Solute Binding to Polymers Containing Macroheterocyclic Rings
Abstract Interactions of macroheterocycles and polymers endowed with such cation binding ligands as pendant groups, with ions or ion pairs are discussed, emphasis being placed on the binding properties of the macrocyclic polyethers or crown ethers. The use of fluorenyl and picrate salts permitted a spectrophotometric investigation of ligand interactions with ion pairs and a determination of ion pair-crown ether structures, which is of importance in the study of ion transport through low polarity media. Conductometric and spectrophotometric studies were carried out to obtain the complex formation constants of bis(crown ethers) (e.g. crown compounds with two crown moieties at opposite ends of a short aliphatic chain) to cations and their picrate tight ion pairs, as a function of the length and structure of the bis(crown ether) chain. Studies of cation binding to homopolymers and styrene copolymers of vinylbenzo-15-crown-5 and of vinylbenzo-18-crown-6 using extraction equilibria, ion transport, conductance and viscosity, demonstrated the formation of 1:1 and 2:1 crown-cation complexes, selectivity of cation binding, the dependence of the complexation constant on the number of cations bound to the chain, and the possibility of intermolecular 2:1 crown-cation complex formation and crosslinking in copolymers with a low crown content. The polymer poly(vinylbenzo-18-crown-6) exhibits unusually strong binding of organic neutral and anionic solutes in aqueous media. Binding of picrate salts, methyl orange, phenolphtaleine and other solutes were studied spectrophotometrically. The hydrophobic adsorption of organic solutes also causes this polymer to catalyze the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate by dehydrating the anion. The reaction is accelerated in the presence of complexable cations, which are bound to the polycrown ether, thereby further enhancing the adsorption of organic anions by electrostatic interactions. The same polymer was found to precipitate polynucleotides in water in the presence of complexable cations such as K + . It also exerts a strong inhibitory effect on the polyriboadenylate templated elongation of oligodeoxythymidine catalyzed by murine leukemia virions.