are chlorinated, aliphatic, aromatic and cyclic hydrocarbons, alcohols, esters, ethers, aldehydes and ketones.2 Due to the harmful effects of these solvents on the environment and wildlife, alternative, “green” solvents are sought. An ideal solvent in this regard should not only exhibit the desired physicochemical properties, but is also required to fulfil features such as having low production cost, non-toxicity, biodegradability, recyclability and durability/stability.3 These requisites and the need to limit the use of toxic chemicals prompted the search for alternatives and have led to many discoveries.

In search of the beginnings of research on ionic liquids (ILs), we must go back to the mid-nineteenth century – it was then that low-melting organic salt was first observed.

In the Friedel–Crafts alkylation of benzene, a so-called “red oil” was formed as a by-product of the reaction. Because it was not possible to analyze the composition of this liquid at that time, for over 100 years and until the discovery of the nuclear magnetic resonance (NMR) technique, this “red oil” was not identified. NMR analysis showed that it was heptachlorodialuminate salt formed during the AlCl3-catalyzed Friedel–Crafts reaction, and was the first low-melting organic salt identified. This and all subsequent discoveries regarding ILs were the beginning of changes in the context of caring for the condition of the environment. ILs quickly became very popular – they were considered as a “green” solvent with environmentally friendly properties. However, the theory of their low toxicity,4 based on their low vapor pressure,5 has been repeatedly questioned6–8 due to the toxicity of the components used for ILs’ synthesis, and the threat they pose to aquatic and terrestrial ecosystems.9 Depending on the structure of ILs, they may exhibit harmful effects equal to or greater than organic solvents.10 Toxicological analysis of ILs has shown that conventional ionic liquids damage cell membranes, and cause increased production of reactive oxygen species (ROS) and severe DNA damage. In mammals, contact of cells with ILs causes necrosis.10

Another groundbreaking discovery came shortly after the discovery of ionic liquids. In 2003, Abbott et al. described the invention of the first deep eutectic solvent (DES).11 These solvents represent a promising alternative to conventional organic solvents. The method of obtaining them is very simple – it is enough to mix (in some cases heating may be necessary) at least two components (hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD)) in the appropriate proportion. As a result of the interaction based on the formation of hydrogen bonds between the components, the charge is relocated. Consequently, a significant lowering of the melting point of DESs compared with the melting points of the pure components is observed. DESs have unique features such as a low toxicity, low flammability, high conductivity, low cost of components, biodegradability, and easy fabrication, which make them applicable in many processes.12–14 There is also the possibility of selecting from an unlimited number of HBDs and HBAs as their components and mixing them in different molar ratios, and the possibility of diluting DESs with water to reduce their viscosity. The hydrogen bonds network in DESs and the ability of DESs to interact with other compounds, e.g., due to the formation of hydrogen bonds, give them an excellent ability to dissolve many substances. DESs have so far been used in many processes such as extraction of phenolic compounds,15–19 sulfuric compounds,20,21 polycyclic aromatic hydrocarbons22–24 and flavonoids.25,26 DESs have also been used in Friedel–Crafts alkylation,27 in the Sonogashira coupling reaction,28 in the Suzuki–Miyaura cross-coupling reactions,29 as a liquid membrane for electromembrane extraction,30 as efficient absorbents for biogas purification31–34 and for the analysis of organic compounds in environmental samples.35

The numerous advantages of DESs have made the topic of their synthesis and application very popular in recent years. Research on DES synthesis has led to the discovery of an interesting subgroup of them: supramolecular deep eutectic solvents (SUPRADESs).36 So far, all of the described SUPRADESs are composed of cyclodextrins as HBA linked to a HBD – most often levulinic acid. The specific milestones of the way of SUPRADES were introduced into the scientific world are presented in Fig. 1.


image file: d2gc00906d-f1.tif
Fig. 1 The path to the introduction of SUPRADESs: specific milestones.

The property responsible for the supramolecular nature of SUPRADESs is their non-standard structure based on the presence of the key component – cyclodextrins. Cyclodextrins (CDs) are one of the most remarkable macrocyclic molecules.37 CDs are a family of cyclic oligosaccharides obtained by relatively simple enzymatic degradation of one of the most essential polysaccharides, starch.36,38,39 It is found in many food products such as butter, mayonnaise, coffee, tea, and honey, and cleaning products such as toothpaste and shampoos.37 Native CD forms usually have six (α-CD), seven (β-CD) or eight (γ-CD) D-glucopyranose units which are linked by α- (1–4) bonds (Fig. 2).


image file: d2gc00906d-f2.tif
Fig. 2 Structures of native forms of cyclodextrins.

Depending on the number of glucopyranose units in their structure, CDs have a truncated cone structure with different sizes of cavities36 (Fig. 3). The combination of the hydrophilic outer surface with the relatively hydrophobic cavity makes CDs capable of forming inclusion complexes in aqueous solutions with a wide variety of molecules with low hydrophilicity and suitable geometric size, allowing non-covalent host–guest interactions.36,39–42 CDs are capable of “encapsulating” many compounds by forming inclusion complexes through host–guest interactions. Due to this structure, CDs have a very high potential for use in environmental chemistry as compounds which are capable of dissolving low-polarity organic compounds and heavy metals.43–47 They are also used in the food industry48–50 and cosmetics.51,52 Moreover, they are very effective solubilizers that enable the oral and parenteral absorption of many drugs. Cyclodextrins are capable of forming inclusion complexes in water with drug molecules showing poor water solubility. CDs increase the water solubility of many drugs.53 An increase in the solubility of a drug also accelerates the rate of its dissolution, leading to an increase in the bioavailability of the drug after oral administration. The ability of cyclodextrins to mask the undesirable physicochemical properties of drugs has allowed the development of numerous cyclodextrin-based products.53 Cyclodextrins interact with numerous agricultural chemicals (such as herbicides, pheromones, fungicides, insecticides, repellents or plant growth regulators). The use of CDs in the process of slowing down the germination of seeds allows the plant growth rate to be modified (which initially increases the weight at a low rate, but later to achieve better growth), enabling a 20–45% increase in the yield.54


image file: d2gc00906d-f3.tif
Fig. 3 Representation of the native forms of α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin.

In addition to the naturally occurring cyclodextrins, numerous derivatives are known with different properties compared with the native forms. In order to obtain cyclodextrin derivatives, their primary and secondary hydroxyl groups are modified by amination, etherification or esterification reactions.54 The modifications can achieve many benefits, including increasing their water solubility, changing the volume of the hydrophobic cavity, increasing the stability of the guest molecule in the presence of heat, light and oxidizing conditions, and to help control the chemical activity of molecules that interact with CD as a guest. Additionally, due to the interaction of organic compounds with the CD's cavity, it is possible to reduce the volatility of the “absorbed” compound.54

Many authors working on supramolecular deep eutectic solvents do not classify cyclodextrin-based DESs as SUPRADESs. The lack of a full classification of DESs as SUPRADESs may be due to the fact that the first work which clearly separated cyclodextrin-based DESs from typical DESs was published in 2020.36 The authors of the work literally wrote: “Therefore, this randomly methylated-β-cyclodextrin (RAMEB): Levulinic Acid (LevA) system is the first example of a low melting mixtures (LMM) solvent with supramolecular properties, thus introducing an emerging class of solvents that could be called SUPRADES”.36 Until the publication of this work, and even after it, the term SUPRADESs was not widely used in the context of inclusion-capable DESs. The current list of publications containing the keyword “supramolecular deep eutectic solvent” generated on the basis of the Web of Science website database returned only two results (January 2022).

