Neutral receptors for the transport of anions across lipid membranes

Abstract

This report describes a novel method, using 33S NMR techniques, for the detection of sulfate transport across synthetic lipid membranes comprised of 1-palmitoyl-2 oleoylphosphatidylcholine. With this method it was possible to verify that tris(2 aminoethyl)amine based (thio)ureas and cyclic peptide based cryptands can promote the transmembrane transport of sulfate anions. This is a particularly notable accomplishment due to the highly hydrophilic nature of the sulfate anion, and the associated challenges with partitioning such a species into a hydrophobic lipid membrane. Furthermore, a series of bis(thio)urea compounds, based on the 1,2- bisaminocyclohexane scaffold are reported as ion transporters, capable of facilitating both chloride/nitrate and chloride/bicarbonate antiport transport processes. They have also been investigated for binding properties with a variety of anions, using 1H NMR techniques. The influence of stereochemistry on the anion binding and transport ability of the receptors is discussed in detail, with cis-stereoisomers being superior anion transporters to the transanalogues. Receptors based on the ortho-phenylenediamine bis-urea motif have been demonstrated as highly effective anion transporters and function by an antiport mechanism of anion transport. Modification of existing transporters, by adding fluorination at the central phenyl ring or by increasing fluorination at the peripheral phenyl groups, yielded highly potent anion transporters capable of surpassing the activity of the natural anion transporter prodigiosin, for chloride/bicarbonate exchange.

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Identifiers

ORCID for Philip A. Gale: orcid.org/0000-0001-9751-4910

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