【摘要】 研究了一种微生物脂肽——表面活性素与二肉豆蔻酰磷脂酰胆碱(DMPC)在气/液界面形成的混合单分子膜性质。测定了混合单分子膜的表面压-分子面积(π-A)曲线,根据π-A曲线获得了不同表面压下混合单分子膜的过剩面积(Aex)和混合过剩自由能(ΔGmex)与混合单分子膜中表面活性素摩尔分数的关系。Aex和ΔGemx的计算结果均表明,表面活性素与DMPC在纯水亚相上形成的混合单分子膜中不相容,二者之间的相互作用主要是排斥力。通过原子力显微镜观察了在表面压15mN/m下的混合单分子膜的LB膜,发现表面活性素与DMPC发生了微相分离,说明二者在混合膜中的烷基链取向不同,这可能是二者发生排斥作用的主要原因之一。此外,还研究了亚相pH对混合单分子膜相容性的影响,发现表面活性素与DMPC在混合单分子膜中的相容性在碱性环境下增强,这可能与二者极性头基之间的相互作用有关。更多还原

【Abstract】 Mixed monolayers of microbial lipopeptide surfactin and dimyristoylphosphocholine(DMPC) at the air-water interface were studied by measuring the surface pressure-molecular area(π-A) isotherms.The excess area(A_ex) and the excess free energy of mixing(ΔGex_m) were analyzed as a function of the surfactin molar fraction under various surface pressures.Both the A_ex and ΔGex_m indicate that surfactin and DMPC in mixed monolayers are completely immiscible on pure water surface.The LB film of mixed monolayer at 15mN/m was imaged by atomic force microscopy(AFM).AFM image reveals phase separation for the mixed monolayer,suggesting a difference for surfactin and DMPC in molecular orientation.Furthermore,the effect of subphase pH on miscibility of surfactin and DMPC in mixed monolayers was investigated.It is observed that surfactin and DMPC are miscible on alkaline subphase.All results presented here provide a presumption that the molecular interactions in mixed surfactin/DMPC monolayer could be related with different molecular orientation of their alkyl chains and interactions between their polar heads.更多还原