Lyotropic Lamellar Phase Formed from Monolayered θ-Shaped Carborane-Cage Amphiphiles
Lyotropic Lamellar Phase Formed from Monolayered θ-Shaped Carborane-Cage Amphiphiles
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DOI：
10.1002/anie.201307357
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发表时间：
2013-11-11
影响因子：
16.6
通讯作者：
Diat, Olivier
中科院分区：
文献类型：
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作者：
Brusselle, Damien;Bauduin, Pierre;Diat, Olivier
溶致层状相自然发生，是生命发展的关键结构特征，因为它们能够形成闭孔拓扑结构。[1]但除了闭孔拓扑结构，使生命意味着相同的溶剂必须在细胞膜的两侧，因此至少需要双层膜结构。为此，必须启用层状相。在这里，我们表明，层状相的形成是不是排他性的烷基链为基础的表面活性剂具有明确的两亲性结构，但它也可以得到与metallacarborane集群，前面描述为θ-形两亲物。[2]与磷脂细胞膜类似，所形成的层可以根据温度以液态和固态存在。二维分子排列的测定表明，分子间氢键的形成，如-C-H δ+··· δ-H-B-，是片层自组装过程的驱动力。与源于疏水效应的常见双层结构相比，[3] θ形两亲物形成具有独特单分子结构的层状结构，让人想起无机层状系统中观察到的层状片。[4]平面有机-无机杂化片材的纳米级有序化通过自组装过程由温度和浓度控制。溶致层状相是迄今为止最常见的表面活性剂中间相，其特征在于基本近晶液晶对称性。[5]大量的文献可以在这个主题上找到，因为它显示了在许多不同领域的实际应用，例如在洗涤剂，制药，[6]食品，[7]或材料合成中作为模板。[8]它的介观结构由平行堆叠的双层组成，双层是生物膜的结构单元，被水层隔开。为了区分表面活性剂烷基链的熔融和冻结状态，层状相被称为Lα和Lβ（或“凝胶相”）。[9]因此，表面活性剂在Lα中具有类似液体的流动性，而链运动在Lβ中受到高度限制，主要限于围绕链轴的旋转，如在长链烷烃中形成的旋转体相的情况。双层膜中的表面活性剂大多具有全反式烷基链构象，在Lβ的情况下可能具有链叉指或链倾斜。仅在具有明确两亲性特征的分子中观察到溶致层状相。在这里，我们发现，metallabis（二卡宾衍生物），[10]具有两亲性的大阴离子，在高浓度下在水中形成溶致层状相。在以前的研究中，钴双（-二羧）阴离子（[COSAN]与H+作为抗衡离子）的表面活性剂的性质是突出的。[2，11]尽管[COSAN]的中心区域在钴原子周围比它的两个末端更极性（和局部带电），[12] H [COSAN]（图1）没有显示出经典的两亲结构，因此根据其分子形状被命名为θ形两亲物。H [COSAN]通过形成各向同性相在水中自组装：在稀释状态下，单分子厚度的囊泡通过增加浓度变成小胶束。（[I2COSAN]-以H+作为抗衡离子，图1）通过确定含有水的二元体系的温度-浓度（T/φ）相图[13]，该相图显示了各向异性双折射相的出现（见图2）。通过结合视觉观察，
Lyotropic lamellar phases occur naturally and are a key architectural feature for life to develop as they enable the formation of closed-cell topologies.[1] But in addition to closed-cell topologies, enabling life means that the same solvent must be on both sides of the cell membrane, hence at least a double-layered membrane structure is necessary. For this a lamellar phase must be enabled. Herein we show that the formation of lamellar phases is not exclusive to alkylchain-based surfactants with a well-defined amphiphilic structure but that it can also be obtained with metallacarborane clusters, described previously as θ-shaped amphiphiles.[2] Similarly to phospholipid cell membranes the lamellae formed can exist both in the liquid and in the solid states depending on temperature. The determination of the 2D molecular arrangement in the lamella demonstrated that the formation of intermolecular dihydrogen bonds, such as-C-Hδ+··· δÀH-B-, is the driving force in the lamella self-assembly process. Compared to the common bilayer structure that originates from the hydrophobic effect,[3] θ-shaped amphiphiles form lamellae with a peculiar monomolecular structure reminiscent of lamellar sheets observed in inorganic layered systems.[4] Nano-scale ordering of planar organic–inorganic hybrid sheets is controlled by temperature and concentration through a self-assembly process. The lyotropic lamellar phase, characterized by an elementary smectic liquid-crystal symmetry, is by far the most common surfactant mesophase.[5] A vast literature can be found on the topic as it shows practical applications in many different fields, such as in detergents, pharmaceutics,[6] food,[7] or materials synthesis as templates.[8] Its mesostructure consists of parallel stacks of bilayers, the structural unit of biological membranes, separated by water layers. To distinguish between molten and frozen states of the surfactant alkyl chains, lamellar phases are referred to as Lα and Lβ (or “gel phase”).[9] Therefore the surfactant has a liquid-like mobility in Lα whereas chain motions are highly restricted in Lβ, mostly limited to rotation about the chain axis as is the case in rotator phases formed in long-chain alkanes. Surfactants in the bilayers have mostly an all-trans alkyl-chain conformation with possible chain inter-digitation or chain tilt in the case of Lβ. Lyotropic lamellar phases have only been observed with molecules that have a well-defined amphiphilic character. Herein, we show that metallabis (dicarbollide derivatives),[10] large anions with amphiphilic properties, form lyotropic lamellar phases at high concentrations in water. In previous studies, the surfactant-like properties of cobaltabis (-dicarbollide) anion ([COSAN] À with H+ as the counterion) were highlighted.[2, 11] Even though the central region of [COSAN] À around the cobalt atom is more polar (and locally charged) than its two extremities,[12] H [COSAN](Figure 1) does not show a classical amphiphilic structure and was therefore named θ-shaped amphiphile in reference to its molecular shape. H [COSAN] self-assembles in water by forming isotropic phases: vesicles of monomolecular thickness in diluted regime that turn into small micelles by increasing concentration.We focus herein on the diiodo-COSAN ([I2COSAN] À with H+ as counterion, Figure 1) by determining the temperature–concentration (T/φ) phase diagram [13] of the binary system with water that shows the occurrence of anisotropic birefringent phases (Figure 2). By combining visual observa-