Modulation of Phase Behavior and Microscopic Dynamics in Cationic Vesicles by 1-Decyl-3-methylimidazolium Bromide

Abstract

Synthetic cationic lipids have garnered significant attention as promising candidates for gene/DNA transfection in therapeutic applications. The phase behavior of the vesicles formed by these lipids is intriguing, revealing intricate connections to the structure and dynamics of the membrane. These phenomena emerge from the complex interplay between hydrophobic and electrostatic interactions of the lipids. In this study, we explore the impact of an ionic liquid-based surfactant, 1-decyl-3-methylimidazolium bromide (DMIM-[Br]), on the structural, dynamical, and phase behavior of cationic dihexadecyldimethylammonium bromide (DHDAB) vesicles. Our investigations indicate that the addition of DMIM[Br] increases the vesicle size while thinning the membrane. Further, DMIM[Br] also induces substantial changes in the membrane phase behavior. At 10 and 25 mol %, DMIM[Br] eliminates the pre-transition from coagel to intermediate crystalline (IC) phase and decreases the onset temperature of the main phase transition to the fluid phase. In the cooling cycle, the addition of DMIM[Br] further induces the formation of an intermediate gel phase. This behavior is reminiscent of the non-synchronous ordering observed in the DODAB membrane, a longer-chain counterpart of DHDAB. Interestingly, at 40 mol % of DMIM[Br], the formation of the intermediate gel phase is largely suppressed. Neutron scattering data provide evidence that the addition of DMIM[Br] enhances lipid mobility in coagel and fluid phases, suggesting that DMIM[Br] acts as a plasticizer, enhancing membrane fluidity across all of the phases. Our findings infer that DMIM[Br] modulates the membrane's phase behavior and fluidity, two essential ingredients for the efficient transport of cargo, by controlling the balance of electrostatic and hydrophobic interactions.

The Physics of Antimicrobial Activity of Ionic Liquids

“…The DPPC membrane presents significant dynamical activity in the spatiotemporal range of the IRIS spectrometer, as revealed by the strong quasielastic broadening, with the incorporation of the IL accelerating the membrane dynamics. Within the spatiotemporal domain of the IRIS spectrometer, lipid molecules predominantly exhibit two distinct dynamical modes: (i) lateral motion within the leaflet and (ii) localized internal motions of lipid alkyl chains. ,,− The observed scattering data can be described as a convolution of two scattering laws, each associated with one of the two motions, expressed as: S normalm normale normalm ( Q , E ) = A ( Q ) italicL normall normala normalt ( Γ l a t , E ) + false( 1 − A ( Q ) L normalt normalo normalt ( Γ l a t + Γ int , E ) …”