Johannes Smid

Effect of charge on anion and cation binding to poly(vinylbenzo-18-crown-6) in water

Abstract Complex formation constants, K , of cation to poly(vinylbenzo-18-crown-6) (P18C6) and to its monomeric analogue 4′-methylbenzo-18-crown-6 (MB 18C6) were measured in water potentiometrically or spectrophotometrically. The constants for Na + , K + and Cs + to P18C6, extrapolated to zero charge density, were found to be 2.4, 110 and 300 M −1 , respectively, and 27, 110 and ≈20 for MB18C6. Binding of K + and of picrate anions to P18C6 was measured as a function of the number of K + ions, Z , on the P18C6 chain. The charge effect (a decrease in K + binding with increasing Z , and an increase in picrate binding) can be reasonably well-described by assuming the macroion to be a solvent- and ion-impenetrable sphere, the potential of which can be calculated by using a Debye-Huckel approximation. A linear plot is predicted and found (at least for picrate binding) between In K and Z , the slope yielding information on the radius of the P18C6 macroion. The cation effect on picrate binding to P18C6 was utilized to determine spectrophotometrically the order of binding of a series of cations to P18C6. The results were confirmed by using the dye, 2-(4′-hydroxybenzeneazo)benzoate which produces a much larger bathochromic shift on binding to P18C6 in water than does the picrate anion.

Macrocyclic ligands on polymers

Abstract The ion binding properties of linear polymers carrying crown ether ligands as pendent groups are reviewed. The polymers often exhibit selective cation binding different from that of their monomeric crown analogues. One of the polymers, poly(vinylbenzo-18-crown-6), behaves in water as a neutral polysoap and strongly interacts with organic anions. The binding is enhanced and also can be regulated by charging the polymer with crown complexable cations. This polymer also catalyzes solvent sensitive reactions by a micellar type mechanism. In the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate in water the substrate bound to the Cs+ charged poly(crown ether) decomposes 14000 times more rapidly than in water. In benzene the decarboxylation is also accelerated by poly(crown ethers), but in this case as a result of anion activation. Poly-(crown ethers) were also found to form polysalt complexes in water with several polyanions in the presence of crown complexable cations. In the absence of salts, complexes can be formed with polyacids through hydrogen bonding.

Ionophorous polymers. Interaction with polynucleotides and effects on RNA-directed DNA polymerase activity.

Poly(vinylbenzo-18-crown-6), a water-soluble polymer endowed with ion-binding crown moieties as pendent groups, forms insoluble complexes with polyadenylate in the presence of K+; the corresponding monomeric benzo-18-crown-6, does not form a precipitate under the same conditions. In the presence of Na+ and Mn2+ which in aqueous solution complex weakly to crown compounds, no coprecipitation of the crown polymer and polyadenylate occurs; nevertheless, the crown polymer strongly binds to immobilized polyadenylate even under these conditions. The interactions of crown polymer with the poly-nucleotide result in a loss of templating ability of the latter. Using RNA-dependent DNA polymerase of murine leukemia virus it was found that (1) enzymatic action is efficiently inhibited even in the absence of ions which coprecipitate crown polymer and template, (2) inhibition is reversed by addition of excess polynucleotide and (3) monomeric crown does not inhibit the reaction.

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.

Viscosity studies of crown ether-containing polymers in solutions of alkali salts. Intra- versus intermolecular crown-cation complexes

Abstract The complexation of cations to poly(vinylbenzocrown ethers) strongly affects the viscosity of the polymers. In mixtures of THF-MeOH the reduced viscosities of the polymer-salt solutions at constant polymer concentration pass through a maximum, their values depending on the cation-to-crown ratio and the binding constant of the cations to the poly(crown ethers). Crosslinking and abnormally high viscosities are found when a cation can complex simultaneously with two crown ligands, e.g. in mixtures of potassium salts with styrene copolymers containing pendent benzo-15-crown-5 moieties. In such systems competition exists between the formation of inter- and intramolecular 2:1 crown-cation complexes, and their relative importance depends on the crown content of the copolymer. Spectrophotometric measurements in THF mixtures of styrene-vinylbenzo-15-crown-5 copolymers and potassium picrate reveal that at low crown concentration, intramolecular complexes can form when crown ligands are separated, on the average, by less than four styrene units. The data, in combination with calculations on the distribution of crown ligands along a chain as a function of crown content, can be used to rationalize the viscosity behaviour of these polymer solutions.

Effect of chain length on the glyme-separated ion-pair formation in bolaform salts of α,ω-(9-fluorenyl)polymethylenes

Formation constants of tetraglyme (glyme 5) separated ion pairs of bolaform electrolytes of the type Na+,−Fl(CH2)nFl−, Na+ (Fl− denoting a fluorenyl carbanion) were measured spectrophotometrically in tetrahydrofuran (THF) and tetrahydropyran (THP) at 25°C as a function of the chain lengthn, withn=2, 3, 4, or 6. The ratiosK1/K2 of the first and second glyme ion-pair separation steps were found to be equal to the statistical factor 4 in all cases except in THP for the compoundn=2, where the ratio is 15. Values ofK1 as well as K2 increase considerably with chain length, the former by a factor 19 asn increases from 2 to 6. The ion-pair separation with glyme 5 is easier in THP than in THF. The results are discussed in terms of differences in external cation solvation and the possible involvement of cyclized structures or curled conformations as a result of interactions between the terminal ion pairs.

Star-Shaped Alkyl Carbamates as Pour Point Depressants

A series of trialkyl carbamates of the general formula HC(Ph NHCOOCnH2n+1)3 with n = 16, 18, 20 and 22 were synthesized from alkanols and tris(p-isocyanatophenyl)methane. The star-shaped compounds effectively depress the pour point of wax-containing paraffin oil. A quantity of 0.1 wt.% of the C18 derivative, by far the most effective depressant, reduces the pour point of paraffin oil containing 11.5 wt.% wax (mp 56–61° C) from 33° C to - 4°C. The extent of the depression varies with the concentration and composition of the wax. The depressants are ineffective when pure alkane waxes are added to the paraffin oil.

SOLUTE BINDING TO POLYMERS CONTAINING MACROHETEROCYCLIC RINGS

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.