This paper is the first review to focus on a new DES subclass characterized by inclusion properties, as new green solvents. It summarizes the available knowledge about SUPRADESs including their composition, physicochemical properties, applications and perspectives. The critical point of view of future application is also presented. We believe that this work will inspire future readers to deepen their knowledge of the application of SUPRADES in specific research areas.

2. Definition of a SUPRADES

The adjective “supramolecular” has been used for different meanings in the literature.55 According to Jean-Marie Lehn – the creator of the definition – supermolecules are organized, complex units obtained by combining at least two chemical compounds that interact with each other through intermolecular forces.56 In the case of supermolecular structures, there are additive and cooperative interactions (hydrogen bonds, coordination interactions, hydrophobic interactions), and their properties differ (preferably) from the sum of the properties of individual components. Good organization and a well-chosen combination of elements in supramolecular mixtures allow us to obtain systems with incredible efficiency.57

According to József Szejtli, supramolecular chemistry is a part of chemistry that describes all intermolecular interactions in which interacting molecules, ions, or radicals are not joined by a covalent bond; most of them are of the host–guest type.39

Ariga and Kunitake57 defined a super molecule as “molecule beyond a molecule” – a large, complex molecule obtained by combining other, smaller molecules. Molecules in a supermolecule interact with each other through weak interactions (hydrogen bonding, hydrophobic interactions and coordination interactions) – these interactions create new units that exhibit new properties (and, consequently, exhibit new functions).

SUPRADESs, as a recently discovered subgroup of DESs, showed extraordinary properties, including their ability to dissolve many substances efficiently. This is due to the presence of an extensive hydrogen bond network in their structure that supports the dissolution of individual substances, and at the same time the host–guest interaction allows efficient capture of molecules of appropriate size, geometry and polarity. As mentioned earlier, the hydrophilic outer surface of CDs with the relatively hydrophobic cavity makes them capable of forming inclusion complexes in aqueous solutions with a wide variety of molecules with low hydrophilicity and a geometric size for non-covalent host–guest interaction36,39–42 (Fig. 4). Therefore, the combination of the unusual properties of deep eutectic solvents with the properties of cyclodextrins make a SUPRADES an extremely multi-active mixture which is able to bind to numerous substances by creating hydrogen bonds, and at the same time by penetrating particles into its CD cavities. This is a property which cannot be found in other DESs. Therefore, they represent a new, promising class of green solvents which may find many applications in pharmacy, cosmetics, food, catalysis and environmental protection.58–60 CDs are capable of forming hydrogen bonds as an acceptor and at the same time, due to their special structure, can increase the dissolution of non-polar compounds in SUPRADESs. Successful attempts have been accomplished in applying CDs as effective absorbents in the purification of waste gas streams from volatile organic compounds (VOCs).61


image file: d2gc00906d-f4.tif
Fig. 4 Inclusion complex formation: host–guest interactions.

The high VOCs’ absorption capacity of CDs is promising, but the use of cyclodextrins independently can be very costly. Therefore, it is worth considering the use of cyclodextrins as an additive. For this reason, SUPRADESs are an interesting research topic.

The possibility of using cyclodextrins as a HBA or additive to DES opens up wide opportunities for the development of green chemistry at both lab and industrial scale.

3. Starting components, their structure and the mechanism of SUPRADES synthesis

The composition of SUPRADESs is based on cyclodextrins, which guarantees unique properties of this solvent. For any synthesis containing a CD, high pH values are advisable, since low pH values cause ring breakage and result in the formation of linear oligosaccharides; however, in alkaline media CDs are stable.66 Depending on their structure (chain length), natural cyclodextrins (γ-CD, β-CD and γ-CD) have a different ability to dissolve in water. β-CD is the least soluble in water compared with α-CD and γ-CD, which is due to its rigidity and the presence of intermolecular hydrogen bonds in its crystalline state.66–68 In order to increase the solubility of CDs in water, their derivatives are synthesized. The increase in water solubility of a CD's derivatives mainly depends on the type of substituent and the degree of substitution.66 Therefore, the difference in the solubility of CDs caused by modification is very large. For instance, in pure water at 25 °C and under atmospheric pressure, for α-cyclodextrin, β-cyclodextrin, 2-hydroxypropyl-β-cyclodextrin, sulfobutylether β-cyclodextrin sodium salt, randomly methylated β-cyclodextrin, 6-O-maltosyl-β-cyclodextrin, γ-cyclodextrin, and 2-hydroxypropyl-γ-cyclodextrin, the water solubility values are 145 mg mL−1, 18.5 mg mL−1, >600 mg mL−1, >500 mg mL−1, >500 mg mL−1, >1500 mg mL−1, 232 mg mL−1 and 500 mg mL−1, respectively(Table 1).53,69–71As can be seen, substitution of at least one of the hydroxyl groups forming the hydrogen bond (even by lipophilic functions) causes a significant increase in the water solubility of a CD. The water solubility of cyclodextrins is one of their most important properties, because if a CD can be dissolved in water, it will be able to increase the solubility of non-polar compounds due to the guest–host interactions.53
Table 1 Solubility of cyclodextrins and their derivatives in pure water at 25 °C (ref. 53)
Cyclodextrin Substituent -OR Solubility (mg mL−1)
α-Cyclodextrin –H 145
β-Cyclodextrin –H 18.5
2-Hydroxypropyl-β-cyclodextrin –CH2CHOHCH3 >600
Sulfobutylether β-cyclodextrin sodium salt –(CH2)4SO3− Na+ >500
Randomly methylated β-cyclodextrin –CH3 >500
6-O-Maltosyl-β-cyclodextrin Maltosyl– >1500
γ-Cyclodextrin –H 232
2-Hydroxypropyl-γ-cyclodextrin –CH2CHOHCH3 >500

Conventional DESs are usually obtained from inexpensive ingredients. SUPRADESs’ synthesis requires the use of small amounts of CDs, which can make them more expensive. However, SUPRADESs generally are synthesised using a definitely larger amount of HBD over CDs (HBA) (e.g. 1[thin space (1/6-em)]:[thin space (1/6-em)]44; CD[thin space (1/6-em)]:[thin space (1/6-em)]HBD).62 Similarly, in the case of the synthesis of SUPRADESs by addition of CDs to DESs, CD accounts for only 1.5% (w/v) of the DES volume.63

Due to the superior properties of SUPRADESs, which significantly increase the efficiency of many processes compared with use of conventional DESs, the use of CDs as a component of SUPRADESs may prove to be economical. Reduction in the amount of solvent used, associated with a significant increase in the efficiency of the processes, will contribute to the reduction of energy costs for the required processes, including heating, mixing or shaking. Reducing the use of substances is a response to the 1st and 6th Green Chemistry Principles64 and 7th and 9th Green Analytical Chemistry Principles,65 which are the pathway for responsible green process planning. The reduction of the costs of transport, storage and utilization of the solvent related to the reduction of the amount of substances used is another advantage that positively influences the economy of using SUPRADESs. Therefore, despite the relatively higher price of CD as a component of SUPRADESs, overall its employment can be an economical solution.

