Simona Schwarz

Hyperbranched PEI with Various Oligosaccharide Architectures : Synthesis, Characterization, ATP Complexation, and Cellular Uptake Properties

We present a rapid synthetic method for the development of hyperbranched PEIs decorated with different oligosaccharide architectures as carrier systems (CS) for drugs and bioactive molecules for in vitro and in vivo experiments. Reductive amination of hyperbranched PEI with readily available oligosaccharides results in sugar functionalized PEI cores with oligosaccharide shells of different densities. These core-shell architectures were characterized by NMR spectroscopy, elemental analysis, SLS, DLS, IR, and polyelectrolyte titration experiments. ATP complexation of theses polycations was examined by isothermal titration calorimetry to evaluate the binding energy and ATP/CS complexation ratios under physiological conditions. In vitro experiments showed an enhanced cellular uptake of ATP/CS complexes compared to those of the free ATP molecules. The results arise to initiate further noncovalent complexation studies of pharmacologically relevant molecules that may lead to the development of therapeutics based on this polymeric delivery platform.

The Influence of Densely Organized Maltose Shells on the Biological Properties of Poly(propylene imine) Dendrimers: New Effects Dependent on Hydrogen Bonding

Maltose-modified poly(propylene imine) (PPI) dendrimers were synthesized by reductive amination of unmodified second- to fifth-generation PPI dendrimers in the presence of excess maltose. The dendrimers were characterized by using (1)H NMR, (13)C NMR, and IR spectroscopies; laser-induced liquid beam ionization/desorption mass spectrometry; dynamic light scattering analyses; and polyelectrolyte titration. Their scaffolds have enhanced molecular rigidity and their outer spheres, at which two maltose units are bonded to the former primary amino groups on the surface, have hydrogen-bond-forming properties. Furthermore, the structural features reveal the presence of a dense shell. Experiments involving encapsulation (1-anilinonaphthalene-8-sulfonic acid) and biological properties (hemolysis and interactions with human serum albumin (HSA) and prion peptide 185-208) were performed to compare the modified with the unmodified dendrimers. These experiments gave the following results: 1) The modified dendrimers entrapped a low-molecular-weight fluorescent dye by means of a dendritic box effect, in contrast to the interfacial uptake characteristic of the unmodified PPI dendrimers. 2) Both low- and high-generation dendrimers containing maltose units showed markedly reduced toxicity. 3) The desirable features of bio-interactions depended on the generation of the dendrimer; they were retained after maltose substitution, but were now mainly governed by nonspecific hydrogen-bonding interactions involving the maltose units. The modified dendrimers interacted with HSA as strongly as the parent compounds and appeared to have potential use as antiprion agents. These improvements will initiate the development of the next platform of glycodendrimers in which apparently contrary properties can be combined, and this will enable, for example, therapeutic products such as more efficient and less toxic antiamyloid agents to be synthesized.

Maltose- and maltotriose-modified, hyperbranched poly(ethylene imine)s (OM-PEIs): Physicochemical and biological properties of DNA and siRNA complexes

