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Werner Kunz

Publications and source records attributed to Werner Kunz.

At least 19 recordsLinked to original sources
PubMed2006

New anisotropic ceramic membranes from chemically fixed dissipative structures.

The formation of highly ordered capillaries in alginate gels is due to a dissipative convective process resulting from opposing diffusion gradients and friction. Ceramic membranes with an anisotropic pore structure have been gained from this self-organization process by incorporating inorganic particles into the gel matrix, followed by subsequent ion exchange, drying, and sintering. The aim of this study was to overcome existing preparative deficiencies and to optimize the capillary structure and surface properties with respect to specific technical applications. A new method of ion exchange was introduced, and the sintering program was improved to obtain reproducible product quality. By controlling the parameters of the self-organization reaction, the overall porosity of the ceramic membranes was adjusted to selected values between 60% and 83%. Capillary sizes were varied between 8 and 50 microm. Further modification by metal plating, particle coating, or hydrophobization led to an extended spectrum of applicability of the ceramic membranes. For the first time, anisotropic capillary ceramics have been characterized in detail as to their technical use as catalyst supports, filter membranes, or other solid-fluid and solid-gas contact processes.

Journal Article↗
PubMed2006

Propensity for the air/water interface and ion pairing in magnesium acetate vs magnesium nitrate solutions: molecular dynamics simulations and surface tension measurements.

Molecular dynamics simulations in slab geometry and surface tension measurements were performed for aqueous solutions of magnesium acetate and magnesium nitrate at various concentrations. The simulations reveal a strong affinity of acetate anions for the surface, while nitrate exhibits only a very weak surface propensity, and magnesium is per se strongly repelled from the air/water interface. CH3COO- also exhibits a much stronger tendency than NO3- for ion pairing with Mg2+ in the bulk and particularly in the interfacial layer. The different interfacial behavior of the two anions is reflected by the opposite concentration dependence (beyond 0.5 M) of surface tension of the corresponding magnesium salts. Measurements, supported by simulations, show that the surface tension of Mg(NO3)2(aq) increases with concentration as for other inorganic salts. However, in the case of Mg(OAc)2(aq) the surface tension isotherm exhibits a turnover around 0.5 M, after which it starts to decrease, indicating a positive net solute excess in the interfacial layer at higher concentrations.

Journal Article↗
PubMed2006

Herbimycin A suppresses mitotic activity and egg production of female Schistosoma mansoni.

The eggs of the endoparasite Schistosoma are the causative agent of schistosomiasis, an important disease of humans, which is endemic in (sub-) tropical regions. The absence of a vaccine with sufficient protective qualities and increasing resistance to approved and established drugs like praziquantel, justify the exploration of novel ways to fight schistosomes. Our strategy is based on interference with the sexual maturation of the female. Prerequisites for gonad development in adult females are a continuous pairing contact with the male and significantly increased mitotic activity. In this study we show that the male governs sexual maturation of the female, as the separation of couples causes a clear reduction of female mitotic activity and, consequently, egg production. We demonstrate that treatment of schistosomes with Herbimycin A, an inhibitor of protein tyrosine kinases (PTKs), mimics the separation of couples as the drug blocks mitotic activity and egg production of paired females. However, the synthesis of the eggshell precursor protein p14 is elevated. Furthermore, we show for the first time in invertebrates that Herbimycin A decreases tyrosine phosphorylation and PTK stability in schistosomes. Summarised, our data provide evidence that PTKs have key functions in regulating gonad development, eggshell gene expression and, consequently, egg production. Therefore, we suggest envisaging schistosome PTKs as novel targets for strategies to combat schistosomiasis.

Animals↗
PubMed2006

Similarity of salt influences on the pH of buffers, polyelectrolytes, and proteins.

Changes in pH induced by the addition of electrolytes to buffers, polyelectrolytes (a polycarboxy polymethylene and a polyethyleneimine), and proteins (casein, whey, and lysozyme) solutions are explored systematically. The two buffer systems are triethanolamine/triethanolammonium chloride and citric acid/sodium citrate. These are chosen because of the similarity of their acid-base equilibria with those of amino acids predominant in most proteins, that is, amino acids that include carboxylate or ammonium groups in their structures. The pH of triethanolamine and of citrate buffers respectively increases and decreases when salt is added. At low electrolyte concentrations (<0.15 mol/kg), the phenomenon is well accounted for by standard electrostatic theories. pH values at higher salt concentrations are not reliable when measured with a commercial glass electrode without cross-checking by a standard hydrogen electrode. The changes of the pH values of polyelectrolyte and protein solutions with added salts turn out to be remarkably similar to the salt induced pH changes in the buffer solutions. It is even possible to qualitatively predict these changes in protein solutions simply from the primary protein structure. At least in the systems considered here, the specific ion effects on pH seem to correlate with the bulk activity coefficients of the added electrolytes, at least at moderate salt concentrations.

