Stability Of Polyelectrolyte Complexes Research Articles

Self-Assembled Polyelectrolyte Nanocomplexes between Chitosan Derivatives and Insulin

Polyelectrolyte complexes (PEC) formed from chitosan derivatives and insulin was prepared and parameters influencing complex formation were characterized. Turbidimetric titration, in combination with dynamic light scattering (DLS) and laser doppler anemometry (LDA), were used to study the complexation process. The morphology of the PECs was determined using atomic force microscopy (AFM). PEC formation was predominantly pH-dependent. Complexation with insulin occurred only above critical pH value (pHc) of 6.0 for all the chitosan derivatives investigated. Soluble PECs in the size range of 200-500 nm with spherical or subspherical morphology and smooth surface structure were obtained at optimized polymer/insulin charge ratios. Optimal conditions were obtained when the pH of PECs was in the range of 6.5-8.0, depending on polymer structure. The stability of PECs was influenced by polymer chain length. Only when the MW of the polymers was > or =25-kDa PEC precipitation could be avoided. An increase in the ionic strength of the medium accelerated complex dissociation. Chitosan methylation and PEGylation significantly improved the stability of insulin in the PECs. Moreover, the PEC could protect insulin from degradation even at 50 degrees C for at least 6 h. All complexes could be lyophilized without influencing the particle size, complex concentration, and stability of insulin. On the basis of our results, we suggest that interactions involved in PEC formation were predominantly electrostatic in nature, involving the positively charged amino groups of chitosan and the negatively charged insulin above its isoelectric point. Intranasal absorption of the polyelectrolyte nanocomplexes will be studied in vivo.

Influence of polyelectrolyte complexes on the strength properties of papers from unbleached kraft pulps with different yields

For economical reasons filler particles and less expensive fibre raw materials are more frequently used in papermaking. This influences the mechanical properties of the formed papers in a negative way and it is therefore necessary to add strength-enhancing agents to the papermaking furnish. Traditionally cationic starch has been the dominating additive used for strength enhancement but new techniques are continuously being developed and in the present work the use of polyelectrolyte complexes (PEC) for improvements of different paper strength properties has been evaluated. Large focus has also been given to evaluating the properties of the polyelectrolyte complexes since these properties are largely dependant on molecular mass of the polyelectrolytes, the mixing conditions and ionic strength of the polyelectrolyte solutions. The PEC formation was studied between chemicals already used for strength enhancing purposes in real papermaking systems, i.e. poly (amido-amine) epichlorohydrin (PAE) and carboxymethylcellulose (CMC). The PEC formation was studied with respect to fundamental characteristics and the ability for use as strength additives. The PEC formation was also studied using model polyelectrolytes (PEL) poly(allylamine hydrochloride) (PAH), as the cationic component, and poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA), as the anionic components. The fundamental studies involve the PEC formation by varying the mixing ratio between the polyelectrolytes, the charge density or molecular weight of a component, structure of the one polyelectrolyte component, the mixing order, together with solution conditions. The main techniques used for these purposes were the static and dynamic light scattering, AFM tapping mode and Cryo-TEM. The adsorption of PECs onto surfaces of silica and lignin was investigated, using the stagnation point adsorption reflectometry (SPAR) and QCM-D (quartz crystal microgravimetry with dissipation). With these two techniques the amount of adsorbed chemical is obtained an also the viscoelastic properties of the adsorbed layer. The stability of PECs towards an increase in salt concentrations was investigated and the PECs were stable up to 0.2-0.4 M NaCl before complete dissolution, suggesting that the driving force for the formation of the PECs (from CMC-PAE) is a combination of the entropic effect of the released counterions and an enthalpy contribution from the interaction between the polymer segments. The PECs did not change their 3D-structure upon drying. It was also found that the swollen 3D structure of the complexes is achieved by an incorporation of a large amount of water into the complexes. Calculations based on the collected results show that the complexes consist of between 60 % and 95 % water. The PECs formed from PAA and PAH displayed higher water content when formed from low PEL concentration and salt concentrations up to 0.1 M NaCl than the PMAA-PAH PECs. At high PEL concentration and high salt concentration the opposite was observed. The use of the complexes as dry strength additives has two large benefits. First of all the 3D structure of the complexes allows for an efficient bridging between the microscopically rough fibre surfaces. Secondly the complexes allows for a higher saturation adsorption of polyelectrolytes on the fibre surface compared with a single polyelectrolyte addition. The PEC addition also leads to an increase in density, but the PECs showed the same benefits as beating when added to the unbeaten fibres. The effect on the fibre material, with regard to paper properties, varies depending on the pulp used.

