摘要/Abstract
以阳离子二苯丙氨酸（Cationic dipeptide，CDP）为组装基元，通过控制熟化时间，在乙醇溶液中分别获得了平滑的纳米纤维和螺旋纤维结构.通过红外光谱和圆二色光谱系统研究了CDP在乙醇溶液中的组装体随时间的变化.研究发现，CDP在乙醇中可以组装成纳米纤维的结构.随着在乙醇中熟化时间的增加，CDP纳米纤维发生扭曲，最终组装成绳状的螺旋纤维结构.光谱数据分析表明纳米纤维转变成螺旋纤维主要源于相邻肽分子中的正电荷之间的强静电排斥作用和肽分子间氢键作用控制的β-折叠二级结构.这项工作通过简单的控制熟化时间实现了对超分子组装体结构的调控，为超分子手性组装体的可控制备提供了一种简单可行的方法.
关键词: 阳离子二苯丙氨酸, 分子组装, 分子手性
Chirality is ubiquitous in nature and it plays an important role in both biological and material sciences. Inspired by nature, scientists have prepared various chiral structures or hybrid materials by self-assembly of polypeptides, amino acids, carbohydrates and their derivatives. These studies provide a good model for understanding of supramolecular chirality and mimicking the self-assembly of organisms. In the past decade, diphenylalanine (FF) and its derivatives have attracted great attentions and have been substantially studied. FF is derived from the core recognition motif of the Alzheimer's disease β-amyloid polypeptide, and it could readily self-assemble into nanotubes, nanowires, nanovesicles, nanofibers and microtubes. Moreover, the polymorphisms of FF-based assemblies can be easily manipulated by controlling the experimental conditions such as concentrations, solvents, pH and temperatures. However, there is few report on the chiral structures obtained from the self-assembly of FF and its derivatives. In this paper, we selected cationic diphenylalanine peptide (CDP) as the assembly units and have obtained CDP nanofibers and helical fibers in ethanol solution by controlling the aging time. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to characterize the morphologies of CDP assemblies. The mechanism for the formation of CDP nanofibers and helical fibers in ethanol solution was studied by infrared spectroscopy and circular dichroism spectroscopy. It was found that CDP was first assembled into nanofibers. With the increase of aging time, CDP nanofibers twisted and finally assembled into helical fibers similar to the ropes. Spectral data analysis showed that the transformation of nanofibers into helical fibers was mainly due to the strong electrostatic repulsion between positive charges in adjacent peptide molecules and the β-sheet secondary structure controlled by hydrogen bonding between peptide segments. This work realizes the regulation of supramolecular assembly structure by simply controlling the ripening time, and provides a simple and feasible method for the controlled preparation of supramolecular chiral assembly.
Key words: cationic diphenylalanine, molecular assembly, molecular chirality
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