Buffers↗
PubMed2006

Specific ion effects at protein surfaces: a molecular dynamics study of bovine pancreatic trypsin inhibitor and horseradish peroxidase in selected salt solutions.

The distribution of sodium, choline, sulfate, and chloride ions around two proteins, horseradish peroxidase (HRP) and bovine pancreatic trypsin inhibitor (BPTI), is investigated by means of molecular dynamics simulations with the aim to elucidate ion adsorption at the protein surface. Although the two proteins under investigation are very different from each other, the ion distributions around them are remarkably similar. Sulfate is always strongly attached to the proteins, choline shows a significant, but unspecific, propensity for the protein surfaces, and sodium ions have a weak surface affinity, while chloride has virtually no preference for the protein surface. In mixtures of all four ion species in protein solutions, the resulting distributions are almost a superposition of the distributions of sodium sulfate and choline chloride, except that sodium partially replaces choline close to the proteins. The present simulations support a picture of ions interacting with individual ionic and polar amino acid groups rather than with an averaged protein surface. The results thus show how subtle the so-called Hofmeister and electroselectivity effects are in salt solution of proteins, making all simplified interaction models questionable.

Amino Acids↗
PubMed2006

The promotion of oriented axonal regrowth in the injured spinal cord by alginate-based anisotropic capillary hydrogels.

Appropriate target reinnervation and functional recovery after spinal cord injury depend on longitudinally directed regrowth of transected axons. To assess the capacity to promote directed axon regeneration, alginate-based highly anisotropic capillary hydrogels (ACH) were introduced into an axon outgrowth assay in vitro and adult rat spinal cord lesions in vivo. In an entorhino-hippocampal slice culture model, alginate-based scaffolds elicit highly oriented linear axon regrowth and appropriate target neuron reinnervation. Coating of alginate-based ACH with the extracellular matrix components collagen, fibronectin, poly L-ornithine and laminin did not alter the axon regrowth response as compared to uncoated alginate-based ACH. After implantation into acute cervical spinal cord lesions in adult rats, alginate-based ACH integrate into the spinal cord parenchyma without major inflammatory responses, maintain their anisotropic structure and in parallel to findings in vitro induce directed axon regeneration across the artificial scaffold. Furthermore, adult neural progenitor cells (NPC), which have been shown to promote cell-contact-mediated axon regeneration, can be seeded into alginate-based ACH as a prerequisite to further improve the regenerative capacity of these artificial growth supportive matrices. Thus, alginate-based ACH represent a promising strategy to induce directed nerve regrowth following spinal cord injury.

Alginates↗
PubMed2006

Effects of nonionic surfactant C12E5 on the cooperative dynamics of water.

A dielectric relaxation study of binary mixtures of nonionic surfactant C12E5 + water has been made as a function of temperature in the isotropic micellar, lamellar, and hexagonal regions of the phase diagram. Two dielectric dispersion steps were found and could be assigned to the intermolecular cooperative dynamics of water at the micellar interface and in the bulk water domains. A quantitative analysis is given. The relaxation amplitudes were used to determine effective hydration numbers. The activation energies of water relaxation were calculated from the relaxation times. The data indicate weaker surfactant-water and water-water interactions near the micellar interface compared to those of bulk liquid water. Further analysis revealed the presence of water clusters large enough to show a cooperative relaxation mode even at high surfactant concentrations. However, the relaxation time of this mode is larger compared to that of pure water. This points out the importance of confinement effects on water dynamics.

Journal Article↗
PubMed2005

Ultrasonic velocities, densities, viscosities, electrical conductivities, Raman spectra, and molecular dynamics simulations of aqueous solutions of Mg(OAc)2 and Mg(NO3)2: Hofmeister effects and ion pair formation.

