Scanning Tunneling Microscopy on Complex Formation of Cyclodextrins and on Their Catalytic Mechanism for Selective Organic Synthesis

利用扫描隧道显微镜（STM）对环糊精及其与各种客体的配合物进行了观察，获得了这些有吸引力的环低聚糖的分子水平信息。通过选择合适的STM测量条件，首次获得了环糊精分子结构的清晰图像。典型的例子是：(1)母体环糊精，(2)与乙二醇配合，(3)与金刚烷羧酸配合，(4)具有葡萄糖分支的环糊精衍生物，(5)与苯酚配合，(6)与氯仿配合。(5)和(6)项中的配合物与作者先前发现的选择性有机合成直接相关。本研究结果将极大地促进环糊精配合物的分子设计，使其具有理想的物理化学和催化性能。同时还发现环糊精具有一定的自聚集活性。聚集体的结构高度依赖于客体化合物、环糊精衍生物和底物的种类，这表明人工控制聚集体的可能性（从而制备环糊精的纳米结构组件）。

Scanning tunneling microscopy (STM) on cyclodextrins and their complexes with various guests has been achieved to obtain molecular-level information on these attractive cyclic oligosaccharides. By choosing appropriate conditions for the STM measurements, clear images of molecular structures of cyclodextrins were for the first time obtained. Typical examples are the images of (1) parent cyclodextrins, (2) the complexes with ethylene glycol, (3) complexes with adamantanecarboxylate, (4) cyclodextrin derivatives having a glucose branch, (5) the complexes with phenol, and (6) the complexes with chloroform. The complexes in the items (5) and (6) are directly associated with the selective organic synthesis which was previously found by the authors. The present results should greatly facilitate the molecular design of cyclodextrin complexes which have desired physicochemical and catalytic properties. It was also found that cyclodextrins have specific activities for self-aggregation. The structures of the aggregates are highly dependent on the kind of guest compounds, cyclodextrin derivatives, and substrates, indicating the possibility of artificial control of the aggregation (and thus the preparation of nano-structures assemblies of cyclodextrins).