【摘要】 表面活性素是一类具有较强表面活性的微生物脂肽类化合物, 能在空气/水界面形成不溶性单分子膜.利用Langmuir膜天平测定了表面活性素单分子膜的压缩-扩张循环曲线, 发现单分子膜在经历了"平台区"后出现较大的迟滞环, 迟滞环的形状与亚相pH有关. 将"平台区"的单分子膜转移到云母表面后, 用原子力显微镜(AFM)和扫描电子显微镜(SEM)均观察到高度达几十至数百纳米的表面聚集体, 说明表面活性素在单分子膜的"平台区"伴随着自聚集. 研究结果表明, 表面活性素单分子膜在空气/水界面的迟滞现象是分子浸入亚相和形成三维表面聚集体共同作用的结果.更多还原

【Abstract】 Surfactin,one of the most surface-active microbial lipopeptides,can readily form an insoluble monolayer at the air/water interface.Consecutive compression-expansion cycles of surfactin with a β-hydroxyl fatty acid chain consisting of 14 carbon atoms were studied by a Langmuir film balance.A larger hysteresis loop was observed when the compression isotherm reached a plateau compared with that expanded at a lower surface pressure(20 mN·m-1).The 2nd cycle was shifted towards smaller molecular areas compared with the 1st cycle.We also studied the hysteresis cycles of the surfactin monolayer on subphase of different pH values.With a decrease in the subphase pH the hysteresis loop became smaller and the expansion isotherm curve underwent a longer pseudo plateau.Furthermore,the morphologies of the surfactin monolayers in the plateau region,which were transferred onto a mica surface,were characterized by atomic force microscopy(AFM) and scanning electron microscopy(SEM).Both AFM and SEM images gave three-dimensional surface aggregates with heights ranging from tens to hundreds of nanometers.The above results suggest that the formation of three-dimensional surface aggregates at the plateau region induces a large hysteresis loop in the surfactin monolayer,which can also be attributed to the submergence of molecules into the subphase when the peptide loop in the surfactin molecule is ionized.更多还原