title: Artificial ion channel formed by cucurbit[n]uril derivatives with a carbonyl group fringed portal reminiscent of the selectivity filter of K+ channels.
abstract: Novel artificial ion channels (1 and 2) based on CB[n] (n = 6 and 5, respectively) synthetic receptors with carbonyl-fringed portals (diameter 3.9 and 2.4 A, respectively) can transport proton and alkali metal ions across a lipid membrane with ion selectivity. Fluorometric experiments using large unilamellar vesicles showed that 1 mediates proton transport across the membranes, which can be blocked by a neurotransmitter, acetylcholine, reminiscent of the blocking of the K+ channels by polyamines. The alkali metal ion transport activity of 1 follows the order of Li+ > Cs+ approximately Rb+ > K+ > Na+, which is opposite to the binding affinity of CB[6] toward alkali metal ions. On the other hand, the transport activity of 2 follows the order of Li+ > Na+, which is also opposite to the binding affinity of 2 toward these metal ions, but virtually no transport was observed for K+, Rb+, and Cs+. It is presumably because the carbonyl-fringed portal size of 2 (diameter 2.4 A) is smaller than the diameters of these alkali metal ions. To determine the transport mechanism, voltage-clamp experiments on planar bilayer lipid membranes were carried out. The experiments showed that a single-channel current of 1 for Cs+ transport is approximately 5 pA, which corresponds to an ion flux of approximately 3 x 107 ions/s. These results are consistent with an ion channel mechanism. Not only the structural resemblance to the selectivity filter of K+ channels but also the remarkable ion selectivity makes this model system unique.
authors.affiliation: National Creative Research Initiative Center for Smart Supramolecules, and Department of Chemistry, Division of Molecular and Life Sciences, Pohang University of Science and Technology, San 31 Hyojadong, Pohang 790-784, Republic of Korea.
authors.forename: Young Jin
authors.initials: YJ
authors.lastname: Jeon
authors.forename: Hyejung
authors.initials: H
authors.lastname: Kim
authors.forename: Sangyong
authors.initials: S
authors.lastname: Jon
authors.forename: Narayanan
authors.initials: N
authors.lastname: Selvapalam
authors.forename: Dong Hyun
authors.initials: DH
authors.lastname: Oh
authors.forename: Inra
authors.initials: I
authors.lastname: Seo
authors.forename: Chul-Seung
authors.initials: CS
authors.lastname: Park
authors.forename: Seung Ryoung
authors.initials: SR
authors.lastname: Jung
authors.forename: Duk-Su
authors.initials: DS
authors.lastname: Koh
authors.forename: Kimoon
authors.initials: K
authors.lastname: Kim
mesh_terms: D040761:Biomimetic Materials / Q000138:chemical synthesis / Q000737:chemistry*; D001952:Bridged-Ring Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D002412:Cations; D005453:Fluorescence; D007093:Imidazoles / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008564:Membrane Potentials; D008670:Metals / Q000737:chemistry / Q000378:metabolism; D015221:Potassium Channels / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D013379:Substrate Specificity; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils
chemical_list: D001952:Bridged-Ring Compounds; D002412:Cations; D007093:Imidazoles; D008051:Lipid Bilayers; D008670:Metals; D015221:Potassium Channels; C454805:cucurbit(6)uril; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils