Bioengineering and Drug Designing Lab, Department of Biotechnology, Indian Institute of Technology Madras, Chennai 600036, India.
Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamil Nadu, India.
Colloids Surf B Biointerfaces. 2014 Apr 1;116:396-402. doi: 10.1016/j.colsurfb.2013.12.034. Epub 2013 Dec 27.
Myriad applications of surfactin in environmental and biomedical field prompt understanding the self-assembly behaviour of surfactin in aqueous solution as well as its interaction with counterions. Effect of four divalent counterions namely, Ni(2+), Zn(2+), Cd(2+), and Ca(2+) on the self-assembly of the surfactin, a biosurfactant isolated from Bacillus subtilis YB7 is studied by fluorescence spectroscopy, dynamic light scattering, optical and electron microscopic studies. The critical micelle concentration (CMC) and aggregation number (Nagg) of surfactin are 96.76 ± 15.49 μM and 101.12 ± 2.53, respectively. The degree of counterion association increases as its ionic radius decreases. Ni(2+) exhibits the highest and Ca(2+) the least degree of counterion association. Addition of counterion reduces the size of the microstructures, aggregation number (Nagg) and zeta potential. The reduction in the zeta potential indicates the neutralization of the negative charges on the electrical double layer of the microstructures. Differential interference contrast (DIC) and transmission electron microscopic (TEM) images of surfactin show the presence of vesicles and large aggregates including giant vesicles. On the addition of Ca(2+), fusion of vesicles into large aggregates is predominantly observed. Ni(2+) induces the transition of large spherical vesicles into small spherical, worm-like vesicles and multicompartment-like structures (vesosome). Such structures are the evidences for metal ion coordinated intervesicular interactions. This study reveals that the self-assembly process of surfactin can be controlled by the addition of metal ions according to the requirements.
生物表面活性剂表面活性剂在环境和生物医学领域的诸多应用促使人们了解表面活性剂在水溶液中的自组装行为及其与抗衡离子的相互作用。研究了四种二价抗衡离子，即 Ni(2+)、Zn(2+)、Cd(2+)和 Ca(2+)对由枯草芽孢杆菌 YB7 分离得到的生物表面活性剂表面活性剂的自组装的影响，荧光光谱法、动态光散射、光学和电子显微镜研究。表面活性剂的临界胶束浓度（CMC）和聚集数（Nagg）分别为 96.76±15.49μM 和 101.12±2.53。抗衡离子的缔合程度随其离子半径的减小而增加。Ni(2+)表现出最高的抗衡离子缔合程度，而 Ca(2+)则表现出最低的抗衡离子缔合程度。抗衡离子的加入减小了微结构、聚集数（Nagg）和 ζ 电位的尺寸。ζ 电位的降低表明微结构电双层上的负电荷被中和。表面活性剂的微分干涉对比（DIC）和透射电子显微镜（TEM）图像显示存在囊泡和包括巨囊泡在内的大聚集体。在加入 Ca(2+)时，主要观察到囊泡融合成大聚集体。Ni(2+)诱导大球形囊泡向小球形、蠕虫状囊泡和多室样结构（囊泡体）的转变。这些结构是金属离子配位的囊泡间相互作用的证据。该研究表明，根据需要，通过添加金属离子可以控制表面活性剂的自组装过程。
