Gupta Ritika, Sharma Veerendra K, Gupta Jyoti, Ghosh Sajal K
Department of Physics, School of Natural Sciences, Shiv Nadar University, NH 91, Tehsil Dadri, G. B. Nagar, Greater Noida, Uttar Pradesh 201314, India.
Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
Langmuir. 2022 Mar 22;38(11):3412-3421. doi: 10.1021/acs.langmuir.1c03160. Epub 2022 Mar 9.
Amphiphilic imidazolium-based ionic liquids (ILs) have proven their efficacy in altering the membrane integrity and dynamics. The present article investigates the phase-separated domains in a 1,2-dipalmitoyl--glycero-3-phosphocholine (DPPC) membrane induced by 1,3 dialkylated imidazolium IL. Isotherm measurements on DPPC monolayers formed at the air-water interface have shown a decrease in the mean molecular area with the addition of this IL. The positive value of the excess Gibbs free energy of mixing indicates an unfavorable mixing of the IL into the lipid. This leads to IL-induced phase-separated domains in the multilayer of the lipid confirmed by the occurrence of two sets of equidistance peaks in the X-ray reflectivity data. The electron density profile along the surface normal obtained by the swelling method shows the bilayer thickness of the newly formed IL-rich phase to be substantially lower (∼34 Å) than the DPPC phase (∼45.8 Å). This IL-rich phase has been confirmed to be interdigitated, showing an enhanced electron density in the tail region due to the overlapping hydrocarbon chains. Differential scanning calorimetry measurements showed that the incorporation of IL enhances the fluidity of the lipid bilayer. Therefore, the study indicates the formation of an interdigitated phase with a lower order compared to the gel phase in the DPPC membrane supplemented with the IL.
两亲性咪唑基离子液体（ILs）已证明其在改变膜完整性和动力学方面的功效。本文研究了由1,3 - 二烷基咪唑鎓离子液体诱导的1,2 - 二棕榈酰 - sn - 甘油 - 3 - 磷酸胆碱（DPPC）膜中的相分离域。在空气 - 水界面形成的DPPC单分子层的等温测量表明，添加这种离子液体后平均分子面积减小。混合超额吉布斯自由能的正值表明离子液体与脂质的混合不利。这导致在脂质多层膜中出现离子液体诱导的相分离域，这通过X射线反射率数据中出现的两组等距峰得到证实。通过溶胀法获得的沿表面法线的电子密度分布表明，新形成的富含离子液体的相的双层厚度（约34 Å）明显低于DPPC相（约45.8 Å）。已证实这种富含离子液体的相是相互穿插的，由于烃链的重叠，在尾部区域显示出增强的电子密度。差示扫描量热法测量表明，离子液体的掺入增强了脂质双层的流动性。因此，该研究表明在添加离子液体的DPPC膜中形成了一种与凝胶相比有序度较低的相互穿插相。
