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.

Ashish Gupta

Life Sciences

(SoNS) School of Natural Sciences

Sajal Kumar Ghosh

Physics

Bhattacharya G.

Giri R.P.

Saxena H.

Agrawal V.V.

Mukhopadhyay M.K.

<p>Shiv Nadar University is a comprehensive, multidisciplinary, research-focused, and student-centric University offering a full range of academic programs at the undergraduate, postgraduate and doctoral level. With state-of-the-art infrastructure, the University comprises of academic wings, sophisticated labs, international standard sports facilities, amphitheaters, auditorium, conference rooms and smart classrooms. The University&rsquo;s goal is to become internationally recognized for the quality of its research and creative endeavors and their applicability to improving quality of life, generating new insights and expanding the boundaries of human knowledge creativity. Committed to excellence in teaching, research and service, the University aims to serve the higher education needs of India and the world beyond.</p>

Shiv Nadar University

Langmuir

Graphene-based nano-technology is the future of biomedical devices including biosensors and, hence, it is essential to unravel the interaction of graphene oxide (GO) with cellular membrane. Here, the structural reorganization of lipid molecules, which are the building blocks of a cellular membrane, has been demonstrated in presence of GO flakes. The membrane is mimicked by forming a stack of lipid bilayers of zwitterionic phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and its structures have been probed by X-ray reflectivity and grazing incidence X-ray diffraction techniques. Lipid-GO composites have exhibited two sets of lamellar diffraction peaks illustrating GO-rich micro-domains in the matrix of phospholipid bilayers (GO-poor phase). In these domains, the GO flakes are observed to penetrate into hydrophobic core of the bilayer altering the thickness along with the overall electron density profile of the lipid layer. The GO-poor bilayer is closely related to the phase formed by pristine lipid molecules. The lattice parameters of a body-centred rectangular unit cell formed by chains of saturated phospholipids are found to be modified in presence of GO with a significant effect on molecular tilt. The structural description of GO-membrane interaction may pave the way of discerning the physical behaviour of the composites. © 2020 Elsevier B.V.

Applied Surface Science

Unravelling the structural changes of phospholipid membranes in presence of graphene oxide

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

A cellular membrane, primarily a lipid bilayer, surrounds the internal components of a biological cell from the external components. This self-assembled bilayer is known to be perturbed by ionic liquids (ILs) causing malfunctioning of a cellular organism. In the present study, surface-sensitive X-ray scattering techniques have been employed to understand this structural perturbation in a lipid multilayer system formed by a zwitterionic phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine. The ammonium and phosphonium-based ILs with methanesulfonate anions are observed to induce phase-separated domains in the plane of a bilayer. The lamellar X-ray diffraction peaks suggest these domains to correlate across the bilayers in a smectic liquid crystalline phase. This induced IL-rich lamellar phase has a very low lamellar repeat distance, suggesting the formation of an interdigitated bilayer. The IL-poor phase closely related to the pristine lipid phase shows a decrement in the in-plane chain lattice parameters with a reduced tilt angle. The ammonium and phosphonium-based ILs with a relatively bulky anion, p-toluenemethanesulfonate, have shown a similar effect. © 2021 American Chemical Society. All rights reserved.

Fulltext

ACS Omega

Ionic liquid-induced phase-separated domains in lipid multilayers probed by x-ray scattering studies

The potential biomedical applications of ionic liquids (ILs) need an understanding of the effects of the molecules in living organisms. Researchers are still exploring the molecular level description of this interaction. Any foreign molecule affecting a living organism has to interact first with the outer layer of a cell, which is mainly composed of a phospholipid bilayer. Here, to understand the membrane-IL interaction, a zwitterionic lipid has been chosen to prepare multilamellar vesicles (MLVs) which are the model cellular membranes. Small angle x-ray diffraction study has revealed the change in inter-bilayer spacing in the presence of imidazolium based ILs in the ripple phase of the bilayer. The investigation was extended further to understand the role of a negatively charged lipid in the MLVs. This study indicates that the cations of an IL screen electrostatic repulsion between the negatively charged lipids and induce the formation of a vesicle. © 2020 American Institute of Physics Inc.. All rights reserved.

AIP Conference Proceedings

Effect of ionic liquids on the structures of ripple phases of model cellular membranes

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.

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

The cholesterol partitioning and condensing effect in the liquid-ordered (Lo) and liquid-disordered (Ld) phases were systematically investigated for ternary mixture lipid multilayers consisting of 1:1 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/1,2-dioleoyl-sn-glycero-3-phosphocholine with varying concentrations of cholesterol. X-ray lamellar diffraction was used to deduce the electron density profiles of each phase. The cholesterol concentration in each phase was quantified by fitting of the electron density profiles with a newly invented basic lipid profile scaling method that minimizes the number of fitting parameters. The obtained cholesterol concentration in each phase versus total cholesterol concentration in the sample increases linearly for both phases. The condensing effect of cholesterol in ternary lipid mixtures was evaluated in terms of phosphate-to-phosphate distances, which together with the estimated cholesterol concentration in each phase was converted into an average area per molecule. In addition, the cholesterol position was determined to a precision of (±0.7Å) and an increase of disorder in the lipid packing in the Lo phase was observed for total cholesterol concentration of 20∼30\%. © 2016 Biophysical Society.