Department of Chemistry, Indian Institute of Technology , Kharagpur 721302, WB India.
Langmuir. 2017 Sep 26;33(38):9811-9821. doi: 10.1021/acs.langmuir.7b02136. Epub 2017 Sep 11.
In this article, anionic lipophilic dye merocyanine 540(MC540) and cationic surface-active ionic liquid (SAIL) 1-octyl-3-methylimidazolium chloride (CmimCl) are employed to construct highly ordered fibrillar and vesicular aggregates exploiting an ionic self-assembly (ISA) strategy. It is noteworthy that the concentration of the counterions has exquisite control over the morphology, in which lowering the concentration of both the building blocks in a stoichiometric ratio of 1:1 provides a vesicle to fibril transition. Here, we have reported the concentration-controlled fibril-vesicle transition utilizing the emerging fluorescence lifetime imaging microscopy (FLIM) technique. Furthermore, we have detected this morphological transformation by means of other microscopic techniques such as field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and cryogenic-transmission electron microscopy (cryo-TEM) to gain additional support. Besides, multiwavelength FLIM (MW-FLIM) and atomic force microscopy (AFM) techniques assist us in knowing the microheterogeneity and the height profile of the vesicles, respectively. We have replaced the SAIL, CmimCl, by an analogous traditional surfactant, n-octyltrimethylammonium bromide (OTAB), and it provides a discernible change in morphology similar to that of CmimCl, whereas 1-octanol is unable to exhibit any structural aggregation and thus reveals the importance of electrostatic interaction in supramolecular aggregate formation. However, the SAILs having the same imidazolium headgroup with different chain lengths other than CmimCl are unable to display any structural transition and determine the importance of the correct chain length for efficient packing of the counterions to form a specific self-assembly. Therefore, this study reveals the synergistic interplay of electrostatic, hydrophobic, and π-π stacking interactions to construct the self-assembly and their concentration-dependent morphological transition.
在本文中，采用阴离子亲脂性染料甲烯蓝 540（MC540）和阳离子表面活性剂离子液体 1-辛基-3-甲基咪唑氯化物（CmimCl），通过离子自组装（ISA）策略构建高度有序的纤维状和囊泡状聚集体。值得注意的是，抗衡离子的浓度对形态具有精细的控制作用，其中以化学计量比 1:1 降低两种构建块的浓度会导致从囊泡到纤维的转变。在这里，我们利用新兴的荧光寿命成像显微镜（FLIM）技术报告了浓度控制的纤维-囊泡转变。此外，我们还利用场发射扫描电子显微镜（FESEM）、透射电子显微镜（TEM）和低温透射电子显微镜（cryo-TEM）等其他显微镜技术检测到这种形态转变，以获得更多的支持。此外，多波长 FLIM（MW-FLIM）和原子力显微镜（AFM）技术分别帮助我们了解囊泡的微不均匀性和高度轮廓。我们用类似的传统表面活性剂辛基三甲基溴化铵（OTAB）代替 SAIL，CmimCl，发现其形态发生了明显变化，类似于 CmimCl，而辛醇则不能表现出任何结构聚集，从而揭示了静电相互作用在超分子聚集形成中的重要性。然而，具有与 CmimCl 不同链长的相同咪唑啉头基的 SAIL 无法显示任何结构转变，这确定了正确链长对于有效包装抗衡离子以形成特定自组装的重要性。因此，本研究揭示了静电、疏水和π-π堆积相互作用的协同相互作用，以构建自组装及其浓度依赖性的形态转变。
