Polyanions, carboxylated

The results may be compared with the observed sequences O ) for reactions involving equilibrium between the alkali metal cations and carboxylated polyanions, which give an order of affinity Li>Na>K. The equilibrium sequence, which is a measure of the free energy change in the reaction, can only be reconciled with the enthalpy data if the endothermic replacement of the condensed sodium ion by a lithium ion is accompanied by an increase in the total entropy. This would accord with the observed order of volume changes, Li>Na>K, for the site binding (condensation) of alkali metal cations to polycarboxylates,... 

Sulfated polyanions. In the interaction of counterions with sulphated polyanions there is less dehydration of the counterions (2 ) and the reverse sequence of volume changes (26) is observed for the counterion interaction. The enthalpy changes for dilution and mixing of alkali metal salts of dextran sulphate were therefore measured and compared with the results for the carboxylated polyanions. 

CMC hydrates rapidly and forms clear solutions. Viscosity buUding is the single most important property of CMC. DUute solutions of CMC exhibit stable viscosity because each polymer chain is hydrated, extended, and independent. The sodium carboxylate groups are highly hydrated, and the ceUulose molecule itself is hydrated. The ceUulose molecule is linear, and conversion of it into a polyanion (polycarboxylate) tends to keep it in an extended form by reason of coulombic repulsion. This same coulombic repulsion between the carboxylate anions prevents aggregation of the polymer chains. Solutions of CMC are either pseudoplastic or thixotropic, depending on the type. 

High sorption capacities with respect to protein macromolecules are observed when highly permeable macro- and heteroreticular polyelectrolytes (biosorbents) are used. In buffer solutions a typical picture of interaction between ions with opposite charges fixed on CP and counterions in solution is observed. As shown in Fig. 13, in the acid range proteins are not bonded by carboxylic CP because the ionization of their ionogenic groups is suppressed. The amount of bound protein decreases at high pH values of the solution because dipolar ions proteins are transformed into polyanions and electrostatic repulsion is operative. The sorption maximum is either near the isoelectric point of the protein or depends on the ratio of the pi of the protein to the pKa=0 5 of the carboxylic polyelectrolyte [63]. It should be noted that this picture may be profoundly affected by the mechanism of interaction between CP and dipolar ions similar to that describedby Eq. (3.7). 

Ladenheim and Morawetz [23] also showed that the reactivity of the carboxylate units in partially ionized poly(methacrylic acid) (PMA) toward BrCH2COO in the bromine displacement reaction was greatly diminished, while the reaction proceeded at an appreciable rate with uncharged p-bromoacetamide [23]. This inhibition of the reaction of the polyanion with a small anionic reagent can be attributed to the electrostatic repulsion between the polymer and the reagent. 

The values of 9 thus calculated for the polyanions (3) having various charge densities are listed in Table 1. It should be noted that all the carboxylic acid groups in the polyions are assumed to be almost fully dissociated in the pH region where the spectroscopic pH titration of the Me residue was performed. 

In most cases the microspheres were insoluble. The polysaccharides might be partially cross-linked via amido groups formed by the carboxyl groups of the polyanion and the restored free amino group of chitosan. The susceptibility to enzymatic hydrolysis by lysozyme was poor, mainly because lysozyme, a strongly cationic protein, can be inactivated by anionic polysaccharides [207]. 

The galacturonic acids of a plant cell wall mainly belong to smooth chains of homopolygalacturonic acid (PGA) and to hairy regions of rhamnogalacturonan I (RGI). In green plants, other uronic acids can be found in hemicelluloses. Provided they are not methylesterified, all these carboxylic acids deprotonate at the more or less acidic pH of wall water. The electrostatic charges of these polyanions are then compensated by cations ultimately derived from the environment. 

Polymeric aliphatic carboxylates, the poly(alkenoic add)s, were very much more strongly adsorbed than the difunctional carboxylates (Ellis et al., 1990). Results showed that adsorption depended on the conformation of the polyanion. When extended, as in dilute solutions, a polyanion is adsorbed onto a relatively large number of sites and further adsorption is hindered. Thus, increases in acidity (and concentration) were found to result in greater adsorption because the polyanion adopted a more compact... 

Pyromellitate, the tetracarboxylate of benzene, forms red crystals of formula [Co2(C6H2 (C00)4)4]-18H20 from aqueous silica gel, and feature infinite chain-like polyanions with [Co(OH2)4[C6H2(COO)4)]2]ra2" stoichiometry where Co is in an octahedral environment of four waters and two traras-disposed carboxylates.436... 

Poly(starch-g-((l-amidoethylene)-co-(sodium 1-carboxylatoethylene))). Poly(l-amidoethylene) is, however, rarely used as a viscosifier. Instead, the homopolyraer is reacted with base (hydrolyzed with NaOH) to convert some of the amide units of the polymer to carboxylic acid units. The acid units on the hydrolyzed polymer dissociate in water and produce a polyanionic polymer. This polyelectrolyte expands in water because of ion-ion repulsion and, as an enlarged molecule, is a better viscosifier. 

As mentioned repeatedly, a variety of anionic reagents are highly activated in the hydrophobic microenvironment of cationic micelles and polysoaps. The range of anionic reagents studied in the past includes imidazole, hydroxide, thiolates, oximates, hydroxamates, carboxylates and carbanions. Polyanionic coenzymes are similarly activated. These results can be interpreted in a unified way by the concept of hydrophobic ion pairs, and the major source of activation seems to be concentration and desolvation of the anionic reagent in the... 

Synthetic heparinoid polymers such as polyanionic polyesters containing sulfamate and carboxylate groups were synthesized by hydrolysis of p(N chloro-sulfonyl beta lactam) [475]. These materials possess anti-coagulant activity (although lower than heparin) presumably due to the similarity of functional groups of this material and those found in heparin. 

Ta with the polyglucose sulfate was demonstrated by the use of S-labeled inhibitor. 10 12 No loss in viability occurred when the phage was incubated with anions of low molecular weight. Carboxyl derivatives of polyglucose behaved similarly, but higher concentrations of these less acidic polyanions were required in order to achieve similar effects. 12... 

It used to be thought that cations simply precipitated polyanions, but it was recognized later that electrolytes had special valence and solvent-mediated effects on a hydrosol other than neutralization of opposite charges (Holmes, 1922). It is now firmly established that ionization of the carboxyl and sulfuric acid groups in ionic polysaccharides, or adsorption of ions on neutral macromolecules, is an initial step in electrokinetic mechanisms of stabilization and destabilization. 

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