Water-soluble Nonstoichiometric Polyelectrolyte Complexes Research Articles

Water-soluble nonstoichiometric polyelectrolyte complexes of modified chitosan

A modified polysaccharide that, in each deacetylated unit, carries a functional secondary amino group and a quaternized amino group that provides a positive charge and solubility to the polymer throughout the pH range is prepared by the alkylation of primary amino groups of chitosan with glycidyltrimethylammonium chloride. The mixing of modified chitosan solutions with solutions of polystyrenesulfonate or polymethacrylate anions in neutral solutions gives rise to negatively charged nonstoichiometric polyelectrolyte complexes soluble and stable under physiological conditions. The effects of pH, ionic strength, the degree of polymerization, the nature of the lyophilizing polyanion, and the charge-to-charge ratio of components on the boundaries of existence of soluble complexes are ascertained. The collected experimental data may serve as a basis for designing biocompatible and biodegradable means useful for the delivery of genetic material and drugs to living cells.

Nonstoichiometric polyelectrolyte complexes of chitosan soluble in neutral solutions

The technique of preparing nonstoichiometric polyelectrolyte complexes of chitosan soluble in neutral solutions is developed. Chitosan complexes soluble in neutral solutions and meeting the behavioral criteria of water-soluble nonstoichiometric polyelectrolyte complexes are prepared via mixing of strongly acidic solutions of chitosan and polystyrenesulfonate anions taken in a nonequimolar charge-charge ratio and subsequent neutralization of the products by a solution of alkali. Thus, the region of existence of soluble complexes narrows with a decrease in the length of the host polyanion up to its full degeneration in the case of oligomeric anions. The critical concentration of a salt that brings about phase separation decreases with an increase in the relative content of the guest chitosan in a mixture and depends on the ratio of chain lengths of polymer components.

Water-Soluble Cationic Aromatic Dendrimers and Their Complexation with DNA

Water-soluble cationic polypyridylphenylene dendrimers (wPPPDs) of different generations and various contents of pyridyl and phenylene moieties were synthesized. Interaction of wPPPDs with DNA resulted in the formation of polyelectrolyte complexes stable at physiological pH and ionic strength. Noticeable contribution of hydrophobic interactions provided by phenylene groups of the dendrimer in the complex stability was ascertained. Data obtained by turbidimetry and a sedimentation assay, as well as ζ-potential measurements, strongly implied the inaccessibility of positively charged pyridinium groups situated in the inner part of the dendrimer molecules for interaction with the rigid double helix. Positively and negatively charged water-soluble nonstoichiometric polyelectrolyte complexes were prepared and phase separations in their water-salt solutions were investigated. According to DLS measurements supported by the sedimentation assay, the addition of wPPPD in DNA solution in a wide range of the mixture c...

Interaction of water-soluble polypyridylphenylene dendrimers with a polymethacrylate anion

Cationic water-soluble dendrimers have been prepared by the alkylation of pyridyl groups in polypyridylphenylene dendrimers of the first four generations, and their interaction with a polymethacrylate anion has been studied. The stability of polyelectrolyte complexes in aqueoussaline solutions has been studied by fluorimetric titration with the use of the pyrenyl-tagged polyanion, and it has been shown that the stability of these complexes significantly increases with the dendrimer generation number and the content of hydrophobic phenylene groups. Based on sedimentation analysis and turbidimetric titration, it is inferred that a significant part of charged groups of dendrimers are inaccessible to interaction with the polyanion and that water-soluble nonstoichiometric polyelectrolyte complexes develop in mixtures of higher generation dendrimers. Modeling results of this study may be useful for designing efficient cationic dendrimer carriers of genetic material and hydrophobic physiologically active compounds.

Water-soluble nonstoichiometric polyelectrolyte complexes of chitosan with a polystyrenesulfonate anion

Chitosan complexes that meet the performance criteria of water-soluble nonstoichiometric polyelectrolyte complexes have been first prepared via the interaction of chitosan with excess polystyrenesulfonate anions in acidic media. Thus, the region of the existence of soluble complexes can be narrowed down through a decrease in the degree of polymerization of a lyophilizing polyanion until fully degenerates as in the case of oligomeric anions. The critical concentration of a salt that brings about phase separation decreases with an increase in the relative content of a blocking chitosan in a mixture and depends on the ratio of chain lengths of polymer components. This is also typical of nonstoichiometric polyelectrolyte complexes. The results of this study may be useful for designing soluble chitosan complexes with polyanions, including those of biological origin.

