The structural and hydrogen bonding properties of ionic liquid-co-solvent binary mixtures: the distinct behaviors of two anions

In practical applications, ionic liquids are often mixed with co-solvents. Understanding their structures and the interactions between them is a prerequisite for expanding their range of applications. In this work, spectroscopic and theoretical methods were employed to explore the structure and hydrogen bonding behaviors of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI)/1-ethyl-3-methylimidazolium thiocyanate (EMIMSCN) and co-solvents. It can be concluded that the hydrogen bonds associated with C2-H and C4,5-H are enhanced with the addition of co-solvents in the EMIMTFSI-DMSO system, while those associated with C4,5-H are weakened in the EMIMSCN-DMSO system. Infrared and excess spectra in the v(imidazolium C-H) range of EMIMSCN-CD3CN/CD3COCD3 systems further indicate that the abnormal change of hydrogen bonds associated with C4,5-H can be attributed to [SCN]-. These differences can be explained by the change of the primary interaction site. For EMIMTFSI, the primary interaction site in ion pairs and ion clusters is always C2-H, while for EMIMSCN, the primary interaction site in ion pairs is C2-H, and in ion clusters, it becomes C4,5-H. In the EMIMTFSI-DMSO system, the co-solvent primarily interacts with C4,5-H, while in the EMIMSCN-DMSO/CH3CN/CH3COCH3 systems, it primarily interacts with C2-H. In addition, several complexes are identified through excess infrared spectra and DFT calculations.

Comparative study of the hydrogen bonding interactions between ester-functionalized/non-functionalized imidazolium-based ionic liquids and DMSO

There have been some studies on the microscopic properties of ester-functionalized ionic liquids (ILs), but the microscopic properties of their mixtures with co-solvents have seldom been reported. In practical applications, ILs are usually used together with co-solvents. Therefore, it is very important to study the microstructure of ester-functionalized ILs and co-solvents. In this work, the hydrogen bonding interactions between ester-functionalized IL 1-acetoxyethyl-3-methylimidazolium tetrafluoroborate (AOEMIMBF₄) and DMSO were studied using spectroscopic methods and quantum chemical calculations. Non-functionalized IL 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) and DMSO were used for comparison. The results indicate that (1) by adding DMSO, the hydrogen bonding interactions of ν(C2-H) were enhanced, and DMSO could form hydrogen bonds with anions and cations simultaneously. (2) The incorporation of an ester group could enhance the hydrogen bonding interactions. (3) Both the stretching vibration of C2-H and CO indicated changes in the microscopic structure: AOEMIMBF₄ ion clusters first interacted with DMSO, then broke into AOEMIMBF₄-DMSO complexes and finally existed as [AOEMIM]⁺/[BF₄]^--DMSO complexes.

Ammonium-, phosphonium- and sulfonium-based 2-cyanopyrrolidine ionic liquids for carbon dioxide fixation

The development of carbon dioxide (CO₂) scavengers is an acute problem nowadays because of the global warming problem. Many groups around the globe intensively develop new greenhouse gas scavengers. Room-temperature ionic liquids (RTILs) are seen as a proper starting point to synthesize more environmentally friendly and high-performance sorbents. Aprotic heterocyclic anions (AHA) represent excellent agents for carbon capture and storage technologies. In the present work, we investigate RTILs in which both the weakly coordinating cation and AHA bind CO₂. The ammonium-, phosphonium-, and sulfonium-based 2-cyanopyrrolidines were investigated using the state-of-the-art method to describe the thermochemistry of the CO₂ fixation reactions. The infrared spectra and electronic and structural properties were simulated at the hybrid density functional level of theory to characterize the reactants and products of the chemisorption reactions. We conclude that the proposed CO₂ capturing mechanism is thermodynamically allowed and discuss the difference between different families of RTILs. Quite unusually, the intramolecular electrostatic attraction plays an essential role in stabilizing the zwitterionic products of the CO₂ chemisorption. The difference in chemisorption performance between the families of RTILs is linked to sterical hindrances and nucleophilicities of the α- and β-carbon atoms of the aprotic cations. Our results rationalize previous experimental CO₂ sorption measurements (Brennecke et al., 2021).

Structure, Spectroscopic Investigation, Molecular Docking and In vitro Cytotoxicity Studies on 4,7-dihydroxycoumarin: A Breast Cancer Drug

Coumarin derivatives are broadly used as anti-inflammatory, antioxidants, anticancer, and antiviral drugs in recent years. In particular, hydroxy coumarins have great importance because of their various biological and pharmacological purposes. The quantum chemical studies of 4,7-dihydroxycoumarin (DHC) have been performed using the cc-pVTZ level of basis set. The DHC molecular structure has been optimized and the computed frequency assignments have been correlated well with the experimental results. The experimental [Formula: see text]C NMR shifts of DHC have been compared with the computed [Formula: see text]C NMR in the dimethyl sulfoxide (DMSO) solution using the Gauge-invariant atomic orbital (GIAO) method. The electron delocalization within the DHC is shown by highest occupied molecular orbitals (HOMO)-lowest unoccupied molecular orbitals (LUMO) energy analysis, and the resulting small energy gap value reveal the molecule’s bioactive characteristics. The natural bond orbital (NBO) analysis approves the bioactive property of the DHC molecule. The DHC compound has a cytotoxic impact on the MCF-7 breast cancer cell line, according to in vitro cytotoxicity studies. The docking study approves that the DHC works as a new inhibitor of breast cancer targeted proteins such as epidermal growth factor receptor (EGFR), estrogen receptor (ER), and progesterone receptor (PR). Thus, this work covers the approach for the evolution of new drugs against breast cancer.