Polyelectrolyte complexes of soluble poly-2-[(methacryloyloxy)ethyl]trimethylammonium chloride and its hydrogels with poly(acrylic acid)

The complex formation of poly-2-[(methacryloyloxy)-ethyl]trimethylammonium chloride (PMADQUAT) with poly(acrylic acid) (PAA) of different molecular weights has been studied in aqueous solutions by potentiometric, viscometric, turbidimetric and FTIR spectroscopic methods. The formation of insoluble non-stoichiometric polyelectrolyte complexes has been shown. The stability of polyelectrolyte complexes in solutions of different pH and ionic strength has been evaluated. The formation of polyelectrolyte complexes between hydrogels of PMADQUAT and linear PAA of different molecular weights has been studied. It was shown that the molecular weight of PAA considerably affects the kinetics of interaction as well as the final state of gel–polymer complex.

Polyelectrolyte Complexes Formed by Calf Thymus DNA and Aliphatic Ionenes: Unexpected Change in Stability upon Variation of Chain Length of Ionenes of Different Charge Density

The formation of polyelectrolyte complexes (PECs) between aliphatic 2,4- and 2,8-ionenes and calf thymus DNA in water–salt solutions is monitored by a fluorescence-quenching technique using an ethidium bromide probe. As expected, the tolerance of PEC to dissociation in water–salt solutions increased with an increase in both the number of charged groups, i. e., degree of polymerization of the ionenes (DP), and in the charge density of their chains. However, the latter tendency weakened markedly upon the lengthening of the ionenes chains and ceased to hold at DP ≈ 25. Comparison of the stability of PECs formed by DNA and poly(methacrylate) anion, respectively, with the ionenes, disclosed that relatively short ionene chains formed noticeably less stable DNA-containing PECs, whereas upon lengthening of the ionenes the difference in the stability of the PEC successively decreased and evened out at DP ≈ 25, in the case of 2,8-ionene. All these findings imply that in such systems the role of charge–charge conformity of the partners in DNA-containing PECs is evident only for rather short ionenes. The unexpected changes in PEC stability revealed suggest that the short chains of the ionenes are of special interest for the design of self-assembling polyelectrolyte systems with controllable stability attractive for biomedical applications and bioseparation.

Polyelectrolyte complexes from poly(N‐ethyl‐4‐vinylpyridinium bromide) and poly(sodium methacrylate). A stopped‐flow/light scattering investigation

AbstractTime‐resolved light scattering measurements performed in conjunction with the stopped‐flow method revealed information on the formation of polyelectrolyte complexes (PECs) of the weak polyelectrolyte (PE) couple poly(N‐ethyl‐4‐vinylpyridinium bromide) and poly(sodium methacrylate). The stability of the PECs depends, apart from other parameters, on the total ionic strength of the solution [I], the PE concentration and the concentration ratio (Φ) = [PVPE]/[PMA]. On the basis of Φ‐[I] diagrams, obtained for three PE combinations differing in average molar mass, the stability of PECs is characterized by the regimes A, B and C referring to conditions, where PECs are quite stable and water‐insoluble (A), PECs are not very stable and water‐soluble (B) and PECs are instable (not formed). The course of the curves separating regime A from regime B reflects the action of two competing effects regarding the stability of PECs, namely the increase in charge density and the increase in ion condensation with growing total ionic strength: Kinetic measurements revealed that, at low ionic strength right upon mixing, supramolecular complexes and later large aggregates are formed. The aggregates undergo rearrangements leading eventually to smaller complexes. At high ionic strength aggregates are formed rather slowly after mixing. This behavior is related to ion condensation. PECs can form only after the small ions occupying the charged sites at the PE chains are removed. Detachment of small ions from PE chains is a relatively slow process and is the rate‐determining step in PEC formation at moderately high ionic strength of the solution.

Immobilization in polyelectrolyte complex capsules: Encapsulation of a gluconate-oxidizing Serratia marcescens strain

In previous papers, it was shown that eukaryotic microbial systems can be encapsulated in polyelectrolyte complexes (PEC) prepared from sodium cellulose sulfate and poly(dimethyldiallylammonium chloride) with maintainance of vitality. In the present study, prokaryotic cells were successfully encapsulated in these PEC. Serratia marcescens B345 (IMET 11312) was chosen as a model organism. This strain converts gluconic acid to 2-ketogluconic acid. Since the 2-ketogluconic acid produced has very strong complexing properties, the number of applicable immobilization methods is restricted. Due to the high stability of PEC towards complexing agents, these problems can be overcome by the described method. As already described in previous papers, a preimmobilization of cells in a PEC coprecipitate prior to capsule formation proved to be advantageous also for encapsulation of bacilli. The mean productivity of the encapsulated S. marcescens cells was 1–4.4 g l −1 h −1 in comparison to 5 g l −1 h −1 for free cells. The productivity was highly dependent on the flow rate of the reactor. The encapsulated cells were used for 1,200 h in a continuous biotransformation process for the production of 2-ketogluconic acid.