Polyether cation-binding properties

Gokel. C.W. Dishong. D.M. Diamond, C.J. Lariat ethers. Synthesis and cation binding properties of macrocyclic polyethers possessing axially disposed secondary donor groups. J. C. S. Chem. Commun. 1980. 1053-1054. 

As a new series of "open-chain cryptands", "multi-armed cyclams" were designed and employed in the cation transport experiments. Parent polyamine macrocycle (cyclam) is well known to show somewhat different cation binding properties from those of macrocyclic polyethers. It effectively bind ammoniiim cations via strong hydrogen bonding as well as transition metal cations via coordination interaction. Hence, new "multi-armed cyclams" are expected to exhibit unique cation transport abilities. Their cation transport results are summarized in Table 3. 

The discovery of the cation-binding properties of crown ethers renewed interest in studying the ion-binding behavior of linear polyethers and their homologs. Linear oligoethylene glycol dimethyl ethers (glymes) bind cations more weakly by two or three orders of... 

Ionophores, or polyether (PET) antibiotics, produced by various species of Streptomyces, possess broad spectrum anticoccidial activities. They are chemically characterized by several cyclic esters, a single terminal carboxylic acid group, and several hydroxyl groups. Representative members of this class include salinomycin (SAL), monensin (MON), lasalocid (LAS), narasin (NAR), maduramicin (MAD), and semduramicin (SEM). The main chemical properties of interest in the extraction methodology are their low polarities and instability under acidic conditions. They are able to form stable complexes with alkaline cations. All of these compounds, with the exception of LAS, bind monovalent cations (e.g., Na+ and K+). Lasalocid has a tendency to form dimers and can form complexes with divalent cations such as Mg2+ and Ca2+. The formation of metal complexes results in all of these compounds adopting a quasi-cyclic formation consequent to head-to-tail hydrogen bonding. No MRLs have yet been set by the EU for any of the carboxylic acid PETs (98). 

Although some scattered examples of binding of alkali cations (AC) were known (see [2.13,2.14]) and earlier observations had suggested that polyethers interact with them [2.15], the coordination chemistry of alkali cations developed only in the last 30 years with the discovery of several types of more or less powerful and selective cyclic or acyclic ligands. Three main classes may be distinguished 1) natural macrocycles displaying antibiotic properties such as valinomycin or the enniatins [1.21-1.23] 2) synthetic macrocyclic polyethers, the crown ethers, and their numerous derivatives [1.24,1.25, 2.16, A.l, A.13, A.21], followed by the spherands [2.9, 2.10] 3) synthetic macropolycyclic ligands, the cryptands [1.26, 1.27, 2.17, A.l, A.13], followed by other types such as the cryptospherands [2.9, 2.10]. 

Bouquet -shaped molecules based on either a polyether macrocycle [8.205] or a /3-cyclodextrin (/3-CD) [8.206] core, such as 114 and 115 respectively, have been synthesized and their polycarboxylate forms have been incorporated into vesicle bilayer membranes [8.207]. They present structural features suitable for studies of chundle-type molecular channels (1) the functionalized cyclic annulus possesses substrate selection properties (2) it bears axially oriented bundles of oxygen-containing chains, which provide binding sites for metal cations and are long enough for the molecule to span a typical lipid membrane (the overall length with the chains... 

The properties of complexation of different undoped poly(7) with respect to inorganic cations (Ag+, Mn +, Co +, and Sb " ") have been investigated by y-spectrometry, and the principal results are sununarized in Table IV. It can be seen that these polymers exhibited a binding power toward Mn " " and Co + that was much stronger than that toward Sb +. Furthermore, the same affinity was obtained for Co " " (ionic radius, 0.72 A [254]) whatever the polymer, whereas Mn " " (0.80 A) and Ag" " (1.26 A) were more specifically complexed by poly(7a) and poly(7c), respectively. Thus this result is well correlated with the length of the polyether chain. 

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