One of the most popular HBDs used in the synthesis of SUPRADESs is levulinic acid (LevA).36,62,72 LevA is a short-chain fatty acid with a ketone carbonyl group and an acid carboxyl group in its structure. In industry, it is used as an antifreeze, coating material, textile dye, animal feed, solvent, pharmaceutical compound, food flavoring agent and resin.73 LevA has been classified by the USA74 and the European Union75 as one of the most valuable materials obtained from biomass.76 Its widespread commercial use is directly related to its low price, sustainability and biodegradability. The use of LevA in the synthesis of SUPRADESs is therefore an economic and ecological option. Farooq et al. described SUPRADESs77 obtained by combining the native form of β-cyclodextrin and its derivatives (RAMEB), heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CD), and 2-hydroxypropyl β-cyclodextrin (HP-β-CD) as HBA, and lactic acid (LacA) as HBD. The use of LacA in combination with β-CD and its derivatives allows us to obtain liquid SUPRADESs at room temperature.77 In the work of Imperato et al.78 α-cyclodextrin and N,N′-dimethylurea were used for the synthesis of SUPRADESs. The authors named the obtained liquid a “low-melting mixture”. N,N′-Dimethylurea is a non-volatile urea derivative with a boiling point of 269.0 °C. By using this urea derivative, LevA or LacA as HBD, and CDs as HBA in the synthesis process, it is possible to obtain non-toxic SUPRADES solvents. Wu et al.79 described mixtures and named them “deep eutectic supramolecular polymers”. For their synthesis, the native forms of cyclodextrins (α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin) and an organic acid (citric acid, malic acid and tartaric acid) were reacted. After heating at 80 °C with constant stirring, the solid mixture changed to a clear liquid which showed high viscosity and no fluidity at room temperature. The obtained material was classified as “deep eutectic supramolecular polymers” due to their extremely high adhesive strength in relation to glass and steel materials, and non-fluid character. Achkar et al. described in their work a number of solvents composed of β-cyclodextrin derivatives (hydroxypropyl-β-CD, low methylated β-CD and randomly methylated β-CD) as HBA and Levulinic Acid as HBD. The obtained solvents were named in the article as LMM and supramolecular mixtures.72 Alternatively, SUPRADESs can be obtained by mixing conventional deep eutectic solvents with cyclodextrins. In this case, the cyclodextrin content is usually expressed as a percentage concentration (w/w) or percentage by mass/volume (w/v) of CDs in SUPRADESs (Table 2).

Table 2 SUPRADESs obtained by mixing deep eutectic solvents with cyclodextrins
HBA HBD Molar ratio (HBA[thin space (1/6-em)]:[thin space (1/6-em)]HBD) CD CD concentration Ref.
L-Alanine L-Lactic acid 1[thin space (1/6-em)]:[thin space (1/6-em)]7 β-CD 1.5% (w/v) 63
Nicotinamide L-Lactic acid 1[thin space (1/6-em)]:[thin space (1/6-em)]7 β-CD 1.5% (w/v) 63
Choline chloride L-Lactic acid 1[thin space (1/6-em)]:[thin space (1/6-em)]7 β-CD 1.5% (w/v) 63
Glycine L-Lactic acid 1[thin space (1/6-em)]:[thin space (1/6-em)]7 β-CD 1.5% (w/v) 63
Choline chloride Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 α-CD 2% (w/w) 40
10% (w/w)
Choline chloride Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 β-CD 2% (w/w) 40
10% (w/w) 80
20% (w/w) 77
Choline chloride Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 γ-CD 2% (w/w) 40
10% (w/w)

4. Characteristics of SUPRADES

Information about the properties of a solvent is crucial in its design process stage. The selection of an appropriate solvent is based on the requirements of the process. Viscosity, density, melting point, and polarity of the solvent are among the most important parameters in this regard. In SUPRADESs, these values are influenced by composition and type of HBA and HBD utilized, by the structure of employed CDs, and by their water content.

4.1. Physico-chemical properties

4.1.1. Melting point/freezing point. Melting point is one of the criteria determining the choice of a solvent. Most often, the solvent is expected to be liquid at room temperature, which has a positive effect on the total cost of the process – due to the lack of need to heat the solvent in order to liquefy it. SUPRADESs obtained from RAMEB and LevA mixed in a mass proportion of 30[thin space (1/6-em)]:[thin space (1/6-em)]70 (w/w%) allow a clear homogeneous liquid at room temperature to be obtained. Differential scanning calorimetry (DSC) analysis showed that the obtained SUPRADESs are liquid in a wide temperature range. The glass transition temperature was observed at −74.3 °C. Such a low melting point proves that the SUPRADESs described by El-Achkar et al.36 can be used in numerous processes, and in low-temperature conditions.

In another work,81 SUPRADESs were formed by combining β-CD and its derivatives (i.e. CRYSME-β-CD, RAME-β-CD, HP-β-CD and HTMAP-β-CD) with N,N′-dimethylurea (DMU). The obtained SUPRADESs were solid at room temperature; however, at elevated temperatures (about 90 °C), they become liquid.

Generally, a solvent melting point significantly above room temperature is undesirable in the context of industrial applications. It can cause difficulties during the process related to solidification or a significant change in the density and/or viscosity of the solvent due to uneven heating of the reactor. Additionally, carrying out the process at elevated temperatures increases the cost of the process. However, the undeniable advantages of using the solvents proposed by Jérôme et al.81i.e., the non-volatility and non-flammability of the described solvents, have a positive effect on the safety of storage and use of the developed solvents. The use of biodegradable substances in the process of their synthesis and having no harmful effect on the environment and health of living organisms underpin the suitability of their application.

Data in Table 3 reveal that the use of LevA in the synthesis of SUPRADESs allows a solvent with a liquid form in a wide temperature range to be obtained. DSC analysis was performed in a temperature range between −100 °C and 40 °C to determine the phase transformation of the tested liquids. The results showed that all DESs synthesized by combining CDs derivatives with LevA are liquid even at very low temperatures. For HPBCD[thin space (1/6-em)]:[thin space (1/6-em)]LevA (1[thin space (1/6-em)]:[thin space (1/6-em)]32), RAMEB[thin space (1/6-em)]:[thin space (1/6-em)]LevA (1[thin space (1/6-em)]:[thin space (1/6-em)]27) and CRYSMEB[thin space (1/6-em)]:[thin space (1/6-em)]LevA (1[thin space (1/6-em)]:[thin space (1/6-em)]25) DSC analysis did not allow the observation of SUPRADESs’ melting points; instead, the glass transition temperatures of −73.3 °C, −74.3 °C, −73.5 °C were determined for them, respectively. Knowing the glass transition temperature is of importance, because when it is reached, a sharp jump in the viscosity of the cooled liquid occurs and the liquid turns into a glassy form.

