Self-supporting elastic film without covalent linkages as a hierarchically integrated beta-sheet assembly.
Self-supporting elastic film without covalent linkages as a hierarchically integrated beta-sheet assembly.
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DOI：
10.1002/anie.200352185
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发表时间：
2003-11
影响因子：
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通讯作者：
N. Yamada;Tsukasa Komatsu;Hirotsugu Yoshinaga;K. Yoshizawa;Susumu Edo;M. Kunitake
中科院分区：
文献类型：
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作者：
N. Yamada;Tsukasa Komatsu;Hirotsugu Yoshinaga;K. Yoshizawa;Susumu Edo;M. Kunitake
一般来说，可在某种介质中形成聚集体的两亲性分子，特别是水性双层聚集体，当将溶液流延到合适的基底上然后风干时，形成自支撑膜。[1]流延膜内的有序分子排列可用于形成具有很少缺陷的多层膜或涂层。然而，超分子流延膜既没有机械强度也没有弹性。本研究的目的是提高流延膜的机械强度，并形成具有高分子膜的弹性的弹性超分子膜。高分子膜的突出优点，即强度和弹性，归因于构成最低单元分子（单体）序列的共价键。因此，需要一种替代的相互作用来取代共价键，以获得弹性超分子膜。通过使用多个H键作为替代，Meijer及其同事已经证明了超分子聚合物。[2]超分子聚合物的单体在分子的两个边缘具有两组氢键嵌段，例如嘧啶酮，其通过多个氢键连接其它分子。硼型单体产生高粘度的树脂状液体。Rebek，Jr.也报道了类似的物质。和同事[3]此外，Hutchison的研究小组证明，含甘氨酰甘氨酸的两亲物的自组装单层通过氢键的3D网络稳定。[4]另一方面，在含三肽的两亲物的流延膜中观察到作为β-折叠结构的多个氢键。[5]这些两亲物产生自支撑透明膜，但它们非常脆。这一结果意味着需要另一种固定β-折叠的相互作用来提高超分子膜的机械强度。因此，我们尝试使用肽部分的侧链。由于相邻氨基酸残基的侧链位于β折叠平面的相反方向[6]，因此侧链可以与其他β折叠平面的对应物互锁。如图1所示，当肽部分含有至少三个连续的亮氨酸残基时，这种特定的叉指结构应该固定β折叠平面，这类似于拉链或紧固件。为了减少与亮氨酸拉链肽的混淆，我们更愿意将上述结构称为“亮氨酸紧固件”。如果不存在β-折叠结构，则不会形成亮氨酸紧固件。重点放在这个层次上。然而，到目前为止，这种分层整合尚未实现。我们在此展示了超分子单体的分级整合，并且旨在形成单体之间没有共价键的自支撑弹性膜。研究中使用的超分子单体是含亮氨酸的两亲物（N + C11（Leu）nGlu（OC12）2; n = 2，3，4）。这些两亲物溶解在具有低介电常数的溶剂中，即CCl 4、苯、甲苯和环己烷，并且在大于1mm的浓度下形成凝胶。在具有较高介电常数的有机溶剂中，例如CHCl 3，两亲物产生澄清溶液。这些结果与我们以前的结果与其他三肽或四肽含有两亲物是一致的。[5，7]我们从CCl4凝胶和各向同性的CHCl3溶液制备了空气干燥的流延膜;将溶液流延到硅涂层纸上，然后空气干燥。硅涂层纸可用作蒸煮纸，这有助于形成
In general, an amphiphilic molecule that can form an aggregate in a certain medium, especially an aqueous bilayer aggregate, forms a self-supporting film when the solution is cast onto an appropriate substrate then air dried.[1] The orderly molecular alignment within the cast film is useful for forming an ultrathin layer or coating with few defects. However, the supramolecular cast film has neither mechanical strength nor elasticity. Our aim in the present study is to improve the mechanical strength of the cast film, and to form an elastic supramolecular film that has the elastic properties of a macromolecular film. The prominent advantages of macromolecular films, namely, strength and elasticity, are ascribed to the covalent linkage that constitutes a sequence of the lowest unit molecule, the monomer. Therefore, an alternative interaction is needed to replace the covalent linkage to obtain an elastic supramolecular film. By using multiple H bonding as an alternative, Meijer and co-workers have demonstrated a supramolecular polymer.[2] The monomer of the supramolecular polymer has two sets of H-bonding blocks, for example, pyrimidon, at both edges of the molecule, which links the other molecules by multiple H bonding. The bora-type monomers yield a highly viscous, resinlike liquid. A similar substance has also been reported by Rebek, Jr. and coworkers.[3] Furthermore, the research group of Hutchison demonstrated that the self-assembled monolayer of a glycylglycine-containing amphiphile was stabilized by 3D networks of H bonding.[4] On the other hand, multiple H bonding has been observed as a β-sheet structure in the cast films of the tripeptide-containing amphiphiles.[5] These amphiphiles produce a self-supporting transparent film, but they are extremely brittle. This result means that another interaction that immobilizes the β-sheets will be needed for improving the mechanical strength of the supramolecular film. Thus, we attempted to use the side chains of the peptide part. Because the side chains of the adjacent amino-acid residues locate in opposite directions across the β-sheet plane,[6] the side chains could interlock with counterparts of the other β-sheet planes. This specific interdigitated structure should fasten the β-sheet planes when the peptide part contains at least three consecutive leucine residues as illustrated in Figure1, which is similar to a zipper or a fastener. To reduce the confusion with the leucine zipper peptides, we prefer to call the aforementioned structure “leucine fastener”. The leucine fastener will not be formed if a β-sheet structure is absent. Emphasis is placed on this hierarchy. However, until now, such hierarchic integration has not yet been realized. We demonstrate herein the hierarchic integration of supramolecular monomers, and aim to form a self-supporting elastic film without covalent linkage between the monomers. The supramolecular monomers used in the study are leucine-containing amphiphiles (N+C11 (Leu) nGlu (OC12) 2; n= 2, 3, 4). These amphiphiles dissolve in solvents with a low dielectric constant, namely, CCl4, benzene, toluene, and cyclohexane, and form a gel at concentrations greater than 1 mm. In organic solvents with a higher dielectric constant, for example CHCl3, the amphiphiles produce a clear solution. These results are consistent with our previous results with the other tripeptide or tetrapeptide-containing amphiphiles.[5, 7] We prepared the air-dried cast film from a CCl4 gel and an isotropic CHCl3 solution; the solutions were cast onto siliconcoated paper then air dried. The silicon-coated paper is available as cooking paper, which is helpful for the formation