Reactive pseudorotaxanes: Inclusion complexation of reduced viologens by the hosts beta-cyclodextrin and heptakis(2,6-di-O-methyl)-beta-cyclodextrin

The complexation of three guests containing 4,4'-bipyridinium redox-active residues by beta-cyclodextrin (beta-CD) and its heptakis-(2,6-O-dimethyl) analogue (DM-P-CD) was investigated by means of voltammetric techniques. The three 4.4'-bipyridinium (viologen) derivatives used as guests were designed to be water-soluble in all three accessible oxidation states. The N-substituents chosen to enhance aqueous solubility were: 2-(2-(2-ethoxy)ethoxy)ethanol (guest 1(2)+) 6-hexanoate (guest 2), and 3-proganesulfonate (guest 3). Detailed analysis of the voltammetric results by digital simulation techniques revealed that the oxidized forms of the guests did not interact appreciably with either CD host: the two-electron reduced guests formed extremely stable inclusion complexes, with association constants in the range 10(3)-10(4) M-1, while the cation radical forms exhibited intermediate binding affinities (approximate to 10(2) M-1). In all cases. DM-beta-CD was found to form more stable complexes than unmodified beta-CD.