Table 3 Melting points of SUPRADESs
SUPRADES (with water content) Ref.
HBA HBD Molar ratio (HBA[thin space (1/6-em)]:[thin space (1/6-em)]HBD) Water content (%) Glass transition temperature (°C), no melting point observed
HPBCD LevA 1[thin space (1/6-em)]:[thin space (1/6-em)]32 2.7 −73.3 72
RAMEB LevA 1[thin space (1/6-em)]:[thin space (1/6-em)]27 2.5 −74.3 72
CRYSMEB LevA 1[thin space (1/6-em)]:[thin space (1/6-em)]25 3.3 −73.5 72
SUPRADES (no information about water content) Ref.
HBA HBD Mass ratio (%HBA[thin space (1/6-em)]:[thin space (1/6-em)]%HBD) Melting point (°C)
α-CD DMU 30[thin space (1/6-em)]:[thin space (1/6-em)]70 86 82
β-CD DMU 30[thin space (1/6-em)]:[thin space (1/6-em)]70 91 82
β-CD DMU 50[thin space (1/6-em)]:[thin space (1/6-em)]50 67 82
γ-CD DMU 30[thin space (1/6-em)]:[thin space (1/6-em)]70 91 82
HP-α-CD DMU 30[thin space (1/6-em)]:[thin space (1/6-em)]70 87 82
HP-β-CD DMU 30[thin space (1/6-em)]:[thin space (1/6-em)]70 91 82
HP-γ-CD DMU 30[thin space (1/6-em)]:[thin space (1/6-em)]70 94 82
CRYSME-β-CD DMU 50[thin space (1/6-em)]:[thin space (1/6-em)]50 79 82
CRYSME-β-CD DMU 70[thin space (1/6-em)]:[thin space (1/6-em)]30 71 82
RAME-β-CD DMU 50[thin space (1/6-em)]:[thin space (1/6-em)]50 71 82
RAME-β-CD DMU 70[thin space (1/6-em)]:[thin space (1/6-em)]30 51 82

4.2. Density

The density of the solvent is an important property. It dictates the energy consumption needed for effective mass exchange, e.g. in the extraction processes. Understanding the density is also required to perform many calculations related to fluid mechanics and mass transfer, and generates the basic data allowing appropriate design of chemical processes. Most DESs and ILs have higher densities than conventional organic solvents.83 DESs based on metal salts have even higher densities (1.3 to 1.6 g cm−3).84 It has been experimentally proved that the density of a DES may be higher than densities of the pure substances used in its synthesis, due to the special molecular structure of DESs.85 The increase in DESs’ density compared with the density of pure components is explained by the hole theory. According to this theory, the increase in the density value results from the “packing” of molecules, in which the average radius of space between reactant ions is less than the radius of the ions that make up the DES molecules.86Table 4 depicts density and viscosity values of SUPRADESs in comparison with conventional DESs. Water content values (if available) are also included.
Table 4 SUPRADESs’ properties – density and viscosity
DES Property Temp. (°C) Ref.
HBA HBD Molar ratio (HBA[thin space (1/6-em)]:[thin space (1/6-em)] HBD) Additives P [kg m−3] η [mPa s] Water cont. (%)
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 — 1195.2 953.7 0 30 88
— 1190.1 403.2 0 40 88
— 1184.9 195.9 0 50 88
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 — 1188.0 222.5 2.44 30 88
— 1182.7 112.7 2.44 40 88
— 1177.4 66.36 2.44 50 88
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 — 1173.3 35.51 7.21 30 88
— 1168.0 23.37 7.21 40 88
— 1162.6 16.32 7.21 50 88
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 +2% α-CD 1198.9 668 — 30 40
1193.4 295 — 40 40
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 +10% α-CD 1216.1 746 — 30 40
1210.7 332 — 40 40
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 +2% β-CD 1197.8 758 — 30 40
1192.3 322 — 40 40
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 +10% β-CD 1214.2 661 — 30 40
1208.8 302 — 40 40
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 +2% γ-CD 1198.1 775 — 30 40
1192.7 331 — 40 40
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 +10% γ-CD 1215.2 1127 — 30 40
1209.8 477 — 40 40
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 +2% CRYSMEB-CD 1196.9 666 — 30 40
1191.4 289 — 40 40
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 +10% CRYSMEB-CD 1204.2 257 4.18 30 40
1198.7 134 4.18 40 40
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 +10% β-CD 1212.7 639.0 w/o 30 80
1207.3 295.9 w/o 40 80
1202.2 153.8 w/o 50 80
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 +10% β-CD 1205.1 183.7 2.9 30 80
1[thin space (1/6-em)]:[thin space (1/6-em)]2 1199.6 101.0 2.9 40 80
1[thin space (1/6-em)]:[thin space (1/6-em)]2 1194.6 60.38 2.9 50 80
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 +10% β-CD 1189.7 43.42 8.3 30 80
1[thin space (1/6-em)]:[thin space (1/6-em)]2 1184.6 28.3 8.3 40 80
1[thin space (1/6-em)]:[thin space (1/6-em)]2 1179.3 19.50 8.3 50 80
 
ChCl Urea 1[thin space (1/6-em)]:[thin space (1/6-em)]2 +10% β-CD 1157.4 7.993 23.2 30 80
1[thin space (1/6-em)]:[thin space (1/6-em)]2 1152.2 6.074 23.2 40 80
1[thin space (1/6-em)]:[thin space (1/6-em)]2 1146.8 4.742 23.2 50 80
DES Property Temp. (°C) Ref.
HBA HBD Mass ratio (HBA[thin space (1/6-em)]:[thin space (1/6-em)] HBD) Additives ρ [kg m−3] η [mPa s] Water cont. (%)
Properties measured at atmospheric pressure; (—) no information about water content.
RAMEB LevA 30[thin space (1/6-em)]:[thin space (1/6-em)]70 — 1184.5 212.9 2.5 30 36

The density of SUPRADESs is influenced by the mass fraction of CDs. It causes a slight increase in density compared with choline chloride[thin space (1/6-em)]:[thin space (1/6-em)]urea (ChCl[thin space (1/6-em)]:[thin space (1/6-em)]U) (1[thin space (1/6-em)]:[thin space (1/6-em)]2) without addition. However, this change in density is so slight that the described DESs show density values typical for the densities of the DESs described so far (i.e. 1000–1300 kg m−3).72,87 The density increase of SUPRADESs after CD addition is caused by relatively high density of CDs, which have densities higher than the other components of the described SUPRADES (typically 1440.0 kg m−3 for β-CD and 1202.0 kg m−3 and 1320.0 kg m−3, respectively, for choline chloride and urea).

Another feature that determines the solvent density is its water content. Generally, for DESs and ILs with densities higher than that of water, an increase in their water content causes a decrease in the solvent density. Obviously, the same observation is made for SUPRADESs. Another factor influencing density is the presence of different groups capable of forming hydrogen bonds in CD molecules. These interactions affect the packing of the mixture molecules significantly.