Polycationic non-viral polymers are widely employed as delivery platforms of plasmid DNA, or of small interfering RNAs (siRNAs) for the induction of RNA interference (RNAi). Among those, poly(ethylene imine)s (PEIs) take a prominent position due to their relatively high efficacy; however, their biodistribution profiles upon systemic delivery and their toxicity pose limitations which can be addressed by the introduction of PEI modifications. In this paper, we systematically analyse physicochemical and biological properties of DNA and siRNA complexes prepared from a set of maltose-, maltotriose- or maltoheptaose-modified hyperbranched PEIs (termed (oligo-)maltose-modified PEIs; OM-PEIs). We show that pH-dependent charge densities of the OM-PEIs correlate with the structure and degree of grafting, and the length of the oligomaltose. Decreased zeta potentials of OM-PEI-based complexes and changes in the thermodynamics of DNA complex formation are observed, while the complex sizes are largely unaffected by maltose grafting and the presence of serum proteins. Furthermore, although complexation efficacies of siRNAs are not altered, complex stabilities are markedly increased in OM-PEI complexes. DNA complex uptake and transfection kinetics are slowed down upon maltose-grafting of the PEI which can be attributed to decreased zeta potentials, and alterations in the uptake mechanisms (clathrin-dependent/clathrin-independent endocytosis) are observed. Independent of the maltose architecture, DNA and siRNA complexes based on maltose-grafted PEI show considerably lower cytotoxicity as compared to PEI complexes. While maltose grafting generally leads to reduced in vitro transfection efficacies, this effect is less profound in some OM-PEI/siRNA complexes as compared to OM-PEI/DNA complexes. Importantly, upon their systemic application in vivo, OM-PEI/siRNA complexes show marked differences in the siRNA biodistribution profile with e.g. substantially decreased siRNA levels in the liver and increased siRNA levels in the muscle. Taken together, we demonstrate that OM-PEI complexes show structure-dependent physicochemical and biological properties and may represent promising, tailor-made platforms for the delivery of siRNAs, particularly for in vivo applications.

Influence of surface functionality of poly(propylene imine) dendrimers on protease resistance and propagation of the scrapie prion protein

Accumulation of PrP(Sc), an insoluble and protease-resistant pathogenic isoform of the cellular prion protein (PrP(C)), is a hallmark in prion diseases. Branched polyamines, including PPI (poly(propylene imine)) dendrimers, are able to remove protease resistant PrP(Sc) and abolish infectivity, offering possible applications for therapy. These dendrimer types are thought to act through their positively charged amino surface groups. In the present study, the molecular basis of the antiprion activity of dendrimers was further investigated, employing modified PPI dendrimers in which the positively charged amino surface groups were substituted with neutral carbohydrate units of maltose (mPPI) or maltotriose (m3PPI). Modification of surface groups greatly reduced the toxicity associated with unmodified PPI but did not abolish its antiprion activity, suggesting that the presence of cationic surface groups is not essential for dendrimer action. PPI and mPPI dendrimers of generation 5 were equally effective in reducing levels of protease-resistant PrP(Sc) (PrP(res)) in a dose- and time-dependent manner in ScN2a cells and in pre-existing aggregates in homogenates from infected brain. Solubility assays revealed that total levels of PrP(Sc) in scrapie-infected mouse neuroblastoma (ScN2a) cells were reduced by mPPI. Coupled with the known ability of polyamino dendrimers to render protease-resistant PrP(Sc) in pre-existing aggregates of PrP(Sc) susceptible to proteolysis, these findings strongly suggest that within infected cells dendrimers reduce total amounts of PrP(Sc) by mediating its denaturation and subsequent elimination.

Higher efficiency in the flocculation of clay suspensions by using combinations of oppositely charged polyelectrolytes

Abstract Dual systems—the highly charged polycation poly(diallyll-dimethyl-ammoniumchloride) (PDADMAC) in combination with different high molecular weight polyanions of the polyacrylamide type—were tested as flocculants for clay suspensions and natural waste waters from gravel pits. The flocculant performance was characterised by measuring the sedimentation behaviour as well as the residual turbidities and the extent of polymer adsorption. Whereas the molecular weight of the high molecular weight polycation is of lower influence, the removel of suspended particles is greatly affected by the molecular weight of the polyanion. Our experiments showed that degradation of the very high molecular weight polyanions leads to higher turbidity of the supernatant. The order of addition of the two polyelectrolytes influences the flocculation mechanism. Most effective is the addition of polycation followed by the polyanion. So a combination of patching and bridging is obtained.

Polyelectrolyte adsorption on charged surfaces: study by electrokinetic measurements

Abstract In order to describe the influence of cationic polyelectrolytes on flocculation of disperse systems the adsorption of poly (diallyldimethylammonium chloride) (PDADMAC) onto silica, mica and acidic polymer latex was investigated. The plateau value of the adsorption isotherms grows with increasing surface charge density of the substrates and electrolyte concentration. The adsorbed layer of the polycation was characterized by zeta potential measurements with KCl solutions of constant ionic strength and varied pH. The zero point of the charge as well as the shape of the zeta potential–pH plot depends on the coverage of the surface with polycations. For fully covered substrates the zero point of the charge as well as the pKA and pKB values calculated by a stochastic search programme are independent of the substrate. Maximum flocculation was observed at about 30% of the plateau value of the adsorption isotherms.

