Elucidation of the extraction of trivalent actinides using the DOHyA-HDEHP system: an experimental and theoretical approach

A combined solvent system composed of an acidic and a neutral extractant is demonstrated as an effective system for the mutual separation of lanthanides and actinides from nitric acid solutions. The geometry and stability of various possible complexes formed under extraction and stripping conditions in a combined solvent system composed of N,N-dioctyl hydroxyacetamide (DOHyA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) in the n-dodecane medium were studied both experimentally and theoretically. Experimental observations of the distribution ratios of Am(III) and Eu(III) in the combined solvent system revealed synergistic extraction of trivalent metal ions at all nitric acid concentrations. Density functional theory (DFT) calculations were employed to understand the geometric and electronic properties of the ligands and their corresponding complexes with Am(III) and Eu(III). The calculated results indicate that the feasibility and behaviour of complex formation in the combined solvent system using different methods are based on the energetic aspects of the formation reactions. The study also reveals the participation of the neutral and acid extractants in the combined solvent system facilitating the separation of Eu(III) and Am(III) from high-level liquid waste.

Probing the heterogeneity of molecular level organization of ionic liquids: a comparative study using neutral Nile red and cationic Nile blue sulfate as fluorescent probes for butyrolactam-based protic ionic liquids

Ionic liquids (ILs) are liquid salts composed of cations and anions, known for their significant local heterogeneity at the molecular level. To understand the microheterogeneity with regard to their local polarity and local viscosity, we have used two structurally similar but chemically distinguishable fluorescent probes: Nile red (NR), a neutral molecule, and Nile blue sulfate (NBS), a charged molecule. A comparative study of the response of the two probes to the molecular level heterogeneity of ILs is expected to provide a better clarity of understanding regarding the charged polar domain and the uncharged hydrophobic domain of ILs. Towards this, we synthesized two butyrolactam-based protic ionic liquids (PILs), i.e., BTF and BTD, with the same ionic headgroup ([BT]+) and different alkyl tails ([RCOO]-), where {R = H, C11H23}. BTF has no significant hydrophobic domain, whereas BTD has a larger hydrophobic domain. Temperature-dependent fluorescence parameters such as fluorescence intensity, lifetime, and anisotropy were measured for both NR and NBS molecules. The use of a pair of structurally similar but ionically different probes enables differential estimation of parameters like the microviscosity of a domain using the fluorescence anisotropy parameter (r). The absorption and emission spectra of both probe molecules are observed to be blue shifted upon going from BTF to BTD. NR showed a significant blue shift in absorption and emission band maxima. Conversely, NBS exhibited a small wavelength shift, possibly influenced by the preferred location of their charged head group domain. Temperature-dependent rotational relaxation time (θ) of NR in BTD is smaller than that of NBS by 60-70%, indicating that stronger charge-charge interactions exist between the polar domain of BTD and NBS. Moreover, it is observed that the local viscosity of the BTF IL around both probes is similar, whereas there is a considerable difference for the BTD IL. These results are an indication that NBS being charged prefers to locate itself in the charged head group region of the IL, whereas NR being neutral tends to reside both in the hydrophobic domain and in the head group but is predominantly located in the hydrophobic domain.

Synthesis, crystal structure and in silico studies of novel 2,4-dimethoxy-tetrahydropyrimido[4,5-b]quinolin-6(7H)-ones

Herein, acetic acid mediated multicomponent synthesis of novel 2,4-dimethoxy-tetrahydropyrimido[4,5-b]quinolin-6(7H)-one (2,4-dimethoxy-THPQs) was reported. Single-crystal XRD analysis of four newly developed crystals of 2,4-dimethoxy-THPQs and their DFT study were also reported. The structure of all molecules was optimized using DFT B3LYP/6-31G(d) level and compared with the corresponding single-crystal XRD data. As a result, the theoretical and experimental geometrical parameters (bond lengths and bond angles) were found to be in good agreement. Frontier molecular orbital (FMO) and molecule electrostatic potential (MEP) analyses were used to investigate the physicochemical properties and relative reactivity of 2,4-dimethoxy-THPQs. The formation of strong C–H⋯O and N–H⋯O interaction was investigated by Hirshfeld analysis. Furthermore, electronic charge density concentration in 2,4-dimethoxy-THPQs was analysed by the Mulliken atomic charges which helps to predict the ability of 2,4-dimethoxy-THPQs to bind in the receptor. The molecular docking of the crystal structure of 2,4-dimethoxy-THPQs in the main protease (M^pro) of SARS-CoV-2 suggested that all four 2,4-dimethoxy-THPQs efficiently docked in M^pro. Furthermore, 2,4-dimethoxy-THPQs with a 3-chloro substitution in the phenyl ring have the highest binding affinity because of the additional formation of halogen bonds and highest dipole moment.