4.3. Viscosity

The value of a liquid's viscosity determines the amount of resistance to flow, which is in turn dependent on the molecular structure of the fluid.89 Viscosity is a function of temperature and generally decreases with increasing temperature. Important information about any solvent is the amount of change in viscosity upon heating or cooling. SUPRADESs referenced in this article have viscosity values ranging from 4.742 mPa s to 1127 mPa s (Table 4). Ternary SUPRADESs reported by Moufawad et al.40 composed of ChCl and urea (1[thin space (1/6-em)]:[thin space (1/6-em)]2) containing 2 to 10 percent CDs showed a slight change in viscosity compared with that of ChCl[thin space (1/6-em)]:[thin space (1/6-em)]U (1[thin space (1/6-em)]:[thin space (1/6-em)]2). The addition of CDs slightly increased the value of the DESs’ viscosity. In the temperature range tested, ternary SUPRADESs showed relatively high viscosity values, except for SUPRADES ChCl[thin space (1/6-em)]:[thin space (1/6-em)]U + 10% CRYSMEB; a much lower viscosity was observed for this solvent (compared with other SUPRADES). Such a low viscosity value of this solvent is most likely due to the water content of the sample (4.18% w/w), which is significantly higher compared with the rest of the ternary SUPRADES (1.26% to 1.82% w/w).

5. Applications of SUPRADESs

An ideal “green” solvent for industrial and analytical applications should be non-toxic, should have a low environmental impact and be biodegradable – according to the 1st, 3rd and 4th principles of the 12 principles of green chemistry64 and the 11th of 12 principles of green analytical chemistry (GAC).65 A solvent compatible with the idea of green chemistry should also be reusable, cheap and easy to obtain from renewable sources – the 7th principle of green chemistry64 and the 10th principle of GAC.65 Additionally, it should have high solubility and selectivity for selected chemical compounds.90 SUPRADESs show high compliance with the requirements of green chemistry, but there are few data available on the applications of SUPRADESs. In this section, we summarize the tested SUPRADESs applications. Importantly, the oldest of the cited works was written in 2020, indicating that we are at the beginning of the development path of this interesting group of solvents.

5.1. Extraction solvents

One of the main applications of SUPRADES is their use as solvents in extraction processes. Here are some examples. Sereshti et al.41 developed a DLLME method for the simultaneous extraction of three tetracyclines in water samples before their quantitation with high-performance liquid chromatography (HPLC), in which a SUPRADES and a number of DESs were used as extraction and dispersing solvents. Thymol[thin space (1/6-em)]:[thin space (1/6-em)]octanoic acid 1[thin space (1/6-em)]:[thin space (1/6-em)]1 as extracting DES solvent was compared with SUPRADES β-CD/thymol[thin space (1/6-em)]:[thin space (1/6-em)]octanoic acid (1[thin space (1/6-em)]:[thin space (1/6-em)]1) (5 mg β-CD per 175 μL volume of extraction solvent), and it was observed that the extraction efficiency was enhanced by a factor of two. Limits of detection better than 4.38 μg L−1 were obtained (Table 5). An increase in the dispersibility of the extraction solvent was also noted. DES was prepared using a fast, simple and cheap procedure. The described method is ecological and environmentally friendly – it excludes the use of chlorinated organic solvents.
Table 5 Application of SUPRADESs as extractants
SUPRADES composition Extraction technique Analyte Matrix LOD (μg L−1) Analytical instrument Ref.
β-CD/Thy[thin space (1/6-em)]:[thin space (1/6-em)]Oct acid DLLME Oxytetracycline Water samples 4.38 HPLC-UV 41
β-CD/Thy[thin space (1/6-em)]:[thin space (1/6-em)]Oct acid DLLME Doxycycline 1.37 HPLC-UV 41
β-CD/Thy[thin space (1/6-em)]:[thin space (1/6-em)]Oct acid DLLME Tetracycline 4.01 HPLC-UV 41
20 wt% β-CD[thin space (1/6-em)]:[thin space (1/6-em)]LcA HS-SDME Organic pollutants 0.1–14.6 HPLC-UV 77
ChCl[thin space (1/6-em)]:[thin space (1/6-em)] U 1[thin space (1/6-em)]: 2 (+20 wt% β-CD) HS-SDME Organic pollutants Not mentioned HPLC-UV 77

Farooq et al.77 described the use of SUPRADESs as extraction media for the extraction of eighteen aromatic organic pollutants from water samples. The extraction method of headspace single drop microextraction (HS-SDME) coupled with HPLC was employed. The aim of the study was to compare the extraction efficiency for conventional DESs and SUPRADESs. The authors demonstrated that the presence of cyclodextrins significantly improved the extraction efficiency. For eight of the eighteen SUPRADESs tested, the extraction yield of the analytes was two times higher, or much more, compared with the extraction yield obtained by using ChCl[thin space (1/6-em)]:[thin space (1/6-em)]U (1[thin space (1/6-em)]:[thin space (1/6-em)]2) as extractant. The addition of cyclodextrins allowed for a selective increase in the extraction of impurities.

5.2. Absorbents

As mentioned earlier, cyclodextrins are capable of binding to volatile organic compounds (VOCs). The research of Pietro et al. was aimed to investigate whether CDs can retain their properties in SUPRADESs.91 The test results clearly showed that SUPRADESs effectively absorb VOC pollutants and reduce their volatility. The researchers proved that there is a slowdown in the dynamics of the guest molecule in the CD's cavity. Additionally, NMR analysis was done to evaluate the interactions between VOC mixtures molecules with DESs and SUPRADESs. In the case of SUPRADESs, there was a clear downward shift in the peaks of the guest molecule. This observation indicated that the formation of βCD/VOC inclusion complexes occurred. For DESs, no such downward shift was observed. We believe that this study is a great introduction to the use of SUPRADESs in VOCs’ absorption and elimination processes.

Panda et al.62 used SUPRADESs to examine their ability to absorb acetaldehyde, butanone, dichloromethane, toluene and thiophene from air. SUPRADESs showed up to 250-fold reduction in vapor–liquid partition coefficients compared with water (at 30 °C and under atmospheric pressure). Dichloromethane and toluene were also examined and absorbed on RAMEB[thin space (1/6-em)]:[thin space (1/6-em)]LevA (1[thin space (1/6-em)]:[thin space (1/6-em)]27) SUPRADES with very satisfactory yields (95% and 99%, respectively). Saturation was not observed in the chromatographic peak even for a high VOC concentration of 600 g m−3. At this concentration, Captisol[thin space (1/6-em)]:[thin space (1/6-em)]LevA, CRYSMEB[thin space (1/6-em)]:[thin space (1/6-em)]LevA, HP-β-CD[thin space (1/6-em)]:[thin space (1/6-em)]LevA and RAMEB[thin space (1/6-em)]:[thin space (1/6-em)]LevA could absorb 2.82, 2.85, 2.84 and 2.87 mg VOC per g of SUPRADESs, respectively (Table 6). SUPRADES RAMEB[thin space (1/6-em)]:[thin space (1/6-em)]LevA 1[thin space (1/6-em)]:[thin space (1/6-em)]27 exhibits toluene vapor–liquid partition coefficient values up to four times lower (0.001) than choline chloride-based DES (0.004), indicating active synergistic absorption of SUPRADESs. The applied SUPRADESs retained their properties and high absorption capacity even after five absorption/desorption cycles.