The ultrasonic velocities, densities, viscosities, and electrical conductivities of aqueous solutions of magnesium nitrate and magnesium acetate have been measured from dilute to saturation concentrations at 0 < or = t/degrees C < or = 50. The temperature derivative of the isentropic compressibility, kappa(s), became zero at 2.28 and 2.90 mol kg(-1) for Mg(OAc)2 and Mg(NO3)2 solutions, respectively, at 25 degrees C. The total hydration numbers of the dissolved ions were estimated to be, respectively, 24.3 and 19.2 at these concentrations. Differences in kappa(s) for various M2+ salts, using the present and literature data, correlated with reported M2+-OH2 bond lengths and to a lesser extent with cationic charge densities (ionic radii). The influence of anions on kappa(s) appears to follow the Hofmeister series and also correlates approximately with the anionic charge density. Substantial differences between Mg(OAc)2(aq) and Mg(NO3)2(aq) occur with respect to their structural relaxation times (derived from compressibility and viscosity data) and their electrical conductivities. These differences were attributed to a much greater ion association in Mg(OAc)2 solutions. Raman spectra recorded at 28 degrees C confirmed the presence of various types of contact ion pairs including mono- and bidentate complexes in Mg(OAc)2(aq). In Mg(NO3)2(aq), only noncontact ion pairs appear to be formed even at high concentrations. The experimental results are supported by molecular dynamics simulations, which also reveal the much stronger tendency of OAc- compared to NO3- to associate with Mg2+ in aqueous solutions. The simulations also allow an evaluation of the ion-ion and ion-water radial distribution functions and cumulative sums and provide a molecular picture of ion hydration in Mg(OAc)2(aq) and Mg(NO3)2(aq) at varying concentrations.

Journal Article↗
PubMed2005

Relation between dielectric and low-frequency Raman spectra of hydrogen-bond liquids.

We analyzed the complex dielectric and Raman spectra of hydrogen-bond liquids in the microwave to terahertz frequency range. As for water and methanol, the high-frequency component of the dielectric spectrum, i.e., the small deviation from the principal Debye relaxation, clearly corresponds to the Raman spectrum. This indicates that the cooperative relaxation, accompanied by huge polarization fluctuation, is virtually not Raman active, whereas the faster processes reflect common microscopic dynamics. For ethylene glycol, the shape of the Raman spectrum also resembles that of the high-frequency deviation of the dielectric spectrum, but, additionally, a weak manifestation of the cooperative relaxation arising from quadrupolar conformers is detected.

Journal Article↗
PubMed2005

Is there an anionic Hofmeister effect on water dynamics? Dielectric spectroscopy of aqueous solutions of NaBr, NaI, NaNO3, NaClO4, and NaSCN.

A systematic study of the dielectric relaxation spectra of aqueous solutions of NaBr, NaI, NaNO(3), NaClO(4), and NaSCN has been made over a wide range of frequencies (0.2 < or = nu/GHz < or = 89) and solute concentrations (0.05 < or = c/M < or = 1.5) at 25 degrees C. The spectra could be adequately described by a single Cole-Cole (CC) process, symmetrically broadened relative to that of pure water. However, similar quality fits were also obtained with a three-Debye-process (3D) model consisting of a small ion-pair contribution at lower frequencies and two solvent relaxations at higher frequencies. Assuming the ions to be solvent separated, the 3D model provided estimates of their association constants and their rate constants for formation and dissociation. The bulk water relaxation times obtained from both models showed almost no dependence on the nature of the anion. Nevertheless, there were subtle differences in the concentration dependences of the relaxation times which correlated with some, but not all, of the anion properties that are believed to be relevant for explaining the anionic Hofmeister series.

Journal Article↗
PubMed2005

Design of low-toxic and temperature-sensitive anionic microemulsions using short propyleneglycol alkyl ethers as cosurfactants.

The phase behavior of anionic microemulsions composed of water, sodium dodecyl sulfate (SDS), dodecane, and short propyleneglycol monoalkyl ethers (C(n)()PO(m)(); n = 3, m = 1 and n = 4, m = 2, 3) is studied. From the pseudoternary phase diagrams, it is inferred that C(n)()PO(m)() compounds have cosurfactant behaviors comparable to those of 1-butanol and 1-pentanol, which are the most efficient and widely used cosurfactants. In contrast to these alcohols, the C(n)()PO(m)() cosurfactants induce high temperature dependences in the SDS microemulsion systems. Furthermore, SDS/C(n)()PO(m)() microemulsions can be formed with small SDS concentrations (SDS/C(4)PO(3) mass ratio of 1/6.26). These have a low toxicity in contrast to systems containing genotoxic short ethyleneglycol ethers (C(n)()EO(m)()) as the cosurfactant. The strong temperature dependence can be favorable in the recovery of reaction products when the microemulsion is used either as a reaction medium or in extraction processes.

Alkylation↗
PubMed2005

Ternary systems of nonionic surfactant Brij 35, water and various simple alcohols: Structural investigations by small-angle X-ray scattering and dynamic light scattering.

