A comparison of ether- and alkyl-imidazolium-based ionic liquids diluted with CH3CN: A combined FTIR and DFT study

The ionic liquid-based electrolytes during their charging process: Movable endpoints of overscreening effect near the electrode interface

HYPOTHESIS

Adding solvents to ionic liquids (ILs) can lead to the suppression of the overscreening effect near an electrode interface. Also, this suppression can be observed in neat ILs by elongating the length of the nonpolar chains on their ions. Most neat ILs, unlike the ideal model, do not exhibit a crowding effect in experiments. Through molecular dynamics (MD) simulations, researchers can model and analyze these systems in order to understand them.

SIMULATIONS

In this study, the dynamic change near the electrode interface of ILs-based electrolytes was investigated using MD simulations. The phenomena observed in MD simulations are generally understandable because factors can attenuate charge densities calculated from these simulations.

FINDINGS

The study findings reveal that both the solvents or nonpolar chains contributed to the formation of nonpolar domains. Also, the microscopic mechanisms and influences of these nonpolar domains were clearly identified. The results are important for real life applications. Some ions form a "point to surface" layer near the electrode of neat ILs. When ILs contain long nonpolar chains, they can suppress the crowding effect through self-assembly behavior. However, when they do not have any chains or short nonpolar chains, it can be difficult to stop the overscreening effect. This means it can become challenging to begin the next stage of the crowding effect.

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.

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.

Fabrication of doxorubicin conjugated methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) nanoparticles and study on their in vitro antitumor activities

The purpose of this study was to develop a novel drug-polymer conjugation (mPEG-b-PCL-DOX) and study on its toxicity, bio-safety, and in vitro antitumor activity of mPEG-b-PCL-DOX. The polymer methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) (mPEG-b-PCL) was prepared by ring-opening polymerization. Then, succinic anhydride was reacted with mPEG-b-PCL via esterification reaction to produce mPEG-b-PCL-COOH. Finally, the polymer mPEG-b-PCL-DOX was obtained by conjugating DOX to mPEG-b-PCL-COOH by amidation. The Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance (¹H NMR) spectra were used to study the structures of obtained polymers. Transmission electron microscope (TEM) and Dynamic laser scattering (DLS) were employed to monitor the morphology and size distribution of mPEG-b-PCL-DOX nanoparticles (NPs). The mPEG-b-PCL-DOX NPs were administrated to KM rats by intraperitoneal injection to study the bio-safety of final NPs. The cell uptake and in vitro anti-tumor activity of final NPs were carried out with HCT116 cells as models. FTIR and ¹H NMR spectra confirmed the obtaining of mPEG-b-PCL-DOX. The fabricated NPs were in round shapes with an average diameter of 300 nm. These NPs did not induce hemolysis and physiological or pathological changes in rats's organs. Finally, cell teats showed that these NPs could be endocytosed by HCT 116 cells, and they had better anti-tumor effects than free DOX did. Therefore, the mPEG-b-PCL-DOX NPs had a potential application in anti-cancer therapy.

The effect of introducing an ether group into an imidazolium-based ionic liquid in binary mixtures with DMSO

Combined DFT and FTIR investigations reveal interesting hydrogen bonding interactions between dimethyl sulfoxide and an ether-functionalized imidazolium-based ionic liquid.