Tracking the Micro-Heterogeneity and Hydrogen-Bonding Interactions in Hydroxyl-Functionalized Ionic Liquid Solutions: A Combined Experimental and Computational Study

Ionic liquids (ILs) are an important class of media that are usually used in combination with polar solvents to reduce costs and tune their physicochemical properties. In this regard, it is essential to understand the influence of adding solvents on the properties of ILs. In this work, the micro-heterogeneity and H-bonding interactions between a hydroxyl-functionalized IL, [HOEmim][TFSI], and acetonitrile (ACN) were investigated by attenuated total reflection Fourier transform infrared spectroscopy and molecular simulations. All studied IL-ACN mixtures were found to deviate from the ideal mixtures. The degree of deviations reaches the maximum at about x(ACN)=0.7 with the presence of both homogeneous clusters of pure IL/ACN and heterogeneous clusters of IL-ACN. With the addition of ACN to IL, the mixtures undergo the transformation from "ACN solvated in [HOEmim][TFSI]" to "[HOEmim][TFSI] solvated in ACN". It is found that the newly formed H-bonding interactions between the IL and ACN is the main factor that contributes to the red shifts of O-H, C₂ -H, C_4,5 -H, and C_alkyl -H of [HOEmim]⁺ cation, and the blue shifts of C-D, C≡N of ACN, and C-F, S=O of [TFSI]^- anion. These in-depth studies on the mixtures of hydroxyl-functionalized IL and acetonitrile would help to understand the micro-heterogeneity and H-bonding interactions of miscible solutions and shed light on exploring their applications.

The molecular behavior of pyridinium/imidazolium based ionic liquids and toluene binary systems

Imidazolium and pyridinium-based ionic liquids (ILs) have attracted increasing attention in the extraction of aromatic VOCs. However, fundamental studies on the mechanism of capturing aromatic VOCs have been less reported. In this work, the interactions between two ILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) and N-butylpyridinium bis(trifluoromethylsulfonyl)imide (BpyTFSI), and toluene (C₆H₅CH₃), were investigated by using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), excess infrared spectroscopy, hydrogen nuclear magnetic resonance (¹H NMR) spectroscopy and quantum chemical calculations. Some conclusions were obtained as follows: (1) H atoms on EMIMTFSI/BpyTFSI were located above or below the benzene ring and were mainly formed as C2-Hπ bonds and C2,6-Hπ bonds with C₆H₅CH₃, respectively. C-Hπ bonds played a significant role in capturing aromatic compounds. (2) Upon adding C₆H₅CH₃, the two IL-C₆H₅CH₃ system's interaction strength was as follows: EMIMTFSI-C₆H₅CH₃ > BpyTFSI-C₆H₅CH₃. (3) Since C₆H₅CH₃ was unable to disrupt the interactions between cations and anions of ion pairs in the two studied IL-C₆H₅CH₃ systems, only ion cluster-C₆H₅CH₃ and ion pair-C₆H₅CH₃ complexes were observed. This work may provide theoretical insights into the separation mechanism for capturing VOCs.

Phase transition-induced changes in the Raman properties of DMSO/benzene binary systems

The Raman spectra of dimethylsulfoxide (DMSO)/benzene binary mixtures were studied by decreasing the temperature from 333 K to 263 K with the aim to reveal the molecular interaction properties during phase transition. The intensity of the Raman band for benzene at 992 cm-1 showed an increasing trend in the liquid and solid phases, while it exhibited a highly decreasing trend during the liquid-solid phase transition. The potential energy was calculated to study the effect of intermolecular interaction distance between DMSO and benzene on Raman intensity. The observations indicated that the blueshift of the low-frequency bands of DMSO was significantly different from the redshift of its high-frequency bands. The hydrogen bond generated between DMSO and benzene was well formed in the binary systems. This interaction inducing an enhanced hydrogen bond between the binary systems and attenuated C-H bonds led to opposite Raman shift variations with decreasing temperature. The Raman bands of DMSO at 1425 cm-1, 2899 cm-1, and 2992 cm-1 each split into two peaks after phase transition. The splitting of the Raman bands of DMSO at 1417 cm-1, 2895 cm-1, and 2982 cm-1 cropped up as the temperature dropped to the transformation point of 288 K. This is attributed to the phase transition-induced latent def.(C7) atomic vibrations corresponding to the individual methyl groups of DMSO. The implications of these analyses are expected to be helpful to understand the effect of phase transition on the Raman properties of binary solutions.

Structures and non-covalent interaction behaviours of binary systems containing the ionic liquid 1-(2'-hydroxylethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and chloroform

Mixtures of ionic liquids (ILs) and molecular solvents can overcome the drawbacks (high viscosity, high polarity, and high cost) of pure ILs and extend their practical use. The structural and interaction properties of ILs form the bases for understanding their properties. In this work, the structural properties of the mixtures of an IL, 1-(2'-hydroxylethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2OHMIM][Tf₂N]), with chloroform, a molecular solvent of weak polarity, in various concentrations were analysed using Fourier transform infrared spectroscopy and density functional theory calculations. Excess spectra were used to analyse the infrared spectra. The IL forms a stable ion cluster-CDCl₃ complex with CDCl₃ in the concentration range investigated. In the ion cluster-CDCl₃ complex, the hydrogen atom of CDCl₃ forms hydrogen-bonds with the fluorine atoms of the anion. In addition, the chlorine atom of CDCl₃ forms a halogen-bond with the oxygen atom of the anion. All the hydrogen and halogen-bonds identified between the [C2OHMIM][Tf₂N] ion cluster and CDCl₃ exhibit low strength, closed shells, and electrostatically dominant interactions.