Soluble polyelectrolyte complexes of biopolymers

This review analyzes the papers reflecting the state of the art and achievements in the field of experimental investigations of solutions of polyelectrolyte complexes containing biopolymers, specifically oligomeric enzymes, cationic polysaccharide chitosan, or DNA. The analysis shows that the use of soluble complexes is promising for solving urgent practical problems. The development of methods for suppressing thermal aggregation of globular proteins without any substantial loss in functional activity, for imparting chitosan the ability to dissolve under physiological conditions and to form polyelectrolyte complexes, and for creating dual-action dendrimer carriers that can simultaneously deliver genetic material and drugs to cells are among the most significant directions.     

Highly stable neutral and positively charged dicarbollide sandwich complexes

Novel sandwich metallacarboranes commo-[3,3'-Ni(8-SMe2-1,2-C2B9H10)2] (1), commo-[3,3'-Co(8-SMe2-1,2-C2B9H10)2]+ (2+), commo-[3,3'-Ru(8-SMe2-1,2-C2B9H10)2] (4) and commo-[3,3'-Fe(8-SMe2-1,2-C2B9H10)2] (5) have been prepared by reaction of [10-SMe2-7,8-nido-C2B9H10]- with NiCl2 x 6 H2O, CoCl2, [RuCl2(dmso)4] and [FeCl2(dppe)], respectively. Reduction of 2+ with metallic Zn leads to the neutral and isolable complex commo-[3,3'-Co(8-SMe2-1,2-C2B9H10)2] (3). Theoretical calculations using the ZINDO/1 semiempirical method show three energy minima for complexes 1-3 and 5 that agree with the presence of three different rotamers in solution at low temperature, while four relative energy minima have been found for 4. The calculated rotational energy barriers for complexes 1-5 have been found in the range 5.2+/-0.2 and 11.5+/-0.2 kcal mol(-1). These values are in agreement with the experimental data calculated for complexes 2+ and 5. Only one rotamer is found in the X-ray crystal structure of complexes 1-3, while two are observed for 4. Neutral complexes 1, 3 and 4 exhibit a gauche conformation, whereas a cisoid conformation is found for the 2+ ion. Rotamers evident from X-ray diffraction studies are in agreement with the global energy minimum calculated by the ZINDO/1 method. The electrochemical studies conducted on 1, 3, 4 and 5 support the proposal that the charge-compensated ligand [10-SMe2-7,8-nido-C2B9H10]- stabilises lower oxidation states in metals than the dianionic [7,8-nido-C2B9H11]2- and even the [C5H5]- ligands.     

Surface properties of fluids of charged platelike colloids

Surface properties of mixtures of charged platelike colloids and salt in contact with a charged planar wall are studied within density functional theory. The particles are modeled by hard cuboids with their edges constrained to be parallel to the Cartesian axes corresponding to the Zwanzig model [J. Chem. Phys. 39, 1714 (1963)] and the charges of the particles are concentrated at their centers. The density functional applied is an extension of a recently introduced functional for charged platelike colloids. It provides a qualitative approach because it does not determine the relation between the actual and the effective charges entering into the model. Technically motivated approximations, such as using the Zwanzig model, are expected not to influence the results qualitatively. Analytically and numerically calculated bulk and surface phase diagrams exhibit first-order wetting for sufficiently small macroion charges and isotropic bulk order as well as first-order drying for sufficiently large macroion charges and nematic bulk order. The asymptotic wetting and drying behaviors are investigated by means of effective interface potentials which turn out to be asymptotically the same as for a suitable neutral system governed by isotropic nonretarded dispersion forces. Wetting and drying points as well as predrying lines and the corresponding critical points have been located numerically. A crossover from monotonic to nonmonotonic electrostatic potential profiles upon varying the surface charge density has been observed. Nonmonotonic electrostatic potential profiles are equivalent to the occurrence of charge inversion. Due to the presence of both the Coulomb interactions and the hard-core repulsions, the surface potential and the surface charge do not vanish simultaneously, i.e., the point of zero charge and the isoelectric point of the surface do not coincide.     