Controlled phase separations in solutions of polyelectrolyte complexes Potential for gene delivery

Salt-induced phase separations in solutions of water soluble non-stoichiometric polyelectrolyte complexes (WPECs) formed by poly(N-ethyl-4-vinylpyridinium) polycation with different polyanions – sodium poly(methacrylate), sodiumpoly(styrenesulfonate), and DNA – have been explored. Stability of both negatively charged WPECs (with host polyanion) and positively charged WPECs (with host polycation) with respect to the added salt was dependent, regarding the analogous manner, on the ratio R of degrees of polymerization of host and guest polyions, R = DPHost/DPGuest. Thus, host oligomers (low R values) were not able to endow the complexes with the solubility, whereas their lengthening (an increase in R at R < 1) resulted in significant extension of the ionic strength region corresponding to homogeneous WPECs solution. At R > 1, the increase in DPHost stabilized WPECs only slightly. Whilst WPECs with host sodium poly(styrenesulfonate) were extremely stable in water-salt media, their phase behavior also obeyed above dependence on R. Variation in DPGuest exerted the same effect; specifically, positively charged WPEC with guest DNA polyanion was markedly stabilized on substitution of “highly polymerized” calf thymus DNA with DNA sample which possessed only 300-500 base pairs, i.e. with increase in R at R < 1. This finding implies that the use of relatively short DNA preparations, most notably oligonucleotides, extends the DP range of polycations feasible for preparing of positively charged WPECs that are soluble at physiological ionic strength and hence, are the most suitable for gene delivery.

Physical and Biological Properties of Water Soluble Polyelectrolyte Complexes

Water soluble non-stoichiometric polyelectrolyte complexes have been investigated as potential drug carrier systems for parenteral administra tion. Complexes between the polycationic quaternized poly(vinyl imidazole) (QPVI) and an excess of a higher molecular weight partially sulfonated dextran (pDS) were designed to inherit the biocompatible properties of dextran. Polyelectrolyte complexes with an overall anionic nature prepared from excess poly(methacrylic acid) (PMAA) and low molecular weight quaternary poly amines were also studied. Sedimentation velocity techniques and size exclu sion chromatography showed that complexation was present in all of the systems studied under the appropriate conditions. These studies also indicated that an increasing [polycation]/[polyanion] ratio resulted in a smaller, more compact complex conformation. Platelet aggregation studies showed that toxic aggregatory effects normally induced by the polycations, and to a lesser extent the pDS, were eliminated in vitro when they formed part of a soluble polyelec trolyte complex. In vivo distribution studies in mice using 125I-labelled polyca tion complexed with pDS or PMAA showed accumulation of 40-50% of the ad ministered dose in the liver after 2 hours. The polycation present in these com plexes appears to have been prevented, to some extent, from interacting with negatively-charged biological surfaces, such as platelets in vitro. However this complexation was not sufficient, at least for the macromolecules we have ex amined, to prevent the extensive incidence of unwanted interactions in vivo, lead ing to removal of the polyelectrolyte complexes from the circulation. In conclusion it has been shown that the ionic bonds which hold this type of complex to gether, are not sufliciently strong in vivo to preserve a stable complex structure.

Cooperative interpolyelectrolyte reactions

Water-soluble nonstoichiometric polyelectrolyte complexes (NPEC) are formed as a result of interaction of opposite charged polyelectrolytes used in nonequivalent ratios. One of the most important properties of NPEC is their ability to participate in intermacromolecular exchange and substitution reactions in aqueous solutions. The kinetics of exchange and substitution reactions has been studied by the method of luminescence quenching. It has been found that such reactions proceed by the contact mechanism and that addition of low molecular electrolytes to the reaction mixtures results in a dramatic increase in the rates of the reactions. The kinetics of the reactions is well described by the equation q = 1-exp(- kt∝) (here q is the degree of conversion and ∝ < 1), deduced under the assumption that exchange and substitution occur by the nucleation mechanism and the development of nuclei is inhibited in time. The studied reactions represent a new class of interpolymer reactions and they can be very important, in particular, for understanding the mechanism of functioning of biologically important macromolecules and for the interpretation of the physiological activity of polyelectrolytes.

