Abstract.: The physical properties of an aqueous solution of a macromolecule primarily depend on its chemical structure and the mesoscopic aggregates formed by many of such molecules. Ionic liquids (ILs) are the macromolecules that have caught significant research interests for their enormous industrial and biomedical applications. In the present paper, the physical properties, such as density, viscosity, ionic conductivity of aqueous solutions of various ILs, have been investigated. These properties are found to systematically depend on the shape and size of the anion and the cation along with the solution concentration. The ionic conductivity and viscosity behavior of the solutions do not strictly follow the Walden rule that relates the conductivity to the viscosity of the solution. However, the modified Walden rule could explain the behavior. A simple calculation based on the geometry of a given molecule could shed the light on the observed results. Graphical abstract: [Figure not available: see fulltext.] © 2020, EDP Sciences, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.

Sajal Kumar Ghosh

Physics

(SoNS) School of Natural Sciences

De Sarkar S.

Mitra S.

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Shiv Nadar University

European Physical Journal E

Ionic liquids (ILs) are the attractions of researchers today due to their vast area of potential applications. For biomedical uses, it becomes essential to understand their interactions with cellular membrane. Here, the membrane is mimicked with lipid bilayer and monolayer composed of liver lipids extract. Three archetypal imidazolium based ILs, 1-decyl-3-methylimidazolium tetrafluoroborate ([DMIM][BF4] or [C10MIM][BF4]), 1-octyl-3-methylimidazolium tetrafluoroborate, ([OMIM][BF4] or [C8MIM][BF4]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4] or [C2MIM][BF4]) having different alkyl chain lengths are used in the present study. The isothermal titration calorimetry (ITC) measurements showed that [DMIM][BF4] interacts strongest with the liver lipid membrane compared to other two ILs which have relatively shorter alkyl chain length. The low values of stoichiometry ratio of ILs indicates that ILs penetrate within the core of the lipid bilayer. The interaction of ILs with the liver lipid membrane is found to be mainly driven by entropy which could be due to the change in the structure of the lipid membrane at local or global scales. Dynamic light scattering (DLS) measurements indicate that there are no changes in the size of vesicles due to addition of [DMIM][BF4] indicating stability of the vesicles. On the other hand, x-ray reflectivity (XRR) measurements showed a concentration dependent change in the monolayer structure. At low concentration of the IL, the monolayer thickness decreases, exhibiting an increase in the electron density of the layer. However, at higher concentrations, the monolayer thickness increases proving a concentration dependent effects of the IL on the arrangement of the molecules. © 2021

Biochimica et Biophysica Acta - Biomembranes

Thermodynamics and structure of model bio-membrane of liver lipids in presence of imidazolium-based ionic liquids

Here, we report the toxic effects of various imidazolium-based ionic liquids (ILs) with varying hydrocarbon chain lengths, on different human cell lines. Multiple biological assays have shown that the ILs with long hydrocarbon chains have stronger adverse effect especially on human liver cancer cells (Huh-7.5 cells). Further, our study has confirmed that the ILs induce necrosis dependent cell death and that it is related to cell membrane damage. To understand the molecular mechanism of such an effect, the cellular membranes were mimicked as lipid monolayers formed at the air-water interface and then as lipid bilayer vesicles. The pressure area-isotherms measured from the monolayer have shown that the interaction of ILs with the lipid layer is energetically favourable. The addition of these ILs reduces the in-plane elasticity of the self-assembled molecular layer. Quasielastic neutron scattering data clearly indicate that ILs in liver lipid vesicles significantly affects the dynamics of the lipid, in particular, the lateral motion of the lipids. It has been concluded that the mammalian cell death induced by these ILs is due to the modulated structure and altered physical properties of the cellular membrane. © 2019 Elsevier B.V.

Fulltext

Imidazolium-based ionic liquids cause mammalian cell death due to modulated structures and dynamics of cellular membrane

There are great efforts of synthesizing imidazolium-based ionic liquids (ILs) for developing new antibiotics as these molecules have shown strong antibacterial activities. Compared to a single-hydrocarbon-chained IL, the lipid analogues (LAs) with two chains are more effective. In the present study, the LA molecule MeIm(COOH)Me(Oleylamine)Iodide has been synthesized and its surface activities along with the effectiveness in restructuring of a model cellular membrane have been quantified. The molecule is found to be highly surface active as estimated from the area-pressure isotherm of a monolayer of the molecules formed at the air-water interface. The X-ray reflectivity (XRR) studies of a monolayer dip-coated on a hydrophilic substrate have shown the structural properties of the layer which resembles to those of unsaturated phospholipids. The LA molecules are observed to fluidize a phospholipid bilayer formed by the saturated lipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). At a lower surface pressure, the lipid monolayer of DPPC has exhibited a thickening effect at a low concentration of added LA and a thinning effect at higher concentration. However, at a high surface pressure of the monolayer, the thickness is found to decrease monotonically. The in-plane pressure-dependent interaction of LA molecules with model cellular membrane and the corresponding perturbation in the structure and physical properties of the membrane may be linked to the strong lysing effect of these types of molecules. © 2019 American Chemical Society.

