title: Substituent control of potassium and rubidium uptake by asymmetric calix[4]-thiacalix[4]tubes.
abstract: Herein we report on the synthesis and ionophore properties of the first asymmetric p-tert-butylcalix[4]-p-R-thiacalix[4]tubes 7a-c (R = t-Bu, H, 1-adamantyl). The target compounds were obtained by the condensation of tosyloxyethoxy-p-tert-butylcalix[4]arene with the corresponding p-R-thiacalix[4]arenes in the presence of K2CO3 in acetonitrile. The complexation with sodium, potassium and rubidium iodides was studied in CDCl3-CD3OD (4:1) medium by means of 1H NMR measurements. It was found that the ionophore properties of calixtubes 7a-c are controlled by the character of the substituents at the upper rim of the thiacalix[4]arene fragment and it was shown that only the molecular tube 7c with an adamantane-containing thiacalixarene unit is capable of quantitatively binding potassium (swiftly) and rubidium (slowly) cations.
authors.affiliation: Laboratory of Macrocyclic Receptors, Chemistry Department, Moscow State University, Lenin's Hills, 119992, Moscow, Russia.
authors.forename: Elena
authors.initials: E
authors.lastname: Khomich
authors.forename: Marat
authors.initials: M
authors.lastname: Kashapov
authors.forename: Ivan
authors.initials: I
authors.lastname: Vatsouro
authors.forename: Elvira
authors.initials: E
authors.lastname: Shokova
authors.forename: Vladimir
authors.initials: V
authors.lastname: Kovalev