Polyion complex nanomaterials from block polyelectrolyte micelles and linear polyelectrolytes of opposite charge. 2. Dynamic properties.

The present study investigates the relationship between the aggregation state and dynamic properties of block ionomer complexes (BICs) based on amphiphilic ionic block copolymers. The polyion coupling of 4'-(aminomethyl)fluorescein (AMF)-labeled poly(sodium methacrylate) (PMANa) or polystyrene- block-poly(sodium carboxylates) with poly(N-ethyl-4-vinylpyridinium bromide), PEVP was studied at an excess of carboxylate groups [PEVP]/[COO(-)] TOTAL = 0.3 and detected by fluorescence quenching. The polyion interchange reactions included migration of PEVP between the following: (1) two linear polyanion chains, (2) linear polyanion chain and anionic polyion shell micelle, or (3) two anionic polyion shell micelles. Additionally, the interchange of AMF-labeled PMANa with unlabeled PMANa in the shell of polystyrene- block-PEVP micelles was studied. The interchange reactions were carried out at [PEVP]/[COO(-)] TOTAL = 0.15 and detected by fluorescence quenching (direct reaction) or ignition (reverse reaction). The rates of these reactions were compared using half-conversion times and, when possible, second-order reaction kinetic constants. The dependences of the rates on the ionic strength and polyion length observed for BICs were similar to those previously reported for regular interpolyelectrolyte complexes (IPECs) of linear polyions. However, the interchange reactions involving polyion shell micelles were much slower than those reactions observed in IPECs. The coupling reactions involving polyion shell micelles were also slower compared with the coupling of linear polyions. The observed phenomena were attributed to the aggregation state of polyion shell micelles and discussed using the collision model for polyion interchange reactions previously proposed for IPECs.

Polyion complex nanomaterials from block polyelectrolyte micelles and linear polyelectrolytes of opposite charge: 1. Solution behavior.

The present study investigates whether block polyelectrolyte micelles can form soluble complexes upon interaction with oppositely charged linear polyelectrolytes. The phase behavior and molecular characteristics of the complexes were examined by turbidimetry, phase analysis, dynamic light scattering, and sedimentation velocity techniques. At an excess of polyelectrolyte micelles, soluble complexes were formed either independently on the route of preparation or, for select linear polyelectrolytes, through routes that avoided macrophase separation. Such soluble complexes are in a thermodynamic equilibrium state for all polyion pairs. The hydrodynamic sizes and sedimentation coefficients did not depend on the chemical nature of the linear polyelectrolyte, but were determined by the charge ratios and the hydrodynamic properties of the initial micelles. At an excess of linear polyelectrolyte, complex solubility and molecular characteristics depended on the chemical nature of the linear polyelectrolyte. In this region, linear polyelectrolytes formed soluble complexes with micelles if soluble complexes could be formed with the corresponding linear analogues of the block polyelectrolyte.

Block polyelectrolyte networks from poly(acrylic acid) and poly(ethylene oxide): sorption and release of cytochrome C.

A new family of block polyelectrolyte networks containing cross-linked poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) was synthesized by copolymerization of acrylic acid and bisacrylated PEO (10 kDa). Two materials with different PEO/PAA ratios were compared with a weakly cross-linked PAA homopolymer network. The networks bound a cationic protein, cytochrome C, due to the polyion coupling, leading to the network contraction. After binding the protein the block polyelectrolyte networks were more porous compared to a homopolymer network, facilitating protein absorption within the gel. The protein was released by adding Ca2+ ions or a polycation. Ca2+ ions migrated within the gels and reacted with PAA chains, thus displacing the protein. The polycation transfer into hydrogels, as a result of polyion substitution reactions, was inhibited by the excess of PEO chains in the block polyelectrolyte networks. Overall, these findings advance development of functional polyelectrolyte networks for immobilization and controlled release of proteins.

Nanomaterials from ionic block copolymers and single-, double-, and triple-tail surfactants.

Block ionomer complexes (BICs) are prepared from anionic block copolymers and cationic surfactants of different structure or from their mixtures. Drastic changes in the morphology and stability of BIC nanoparticles caused by changes in the composition of the surfactant mixture are demonstrated. Single-tail and double-tail surfactants appear to mix within the BIC, resulting in the formation of rather uniform BIC particles. Morphologies of the particles of these mixed BICs are intermediate between those prepared from pure single- and double-tail surfactants. Particles of BIC prepared from mixtures of single- and triple-tail surfactants are heterogeneous, and FRET experiments indicate that surfactant components in these systems are strongly segregated. The results of this study provide important insights into the formation and structure of the BIC and have implications for various applications of the BIC (e.g., nanomedicine), in which precise control of the shape, size, and other properties is needed.

Self-organization of cationic dendrimers in polyanionic hydrogels.