Table 6 SUPRADESs applications as absorbents
SUPRADES composition HBA[thin space (1/6-em)]:[thin space (1/6-em)]HBD molar ratio Water content (%) Amount of absorbed VOCs on the adsorbent (mg g−1) Ref.
Captisol[thin space (1/6-em)]:[thin space (1/6-em)]LevA 1[thin space (1/6-em)]:[thin space (1/6-em)]44 3.9 2.82 62
CRYSMEB[thin space (1/6-em)]:[thin space (1/6-em)]LevA 1[thin space (1/6-em)]:[thin space (1/6-em)]25 3.3 2.85 62
HP-β-CD[thin space (1/6-em)]:[thin space (1/6-em)]LevA 1[thin space (1/6-em)]:[thin space (1/6-em)]32 2.7 2.84 62
RAMEB[thin space (1/6-em)]:[thin space (1/6-em)]LevA 1[thin space (1/6-em)]:[thin space (1/6-em)]27 2.5 2.87 62

Although SUPRADESs are recently introduced and the number of reports on their application as absorbents is limited, they have shown a very high potential in applications such as in the process of VOC absorption, either when they were used as pure sorbents, or as modifiers for solid sorbents such as silica gel or activated carbon.92 We believe that there is still a lot to discover regarding various applications of these high-adsorbent, stable molecules.

5.3. Supramolecular polymeric adhesive materials

SUPRADESs have been employed as adhesive materials. Wu et al.79 tested a number of SUPRADESs and measured their adhesion strengths on different substrates such as glass, steel, polymethyl methacrylate (PMMA) and polytetrafluoroethylene (PTFE). High values of adhesive strength were demonstrated for many of the tested DESs (Table 7).
Table 7 Adhesion strength of SUPRADESs measured under room temperature and 55% relative humidity
SUPRADESs composition HBA[thin space (1/6-em)]:[thin space (1/6-em)]HBD molar ratio Substrate Adhesion strength (MPa) Ref.
α-Cyclodextrin L-(+)-tartaric acid 1[thin space (1/6-em)]:[thin space (1/6-em)]10 Glass 3.04 ± 0.64 79
Steel 6.01 ± 0.64 79
PMMA 1.55 ± 0.28 79
PTFE 0.19 ± 0.04 79
 
β-Cyclodextrin citric acid 1[thin space (1/6-em)]:[thin space (1/6-em)]5 Glass 4.38 ± 1.24 79
Steel 3.37 ± 1.35 79
PMMA 1.25 ± 0.21 79
PTFE 0.30 ± 0.02 79
 
β-Cyclodextrin citric acid 1[thin space (1/6-em)]:[thin space (1/6-em)]10 Glass 3.20 ± 0.45 79
Steel 4.82 ± 0.96 79
PMMA 1.68 ± 0.05 79
PTFE 0.23 ± 0.03 79
 
β-Cyclodextrin L-(−)-malic acid 1[thin space (1/6-em)]:[thin space (1/6-em)]10 Glass 3.23 ± 0.67 79
Steel 6.57 ± 1.5 79
PMMA 1.36 ± 0.29 79
PTFE 0.26 ± 0.01 79
 
β-Cyclodextrin L-(−)-malic acid 1[thin space (1/6-em)]:[thin space (1/6-em)]15 Glass 2.81 ± 0.67 79
Steel 4.50 ± 1.11 79
PMMA 1.48 ± 0.07 79
PTFE 0.48 ± 0.07 79

All of the tested DESs showed high adhesion on hydrophilic surfaces (on glass up to 4.38 MPa, and on iron up to 6.57 MPa). Good adhesion was also observed on the hydrophobic surfaces of PMMA and PTFE (up to 1.68 and 0.48 MPa, respectively). It has been experimentally confirmed that the adhesive strength is constant for the tested adhesive materials within 90 days, which proves the long-term durability of the adhesive properties of the tested SUPRADESs.79

6. Conclusions and future perspectives

SUPRADESs have unique characteristics because of combining the features of DESs and supermolecules, which makes them a very powerful solvent with potentially many applications. Currently, the number of scientific articles available on SUPRADESs and their applications is very limited, because these novel solvents are very recently introduced. However, the available data show that β-CDs are the most widely used. It can be assumed that this is related to their price and the optimal size of the CD cavity for many applications. Certainly, the use of SUPRADESs as extraction media, sorbents and adhesive materials, as well as many more potential applications, requires attention from the scientific community, especially considering the importance of green chemistry and its widest possible implementation. This review of the available literature demonstrates the enormous potential of this new class of solvents. The results of research on their properties and applications described so far prove that the use of DESs based on cyclodextrins as green solvents is justified. The discovery of SUPRADESs is undeniably a step towards sustainable and green industrial and laboratory processes. We sincerely hope that our work will support further research on these unusual mixtures.

Author contributions

Conceptualization – Patrycja Janicka and Massoud Kaykhaii; writing (original draft preparation) – Patrycja Janicka; review and editing – Jacek Gębicki, Massoud Kaykhaii, Justyna Płotka-Wasylka; substantive support – Jacek Gębicki, Justyna Płotka-Wasylka; supervision Jacek Gębicki.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

Prof. Massoud Kaykhaii acknowledges the Polish National Agency for Academic Exchange (NAWA) under the Ulam Programme (Agreement No. PPN/ULM/2020/1/00014/DEC/1) for financial support of his stay at PG.

