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Effect of the Alkyl Chain Length of Amphiphilic Ionic Liquids on the Structure and Dynamics of Model Lipid Membranes.

Sandeep KumarHolger A ScheidtNavleen KaurTejwant Singh KangGagandeep Kaur GahlayDaniel HusterVenus Singh Mithu
Published in: Langmuir : the ACS journal of surfaces and colloids (2019)
We compare the biophysical and structural aspects of the interaction of amphiphilic ionic liquids containing 1-alkyl-3-methylimidazolium cation ([CnMIM]+, n = 8, 12, or 16) with membranes composed of zwitterionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or anionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-rac-glycerol (POPG). Liposome affinity and permeabilization were determined using ζ-potential and fluorescence studies, correlated with the cytoxicity of [CnMIM]+Br- toward HeLa cell lines. Membrane affinity is strongest in the case of [C16MIM]+Br- followed by [C12MIM]+Br- and [C8MIM]+Br- for both membranes, and trends remained the same in the case of membrane permeability and cytotoxicity. Solid-state NMR spectroscopy was used to localize [CnMIM]+ inside the lipid bilayers and to study their impact on the head group and acyl chain structures and dynamics of the lipid molecules. The charged ring moiety of the [CnMIM]+ is localized in the lipid-water interface of the membranes irrespective of the chain length and membrane surface charge. While [C8MIM]+ binds the membrane most weakly, it induces the largest disorder in the lipid chain region. A lack of fast flip-flop motions of the amphiphiles in the case of long chain [C16MIM]+ is suggested to render the membrane unstable, which increases its permeability. Between the lipid molecules, the POPC membrane incurs larger disorder in lipid chain packing upon insertion of [CnMIM]+ molecules. The study provides structural details of the impact of increasing chain lengths in [CnMIM]+ on the structural properties of lipid bilayers.
Keyphrases
  • ionic liquid
  • fatty acid
  • room temperature
  • high resolution
  • endothelial cells
  • molecular dynamics simulations
  • solid state
  • risk assessment
  • climate change
  • single molecule
  • cell death