Chitosan based polyelectrolyte complexes

Polyelectrolyte complexes (PECs) are formed through the electrostatic interactions between polymers carrying opposite charges. Here are presented results of basic studies on the PECs of chitosan with other polysaccharides such as sodium alginate, carboxymethyl cellulose, polygalacturonic acid and κ‐carrageenan. An extensive study on chitosan/carboxymethyl cellulose membranes, regarding its swelling characteristics and water vapour sorption is offered. Also the interaction of chitosan with polyacrylic acid has been examined from the thermodynamic point of view.     

Novel polyelectrolyte complexes based on diazo-resins

Polyelectrolyte complexes containing diazonium groups (PEC-N₂) with a high ionic crosslinking rate were prepared as a precipitate by mixing the diazo-resin with polyanion solutions. The photochemical decomposition of the complexes from different polyanions was studied. It was shown that PEC-N₂ exhibit high photosensitive properties. Under irradiation of UV light, the complexes which can be dissolved in ternary mixtures such as H₂O-DMF-LiCl,H₂O-DMF-NaSCN or H₂O-DMF-ZnCl₂ (DMF: N,N-dimethylformamide) become indissoluble since the crosslinking structure of the complexes changes from ionic to covalent.     

Determination of traces of heavy metals in positively charged inorganic colloids in fresh waters

Summary Determination of Traces of Heavy Metals in Positively Charged Inorganic Colloids in Fresh Waters After removal of suspended particulate matter by centrifugation followed by filtration through 0.4-m membrane filters, humic substances and other negatively charged species are sorbed on a small column of macroreticular weak-base anion exchanger DEAE-Sephadex A-25 at fast flow rates. Positively charged inorganic colloids pass through the column and are collected on a 0.015-m membrane filter, which is then ultrasonically treated with 1M nitric acid for the determination of copper, lead and cadmium by differential pulse anodic stripping voltammetry with a static mercury drop electrode. Up to O.2g 1^–1 of the heavy metals are found in positively charged inorganic colloids in river, pond and tap waters.     

Photobiological properties of positively charged methylene violet analogs

O-Methyl methylene violet (OMeMV), O-methyl bromomethylene violet (OMeBrMV) and O-methyl iodomethylene violet (OMeIMV) have been prepared in order to test their potential utility as anti-viral and anti-tumor phototoxic dyes. Rates of photosensitized toxicity of KB cells with 633 nm irradiation are (x 10(-19) photon-1): 2.4, 2.2, 1.9 and 0.17 for OMeIMV, OMeBrMV, methylene violet (MV) and OMeMV, respectively. Rates of photosensitized inactivation of Sindbis virus in phosphate-buffered saline with 633 nm irradiation are (x 10(-18) photon-1): 3.3, 1.8, 0.99, 0.15 for MV, OMeIMV, OMeBrMV and OMeMV, respectively. Quantum efficiencies for singlet oxygen formation were determined as OMeIMV, 0.64; OMeBrMV, 0.40; OMeMV, 0.054. Titration of the dyes with double-stranded (ds)DNA resulted in bathochromic shifts and hypochromic effects in the visible absorption spectra. Association constants for interaction of the methylated dyes with dsDNA of approximately 1 x 10(5) M-1 were determined by Scatchard analysis of equilibrium dialysis and UV absorption titration data. Photolysis of the halogenated dyes with DNA under argon led to covalent bond formation with the nucleic acid; there was no evidence of covalent binding in the dark.     

Nanostructure of complexes between cationic lipids and an oppositely charged polyelectrolyte

The morphology of aqueous solutions of polyelectrolytes and oppositely charged lipids is the subject of extensive colloid science research, because of their application in industry and medicine, the latter especially for gene therapy. In this work, we show that complexes of two different cationic lipids with the polyelectrolyte sodium poly(acrylic acid), PAA, share similar morphology with the complexes of those lipids with nucleic acids, implying a broader and universal packing phenomenon. We characterized by direct-imaging cryogenic-temperature transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and zeta (ζ)-potential two cationic lipids, 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and bis(11-ferrocenylundecyl) dimethylammonium bromide (BFDMA), which are used in gene transfection, at equivalent lipid/polyelectrolyte charge ratio. Our results revealed that, for both types of complexes, onion-like multilamellar nanostructures formed, which exhibited similar morphology as in complexes of DNA or oligonucleotides (lipoplexes), based on the same lipids. Our findings suggest that the onion-like packing may be energetically favorable for a wide range of polyelectrolyte-liposome systems, from oligonucleotides and DNA to PAA.     

