Artificial ion channel formed by cucurbit[n]uril derivatives with a carbonyl group fringed portal reminiscent of the selectivity filter of K+ channels.
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.
Jeon
Young Jin
YJ
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.
Kim
Hyejung
H
Jon
Sangyong
S
Selvapalam
Narayanan
N
Oh
Dong Hyun
DH
Seo
Inra
I
Park
Chul-Seung
CS
Jung
Seung Ryoung
SR
Koh
Duk-Su
DS
Kim
Kimoon
K
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
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