lonophores of the bis(crown ether) type, with polyamine linkers, examples of which are known to bind simultaneously to a cation and its counter anion, have been prepared. One-pot reductive amination, used to couple a benzo-crown aldehyde with aliphatic (both linear and cyclic) and aromatic polyamines, proved to be the most efficient route. A strong inhibition of one synthetic route (amine benzylation) was observed.The competitive interaction between chloride and other anions for binding with the protonated ionophores was examined using 35CI N M R spectroscopy. Sandwich complexing of potassium contrasting with single-face complexation of sodium was demonstrated by 13C N MR spectroscopy.Biological systems frequently organise a molecule with two distinct subunits by a strong ionic or co-ordinative type interaction with a metal ion, which holds the units in position for some other biological strategy. For example the two halves of the iron protein of the nitrogenase complex are organised by an Fe,S, cluster linked to cysteines coming from each half, forming a receptor site into which fits the ATP/ADP unit involved in energy transfer for the hydrogenation of dinitrogen. Such examples have prompted chemical mimicry. In this work a promising bis(crown ether) structure was designed to co-ordinate anions within a cavity produced by organisation of the two ends of the molecule with a strong interaction. In the examples tried ' this 'organisation' is a sandwiching of an alkalimetal cation between two crown ethers. Molecules containing two crown ether moieties, separated by a linking group, are known to sandwich potassium but crystallographic evidence of the structure has been sparse. A recent crystal structure determination of a rubidium complex of a Schiffbase-linked bis(crown ether) shows a double sandwich structure, not previously demonstrated.' This has a potential binding site between the two aromatic fragments which link the two crowns of each individual bis(crown ether), which may be represented as shown in Scheme 1, which we have used previously to describe our designThe 1 : 1 sandwich structure (see Scheme 1) has also been demonstrated crystallographically.6 This paper gives details of synthetic routes to, and the separation and characterisation of, multireceptors which should exhibit multiple binding as outlined by us previously in a preliminary report.' 1980,47,81.
Two novel thiamacrocycles have been synthesised with a biphenyl unit and SCCSCCS or SCCOCCS linkers in the ring backbone. Their crystal structures have been determined, showing the trithia ligand to have both SCCS torsions anti ( a ) whilst the dithioxa ligand has both its SCCO torsions in a plus gauche ( 9 ' ) conformation. Molecular dynamics simulations of these two ligands at several temperatures again show differences, the trithia being more rigid; in addition, the conformations predominating in the dynamics simulations of the dithioxa ligand are different from that of the crystal structure. No conformation occurred with any frequency which could be considered to have potential as a tridentate ligand (all-endo sulfurs or oxygens). Derivatives built with additional o-Me substituents were also examined. The cavity size provided by two of the ligands (operating as tridentate ligands) was calculated, and the implications for coordination of the new ligands are considered. * See footnote on p. 1310.Paper 3/07267C
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