Enzymes in polyelectrolyte complexes. The effect of phase transition on thermal stability.

Penicillin amidase, alpha-chymotrypsin and urease have been immobilized in water-soluble nonstoichiometric polyelectrolyte complexes (N-PEC). N-PEC are formed by modified poly(N-ethyl-4-vinyl-pyridinium bromide) (polycation) and excess poly(methylacrylic acid) (polyanion). N-PEC are a new class of polymers capable, characteristically, of phase transitions solution in equilibrium precipitate induced by slight change in pH or ionic strength. Neither the chemical structure of the carrier nor the number of cross-linkages between an enzyme and a carrier change on phase transition. That gives an unique opportunity to elucidate the difference between enzymes immobilized on water-soluble and water-insoluble supports. A detailed study of the phase transition effect on thermal stability of the enzymes and protein-protein interactions has been carried out. The following effects were found. Pronounced thermal stabilization of penicillin amidase and urease may be achieved on two conditions: the enzyme is in the precipitate; (b) the enzyme is linked to the N-PEC nucleus. Then the thermal stability of N-PEC-bound penicillin amidase increases 7-fold at pH 5.7, 60 degrees C, and 300-fold at pH 3.1, 25 degrees C, compared to the native enzyme. For urease, the thermal stabilization increases 20-fold at pH 5.0, 70 degrees C. The localization of enzyme on N-PEC has been established by titration of alpha-chymotrypsin bound to a polycation or polyanion with basic pancreatic trypsin inhibitor. Both in solution (pH 6.1) and in N-PEC precipitate (pH 5.7), an alpha-chymotrypsin molecule bound to a polyanion is fully exposed to the solution. If the enzyme is bound to a polycation, only 20% of alpha-chymotrypsin molecules in the precipitate and 40% in solution retain their ability for protein-protein interactions. This means that a polycation-bound enzyme is localized in the hydrophobic nucleus of the complex, whereas the polyanion-bound enzyme sits on the hydrophilic shell of the complex. On pH-induced phase transition (pH decreases from 6.1 to 5.7), there occurs a stepwise decrease in penicillin amidase activity which is due to a 9.8-fold increase in the Km for 2-nitro-4-phenylacetamidobenzoic acid. Change of the catalytic activity and thermal stability of N-PEC-bound penicillin amidase is fully reversible and reproducible. Such soluble-insoluble immobilized enzymes with controllable thermal stability and activity may be used for simulating events in vivo and in biotechnology.

A new class of complex water-soluble polyelectrolytes

Water-soluble nonstoichiometric polyelectrolyte complexes (N-PEC) constitute a new class of polyelectrolytes. N-PEC are formed as a result of interaction between oppositely charged polyelectrolytes taken in non-equivalent rations and thus they are macromolecular compounds. An N-PEC particle can be represented as a macromolecule of a segmented block copolymer. The behaviour of the N-PEC in aqueous-salt media shows their polyelectrolyte nature, but in contrast to ordinary polyelectrolytes, they undergo considerable conformational changes. These transitions precede phase separations, which are unique and are accompanied by the phenomena of disproportionation. Using N-PEC as enzyme carriers it is possible to produce self-regulating systems with a feedback and also thermostable systems, which are the simplest models of a spore. The N-PEC formed by synthetic polyelectrolytes and some proteins, show a pronounced physiological activity and belong to the class of highly immunogenic antigens.

Non-stoichiometric polyelectrolyte complexes: New, water soluble macromolecular compounds

Non-stoichiometri cpolyelectrolyte complexes (NSPELC) consisting of completely interacted polyelectrolyte pairs bearing opposite charges are examined. These are soluble in aqueous media, due to the presence of a sufficient number of free, ionized chain units which have not formed salt bonds between the chain, as a property. All the polyelectrolyte pairs are formed in the same way; it consists of mixing the two fully ionized compounds in the necessary proportions in the presence of a low mol. wt. salt. Where one of the components is present in excess and is a weak polyelectrolyte, water soluble NSPELC can be produced by titrating the incomplete reaction product with an acid or alkali until all the main chain units of the part present as excess are completely ionized. The molecular characteristics of the particles of such polyelectrolyte complexes (PELC) have been found to be independent of the synthesis method used. Proof of this is that the complex is present at an equilibrium.