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Helmuth Möhwald

Publications and source records attributed to Helmuth Möhwald.

14 recordsLinked to original sources
PubMed2003

Phospholipase A2 hydrolysis of mixed phospholipid vesicles formed on polyelectrolyte hollow capsules.

Mixtures of the phospholipids L-alpha-dimyristoylphosphatidic acid (DMPA) and L-alpha-dipalmitoylphosphatidylcholine (DPPC) have been successfully adsorbed onto the charged surface of multilayer polyelectrolyte capsules to form a novel vesicle. Leaving such vesicles in phospholipase A(2) solution, we observed the hydrolysis reaction on the surface of the lipid/polymer vesicles and a permeability change before and after the reaction by confocal-laser scanning microscopy (CLSM). A capsule with adjustable permeability was constructed. This method may provide new features for drug-release vesicles.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2003

Direct observations of the cleavage reaction of an L-DPPC monolayer catalyzed by phospholipase A2 and inhibited by an indole inhibitor at the air/water interface.

The enzymatic hydrolysis of an L-dipalmitoylphosphatidylcholine (L-DPPC) monolayer at the air/water interface, catalyzed by phospholipase A(2) (PLA(2)), serves as a model for biospecific interfacial reactions. The cleavage of L-DPPC was investigated by Brewster angle microscopy. Different types of domain defects were observed to form in the coexisting liquid expanded and liquid condensed phases during the hydrolysis reaction. The adsorption of the enzyme was quantitatively recorded as the increase of the surface pressure over a fixed molecular area with time. In the case of L-DPPC, the surface pressure first increases and then starts to decrease, which indicates that a soluble product (lysolipid) is produced during the catalytic cleavage reaction. The increase and decrease of the surface pressure, which corresponds to the change of shape and number density of domains, indicated the occurrence of the following processes: adsorption of PLA(2), cleavage reaction, and rearrangement of substrate and product molecules at the interface. Addition of a PLA(2) inhibitor to the lipid monolayer leads to a fast surface pressure increase after enzyme injection. The surface pressure reaches a maximum value and then does not change for a long time. During this period, no change in the domain shape and number density was observed, which indicates that the enzyme is inhibited for a certain period of time. The experimental results provide the possibility of a direct way to prove inhibitor activity.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2003

Polymer-stabilized phospholipid vesicles formed on polyelectrolyte multilayer capsules.

Phospholipid vesicles on polyelectrolyte multilayer shells can be stabilized against ethanol by coating a single cationic polyelectrolyte. Confocal laser scanning microscopy (CLSM) proved that the lipids were stabilized by cationic polyelectrolytes and the permeability to small hydrophilic dyes was decreased. Measurements of fluorescence recovery after photo-bleaching (FRAP) with individual capsules enable quantification of release profiles.

Biopolymers↗
PubMed2003

Langmuir monolayers to study interactions at model membrane surfaces.

Langmuir monolayers at the liquid-air interface are well-defined interfacial systems and, therefore, excellent model systems to learn about interactions at interfaces beyond the classical DLVO description. Many parameters can be independently varied over a broad range and the structure can be analyzed with A precision. In the first part of the paper, the rich polymorphism in monolayers composed of amphiphilic molecules is demonstrated. Using homologues series generic phase diagrams can be derived. The delicate interplay of interactions causes a richness of phases which in turn can be used to measure fine variations in these interactions. Based on the understanding of the polymorphism in pure or mixed lipid monolayers, one can study the interaction of molecules dissolved in the subphase with monolayers. Samples presented are chemical reactions catalyzed by enzymes and coupling of polyelectrolytes to oppositely charged monolayers. To relate structure and reactivity, the activity of enzymes at the interface can be studied, predominantly combining X-ray diffraction and FTIR-spectroscopy. It is shown that the activity depends on monolayer structure. In one case, the reaction product leads to structural changes in the monolayer and stops the reaction, hence, indicating a subtle case of product inhibition via the membrane. On the other hand it has become possible to manipulate the organization of polyelectrolytes at interfaces via lipid charge density and ionic strength. In the most important case of DNA interacting with a membrane surface we show that DNA arranges at the interface in a lamellar manner, and the intermolecular distances, measured by Synchrotron X-ray diffraction can be varied by the lipid density.

