Control of Molecular Assembly for Modified Cyclodextrins by Electric Stimulus

我们制备了新型的β-环糊精(1和2)，它们分别通过长烷基链(n=10)键合紫精和烟酰胺基团。用液相色谱分离纯化了环糊精，并用核磁共振进行了鉴定，1H核磁共振和NOE(D_2O)有力地证明了环糊精的亚甲基部分存在于CD空腔中。在循环伏安图中观察到两步可逆波。有趣的是，第一个还原波的电流几乎是第二个还原波的30%，而第二个还原波的电流是可逆单电子转移所需电流的70%。1的小电流可能是由于通过分子间包结形成了一种超分子低聚物，导致扩散系数降低。第一和第二电流之间的巨大差异也可以用2^+形成更高稳定性的包裹体络合物来解释。1的水溶液粘度的增加强烈表明低聚物的形成。第二波的控制电位电解导致了粘度的下降，粘度变化是可逆的。NMR也证实了形成了稳定的包合物。由于烟酰胺部分的弱感应圆二色谱表明在环糊精腔的边缘附近存在电刺激实验，因为阴极波是不可逆的。综上所述，两种环糊精衍生物都形成了高度稳定的包合物，正如我们所预期的那样，1的分子间包合物在电刺激下发生了变化。我们正在研究一种环糊精衍生物，其设计目的是通过电刺激显示粘度的巨大变化。

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.