Protonated poly(propylene imine) dendrimers (Astramol) of five generations: DAB-dendr-(NH2)x (where x=4, 8, 16, 32 or 64) are sorbed by slightly cross-linked polyanionic hydrogels: poly(sodium acrylate) and poly(sodium 2-acrylamido-2-methylpropane sulfonate). As a result highly swollen original hydrogel transforms into compact cross-linked polyelectrolyte-dendrimer complexes. Sorption of dendrimers by the hydrogels is a chemically drawn frontal diffusion process. Driving force comes from the gain in the free energy of interpolyelectrolyte coupling reaction between the charged dendrimer molecules and the oppositely charged hydrogel network, accompanied with entropically favourable release of low molecular salt into environment. The amount of a simple salt released is equivalent to a number of intermolecular salt bonds, formed between protonated dendrimers and hydrogel networks. Apparently the mechanism of dendrimer uptake involves a "relay-race" transfer of dendrimer polycations from one fragment of polyelectrolyte network to the other via interpolyelectrolyte exchange reaction. As a result "core-shell" constructs consisting of outer weakly swollen complex shell and highly swollen hydrogel core are formed at intermediate stages of the process. The rate of sorption is determined by the rate of the interpolyelectrolyte exchange reaction that is the rate of the formation of free fragments of polyelectrolyte network (vacancies) on the inner complex-hydrogel boundary. The amount of vacancies depends on the area of this boundary. Consequently kinetics of dendrimer uptake could not be fitted in terms of Fickian diffusion (except DAB-dendr-(NH2)4), but expressed in terms of the kinetic equation derived for a frontal heterogeneous reaction. Sorbed dendrimers of all studied generations at pH values ensuring complete protonation of primary and tertiary amine groups are closely packed in hydrogel networks, so that all dendrimer cationic units form ion pairs with anionic units of hydrogels. In other words polyanionic network fragments are able to penetrate into the interior of fully protonated DAB-dendr-(NH2)x species as it was earlier shown for flexible linear polyanions. In such case the ultimate amount of sorbed dendrimer molecules is always determined by the condition n(a)/N- = 1, where n(a) is the total number of dendrimer amine groups, N- is the number of the anionic hydrogel units. The latter is also true for the complex shell composition in the heterogeneous reacting samples formed at intermediate stages of dendrimers uptake. Variation of pH and sorption extent is an effective tool to control dendrimer distribution, self-organization and the final structure of dendrimer-hydrogel constructs.

Fluorescence anisotropy study of aqueous dispersions of block ionomer complexes.

Block ionomer complexes (BIC) of "dual hydrophilic" block copolymers containing ionic and nonionic blocks and oppositely charged surfactants spontaneously form colloidal particles of ca. 80 nm in diameter stable in aqueous dispersions at every composition of the mixture. Packing and dynamics of aliphatic groups of the surfactant in BIC were examined by using the quenching-resolved fluorescence anisotropy (QRFA) method with 1,6-diphenyl-1,3,5-hexatriene (DPH) as a probe. The values of the order parameter and rotational relaxation time in the BIC were higher than those in the surfactant micelles. Incorporation of aliphatic alcohols in the BIC decreased the order parameter and increased the rotational relaxation time. The effects on the order parameter were explained by changes in the surfactant aliphatic group conformation to "fill the gaps" induced by insertion of shorter alcohol molecules. The effects on the relaxation time were attributed to a decrease in repulsion of the surfactant headgroups and expulsion of water from the BIC hydrophobic interior as evidenced by the decrease in micropolarity. The results of this study have implications for potential use of the BIC in pharmaceutics and other fields.

Colloidal stability of aqueous dispersions of block ionomer complexes: effects of temperature and salt.

This work characterized colloidal stability of the dispersions, formed by the complexes of poly(ethylene oxide)-b-poly(sodium methacrylate) and hexadecyltrimethylammonium bromide. At room temperature, the dispersion was stabilized by the poly(ethylene oxide) (PEO) chains and did not aggregate for at least several months. Elevation of temperature caused aggregation of the dispersion because of dehydration of the PEO chains. At initial stages (minutes), the aggregation was reversible and the particles spontaneously redispersed once the temperature was decreased. However, it became irreversible at the later stages (hours), probably indicating fusion of the hydrophobic cores of the BIC particles. Addition of elementary salts led to a decrease of the aggregation temperature. The effects of various salts were dependent on the chemical nature of the ions and were consistent with the Hofmeister series. This behavior was discussed in terms of hydration and London (dispersion) interactions between the ions and the PEO.

Synthesis of vesicles on polymer template.

Reactive single-tail cationic surfactants self-assemble on the anionic block copolymer templates. These systems spontaneously arrange in small vesicles of nanoscale size. The vesicles are further stabilized by dimerization of the assembled surfactant monomers forming double-tail surfactants bound to the block copolymer. The resulting systems are resistant to changes in environmental characteristics such as pH, ionic strength, and temperature variations. Hydrophilic macromolecules can be encapsulated in the internal aqueous volume of these vesicles. The simplicity of the preparation makes these systems promising as drug and gene delivery carriers.

Secondary structure of DNA is recognized by slightly cross-linked cationic hydrogel.

Interaction of salmon sperm DNA (300-500 bp) and ultrahigh molecular mass DNA (166 kbp) from bacteriophage T4dC with linear poly(N-diallyl-N-dimethylammonium chloride) (PDADMAC) and slightly cross-linked (#) PDADMAC (#PDADMAC) hydrogel in water has been studied by means of UV-spectroscopy, ultracentrifugation, atomic force, and fluorescence microscopy (FM). It is found that the linear polycation induced compaction of either native (double-stranded) or denatured (single-stranded) DNA by forming PDADMAC-DNA interpolyelectrolyte complexes (IPEC)s. At the same time, #PDADMAC hydrogel is able to distinguish between native and denatured DNA. Native DNA is adsorbed and captured in the hydrogel surface layer, while denatured DNA diffuses to the hydrogel interior until the whole hydrogel sample is transformed into the cross-linked IPEC. Both native and denatured DNA can be completely released from the hydrogel in appropriate conditions with no degradation by adding a low molecular salt. The data observed using conventional physicochemical methods with respect to DNA of a moderate molecular mass remarkably correlate with the pictures directly observed for ultrahigh molecular mass DNA in dynamics by using FM.