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.

Sajal Kumar Ghosh

Physics

(SoNS) School of Natural Sciences

Ma Y.

Dilena D.A.

Bera S.

Lurio L.B.

Parikh A.N.

Sinha S.K.

Fulltext

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Shiv Nadar University

Biophysical Journal

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.

ACS Omega

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

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

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

In this study, we have designed a compact sample chamber that can achieve accurate and continuous control of the relative humidity (RH) in the vicinity of 100\%. A 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) multilayer can be used as a humidity sensor by measuring its inter-layer repeat distance (d-spacing) via X-ray diffraction. We convert from DOPC d-spacing to RH according to a theory given in the literature and previously measured data of DOPC multilamellar vesicles in polyvinylpyrrolidone (PVP) solutions. This curve can be used for calibration of RH close to 100\%, a regime where conventional sensors do not have sufficient accuracy. We demonstrate that this control method can provide RH accuracies of 0.1 to 0.01\%, which is a factor of 10-100 improvement compared to existing methods of humidity control. Our method provides fine tuning capability of RH continuously for a single sample, whereas the PVP solution method requires new samples to be made for each PVP concentration. The use of this cell also potentially removes the need for an X-ray or neutron beam to pass through bulk water if one wishes to work close to biologically relevant conditions of nearly 100\% RH. © the Owner Societies 2015.