Control of Molecular Assembly for Modified Cyclodextrins by Electric Stimulus

点击翻译按钮获取中文摘要

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.