Polyelectrolyte Complexes in Flocculation Applications

This review concentrates on the interactions between oppositely charged polyelectrolytes and on the formation of complexes, which can be used for different applications such as paper retention or water treatment. Three different possibilities for the appearance of polyelectrolyte complexes (PECs) in flocculation applications are described. Starting with the “classical” dual system (step-by-step addition of polycation and polyanion to a negatively charged suspension of fibers or particles), the interaction between a “soluble polyanion” (such as anionic trash) with polycation is described as well as the formation of well-defined pre-mixed PECs and their application as flocculants.

Complex Nanoparticles Based on Chitosan and Ionic/Nonionic Strong Polyanions: Formation, Stability, and Application

Interpolyelectrolyte complex (IPEC) nanoparticles formed between chitosan having different molar masses (470, 670, and 780 kDa) and two random copolymers of 2-(acrylamido)-2-methylpropanesulfonate (AMPS) with tert-butylacrylamide (TBA) [P(AMPS(54)-co-TBA(46)) and P(AMPS(37)-co-TBA(63))] were prepared by the dropwise addition of polyanion onto the chitosan solution. The effect of polyelectrolyte characteristics and the molar ratio between charges on the morphology of the complex nanoparticles and on their colloidal stability was deeply investigated by turbidimetric titration (optical density at 500 nm), dynamic light scattering, and atomic force microscopy. It was found that the lowest sizes of the IPEC nanoparticles were obtained, with both polyanions, when the chitosan having the lowest molar mass (470 kDa) was used as a major component. In this case, the particle sizes varied in a narrow range, even after the complex stoichiometry; i.e., when the polyanion was added in excess, the colloidal stability of these IPEC dispersions was very high. A mechanism of complex formation as a function of the ratio between charges was proposed. According to this mechanism, the nonstoichiometric complex nanoparticles formed at molar ratios between charges, n(-)/n+, lower than 0.2, i.e., far from the complex stoichiometry, would have a high density of positive charges in excess not only because of the chitosan in excess, which forms the shell, but also because of the mismatch of opposite charges, due to both the differences in the flexibility of complementary polyions and the presence of the hydrophobic comonomer, TBA, in the polyanion structure. Nonstoichiometric IPECs prepared at n(-)/n+ around 0.2 proved to be more efficient than chitosan in the destabilization of kaolin from a model suspension, with a lower optimum concentration flocculation and a much larger flocculation window being found compared with chitosan.

Polypropylene surface functionalization with chitosan

Chitosan coatings on oxygen-plasma pre-treated polypropylene (PP) surfaces were formed to improve their wettability, dyeing behavior and reactivity without altering material bulk properties. XPS, electrokinetic potential and contact angle measurements as well as dye uptake tests were carried out for surface characterization of modified PP, evaluation of chitosan coatings stability, and the effects of temperature and pH on coatings formation. About 20–30% of the total amount of chitosan immobilized on PP was found to be covalently bonded to the plasma pre-treated surface through the heat induced reactions with oxygen-containing functional groups at T > 80°C that corresponded to 47% of surface coverage. Subsequent cross-linking reaction with epichlorohydrin proved to be an efficient way to reduce the susceptibility of chitosan coatings to acidic hydrolysis.

Application Relevant Characterization of Aqueous Silica Nanodispersions

This work describes the application relevant characterization of eight commercially available silica powders dependent on dispersing procedure using different instruments: photon correlation spectroscopy, nitrogen adsorption, and particle charge detector. The particle size of silica was found to be different in dispersion from that of all types of fumed silica, where, after proper dispersion, the measured average particle size is similar and much higher than the primary particle size. The different properties of these two silica types will be discussed.