Abstract
Despite the environmentally friendly reputation of ionic liquids (ILs), their safety has been recently questioned given their potential as cytotoxic agents. The fundamental mechanisms underlying the interactions between ILs and cells are less studied and by far not completely understood. Biomimetic films are here important biophysical model systems to elucidate fundamental aspects and mechanisms relevant for a large range of biological interaction ranging from signaling to drug reception or toxicity. Here we use dissipative quartz crystal microbalance QCM-D to examine the effect of aqueous imidazolium-based ionic liquid mixtures on solid-supported biomimetic membranes. Specifically, we assess in real time the effect of the cation chain length and the anion nature on a supported vesicle layer of the model phospholipid DMPC. Results indicate that interactions are mainly driven by the hydrophobic components of the IL, which significantly distort the layer and promote vesicle rupture. Our analyses evidence the gradual decrease of the main phase transition temperature upon increasing IL concentration, reflecting increased disorder by weakening of lipid chain interactions. The degree of rupture is significant for ILs with long hydrophobic cation chains and large hydrophobic anions whose behavior is reminiscent of that of antimicrobial peptides.
Highlights
Ionic liquids (ILs) are a large class of ionic compounds usually composed of an organic cation and an organic or inorganic anion
Stability of DMPC vesicle layers exposed to imidazolium-based ionic liquids
Following is a significant rapid increase of Δf and decrease of ΔD reflecting complete vesicle rupture, until stable and overlapping overtone values Δf ~ –23 Hz, ΔD ~ 0 are reached. These final values correspond to the presence of a thin, rigid supported lipid bilayer [29], and the frequency and dissipation signatures upon addition of the ionic liquid mixture are reminiscent of the so-called disrupting carpet mechanism of antimicrobial forming peptides [32, 46]
Summary
Ionic liquids (ILs) are a large class of ionic compounds usually composed of an organic cation and an organic or inorganic anion. Ionic liquids are often referred to as “Green solvents” due to their negligible vapor pressure, which minimizes their release into the atmosphere and renders them nonflammable All these characteristics provide ILs with great potential for applications in a variety of fields, such as lubricants, electrolytes or bioprocessing, and make them eventually more environmental-friendly and safer substitutes to the traditional organic solvents in many chemical. As a matter of fact, their reputed character as environmentally friendly solvents has motivated a vast number of studies over the last decade [1,2,3,4,5,6,7,8] Their low volatility renders them odorless and hard to detect in the event of a leak to aquatic ecosystems. Biomimetic films are important biophysical model systems to elucidate fundamental aspects and mechanisms relevant for a large range of biological interaction ranging from biosignaling to drug reception or toxicity
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