Control of Molecular Assembly for Modified Cyclodextrins by Electric Stimulus

我们制备了新的β-环糊精（1和2）与紫精和烟酰胺部分，这是通过一个长的烷基链（n=10），分别结合的修饰。用液相色谱法纯化环糊精，并用核磁共振法鉴定。~ 1H NMR和NOE（D_2O）分析表明，1的亚甲基部分包含在CD空腔中。在循环伏安图中观察到两步可逆波。有趣的是，第一还原波的电流几乎是第二还原波的30%，这是可逆单电子转移预期电流的70%。1的小电流可能是由于通过分子间包含形成超分子（一种低聚物）导致扩散系数降低。第一个电流和第二个电流之间的巨大差异也可以通过形成更高稳定性的2^+包合物来解释。1的水溶液的粘度的增加强烈地表明低聚物的形成。第二波的控制电位电解导致粘度下降，粘度变化是可逆的。NMR也证实了包合物的形成，由于烟酰胺基团的存在，在环糊精空腔的一个分支附近有一个弱的诱导圆共振谱。由于阴极波的存在，没有进行电刺激实验。总之，两种环糊精衍生物均形成高度稳定的包合络合物，并且如我们所预期的那样观察到1的分子间包合络合物通过电刺激的变化。我们正在研究一种环糊精衍生物，其被设计为通过电刺激显示出粘度的大变化。

We prepared novel beta-cyclodextrins (1 and 2) modified with viologen and nicotinamide moieties which were bind through a long alkyl chain (n=10), respectively. The cyclodextrins were purified by liquid chromatography and identified by NMR.^1H NMR and NOE (D_2O) strongly suggested that the methylene moiety of 1 was included in the CD cavity. Two-step reversible waves were observed in the cyclic voltammogram. Interestingly, the current of the first reduction wave was almost 30% of that of the second one which was 70% of the current expected from a reversible one electron transfer. The small currents of 1 may be due to formation of a super molecular, a kind of oligomer, through intermolecular inclusion which leads to an decrease in the diffusion coefficient. The large difference between the first and second currents can be also explained by formation of more highly stable inclusion complex for 2^+. An increase in viscosity of an aqueous solution of 1 strongly suggested formation of the oligomer. The controlled-potential electrolysis at the second wave led to an decrease in viscosity, the viscosity change is reversible.For 2, the formation of a stable inclusion complex was also confirmed by NMR.A weak inductive circular dichlonism spectrum due to the nicotinamide moiety suggested the existence in the neighborhood of nhe limb of the cyclodextrin cavity The experiment for the electric stimulus was not performed because the cathodic wave was irreversible.In conclusion, both cyclodextrin derivatives formed highly stable inclusion complexes and the change in an intermolecular inclusion complex of 1 by electric stimulus was observed as we had expected. We are studying a cyclodextrin derivative designed so as to show a large change in viscosity by electric stimulus.