Back to Search Start Over

Synthesis and investigation of host-[2]rotaxanes that bind metal cations.

Authors :
Wang X
Zhu J
Smithrud DB
Source :
The Journal of organic chemistry [J Org Chem] 2010 May 21; Vol. 75 (10), pp. 3358-70.
Publication Year :
2010

Abstract

Materials that bind metal cations are highly sought after for new devices. In this report, we show that rotaxanes can transfer metal cations with picrate, perchlorate, or chloride counterions from an aqueous solution into chloroform. The rotaxanes contain a dibenzyl-24-crown-8 ether as the wheel with either a benzyl-18-crown-6 ether (CEBG-R1-3) or a 3,5-dimethylbenzyl moiety (ArBG-R) as one blocking group. Alkali and alkaline picrate salts were efficiently extracted from an aqueous solution, presented in the millimolar range, into chloroform. Large association constants were derived for the complexes in chloroform, especially for the divalent cation Mg(2+). Switching the counterion to chloride greatly diminished the amount of salt extracted. To explore the transfer mechanism of the rotaxanes, a comparison was made in the amount of NaClO(4), KClO(4), NaCl, and KCl extracted by CEBG-R1, ArBG-R, benzyl-18-crown-6 ether (B18C6), and two model compounds, which were used to represent the crown-ether blocking group and the axle of a rotaxane. Two-dimensional NMR analysis was performed on the rotaxane-cation complexes in CDCl(3). We found that the host rotaxanes transfer the perchlorate salts poorly when compared to B18C6, but they transfer chloride salts from 1 M salt solutions, whereas B18C6 does not. The transfer of chloride salts appears to rely on an allosteric type relationship between the binding of the chloride ion and metal cation to a rotaxane. Accordingly, when chloride binds to the dialkylammonium ion of the axle, the wheel moves along the axle and forms a binding site for a metal cation. In this report we demonstrate that host rotaxanes can bind metal cations, change their geometries upon cation and anion association, and operate through allosteric mechanisms, making them promising candidates for molecular devices.

Details

Language :
English
ISSN :
1520-6904
Volume :
75
Issue :
10
Database :
MEDLINE
Journal :
The Journal of organic chemistry
Publication Type :
Academic Journal
Accession number :
20411910
Full Text :
https://doi.org/10.1021/jo100330e