Polymer Science Unit, Indian Association for the Cultivation of Science, Kolkata, India 700032.
Solid State Physics Division, Bhabha Atomic Research Centre , Mumbai, India 400085.
Langmuir. 2018 Jan 23;34(3):868-875. doi: 10.1021/acs.langmuir.7b01652. Epub 2017 Aug 8.
The article describes the self-assembly of a series of unsymmetrical bola-shaped π-amphiphiles (NDI-1, NDI-1a, NDI-2, NDI-3, and NDI-4) consisting of a hydrophobic naphthalene-diimide (NDI) chromophore attached to a nonionic hydrophilic wedge and an anionic headgroup in the two opposite arms of the central NDI. By design, only a single hydrazide group is linked either on the ionic or nonionic arm of the NDI. NDI-1 and NDI-1a are regioisomers differing only in the location of the hydrazide group, placed in the nonionic or ionic arm, respectively. NDI-2, NDI-3, and NDI-4 are similar to NDI-1 in the placement of the hydrazide group but differ in the nature of the ionic headgroups. Except for NDI-2, all of them exhibit spontaneous vesicle structures in water (pH 9.0) as established by electron microscopy, small-angle neutron scattering, dynamic light scattering, and spectroscopy studies. Supramolecularly assembled oligo-oxyethylene chains of the hydrophobic wedge exhibited a lower critical solution temperature (LCST) at ∼40 °C, similar to that of covalent polymers. Consequently, above the LCST, the bola-amphiphile was converted to a single headgroup surfactant, resulting in the collapse of the vesicular structure to nanoparticles. In all examples, the dominant H-bonding force among the hydrazide groups resulted in unidirectional orientation, leading to the formation of a nonsymmetric membrane with the H-bonded chain located at the inner wall. Therefore, the functional group displayed in these vesicles could be fully dictated by the location of the hydrazide group. Thus, for NDI-1, NDI-3, or NDI-4, the hydrazide group, located at the nonionic arm, directed the nonionic wedge to converge at the inner wall of the vesicle by displaying the anionic headgroups toward the outer surface. In contrast, NDI-1a formed a nonionic vesicle because in this case anionic headgroups were located at the inner wall of the membrane. Furthermore, among NDI-1, NDI-3, and NDI-4, the charge density of the anionic surface and accordingly the radius of curvature and particle size could be tuned precisely as a function of the extent of charge delocalization in the phenoxide or carboxylate headgroup. These distinct self-assembly modes resulted in very different abilities of these vesicles for electrostatic-interaction-driven biomolecular recognition, which was studied by testing their ability to bind with cationic protein chymotripsin and inhibit its enzymatic activity. The enzyme inhibition ability followed the order NDI-1 > NDI-3 > NDI-4 > NDI-2 ≈ NDI-1a, which could be rationalized by their distinct functional group display and surface charge density factors.
本文描述了一系列不对称的棒状π-两亲分子（NDI-1、NDI-1a、NDI-2、NDI-3 和 NDI-4）的自组装，这些分子由疏水萘二酰亚胺（NDI）发色团连接到中央 NDI 的两个相反臂中的非离子亲水头基和阴离子头基组成。通过设计，只有一个单酰肼基团连接在 NDI 的离子或非离子臂上。NDI-1 和 NDI-1a 是仅在酰肼基团位置上不同的区域异构体，分别位于非离子或离子臂上。NDI-2、NDI-3 和 NDI-4 在酰肼基团的位置上与 NDI-1 相似，但离子头基的性质不同。除了 NDI-2 之外，所有这些在水中（pH 9.0）中都表现出自发的囊泡结构，这是通过电子显微镜、小角中子散射、动态光散射和光谱研究确定的。疏水性楔形物的超分子组装聚氧乙烯链表现出约 40°C 的低临界溶液温度（LCST），类似于共价聚合物。因此，在 LCST 以上，棒状两亲分子转化为单一的头基表面活性剂，导致囊泡结构坍塌为纳米颗粒。在所有例子中，酰肼基团之间的主要氢键力导致单向取向，导致形成具有氢键链位于内壁的不对称膜。因此，这些囊泡中显示的官能团可以完全由酰肼基团的位置决定。因此，对于 NDI-1、NDI-3 或 NDI-4，位于非离子臂上的酰肼基团通过将阴离子头基指向外表面，将非离子楔形物引导到囊泡的内壁处，从而使非离子楔形物收敛。相比之下，NDI-1a 形成非离子囊泡，因为在这种情况下，阴离子头基位于膜的内壁处。此外，在 NDI-1、NDI-3 和 NDI-4 中，阴离子表面的电荷密度以及相应的曲率半径和粒径可以作为在酚氧基或羧基头基中电荷离域程度的函数进行精确调节。这些不同的自组装模式导致这些囊泡在静电相互作用驱动的生物分子识别方面具有非常不同的能力，通过测试它们与阳离子蛋白糜蛋白酶结合并抑制其酶活性的能力来研究这种能力。酶抑制能力遵循 NDI-1>NDI-3>NDI-4>NDI-2≈NDI-1a 的顺序，这可以通过它们不同的官能团显示和表面电荷密度因素来合理化。