Structural properties of ternary systems composed of nonionic surfactant dodecyl-poly(ethylene oxide-23) ether (C12E23, commercial name: Brij 35), water and various alcohols from ethanol to 1-decanol have been investigated using small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) techniques. All measurements were performed at the temperature 25 degrees C. SAXS experimental data were put on absolute scale using water as a secondary standard. The data of water-rich mixtures at low to moderate surfactant concentrations were evaluated using the generalized indirect Fourier transformation method (GIFT), which is based on the simultaneous determination of the intra- and inter-particle scattering contributions. In this way, the size and the shape of interacting scattering particles in real space could be deduced. The systems with a relatively low surfactant concentration (5 mass%) were studied most extensively. In these cases, the water-rich regions of the phase diagrams could be investigated into more detail, since in the alcohol-rich regions problems with the GIFT evaluation of the SAXS data were encountered. The presented results demonstrate the level of structural details that can be obtained on the basis of scattering methods and point out the specific stages of data evaluation and interpretation where one must be extremely precautious. As such they reveal the inner structuration of the complex ternary systems of our present interest. In parallel, they also indicate that the longer chain alcohols actually behave as real oil phases in the studied systems, as one might expect, and also confirm the well-known properties of different short to medium chain alcohols that act as co-solvents and/or co-surfactants in microemulsion systems depending on their chain length.

Journal Article↗
PubMed2005

The influence of structure and composition of a reverse SDS microemulsion on enzymatic activities and electrical conductivities.

The activity of the enzyme horse radish peroxidase (HRP) is studied in a series of reverse microemulsions composed of dodecane, aqueous buffer, sodium dodecylsufate (SDS) and alcohols of the homologous series 1-butanol to 1-octanol. The HRP catalyzed reaction is the oxidation of a classical water soluble substrate, the 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) by hydrogen peroxide. In parallel electrical conductivity measurements are performed on the same solutions. The structural changes in the microemulsions, as inferred by the conductivity measurements, correlate remarkably well with the changes in the enzymatic activities. In particular it is found that (a) the maximum activity of the enzyme is always related to its optimum hydration and that this hydration can be related to the microemulsion structures, (b) the enzyme inhibition caused by the alcohols in microemulsions is a consequence of both the solubility of the alcohols in the buffer and the rigidity of the interfacial film. Consequently, it can be concluded that enzymatic activity measurements are a valuable tool to study confined systems such as microemulsions and, in particular, the amount of available hydration water. Enzymatic activities can be finely tuned by small changes in microemulsion structures, probably in a predictive way.

Alcohols↗
PubMed2005

Horseradish peroxidase activity in a reverse catanionic microemulsion.

In this paper we present the first results of enzymatic activities in a reverse microemulsion medium based on a mixture of an anionic and a cationic surfactant, called catanionic microemulsion. The studied system is composed of sodium dodecyl sulfate (SDS)/dodecyltrimethylammonium bromide (DTAB)/n-hexanol/citrate buffer/n-dodecane, with high SDS/(SDS + DTAB) weight fractions. It turns out that the results are similar to those obtained in classical reverse microemulsions, except that the presence of DTAB exerts an inhibiting effect on the enzyme. Nevertheless, enzymatic superactivities are found even at a DTAB to total surfactant ratio of 15%, corresponding to 3% weight fraction of cationic surfactant in the microemulsion. The influence of pH and hexanol content on the enzymatic activities is also studied.

Cations↗
PubMed2005

Cracks in the shell--zooming in on eggshell formation in the human parasite Schistosoma mansoni.

Schistosomiasis, currently the second most common parasitic disease of humans in tropical regions is caused by the eggs of trematode worms of the genus Schistosoma. Understanding egg formation and specifically the synthesis of the eggshell comprises, consequently, a promising starting point to cure and prevent the disease. To shed light on the genetics of the latter process, we analysed the three known S. mansoni eggshell proteins P14, P19 and P48 against the background of the species' inferred proteome and of eggshell proteins identified in other trematode species. Our results suggest that eggshell formation in Schistosoma involves a multitude of different proteins organised in currently three distinct protein families (P14, P48 and P34 eggshell protein family). The first two families are of simple structure. Their respective members share a substantial degree of sequence similarity and are, to date, observed only in the genus Schistosoma. In contrast, the P34 family of eggshell proteins is complex. Its in part highly diverged members share only a conserved motif of 67-aa length on average and are detected in various trematode species. The resulting widespread occurrence of this protein motif suggests an important role during eggshell formation in trematodes. Screening more than 7,000 putative proteins of S. mansoni, we could identify six new members of the P34 protein family that are likely to be involved in eggshell formation in this species.

Amino Acid Sequence↗