Adsorption↗
PubMed2003

Swelling and shrinking of polyelectrolyte microcapsules in response to changes in temperature and ionic strength.

Swelling and shrinking of polyelectrolyte microcapsules consisting of poly(styrene sulfonate, sodium salt) (PSS) and poly(diallyldimethyl ammonium) chloride (PDADMAC) multilayers have been observed in response to temperature and electrolyte exposure, respectively. Heat-induced capsule swelling and capsule wall volume reduction were observed by confocal laser scanning microscopy (CLSM) and scanning force microscopy (SFM). On the other hand, pronounced shrinking in diameter induced by exposure to an electrolyte was observed in parallel to increases in the thickness of the capsule wall. The estimated wall volume was reduced to two thirds of the control for the salt-exposed capsules and one half for the salt-exposed and simultaneously annealed capsules. This reduction in volume was supposedly mainly caused by the compression of the capsule wall due to the ionic screening from the electrolyte. The highly porous microstructure of the multilayers and loosely bound PSS/PDADMAC complex are thought to be responsible for the structure of the PSS/PDADMAC capsules being easily modulated upon annealing and salt-exposure.

Journal Article↗
PubMed2003

Change and stabilization of the amyloid-beta(1-40) secondary structure by fluorocompounds.

The misfolding of the amyloid peptide, which is the result of a well-known alpha-to-beta transition, causes neurodegenerative disorder. Fluorinated alcohols have been described in the literature as potent solvents which can refold the beta-conformation. The present studies demonstrate the effectiveness of differently fluorinated alcohols for the beta-to-alpha refolding process on fibrillar aggregated amyloid beta(1-40). The regenerated helical structure is shown to be maintained in the absence of the fluoroalcohols, a behaviour which was found to contrast with immunoglobulin. We interpret this difference on the basis of the hydrophilic/hydrophobic domains in the amyloid sequence and present some speculations regarding the free-energy levels of the folded states of both proteins. The effect of the -CF(3) group on the observed conformational changes is interpreted as a result of alterations of the hydration shell of the peptides. Moreover, based on the results achieved with fluoroalcohols, we have used novel fluorinated amphiphiles possessing blood-compatibility properties and studied their effect on amyloid beta(1-40). First results point in the direction of a beta-to-alpha transition. Therefore, the use of fluorine groups in the development of new drugs is considered a new possibility requiring further investigation for the prevention of amyloidosis.

Amino Acid Sequence↗
PubMed2002

Hollow polymer shells from biological templates: fabrication and potential applications.

Three-dimensional ultrathin polymer shells have been produced by a combination of step-by-step adsorption of polyelectrolytes on glutaraldehyde-treated human erythrocytes and subsequent solubilization of the cytoplasmatic constituents by means of a deproteinizing agent. The obtained hollow films preserve both the size and shape of the templating cells. This opens a pathway for the fabrication of polymeric capsules within a wide range of size and shape by using various biological templates. They may have exciting potential applications, such as templates for nanocomposites, as containers for a large class of materials, or as cages for chemical reactions. The thickness of the films can be adjusted over a large range: from a few nm up to several tens of nm. The polymer shells are permeable to small molecules and ions but not to macromolecules. An increase in the ionic strength of the solution up to 100 mmol make the capsules permeable for proteins. Permeability and conductivity studies have provided evidence that the adsorption of lipids on polyelectrolyte layers is a means of producing capsules with controlled permeability properties. 6-Carboxyfluorescein and Rhodamin 6G were precipitated within the capsules.

Biotechnology↗
PubMed2002

Highly stable and biocompatible nafion-based capsules with controlled permeability for low-molecular-weight species.

