Pseudocrown ethers

Warshawsky and coworkers have recently reported the synthesis of a class of compounds which they call polymeric pseudocrown ethers . A chloromethylated polystyrene matrix is used here as in 6.6.2, but instead of adding a crown to the backbone, a strand of ethyleneoxy units is allowed to react at two different positions on the chain, thus forming a crown. Such systems must necessarily be statistical, and the possibility exists for forming interchain bridges as well as intrachain species. Nevertheless, polymers which could be successfully characterized in a variety of ways were formed. A schematic representation of such structures is illustrated below as compound 30. ... 

Polymeric pseudocrown ether networks have been generated in situ by the photopolymerization of poly(ethylene glycol) diacrylate transition metal complexes <00CM633>, and the effect of metal ion templation was evaluated. The 1,6,13,18-tetraoxa[6.6]paracyclophane-3,15-diyne (termed pyxophanes) was prepared from hydroquinone and l,4-dichlorobut-2-yne it forms size-selective 7i-complexes with alkali metal cations <00CC2377>. Dibenzo[ ]crown-m have been used in numerous elegant studies in which they were the needles that were threaded by diverse reagents the resultant... 

Polymeric pseudocrown ether resins, containing azathiacrown and oxacrown ethers in 13- and 19-membered rings, were prepared as shown for the former in Scheme 28 <1997JAPS931>. The polymers adsorbed noble metals well. IR spectra of the polymeric azacrown ethers and photoelectron spectra of the uncomplexed and metal-complexed reagents were reported. 

Electropolymerization of a precursor 76 involving two polymerizable groups linked by a flexible polyether chain was initially proposed by Roncali et al. as a possible route to conjugated polymers containing pseudocrown ether cavities [181]. Since then, analog precursors with polyether chains of various lengths have been studied [182,183]. 

The spontaneous formation of Au particles at room temperature in air-saturated aqueous solutions of poly(ethylene glycol)s was investigated using optical, potentiometric and conductivity techniques. The kinetic information is consistent with a mechanism in which Au(III) complexes bind through ion-pairs to pseudocrown ether structures of the polymers. Reduction of the metal centers follows through their reactions with the oxyethylene groups that form these cavities. The particle size of the metal crystallites is controlled by the molar mass of the polymers. Agglomerates of small Au particles are formed as final products when polymers of low molar mass are used in the synthesis. 

It is well known that small cations form crown-ether-like associations with PEG polymers (77). The cations interact with pseudocrown ether structures of the polymers formed by coiling of the macromolecules. Furthermore, it has been shown that AuCU" ions become coordinated to the pseudocrown ether structures via ion-pairs (76). The Au(IU) complexes are attracted through electrostatic interactions to cations that are bound to the oxyethylene groups of the polymers. In our systems Na+ ions can bind to the pseudocrown ether structures, and form ion-pairs with the gold complexes. The bound complexes are reduced via oxidation of the oxyethylene groups by the metal center ... 

This reaction is followed by coalescence of metal atoms to generate Au clusters and small metal particles. The metal atoms are probably stabilized by the macromolecules against oxidative reactions induced by O2 and H+ ions. Since reaction 3 is faster when pseudocrown ether structures are more abundant, the rate of particle formation is higher with increasing number of these structures. Formation of pseudocrown ether structures is favored for PEG polymers with higher molar mass (77), and with increases in the polymer concentration. The simple mechanism represented by reactions 3 and 4 is consistent with the kinetic results of Figure 3. A... 

A new electroactive conductive polymer was synthesized by electrochemical polymerization of (31) in propylene carbonate [62]. A pseudocrown ether structure (32) was expected to occur by the template effect, but the real structure was not clear. The results of the above polymers bearing etheric lateral groups should have practical implications for the design of selective electrode, charge-controllable membrane and drug-release devices. 

Pseudocrown ethers, whose structures are maintained by coordination bonds instead of covalent bonds like typical crown ethers, are among the most suitable candidates for allosteric regulation of ion binding. A linear podand 2 possessing bipyridine moieties at the ends of the polyether chain was converted easily to the corresponding pseudocrown ether quantitatively by complexation with Cu+ (Scheme 1.1). The pseudocrown ether shows a positive allosteric effect on alkali metal ion selectivity in ion transport. The drastic conformational change from a linear to cyclic structure results in a significant macrocyclic effect favorable for ion selectivity. 

Pseudocrown ethers 4 with imine functionalities as binding sites for Ni +, Cu +, Zn + were also synthesized from 3 for recognition of Ba + in the cavity (Scheme 1.2). Similar crown ether analogues 5 were reported (Figure 1.2). In addition, chiral analogues of 6 were applied to chiral recognition (Figure 1.3). ... 

A. Warshawsky, R. Kalir, A. Deshe, H. Berkovitz, and A. Patchornik (1979), Polymeric pseudocrown ethers. 1. Synthesis and complexation with transition metal anions. J, Amer. Chem. Soc. 101, 4249-4258. 

POLYMERIC PSEUDOCROWN ETHERS SYNTHESIS AND COMPLEXATION WITH TRANSITION METAL ANIONS... 

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