Langmuir

Surface Activities of a Lipid Analogue Room-Temperature Ionic Liquid and Its Effects on Phospholipid Membrane

In the present study, an ionic liquid (IL), known as green solvent, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) with four carbons in the hydrophobic chain (C-4) has been used as an additive to modify the self-assembled aggregates of an anionic surfactant sodium dodecyl sulfate (SDS) and then the evolution of the liquid crystalline phases has been investigated. Small angle synchrotron x-ray diffraction study has revealed an unprecedented phase sequence where a hexagonal phase (HI) of direct cylindrical micelles is observed to evolve to another hexagonal phase (HII) of, again, direct cylindrical micelles with a lamellar phase (Lα) as the intermediate. The rheological data and the theoretical calculations have confirmed the phases. To understand such a phase behaviour of the system, the work is extended by considering the ionic liquids with the same head group but of shorter (C-2) and longer (C-10) hydrocarbon chains compared to BMIM-BF4. While the shorter chain IL causes the hexagonal phase to form rectangular (R) phase, the longer chain is observed to induce the lamellar phase (Lα). The molecular mechanism of appearance of such different phases has been discussed. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.

Liquid Crystals

Re-entrant direct hexagonal phases in a lyotropic system of surfactant induced by an ionic liquid

The large number of potential applications of ionic liquids (ILs) requires an understanding of their environmental impacts including their adverse effects on microorganisms living in soil and water. The molecular mechanism of toxic activities of these liquids is yet to be understood in detail. Any foreign molecules, interacting with an organism, have to encounter first the cellular membrane, which is predominantly composed of the lipid bilayer. In this work, multilamellar vesicles (MLV) of phospholipids have been used to shed light on the effect of an IL on the structure of a cellular membrane. The MLVs formed by the zwitterionic lipid, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) are found to shrink as a consequence of interaction with an imidazolium-based IL, 1-decyl-3-methylimidazolium tetrafluoroborate ([DMIM] [BF 4 ]). The absorbed ILs significantly modify the surface charge of the MLVs. While these observations indicate a strong membrane-IL interaction, synchrotron-based small angle X-ray diffraction (SAXD) measurements provide a structural description of the interaction. SAXD and Fourier transform infrared spectroscopy studies clearly reveal a disordering effect of the IL on the conformational organization of the lipid chains. The presence of the negatively charged lipid 1,2-dipalmitoyl-sn-glycero-3-phospho-l-serine sodium salt (DPPS) in MLVs plays an important role in disordering the chains in the membrane and inter-bilayer interactions. © 2018, European Biophysical Societies' Association.

European Biophysics Journal

Probing the effect of a room temperature ionic liquid on phospholipid membranes in multilamellar vesicles

Understanding the interaction of ionic liquids with cellular membrane becomes utterly important to comprehend the activities of these liquids in living organisms. Lipid monolayer formed at the air–water interface is employed as a model system to follow this interaction by investigating important thermodynamic parameters. The penetration kinetics of the imidazolium-based ionic liquid 1-decyl-3-methylimidazolium tetrafluoroborate ([DMIM][BF4]) into the zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid layer is found to follow the Boltzmann-like equation that reveals the characteristic time constant which is observed to be the function of initial surface pressure. The enthalpy and entropy calculated from temperature-dependent pressure–area isotherms of the monolayer show that the added ionic liquids bring about a disordering effect in the lipid film. The change in Gibbs free energy indicates that an ionic liquid with longer chain has a far greater disordering effect compared to an ionic liquid with shorter chain. The differential scanning calorimetric measurement on a multilamellar vesicle system shows the main phase transition temperature to shift to a lower value, which, again, indicates the disordering effect of the ionic liquid on lipid membrane. All these studies fundamentally point out that, when ionic liquids interact with lipid molecules, the self-assembled structure of a cellular membrane gets perturbed, which may be the mechanism of these molecules having adverse effects on living organisms. © 2018, International Union for Pure and Applied Biophysics (IUPAB) and Springer-Verlag GmbH Germany, part of Springer Nature.