Biocompatible hollow capsules have been formed by electrostatic layer-by-layer self-assembly of a perfluorinated ionomer (Nafion) in alternation with ferric ions onto polystyrene latex particles or organic microcrystals, followed by dissolution of the cores by tetrahydrofuran or dimethylformamide. The stepwise growth of multilayers was followed by UV-visible spectroscopy and microelectrophoresis. The formation of hollow capsules was verified by confocal laser scanning microscopy and scanning force microscopy. The hollow Fe3+/Nafion capsules displayed high stability over a wide range of pH values and at high temperature. Fluorescein transport through the Fe3+/Nafion capsule wall was studied by means of photochemical bleaching and recovery (PBR) of the capsule interior. A diffusion model is suggested to calculate the diffusion coefficient for low-molecular-weight species, which was determined to be in the order of 10(-12) cm2s. The permeability can be manipulated by changing the wall thickness of the capsules.

Journal Article↗
PubMed2002

A novel method for encapsulation of poorly water-soluble drugs: precipitation in polyelectrolyte multilayer shells.

A novel method to include poorly water-soluble substances into the polyelectrolyte capsules of defined size, stability, composition and affinity properties is proposed. Encapsulation explores the polarity gradient across the capsule wall. Capsules creation makes use of electrostatic interaction and can involve many substances as layer constituents, such as synthetic polyelectrolytes, proteins, nucleic acids, lipids and multivalent dyes. Using capsules made of synthetic polyelectrolytes as a model system was demonstrated how to prepare, to measure and to use this gradient for low molecular weigh materials encapsulation.

Capsules↗
PubMedDate not supplied

Polyelectrolyte complexes and layer-by-layer capsules from chitosan/chitosan sulfate.

Polyelectrolyte complex formation of chitosans of varying average molecular weight and degree of acetylation with chitosan sulfate or poly(styrene sulfonate) was studied by static light scattering in dilute solution at various ionic strengths. Unlike the molecular weight, the degree of acetylation was found to have a significant effect on the resultant structural densities of the complexes. The same system was applied to the preparation of micrometer-sized hollow shells by means of a layer-by-layer technique (in total eight layers). Their behavior toward fluorescent probes such as fluorescein and rhodamin 6G or fluorescein isothiocyanate labeled dextrans at various ionic strengths and pH (observed by confocal laser light scanning microscopy) could be understood through a discussion of electrostatic forces between the highly charged shells and the probes to be dominant. At an ionic strength of 0.1 M and above, charge effects are largely suppressed (screening effect) and a size-dependent "cutoff" for the permeation of the macromolecular fluorophore was observed.

Acetylation↗
PubMedDate not supplied

Layer-by-layer engineering of biocompatible, decomposable core-shell structures.

The objective of the present investigation was to fabricate composite colloidal particles consisting of a sacrificial, decomposable template of biodegradable nature covered with biocompatible polyelectrolyte multilayers using the layer-by-layer sequential adsorption technique. Poly-dl-lactic acid and poly(dl-lactic-co-glycolic acid) were chosen to design the microparticulate template, and a preliminary feasibility study was carried out with poly(styrene sulfonate sodium)-poly(allylamine hydrochloride) as shell components. The properties of both core-shell and hollow structures obtained by core dissolution were characterized by confocal laser scanning microscopy, microelectrophoresis, scanning force microscopy, and scanning electron microscopy. The concept was then extended to biocompatible polyelectrolytes as shell wall building blocks to deduce stable hollow capsules with tailored properties. Uniform, complete coating with oppositely charged polyelectrolyte pairs was achieved for all the combinations investigated. The results demonstrate that polyester microparticles could serve as viable alternative components to conventionally employed templates to derive hollow capsules with defined size, shape, and shell thickness. With all the components used for fabrication being biocompatible, these polyelectrolyte capsules may find interesting applications in the fields of biology, biochemistry, biotechnology, and drug delivery.

Biocompatible Materials↗