Notes and references

  1. F. D. Dick, Occup. Environ. Med., 2006, 14, 221–226 CrossRef PubMed .
  2. D. R. Joshi and N. Adhikari, J. Pharm. Res. Int., 2019, 1–18 CAS .
  3. Z. Yang, in Deep Eutectic Solvents: Synthesis, Properties, and Applications, ed. D. J. Ramón and G. Guillena, Wiley Onli., 2019, pp. 43–60 Search PubMed .
  4. J. Ranke, S. Stolte, R. Sto, J. Arning and B. Jastorff, Chem. Rev., 2007, 107, 2183–2206 CrossRef CAS PubMed .
  5. M. Deetlefs and K. R. Seddon, Chim. Oggi – Chem. Today, 2006, 24, 16 CAS .
  6. D. Zhao, Y. Liao and Z. D. Zhang, Clean: Soil, Air, Water, 2007, 35, 42–48 CAS .
  7. C. Pretti, C. Chiappe, D. Pieraccini, M. Gregori, F. Abramo, G. Monni and L. Intorre, Green Chem., 2006, 8, 238–240 RSC .
  8. Y. Zhao, J. Zhao, Y. Huang, Q. Zhou, X. Zhang and S. Zhang, J. Hazard. Mater., 2014, 278, 320–329 CrossRef CAS PubMed .
  9. T. Phuong, T. Pham, C. Cho and Y. Yun, Water Res., 2010, 44, 352–372 CrossRef PubMed .
  10. M. C. Bubalo, K. Radošević, I. R. Redovniković, I. Slivac and V. G. Srček, Arh. Hig. Rada Toksikol., 2017, 68, 171–179 CrossRef CAS PubMed .
  11. A. P. Abbott, G. Capper, D. L. Davies, R. K. Rasheed and V. Tambyrajah, Chem. Commun., 2003, 1, 70–71 RSC .
  12. Q. Zhang, K. De Oliveira Vigier, S. Royer and F. Jérôme, Chem. Soc. Rev., 2012, 41, 7108–7146 RSC .
  13. E. L. Smith, A. P. Abbott and K. S. Ryder, Chem. Rev., 2014, 114, 11060–11082 CrossRef CAS PubMed .
  14. M. Bystrzanowska and M. Tobiszewski, J. Mol. Liq., 2021, 321, 1–14 CrossRef .
  15. E. Rodríguez-Juan, C. Rodríguez-Romero, J. Fernández-Bolaños, M. C. Florido and A. Garcia-Borrego, J. Food Sci. Technol., 2021, 58, 552–561 CrossRef PubMed .
  16. C. Fanali, S. Della Posta, L. Dugo, M. Russo, A. Gentili, L. Mondello and L. De Gara, Electrophoresis, 2020, 41, 1752–1759 CrossRef CAS PubMed .
  17. S. Koutsoukos, T. Tsiaka, A. Tzani, P. Zoumpoulakis and A. Detsi, J. Cleaner Prod., 2019, 241, 1–11 CrossRef .
  18. M. Ruesgas-Ramón, M. C. Figueroa-Espinoza and E. Durand, J. Agric. Food Chem., 2017, 65, 3591–3601 CrossRef PubMed .
  19. M. Cvjetko Bubalo, N. Ćurko, M. Tomašević, K. Kovačević Ganić and I. Radojčic Redovniković, Food Chem., 2016, 200, 159–166 CrossRef CAS PubMed .
  20. P. Makoś and G. Boczkaj, J. Mol. Liq., 2019, 296, 1–22 CrossRef .
  21. L. Changping, L. Dan, Z. Shuangshuang, L. Zhuo, Y. Jingmei, W. Ailing, C. Yingna, Y. Zhilong and Z. Qi, Green Chem., 2013, 15, 2793–2799 RSC .
  22. P. Makoś, A. Przyjazny and G. Boczkaj, J. Chromatogr. A, 2018, 1570, 28–37 CrossRef PubMed .
  23. Z. Helalat-Nezhad, K. Ghanemi and M. Fallah-Mehrjardi, J. Chromatogr. A, 2015, 1394, 46–53 CrossRef CAS PubMed .
  24. K. Zhang, Y. Wang, S. Li and G. Zhu, Food Chem., 2021, 348, 1–8 Search PubMed .
  25. M. Yang, J. Cao, F. Cao, C. Lu and E. Su, Chem. Biochem. Eng. Q., 2018, 32, 315–324 CrossRef CAS .
  26. D. Skarpalezos and A. Detsi, Appl. Sci., 2019, 9, 4169 CrossRef CAS .
  27. Z. Hu, G. Jiang, Z. Zhua, B. Gonga, Z. Xiea and Z. Le, Chin. J. Org. Chem., 2021, 41, 325–332 CrossRef .
  28. X. Marset, A. Khoshnood, L. Sotorríos, E. Gómez-Bengoa, D. A. Alonso and D. J. Ramón, ChemCatChem, 2017, 9, 1269–1275 CrossRef CAS .
  29. P. O. Delaye, M. Pénichon, L. Boudesocque-Delaye, C. Enguehard-Gueiffier and A. Gueiffier, SynOpen, 2018, 2, 305–311 Search PubMed .
  30. F. A. Hansen, E. Santigosa-Murillo, M. Ramos-Payán, M. Muñoz, E. Leere Øiestad and S. Pedersen-Bjergaard, Anal. Chim. Acta, 2021, 1143, 109–116 CrossRef CAS PubMed .
  31. P. Makoś-Chełstowska, E. Słupek and J. Gębicki, Green Chem., 2021, 23, 4814–4827 RSC .
  32. E. Słupek, P. Makoś-Chełstowska and J. Gębicki, Materials, 2021, 14, 241 CrossRef PubMed .
  33. E. Słupek and P. Makoś, Sustainability, 2020, 12, 1–16 CrossRef .
  34. E. Słupek, P. Makoś and J. Gębicki, Arch. Environ. Prot., 2020, 46, 41–46 Search PubMed .
  35. R. Rodr, Á. Santana-Mayor, B. Socas-Rodríguez and M. Á. Rodríguez-Delgado, Appl. Sci., 2021, 11, 4779 CrossRef .
  36. T. El Achkar, T. Moufawad, S. Ruellan, D. Landy, H. Greige-Gerges and S. Fourmentin, Chem. Commun., 2020, 56, 3385–3388 RSC .
  37. N. Morin-Crini, S. Fourmentin, É. Fenyvesi, E. Lichtfouse, G. Torri, M. Fourmentin and G. Crini, Environ. Chem. Lett., 2021, 19, 2581–2617 CrossRef CAS .
  38. G. Crini, Chem. Rev., 2014, 114, 10940–10975 CrossRef CAS PubMed .
  39. J. Szejtli, Chem. Rev., 1998, 98, 1743–1753 CrossRef CAS PubMed .
  40. T. Moufawad, L. Moura, M. Ferreira, H. Bricout, S. Tilloy, E. Monflier, M. Costa Gomes, D. Landy and S. Fourmentin, ACS Sustainable Chem. Eng., 2019, 7, 6345–6351 CrossRef CAS .
  41. H. Sereshti, F. Karami and N. Nouri, Microchem. J., 2021, 163, 105914 CrossRef CAS .
  42. M. E. Di Pietro, M. Ferro and A. Mele, J. Mol. Liq., 2020, 311, 113279 CrossRef CAS .
  43. X. Wang and M. L. Brusseau, Environ. Sci. Technol., 1993, 27, 2821–2825 CrossRef CAS .
  44. M. T. Butterfield, R. A. Agbaria and I. M. Warner, Anal. Chem., 1996, 68, 1187–1190 CrossRef CAS PubMed .
  45. T. N. T. Phan, M. Bacquet and M. Morcellet, React. Funct. Polym., 2002, 52, 117–125 CrossRef CAS .
  46. I. Abay, A. Denizli, E. Bişkin and B. Salih, Chemosphere, 2005, 61, 1263–1272 CrossRef CAS PubMed .
  47. E. Fenyvesi, K. Gruiz, S. Verstichel, B. De Wilde, L. Leitgib, K. Csabai and N. Szaniszlo, Chemosphere, 2005, 60, 1001–1008 CrossRef CAS PubMed .
  48. G. Astray, C. Gonzalez-Barreiro, J. C. Mejuto, R. Rial-Otero and J. Simal-Gándara, Food Hydrocolloids, 2009, 23, 1631–1640 CrossRef CAS .