Stoichiometric polyelectrolyte complexes of ionic block copolymers and oppositely charged polyions

Micellization in dilute solutions of diblock copolymers with a polyelectrolyte and a hydrophilic nonionic blocks and oppositely charged polyions is studied using mean-field theory. In aqueous solutions the micelle core consists of the polyelectrolyte complex (PEC) while the corona is formed by hydrophilic blocks of the block copolymers. Describing PEC as a globule in the framework of the Lifshitz [Zh. Eksp. Teor. Fiz. 55, 2408 (1968)] globule theory we calculate the surface tension of the micellar core/solvent interface as a function of the polyion degree of ionization, solvent quality, and concentration of low-molecular-mass salt. The equilibrium aggregation number of starlike micelles formed by block copolymers and homopolymers of opposite charge at stoichiometric mixture compositions is found as a function of the system parameters. It is shown that micelles disintegrate upon addition of salt.     

Monte Carlo simulations of charged dendrimer-linear polyelectrolyte complexes and explicit counterions

We study complexes composed of one dendrimer of generation G = 4 (G4 dendrimer) with N(t) = 32 charged terminal groups and an oppositely charged linear polyelectrolyte accompanied by neutralizing counterions in an athermal solvent using Monte Carlo simulations based on the bond fluctuation model. In our study both the full Coulomb potential and the excluded volume interactions are taken into account explicitly with the reduced temperature τ and the chain length N(ch) as the main simulation parameters. Our calculations indicate that there exist three temperature ranges that determine the behavior of such complexes. At τ(complex) stable charged dendrimer-linear polyelectrolyte complexes are formed first, which are subsequently accompanied by selective counterion localization within the complex interior at τ(loc) ≤ τ(complex), and counterion condensation as temperature is further decreased below τ(cond) < τ(loc). In particular, we observe that condensation takes place exclusively on the excess charges in the complex and thus no condensation is observed at the compensation point (N(ch) = N(t)), irrespective of τ. For N(ch) ≠ N(t) the complex is overally charged. Furthermore, we discuss the size and structure of the dendrimer and the linear polyelectrolyte within the complex, as well as spatial distributions of monomers and counterions. Conformations of the chain in the bound state are analysed in terms of loops, trains, and tails.     

Surface properties of biospecific coatings based on polyelectrolyte complexes of maleic acid copolymers

The surface properties of PE with bilayer and multilayer coatings based on polyelectrolyte complexes of the biospecific modified N-vinylpyrrolidone-maleic acid copolymer with chitosan, amphiphilic chitosan, or albumin have been investigated by atomic force microscopy, multiple attenuated total reflection spectroscopy, X-ray photoelectron spectroscopy, and goniometry. The copolymer of N-vinylpyrrolidone and maleic acid contains affine ligands to plasminogen—fragments of α-amino-bonded lysine—and imparts thromboresistant properties to the surface being modified. The surface morphology and the size of particles of deposited intermediate layers of chitosan or albumin differ from those of the bilayer (multilayer) coatings containing an additional external layer of the biospecific copolymer. The deposition of the multilayer polymeric coatings promotes a more thorough coverage of the protected surface. Characteristic absorption bands that demonstrate the presence of the modifying polymers on the PE surface have been revealed; this fact is also confirmed by the X-ray photoelectron spectroscopy data on the atomic composition of the analyzed surface. A significant increase in the hydrophilicity of the modified surface is established by the contact angle technique.     