Single-crystal XRD analysis of 2,4-dimethoxy THPQs and their relative reactivity with properties were investigated using DFT calculation. Molecular docking studies show they effectively docked with main protease of SARS-CoV-2.

Extraction of phenolic pollutants from industrial wastewater using a bulk ionic liquid membrane technique

The academia and chemical industry are actively searching for alternative solvents to meet technology requirements since the most widely used solvents are harmful and volatile. For ionic liquids, there are several advantages over conventionally using organic membrane solvents, including high thermal stability, negligible vapour pressure, low volatility, etc. Here in this study, we have analyzed the abilities of ionic liquids as pure solvents as well as their binary mixtures, to recover phenolic compounds from the industrial wastewater. The field of phenol extraction from wastewater using ionic liquids remains less exposed, and we presume that the work of this kind would open up more and more opportunities for the scientific community as well as industrial people. Based on all these assumptions, the present work includes experimental data of a work which explains the possibilities of room temperature ionic liquids (RTILs) as potential bulk liquid membranes (BLM) for extracting phenol and other phenolic compounds from the industrial affluents. Four high hydrophobicity ionic liquids namely: 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim][PF₆], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [Bmim][NTf₂], 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim] [PF₆] and 1-ethyl-3-methyimidazolium bis(trifluoromethanesulfonyl) imide [Emim][NTf₂] were used for investigating the Phenol extraction efficiency and stripping efficiency. To provide a best comprehension of the influence of the phenolic structure as well as the nature of cation on the extraction ability of the ILs, we tried to understand the molecular interactions between the phenolic compounds and the solvents. The influence of hydrophobicity of ionic liquids and different kinds of anions on the extraction of phenol and efficiencies of stripping were investigated. All the experimental investigations performed here indicated that the only cation part of the ionic liquid is not an important aspect directly in this extraction, but the hydrogen bonding and the solute-solvent interactions play a significant role in the phenol removal process from aqueous phase to IL phase. First, the optimal conditions of operating (settling time and stirring) were analyzed for the clarity of the experiments performed. Concentration of NaOH in enhancing the performance of ionic liquids was also inspected here in this study. A binary mixture of ionic liquids (BMILs) membrane was examined for the optimized parameters, and the efficiency of phenol extraction was analyzed with the efficiency obtained for the single ionic liquid (SIL) membranes. The phenol concentration was determined by UV/visible spectrophotometer absorbance measurements. The highest phenol extraction efficiencies of 91% and 98.5%, were achieved by using [Bmim][NTf₂] and [Bmim][NTf₂+PF₆] respectively, and the higher stripping efficiencies came up with 79% and 84% respectively, for [Emim][NTf₂] and [Bmim + Emim][NTf₂]. The results show that the binary mixture ionic liquid (BMIL) membrane is a better choice than single ionic liquid (SIL) membrane solvents. Hence, [Bmim] [(NTf₂+PF₆)] is an excellent selection as it provides high phenol stripping and extraction efficiencies with a minimal solvent loss and better stability in transport process.

Revisiting the Physicochemical Properties and Applications of Deep Eutectic Solvents

Recently, deep eutectic solvent (DES) or ionic liquid (IL) analogues have been considered as the newest green solvent, demonstrating the potential to replace harsh volatile organic solvents. DESs are mainly a combination of two compounds: hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD), which have the ability to interact through extensive hydrogen bonds. A thorough understanding of their physicochemical properties is essential, given their successful applications on an industrial scale. The appropriate blend of HBA to HBD can easily fine-tune DES properties for desired applications. In this context, we have reviewed the basic information related to DESs, the two most studied physicochemical properties (density and viscosity), and their performance as a solvent in (i) drug delivery and (ii) extraction of biomolecules. A broader approach of various factors affecting their performance has been considered, giving a detailed picture of the current status of DESs in research and development.