  49. J. J. Kim, T. H. Jung, J. Ahn and H. S. Kwak, J. Dairy Sci., 2006, 89, 4503–4510 CrossRef CAS PubMed .
  50. K. S. Doosh, M. F. Efan and S. O. Mohammad Ali, Pak. J. Nutr., 2013, 12, 837–841 CrossRef .
  51. H. J. Buschmann and E. Schollmeyer, J. Cosmet. Sci., 2002, 53, 185–191 CAS .
  52. N. Sharma and A. Baldi, Drug Delivery, 2016, 23, 739–757 Search PubMed .
  53. M. E. Brewster and T. Loftsson, Adv. Drug Delivery Rev., 2007, 59, 645–666 CrossRef CAS PubMed .
  54. E. M. M. Del Valle, Process Biochem., 2004, 39, 1033–1046 CrossRef CAS .
  55. I. Dance, New J. Chem., 2003, 27, 1–2 RSC .
  56. J.-M. Lehn, Supramolecular Chemistry. Concepts and Perspectives, Wiley, Weinheim, 1995 Search PubMed .
  57. K. Ariga and T. Kunitake, Supramolecular Chemistry – Fundamentals and Applications, Springer, 2006 Search PubMed .
  58. T. Loftsson and M. E. Brewster, J. Pharm. Sci., 1996, 85, 1017–1025 CrossRef CAS PubMed .
  59. J. Conceicao, O. Adeoye, H. M. Cabral-Marques and J. M. S. Lobo, Curr. Pharm. Des., 2017, 24, 1405–1433 CrossRef PubMed .
  60. S. Tilloy, E. Genin, F. Hapiot, D. Landy, S. Fourmentin, J. P. Genêt, V. Michelet and E. Monflier, Adv. Synth. Catal., 2006, 348, 1547–1552 CrossRef CAS .
  61. P. Blach, S. Fourmentin, D. Landy, F. Cazier and G. Surpateanu, Chemosphere, 2008, 70, 374–380 CrossRef CAS PubMed .
  62. S. Panda and S. Fourmentin, Environ. Sci. Pollut. Res., 2021, 29, 264–270 CrossRef PubMed .
  63. C. Georgantzi, A. E. Lioliou, N. Paterakis and D. P. Makris, Agronomy, 2017, 7, 54 CrossRef .
  64. J. C. Warner and P. T. Anastas, Green Chemistry: Theory and Practice, Oxford University Press, 1998 Search PubMed .
  65. A. Gałuszka, Z. Migaszewski and J. Namieśnik, TrAC, Trends Anal. Chem., 2013, 50, 78–84 CrossRef .
  66. P. Saokham, C. Muankaew, P. Jansook and T. Loftsson, Molecules, 2018, 23, 1–15 CrossRef PubMed .
  67. E. Sabadini and T. Cosgrove, Carbohydr. Res., 2006, 341, 270–274 CrossRef CAS PubMed .
  68. A. W. Coleman and I. Nicolis, J. Inclusion Phenom. Mol. Recognit. Chem., 1992, 13, 139–143 CrossRef CAS .
  69. K.-H. Frömming and J. Szejtli, Cyclodextrins in Pharmacy, 1994, vol. 5 Search PubMed .
  70. S. Tavornvipas, H. Arima, F. Hirayama, K. Uekama, T. Ishiguro, M. Oka, K. Hamayasu and H. Hashimoto, J. Inclusion Phenom., 2002, 44, 391–394 CrossRef CAS .
  71. S. Tavornvipas, F. Hirayama, H. Arima, K. Uekama, T. Ishiguro, M. Oka, K. Hamayasu and H. Hashimoto, Int. J. Pharm., 2002, 249, 199–209 CrossRef CAS PubMed .
  72. T. El Achkar, L. Moura, T. Moufawad, S. Ruellan, S. Panda, S. Longuemart, F. X. Legrand, M. Costa Gomes, D. Landy, H. Greige-Gerges and S. Fourmentin, Int. J. Pharm., 2020, 584, 119443 CrossRef CAS PubMed .
  73. J. J. Bozell, L. Moens, D. C. Elliott, Y. Wang, G. G. Neuenscwander, S. W. Fitzpatrick, R. J. Bilski, J. L. Jarnefeld, P. Northwest, P. O. Box and K. Msin, Resour., Conserv. Recycl., 2000, 28, 227–239 CrossRef .
  74. T. Werpy and G. Petersen, Top Value Added Chemicals from Biomass: Volume I – Results of Screening for Potential Candidates from Sugars and Synthesis Gas, 2004 Search PubMed .
  75. L. Nattrass, C. Biggs, A. Bauen, C. Parisi, E. Rodríguez-Cerezo and M. Gómez-Barbero, The EU bio-based industry: Results from a survey, 2016 Search PubMed .
  76. A. Sinisi, M. Degli Esposti, S. Braccini, F. Chiellini, S. Guzman-Puyol, J. A. Heredia-Guerrero, D. Morselli and P. Fabbri, Mater. Adv., 2021, 2, 7869–7880 RSC .
  77. M. Q. Farooq, V. R. Zeger and J. L. Anderson, J. Chromatogr. A, 2021, 1658, 462588 CrossRef CAS PubMed .
  78. G. Imperato, E. Eibler, J. Niedermaier and B. König, Chem. Commun., 2005, 1170–1172 RSC .
  79. S. Wu, C. Cai, F. Li, Z. Tan and S. Dong, Angew. Chem., Int. Ed., 2020, 59, 11871–11875 CrossRef CAS PubMed .
  80. G. C. Dugoni, M. E. Di Pietro, M. Ferro, F. Castiglione, S. Ruellan, T. Moufawad, L. Moura, M. F. Costa Gomes, S. Fourmentin and A. Mele, ACS Sustainable Chem. Eng., 2019, 7, 7277–7285 CrossRef CAS .
  81. F. Jérôme, M. Ferreira, H. Bricout, S. Menuel, E. Monflier and S. Tilloy, Green Chem., 2014, 16, 3876–3880 RSC .
  82. M. Ferreira, F. Jérôme, H. Bricout, S. Menuel, D. Landy, S. Fourmentin, S. Tilloy and E. Monflier, Catal. Commun., 2015, 63, 62–65 CrossRef CAS .
  83. P. Janicka, A. Przyjazny and G. Boczkaj, J. Mol. Liq., 2021, 333, 115965 CrossRef CAS .
  84. T. El Achkar, H. Greige-Gerges and S. Fourmentin, Environ. Chem. Lett., 2021, 19, 3397–3408 CrossRef CAS .
  85. Q. Zhang, K. De Oliveira Vigier, S. Royer and F. Jérôme, Chem. Soc. Rev., 2012, 41, 7108–7146 RSC .
  86. A. P. Abbott, G. Capper and S. Gray, ChemPhysChem, 2006, 7, 803–806 CrossRef CAS PubMed .
  87. B. Tang and K. H. Row, Monatsh. Chem., 2013, 144, 1427–1454 CrossRef CAS .
  88. Y. Xie, H. Dong, S. Zhang, X. Lu and X. Ji, J. Chem. Eng. Data, 2014, 59, 3344–3352 CrossRef CAS .
  89. H. D. Koca, S. Doganay, A. Turgut, I. H. Tavman, R. Saidur and I. M. Mahbubul, Renewable Sustainable Energy Rev., 2018, 82, 1664–1674 CrossRef CAS .
  90. O. Claux, C. Santerre, M. Abert-Vian, D. Touboul, N. Vallet and F. Chemat, Curr. Opin. Green Sustainable Chem., 2021, 31, 100510 CrossRef CAS .
  91. M. E. Di Pietro, G. Colombo Dugoni, M. Ferro, A. Mannu, F. Castiglione, M. Costa Gomes, S. Fourmentin and A. Mele, ACS Sustainable Chem. Eng., 2019, 7, 17397–17405 CrossRef CAS .
  92. P. Makoś, E. Słupek and A. Małachowska, Materials, 2020, 13, 1894 CrossRef PubMed .
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