Formation and transformations of polyelectrolyte gel-ampholyte dendrimer-surfactant ternary complexes

The reactions of complex gels formed via the sorption of a poly(propylenimine) ampholyte dendrimer of the fourth generation by oppositely charged lightly cross-linked polyelectrolyte hydrogels with ionogenic micelle-forming surfactants have been studied. The sorption of surfactant ions likely charged relative to the complexed ampholyte dendrimer by complex gels is associated with two parallel chemical reactions controlled by the concentration of the surfactant and pH which give rise to the formation of network-dendrimer-surfactant tertiary complexes. The reactions of complex gels with surfactant ions likely charged relative to the network polyelectrolyte make it possible at different solution pHs to prepare both negatively and positively charged hydrogels reinforced by disperse particles of the dendrimer-surfactant complex.     

Formation of polyelectrolyte complexes in an organic solvent

The formation of complexes of polyelectrolytes has been investigated with low charged polyelectrolytes soluble in an organic solvent. The degree of complexation has been determined from conductimetric experiments; it is independent of the degree of quaternization of the polycation but decreases as the polymer concentration and the ionic content increase. A change in the conductimetric and in the viscometric curves during addition of polycation to the polyanion (or the reverse) has been found in the range of the ionic stoichiometry. The complex formation corresponds to an electrostatic cross-link the stability of which decreases with the ionic content of the solution.     

Self-assembled architecture based on triiron-substituted polyoxomolybdate anion and positively charged polymer

A new self-assembled multilayer architecture was constructed by successive deposition of poly(4-vinylpyridine) partially quaternized with ethylamine (B) and Keggin trilacunary polyoxomolybdate [Aα-PFe₃^III(H₂O)₃Mo₉O₃₇]⁶⁻ (PFe₃Mo₉) on the Au electrode surface, covered with 3-mercapto-1-propanesulfonic acid (MPS). Surface plasmon resonance and cyclic voltammetry measurements were performed at Au/MPS/B/PFe₃Mo₉/B interface in order to investigate the structure and the electrochemical behavior of this electrode. Due to the presence of PFe₃Mo₉, the Au/MPS/B/PFe₃Mo₉/B-modified electrode showed electrocatalytic activity towards H₂O₂ amperometric detection. Additionally, when GOx was deposited as the outermost layer on the abovementioned multilayer structure, the Au/MPS/B/PFe₃Mo₉/B/GOx-modified electrode was able to detect glucose.     

Molecular structure of single DNA complexes with positively charged dendronized polymers

Positively charged dendronized polymers with protonated amine groups at the periphery and different dendron generations are cylindrically shaped nanoobjects whose radii and linear charge densities can be varied systematically. These polyelectrolytes have been complexed with DNA and subsequently adsorbed on precoated mica substrates. The analysis of scanning force microscopy data indicates that DNA wraps around the dendronized polymers. The calculated pitch is 2.30 +/- 0.27 and 2.16 +/- 0.27 nm for DNA wrapped around dendronized polymers of generation two and four, respectively. The complex with the second generation has been shown to be negatively charged, which is consistent with the theory of spontaneous overcharging of macro-ion complexes, when the electrostatic contribution to the free energy dominates over the elastic energy. The complexes may be of interest for the development of nonviral gene delivery systems.     

Study of interaction between two oppositely charged polyelectrolytes and formation of polyelectrolyte complexes

Polyelectrolyte complex formation has been studied between oppositely charged polyelectrolytes, e.g., polyethylene-imine, polymethacrylic acid, and methacrylic acid–methacrylamide copolymer. Formation of complexes could be shown through several experimental techniques, e.g., viscometry, conductometry, potentiometry, and IR spectra. It is suggested that these complexes are perhaps formed as a result of electrostatic cooperative interaction and a “ladder-like” interaction is likely to be more favorable.     

壳聚糖纳米球和纳米金修饰葡萄糖生物传感器的研究

构造了一种以碳纳米管接枝的壳聚糖为基底,然后将羧基二茂铁电聚合在其氨基化的表面,利用负电荷的表面组装PDDA保护的纳米金,最后通过静电吸附葡萄糖氧化酶,制得了新型的葡萄糖生物传感器。在优化的实验条件下,该传感器的响应电流与其浓度在3.0×10-6~2.9×10-3mol/L范围内呈现良好的线性关系,检测限为1.4×10-6mol/L。此外,该传感器还具有灵敏度高、稳定性好和抗干扰能力强等特点。