A helical molecule that exhibits two lengths in response to an applied potential
A helical molecule that exhibits two lengths in response to an applied potential
复制标题
DOI：
10.1002/anie.200502240
复制
发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Kimura, S
中科院分区：
文献类型：
--
作者：
Kitagawa, K;Morita, T;Kimura, S
分子器件有望在分子二极管、[1]分子晶体管[2]和分子开关等先进电子学中发挥重要作用。[3]然而，有机分子在金属表面的电子转移机制-分子器件的最基本方面-仍然有待阐明。[4-6]为了阐明这个问题，我们应用螺旋肽作为远程电子转移的介质，[7]作为发色团的支架以加速电子转移，[8]以及分子光电二极管的可行系统。[9]通过扫描隧道显微镜（STM）的仔细观察，在许多情况下已经观察到有机分子中分子电导的随机开关现象。[10-13]这些现象被认为是由伴随着分子取向变化的硫原子杂化的波动引起的。我们的重点是在分子存储器设备中使用这种机制，因为一个比特可以通过分子长度的变化来识别。然而，为了这个目的，分子应该能够响应于外部刺激而表现出两种不同的长度。在此，我们提出螺旋肽作为一个适当的系统，控制开关的分子长度上的散装基板。含有α-氨基异丁酸（Aib）的肽具有采用两种不同螺旋结构的独特能力：具有短全长（每个氨基酸残基为1.5）的α-螺旋构象和较长的310-螺旋构象（每个氨基酸残基为2.0）。[14尽管已报道晶体形式的Boc-（Ala-Aib）4-OCH 3采用310-螺旋结构，但Boc-（Ala-Aib）8-OCH 3的晶体倾向于α-螺旋结构（Boc=叔丁氧基羰基）。[16]这表明中等长度的十二肽可能具有双α-螺旋和310-螺旋特征。决定有利螺旋类型的关键链长可能是八肽，因为对溴苯甲酰基-
Molecular devices are expected to play an important role in advanced electronics in the form of molecular diodes,[1] molecular transistors,[2] and molecular switches.[3] However, the electron-transfer mechanism of organic molecules on metal surfaces—the most fundamental aspect of molecular devices—still awaits elucidation.[4–6] In an effort to shed light on this issue, we applied helical peptides as mediators for long-range electron transfer,[7] a scaffold for chromophores to accelerate electron transfer,[8] and a viable system for molecular photodiodes.[9]Stochastic on–off switching phenomena of molecular conductance in organic molecules have been observed in numerous cases through careful observation by scanning tunneling microscopy (STM).[10–13] These phenomena are considered to be caused by fluctuations in the hybridization of the sulfur atom that accompanies the change in molecular orientation. Our focus is on the use of this mechanism in a molecular memory device, because one bit may be recognized by a change in molecular length. For this purpose, however, the molecule should be able to exhibit two distinct lengths in response to outer stimuli. Herein, we propose helical peptides as an appropriate system for the controlled switching of molecular length on a bulk substrate. Peptides that contain α-aminoisobutyric acid (Aib) have the unique ability to adopt two different helical structures: an α-helical conformation with a short overall length (1.5 for each amino acid residue) and a longer 310-helical conformation (2.0 for each amino acid residue).[14, 15] Whereas Boc-(Ala-Aib) 4-OCH3 in crystalline form has been reported to adopt a 310-helical structure, crystals of Boc-(Ala-Aib) 8-OCH3 favor an α-helical structure (Boc= tert-butoxycarbonyl).[16] This suggests that an intermediate-length dodecapeptide could have dual α-helical and 310-helical character. The critical chain length which determines the favored helix type may be an octapeptide, because para-bromobenzoyl-