Photon Factory Activity Report 2018 #36 (2019)

BL-18 B/2017-IB-02, 2017-IB-27

Quantifying the structural effects of ionic liquids on model cellular membrane
Saheli Mitra, Gourav Bhattacharya and Sajal K. Ghosh*Department of Physics, School of Natural Sciences, Shiv Nadar University,
NH-91, Tehsil Dadri, G. B. Nagar, Uttar Pradesh, 201314, India

1 Introduction
An ionic liquid (IL) is a salt in the liquid state below 100℃.
These molecules are non-explosive, non-flammable, andare having good electrical and thermal conductivities.
They do not pollute air as they have low vapor pressure.
Because of these properties, they have a large number ofindustrial applications. Numerous recent studies haverevealed the lysing effect of these molecules onenvironment-friendly microorganisms living in soil andwater. Even though there are various studies of toxic
activities of ILs, the exact molecular mechanism of theseactivities are not well understood. When an IL interacts
with a living organism, it has to interact first with the outerlayer of the cellular membrane. Recently, there has beensignificant research interest in understanding theinteraction of ILs with the cell membrane to comprehend
the adverse activities of these molecules to livingorganisms.
2 Experiment
A cellular membrane, which is mainly composed ofphospholipids and proteins, is the outer layer of a cell that
protects the inner components and takes part in signalling
processes. Such a membrane is mimicked here with azwitterioniclipid,
1,2-dipalmitoyl-sn-glycero-3phosphocholine(DPPC), and an anionic lipid 1,2dipalmitoyl-rac-glycero-3-phospho-L-serine (DPPS). Xray reflectivity (XRR) technique for soft supported lipid
bilayer [1, 2] and small angle x-ray diffraction (SAXD) for
multilayer vesicles [3] have been used.

semi-kinematical approximation. The thickness of the pure
DPPC bilayer is found to be 47.4 Å with an electron
density of 0.288 e /Å3. With the insertion of ILs, the bilayer
thickness is found to decrease systematically andcorresponding the electron density of the bilayer increases(Fig. 1). To gain more insights of the molecular leveldescription of the IL-membrane interaction, multilamellar
vesicles of DPPC with a combination of negatively
charged lipid DPPS, have been used as model membrane.
For DPPC/DPPS sample, no Bragg peak was observed inthe SAXD measurements (Fig. 2 A). However, in thepresence of IL, the sample displayed a set of Bragg peaks
exhibiting the formation of MLVs. The interbilayer
spacing is observed to decrease with increase ofconcentration of IL (Fig 2 B).
-Fig 2: (A) Small angle X-ray diffraction patterns from the multi lamellar
vesicles (MLV) formed in the aqueous solution of DPPC/DPPS (a, black)and in the presence of 7.5 (b red), 10 (c blue), 15 (d pink) and 20 (d, green)
mol% of the IL. The curves are shifted vertically for clarity. (B) The
corresponding variation in lamellar repeat distance (d-spacing) [3]

4 Conclusion
This study has unveiled the reorganization of selfassembly of lipid molecules in a model bio-membrane in
the presence of ionic liquids. The structural perturbation in
the membrane may be the cause of the ionic liquids tobehave as the toxic elements to living organism.
5 Acknowledgement
We thank DST, India for financial support and SINP for
facilitating the experiments at the Indian Beamline (BL18B) in PF. We are thankful to M. K. Mukhopadhyay andR. P. Giri for their academic and technical supports.

Fig 1: (A) XRR measurements at 48 °C from lipid bilayers formed on apolymer cushion: (a) DPPC bilayer, (b) DPPC bilayer with 5mol %[BMIM][BF4], (c) bilayer with 10 mol % of IL, and (d) bilayer with 15mol % [BMIM][BF4]. For clarity, the curves are shifted vertically. The
solid lines are the fits to the data. (B) Corresponding electron density
profiles extracted from the fits of the above curves (a− d, respectively) [1].

3 Results and Discussions
The electron density profile has been obtained by a box
model fit to XRR data using a MATLAB code that utilizes

References[1] G. Bhattacharya et al., Langmuir (2017), 33, 1295−1304.
[2] G. Bhattacharya et al. Chemistry and Physics of Lipids(2018), 215, 1–10.
[3] S. Mitra et al., European Biophysics Journal (2019), 48, 119129.
* sajal.ghosh@snu.edu.in