Insights into the Formations of Host-Guest Complexes Based on the Benzimidazolium Based Ionic Liquids-β-Cyclodextrin Systems

Inclusion complexation is one of the best strategies for developing a controlled release of a toxic drug without unexpected side effects from the very beginning of the administration to the target site. In this study, three benzimidazolium based ionic liquids (ILs) having bromide anion and cation bearing long alkyl chains, hexyl- ([C₆CFBim]Br), octyl- ([C₈CFBim]Br), and decyl- ([C₁₀CFBim]Br) were designed and synthesized as antibacterial drugs. Inclusion complexes (ICs) of studied ILs have been prepared by the combination of β-cyclodextrin (β-CD), considering these conjugations should enhance the benignity of ILs and make them potential candidates for the controlled drug release. Characterizations and structural analysis of studied ICs have been performed by ¹H NMR, 2D-ROESY NMR, FT-IR, HRMS, TGA, DSC, surface tension, ionic conductivity, dynamic light scattering (DLS), and isothermal titration calorimetry (ITC). Further, the morphology of the ICs has been analyzed by SEM and TEM. Furthermore, neat ILs and ICs have been treated against Escherichia coli and Bacillus subtilis to investigate their antibacterial activity, which confirms the prevention of bacterium growth and the shrinkage of the bacterial cell wall. The findings of this work provide the proof of concept that studied benzimidazolium based ILs-β-CD host-guest complexes should act as a potential candidate in controlled drug delivery and other biomedical applications.

On the Influence of the Menthol Moiety on the Transport Properties of a Homologue Series of Functionalized Bis(trifluoromethylsulfonyl)imide Room-Temperature Ionic Liquids: A Quest for the Structure-Property Relationship

This study explores the transport properties of bis(trifluoromethylsulfonyl)imide-based ionic liquids with a naturally derived (1R,2S,5R)-(-)-menthol moiety in the cationic part. In particular, we investigated the dependence of the dynamic viscosity and electrical conductivity as functions of the alkyl chain length. An important finding of this study is that both properties show nonmonotonic behavior with respect to the alkyl chain length. The nonmonotonic dependency is an obstacle for establishing the relationships between the structure and transport properties of homologues. To overcome this difficulty, we recommend fast property screening using a theoretical model that we developed, which allows for efficient viscosity prediction by means of the group contribution method. As demonstrated in this study, the model allows for reliable predictions of viscosity in the studied series with an overall relative deviation of less than 8%.

Synthesis and in vitro study of antiproliferative benzyloxy dihydropyrimidinones

In this study, we report on antiproliferative benzyloxy dihydropyrimidinones (DHPMs) produced by the Biginelli reaction of benzyloxy benzaldehyde, urea, and diverse 1,3-diones. The reaction was catalyzed by lanthanum triflate and completed within 1-1.5 h, with 74-97% yield. The antiproliferative assay was carried out for all synthesized dihydropyrimidinones against six human solid tumor cell lines. Six compounds showed good antiproliferative activity with GI₅₀ values below 5 μM. Among all the synthesized compounds, the most potent derivative showed good antiproliferative activity against all cell lines with GI₅₀ values in the range of 1.1-3.1 μM. These DHPMs comply with druglikeness. Furthermore, ADMET prediction and the effect of P-glycoprotein on the antiproliferative activity were also studied. Overall, our method allows eco-friendly access to benzyloxy DHPMs as potential anticancer drugs.

