Ionic liquids (ILs) have recently become very popular molecules because of their fascinating properties, which can be exploited in industrial and biomedical applications. There are several recent reports which suggest strong interaction of these molecules with bio-membrane. This interaction, which leads to complete disruption of the cell membrane leading to cell death, can be very useful in designing anti-microbial agents. Here, we have studied the effect of an ionic liquid tetrabutylammonium methanesulfonate (TAM) on a model cellular membrane composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipids. While differential scanning calorimetry study indicates a fluidity effect, the x-ray reflectivity measurements exhibit the formation of a new phase in the membrane. © 2020 American Institute of Physics Inc.. All rights reserved.

Sajal Kumar Ghosh

Physics

(SoNS) School of Natural Sciences

Gupta R.

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Shiv Nadar University

Co-existence of two lamellar phases in phospholipid multilayers induced by an ionic liquid

AIP Conference Proceedings

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.

Fulltext

Biophysical Reviews

Thermodynamics of interaction of ionic liquids with lipid monolayer

Ionic liquids (ILs) are important for their antimicrobial activity and are found to be toxic to some microorganisms. To shed light on the mechanism of their activities, the interaction of an imidazolium-based IL 1-butyl-3-methylimidazolium tetrfluoroborate ([BMIM][BF4]) with E. coli bacteria and cell-membrane-mimicking lipid mono- and bilayers has been studied. The survival of the bacteria and corresponding growth inhibition are observed to be functions of the concentration of the IL. The IL alters the pressure-area isotherm of the monolayer formed at an air-water interface by the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid. The in-plane elasticity of the lipid layer is reduced as a consequence of the insertion of this IL. The X-ray reflectivity study from a polymer-supported lipid bilayer shows strong perturbation in the self-assembled structure of the bilayer due to the interaction. As a consequence, there is a considerable decrease in bilayer thickness and a corresponding increase in electron density. These results, however, depend on the chain configurations of the lipid molecules. © 2017 American Chemical Society.

Langmuir

X-ray Reflectivity Study of the Interaction of an Imidazolium-Based Ionic Liquid with a Soft Supported Lipid Membrane

Ionic liquids (ILs) are potential candidates for new antimicrobials due to their tunable antibacterial and antifungal properties that are required to keep pace with the growing challenge of bacterial resistance. To a great extent their antimicrobial actions are related to the interactions of ILs with cell membranes. Here, we report the effects of ILs on the nanoscopic dynamics and phase behaviour of a dimyristoylphosphatidylcholine (DMPC) membrane, a model cell membrane, as studied using neutron scattering techniques. Two prototypical imidazolium-based ILs 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM[BF4]) and 1-decyl-3-methylimidazolium tetrafluoroborate (DMIM[BF4]), which differ only in terms of the alkyl chain length of cations, have been used for the present study. Fixed Elastic Window Scan (FEWS) shows that the incorporation of ILs affects the phase behaviour of the phospholipid membrane significantly and the transition from a solid gel to a fluid phase shifts to lower temperature. This is found to be consistent with our differential scanning calorimetry measurements. DMIM[BF4], which has a longer alkyl chain cation, affects the phase behaviour more strongly in comparison to BMIM[BF4]. The pressure-area isotherms of the DMPC monolayer measured at the air-water interface show that in the presence of ILs, isotherms shift towards higher area-per lipid molecule. DMIM[BF4] is found to shift the isotherm to a greater extent compared to BMIM[BF4]. Quasielastic neutron scattering (QENS) data show that both ILs act as a plasticizer, which enhances the fluidity of the membrane. DMIM[BF4] is found to be a stronger plasticizing agent in comparison to BMIM[BF4] that has a cation with a shorter alkyl chain. The incorporation of DMIM[BF4] enhances not only the long range lateral motion but also the localised internal motion of the lipids. On the other hand, BMIM[BF4] acts weakly in comparison to DMIM[BF4] and mainly alters the localised internal motion of the lipids. Any subtle change in the dynamical properties of the membrane can profoundly affect the stability of the cell. Hence, the dominant effect of the IL with the longer chain length on the dynamics of the phospholipid membrane might be correlated with its cytotoxic activity. QENS data analysis has provided a quantitative description of the effects of the two imidazolium-based ILs on the dynamical and phase behaviour of the model cell membrane, which is essential for a detailed understanding of their action mechanism. © 2017 The Royal Society of Chemistry.