title: Molecular pop-up toy: a molecular machine based on folding/unfolding motion of alkyl chains bound to a host.
abstract: We have designed and synthesized a new type of molecular machine based on the folding/unfolding motion of an alkyl chain bound to a host, triggered by a redox stimulus. A guest molecule containing a viologen unit with a long alkyl chain 1(2+) and its one-electron reduced species 1 + . form very stable 1:1 host-guest complexes 2(2+) and 2 + ., respectively, with cucurbit[8]uril (CB[8]), where the long alkyl chain of the guests is in a folded conformation inside the host cavity. Upon addition of 2,6-dihydroxynaphthalene as an electron donor, the binary complex 2(2+) turns into a ternary complex 3(2+) through host-stabilized charge-transfer complex formation with the alkyl chain extended into the solution outside the host cavity. The ternary complex behaves like a molecular machine reminiscent of a pop-up toy, as it shows reversible folding/unfolding motion of the alkyl chain of the guest in response to a redox stimulus. For example, one-electron reduction of 3(2+) results in the rapid generation of the 2 + . complex, accompanied by a dramatic conformational change of the alkyl chain from an extended to a folded conformation, and the process can be reversed by oxidation.
authors.affiliation: Center for Self-assembly and Complexity, Institute for Basic Science (IBS), Pohang, 790-784 (Republic of Korea).
authors.forename: Young Ho
authors.initials: YH
authors.lastname: Ko
authors.forename: Ilha
authors.initials: I
authors.lastname: Hwang
authors.forename: Hyunuk
authors.initials: H
authors.lastname: Kim
authors.forename: Youngkook
authors.initials: Y
authors.lastname: Kim
authors.forename: Kimoon
authors.initials: K
authors.lastname: Kim
keywords: alkanes; cucurbiturils; folded conformations; host-guest chemistry; molecular machines