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

对环糊精及其与不同客体的络合物进行了扫描隧道显微镜(STM)研究，以获得这些具有吸引力的环状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)与乙二醇的络合物，(3)与金刚烷酸的络合物，(4)具有葡萄糖支链的环糊精衍生物，(5)与苯酚的络合物，以及(6)与氯仿的络合物。第(5)项和第(6)项中的络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络合物的分子设计，使其具有理想的物理化学和催化性能。研究还发现，环糊精具有特定的自聚集活性。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，这表明了人工控制聚集的可能性(从而制备了环糊精的纳米结构组装)。

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).