Structure and Stability of Phospholipid Bilayers Hydrated by a Room-Temperature Ionic Liquid/Water Solution: A Neutron Reflectometry Study

Abstract

Neutron reflectometry (NR) measurements were carried out to probe the structure and stability of two model biomembranes consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) phospholipid bilayers hydrated by water solutions of two prototypical room-temperature ionic liquids (RTILs), namely, 1-butyl-3-methyl-imidazolium chloride ([bmim][Cl]) and choline chloride ([Chol][Cl]) at concentrations of 0.1 M and 0.5 M, respectively. The raw data were analyzed by fitting a distribution of scattering length densities arising from the different chemical species in the system. The results of this analysis show that (a) for all systems and concentrations that we considered, the thickness of the bilayers shrinks by ∼1 Å upon dissolving the ionic liquid into water and that (b) the RTIL ions enter the bilayer, finding their way to a preferred location in the lipid range that is nearly independent of the lipid and of the [bimim](+) or [Chol](+) choice. The volume fraction of RTIL sorbed in/on the bilayer, however, does depend on the lipid, but, again, is the same for [bmim][Cl] and for [Chol][Cl]. Thus, the RTIL occupies ∼5% of the bilayer volume in POPC, rising to ∼10% in DMPC. Repeating the measurements and data analysis after rinsing in pure water shows that the changes in the bilayer due to the RTIL sorption are irreversible and that a measurable amount of IL remains in the lipid fraction, that is, ∼2.5% of the bilayer volume in POPC and ∼8% in DMPC.

Room-temperature ionic liquids meet bio-membranes: the state-of-the-art

“…These have two hydrocarbon chains as phospholipids. A second intriguing overlap is with the ionic liquids of amino-acids (AAIL), in which anions are deprotonated amino-acids, and cations are either a protonated choline or phosphocholine that are present in phospholipid head groups (Benedetto et al 2014a). In these two cases, but also in general, the similarities between phospholipids and RTILs are certainly responsible for their mutual affinity.…”

“…Multi-lamellar structures can also be formed Fig. 1 Chemical sketches of some selected RTILs cations: (a),(b),(c) the most common imidazolium and pyrridinium RTIL cations; (d),(e) the doubletail lipid-mimic imidazoliumbased RTILs (Wang et al 2015a); (f),(g) the ethylammonium and guanidinium RTIL cations that help and contrast protein amyloidogenesis, respectively (Byrne et al 2007, Byrne and Angell 2008, 2009); (h) a phosphonium-based RTIL cation; and (i),(l) the choline and phosphocholine cations also used in RTILs made of amino acids (Benedetto et al 2014a) between RTILs and model biomembranes. Their aim is to determine the microscopic mechanisms behind their observed biological effects.…”

Effects of phosphonium-based ionic liquids on phospholipid membranes studied by small-angle X-ray scattering

“…computational means Cromie et al, 2009;Yoo et al, 2016), although the size of the sample may currently be too limited 80 for all effects to show in computations . Also physical probes, such as neutron reflectometry (Benedetto et al, 2014), fluorescent microscopy (Yoo et al, 2016), or small-angle X-ray scattering (SAXS) , have been used. For example, the effects of two commonly used ILs, 1-butyl-3-methyl-imidazolium chloride and choline chloride, on model membranes composed of 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine, have 85 been studied by neutron reflectometry to provide insight into the penetration of the ILs into the lipid bilayer (Benedetto et al, 2014).…”

Overview of the “Ionic Liquids meet Biomolecules” session at the 19th international IUPAB and 11th EBSA congress

“…The results of these investigations suggest that the ILwater-protein interaction is a complex balance of different contributions by the different components, which is not possible to predict a priori. There is sufficient evidence in the literature to lead to the conclusion that the interaction between proteins and ILs depends on the protein as well as on the cations and anions present in the ILs.Antonio Benedetto (University College Dublin, Ireland, and Paul Scherrer Institut, Switzerland) presents results from joint experimental and computational studies on the interaction between ILs and (model) biomembranes (Benedetto 2017;Benedetto et al 2015, Benedetto et al 2014. Combining neutron scattering and computer simulations these studies show how it is possible to describe the mechanisms of interaction at the molecular level: IL cations penetrate the biomembrane, finding a preferential location between the tails and the heads of the phospholipids.…”

“…Antonio Benedetto (University College Dublin, Ireland, and Paul Scherrer Institut, Switzerland) presents results from joint experimental and computational studies on the interaction between ILs and (model) biomembranes (Benedetto 2017;Benedetto et al 2015, Benedetto et al 2014. Combining neutron scattering and computer simulations these studies show how it is possible to describe the mechanisms of interaction at the molecular level: IL cations penetrate the biomembrane, finding a preferential location between the tails and the heads of the phospholipids.…”