Abstract
Quartz crystal microbalance with dissipation (QCM-D) monitoring and atomic force microscopy (AFM) were combined to evaluate the defects created by an ionic liquid anion and a cation in a supported phospholipid bilayer composed of zwitterionic lipids on a silica surface. The cation 1-octyl-3-methyl imidazolium (OMIM(+)) was shown to remove lipids from the bilayer, increase the roughness to approximately 2.8 nm (~0.2 for stable supported bilayer) and possibly redeposit lipids with entrapped water. The anion bis(trifluoromethylsulfonyl)imide (Tf(2)N(-)) was found to leave distinct defects within the bilayer that had large pore-like interiors which left the surrounding bilayer intact. However, the ionic liquid 1-butyl-1-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-Tf(2)N) formed a film over the supported bilayer. This work demonstrates, for the first time, the direct effects common components of ionic liquids have on a supported phospholipids bilayer.
Highlights
Over the past few years, considerable interest in developing biocatalytic systems in non-aqueous environments [1,2,3] has developed
All measurements were conducted with DEPC vesicles at 125μM and at 20°C (this ensures vesicle interactions with 1-octyl-3-methyl imidazolium chloride (OMIM-Cl) and LiTf2N are not affected by lipids in a gel phase)
In the case for DMPC, it was found that the presence of a minimum of 90mM NaCl was required for vesicles to form a Supported phospholipid bilayer (SPB) through a two-step pathway which started with the collection of vesicles on the surface at a critical density followed by the final SPB formation [22]
Summary
Over the past few years, considerable interest in developing biocatalytic systems in non-aqueous environments [1,2,3] has developed. By conducting biocatalytic processes in non-aqueous systems, one can extend catalytic specificity of the enzymes and substrates toward new substrates in novel reactions systems. Substrates such as plant sterols [4], cinnamoylated lipids [5] and commodity vegetable oils [6], which are less soluble in water, could benefit significantly from non-aqueous media in which the substrates dissolve and the reaction occurs at a reasonable rate. Room-temperature ionic liquids have little or none of the hazards associated with typical organic solvents and have shown to maintain chemical/thermal stability along with high ionic conductivity [7, 8]. The intent is to shed more light on the details of interactions of these components with phosphatidylcholine bilayers
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