Chen Cheng-Hao, Tian Ching-An, Chiu Chi-Cheng
Department of Chemical Engineering, National Cheng Kung University, Tainan City 701, Taiwan.
Bioengineering (Basel). 2017 Oct 11;4(4):84. doi: 10.3390/bioengineering4040084.
Ion pair amphiphile (IPA), a lipid-like complex composed of a pair of cationic and anionic surfactants, has great potentials in various pharmaceutical applications. In this work, we utilized molecular dynamics (MD) simulation to systematically examine the structural and mechanical properties of the biomimetic bilayers consist of alkyltrimethyl-ammonium-alkylsulfate (CTMA⁺-CS) IPAs with various alkyl chain combinations. Our simulations show an intrinsic one-atom offset for the CTMA⁺ and CS alignment, leading to the asymmetric index definition of ΔC = m - (n + 1). Larger |ΔC| gives rise to higher conformational fluctuations of the alkyl chains with the reduced packing order and mechanical strength. In contrast, increasing the IPA chain length enhances the van der Waals interactions within the bilayer and thus improves the bilayer packing order and mechanical properties. Further elongating the CTMA⁺-CS alkyl chains to m and n ≥ 12 causes the liquid disorder to gel phase transition of the bilayer at 298 K, with the threshold membrane properties of 0.45 nm² molecular area, deuterium order parameter value of 0.31, and effective bending rigidity of 20 kT, etc. The combined results provide molecular insights into the design of biomimetic IPA bilayers with wide structural and mechanical characteristics for various applications.
离子对两亲物（IPA）是一种由一对阳离子和阴离子表面活性剂组成的类脂复合物，在各种药物应用中具有巨大潜力。在这项工作中，我们利用分子动力学（MD）模拟系统地研究了由具有各种烷基链组合的烷基三甲基硫酸铵-烷基硫酸盐（CTMA⁺-CS）IPA组成的仿生双层膜的结构和力学性能。我们的模拟显示CTMA⁺和CS排列存在固有的单原子偏移，导致不对称指数定义为ΔC = m - (n + 1)。|ΔC|越大，烷基链的构象波动越高，堆积顺序和机械强度降低。相反，增加IPA链长会增强双层膜内的范德华相互作用，从而改善双层膜的堆积顺序和力学性能。将CTMA⁺-CS烷基链进一步延长至m和n≥12会导致双层膜在298 K时从液态无序相转变为凝胶相，其阈值膜性能为分子面积0.45 nm²、氘序参数值0.31和有效弯曲刚度20 kT等。综合结果为设计具有广泛结构和力学特性的仿生IPA双层膜以用于各种应用提供了分子层面的见解。