Molecular-Level Insights into the Microstructure of a Hydrated and Nanoconfined Deep Eutectic Solvent

Despite the recent advancements in the field of deep eutectic solvents (DESs), their high viscosity often prevents practical applications. A versatile strategy to overcome this problem is either to add a co-solvent or to confine the DES inside a nanoscaled self-organized system. This work assesses the microstructures of a hydrated and nanoconfined DES comprising benzyltripropylammonium chloride [BTPA]Cl and ethylene glycol (EG). They act as a hydrogen-bond acceptor and a donor, respectively. The hydrogen bonding between [BTPA]Cl and EG in the DES (i.e., BTEG) and the molecular states of water in the hydrated BTEG were studied by Raman spectroscopy. The results show different hydrogen-bonding associations between water-water and water-BTEG or EG molecules. In addition, we investigated the confinement effects of BTEG in a Polysorbate 80 (Tween-80)/cyclohexane reverse micellar (RM) system. The results are compared with those of an ionic liquid-encapsulated RM system. The formation, bonding characteristics, and thermal stability of the RM droplets were studied by solubilization, dynamic light scattering, rheology, and Raman spectroscopy experiments. Furthermore, it is shown that hydrogen bonding between the DES and the surfactant leads to a stable RM system. Interestingly, the viscosity of the RM system is significantly lower than that of the neat DES suggesting that DESs have a much wider practical applicability in the form of RMs.

Zwitterions as novel phase forming components of aqueous biphasic systems

A novel class of aqueous biphasic systems (ABS) formed by zwitterions (ZI) has been investigated in the present work. A series of water soluble ZIs have been synthesized using triethylamine, N-Methylimidazole, N-Vinylimidazole, pyridine, N-Methylpyrrolidine, N-Ethylpiperidine and 1,4 butane sultone. The synthesized ZIs were explored for their ability to form biphasic systems in combination with aqueous inorganic salt solutions of K3PO4, K2HPO4 and K2CO3. The phase diagrams for all systems have been constructed through cloud point titration method at 298.15 K and atmospheric pressure. The phase behavior of ZI based ABS have been analyzed to understand the structural effects of ZIs as well as the effect of nature of salt used on the overall phase formation. Further the temperature dependence of the ZI based ABS was also explored by studying the phase behavior at variable temperatures of 298.15, 308.15 and 318.15 K. In order to estimate the applicability of proposed ZI based ABS, extraction experiments have been performed for an alkaloid i.e. caffeine for all synthesized ZIs with K3PO4 and at 298.15 K. ZI based ABS have been found to be capable of single step extraction of caffeine similar to IL based ABS thus providing the possibilities to explore these ZI based ABS as efficient extraction and separation systems.

Aggregation behaviour of biocompatible choline carboxylate ionic liquids and their interactions with biomolecules through experimental and theoretical investigations

The self-assembly of long-chain choline carboxylates accompanied by their interaction with BSA protein were investigated with focus on environmental sustainability.

How water manifests the structural regimes in ionic liquids

Ionic liquids (ILs) are being considered as greener alternatives to the conventional organic solvents. However, highly viscous nature of ILs often limits their applications. Hence studies on IL/water binary mixtures have received tremendous attention. These mixtures exhibit much lower viscosity, but almost similar density, compressibility and other properties as that of the neat ILs, up to certain water content. Hence, determining the IL-water ratio till which the solution behaves like IL and subsequently changes to a state of solute IL dissolved in continuous water phase is of paramount importance. Noting the very different and characteristic behaviours of neat ILs and pure water over a temperature range, herein, we measured the various thermophysical properties of the binary mixtures of tetramethylguanidinium benzoate/water and tetramethylguanidinium salicylate/water with water content varying from 20 wt% to 95 wt% for a temperature range of 298 K to 343 K. The results show that similar to neat ILs, the measured densities and compressibility of these mixtures display a linear change, and viscosity decreases rapidly as temperature is increased for water content up to 50 wt%. At higher water concentrations, the measured density and compressibility exhibit nonlinear behaviour and the decrease in viscosity with increased temperature is minute, mimicking the behaviour of bulk water. MD simulations were carried out to explain the experimental observations. Simulation results show a greater temperature-induced disintegration of IL ion-water interactions in dense systems, explaining the rapid decay of the properties with temperature. The results also exhibit the presence of a neat, IL-like, H-bond mediated expanded structure in concentrated solution versus a collapsed IL structure in dilute solution.