Molecular recognition of alkylamines: conformational and binding properties of calix[6]arene-based ester ligands
- 1 January 1994
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 4,p. 835-839
- https://doi.org/10.1039/p29940000835
Abstract
A series of alkyl 15,35,55,75,95,115-hexa-tert-butyl-1,3,5,7,9,11-hexa[1,3]benzenacyclododecaphane esters have been prepared that selectively bind to alkylammonium cations. Ester ligands showed extraction efficiency toward alkylamines in the sequence of ammonium < Me ≃ Et > Pr > Pri > Bu > Bui≃ Bus > tert-butylammonium guests. Single and competitive transport experiments of butylamines also confirmed the binding properties obtained with extraction experiments and the transport selectivity for Bu/But pair exceeds 25. Conformational properties, such as Tc and ΔGc‡, of ester ligands were investigated by means of temperature-dependent 1H NMR spectroscopy. Conformational freedom was generally found to decrease as the size of substituent of ester side chain increased. 1H NMR complexation studies of ethyl ester 2 with caesium tetraphenylborate and butylammonium picrate guests suggest that the conformational reorganization into a cone conformation has provoked complex formation.Keywords
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