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Gerald Brezesinski

Publications and source records attributed to Gerald Brezesinski.

24 records · Page 2Linked to original sources
PubMed2003

In-plane structures of synthetic oligolactose lipid monolayers--impact of saccharide chain length.

Grazing incidence X-ray diffraction (GIXD) was used to investigate the in-plane structure of monolayers of synthetic glycolipids with oligolactose head groups (Lac N, with N = number of lactose units) at the air/water interface. The Lac 1 monolayer exhibits three sharp diffraction peaks. One peak can be deconvoluted into two diffraction peaks, which suggests that alkyl chains in the monolayer form an orthorhombic lattice. On the other hand, the other two peaks are related to bulk crystalline materials residing at the interface. Another weak peak from the head group correlation, either in a monolayer or in bulk crystals, can also be observed in some experiments. The scattering patterns of the Lac 2 monolayer indicate that the alkyl chains order in an orthorhombic lattice, where a shift in the hydrophilic/hydrophobic balance seems to fluidize the film. Alkyl chains in the Lac 3 monolayer also seem to assume an orthorhombic lattice; however, a weak diffraction peak from the correlation between trilactose head groups can also be observed. The estimated lattice dimensions are compared systematically to those of bulk dispersions, as well as to the viscoelastic properties of the monolayer. The obtained results strongly suggest that the in-plane structure of synthetic glycolipid monolayers can provide a well-defined basis to understand the impact of the chemical structure on the cooperativity and function of the glycocalix of cellular surfaces.

Lactose↗
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

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↗
PubMed2002

Generic phase behavior of branched-chain phospholipid monolayers.

Monolayers of chemically modified triple-chain phospholipids have been investigated at the air/water interface using pressure-area isotherms. The condensed phases of the lipids were characterized by grazing incidence X-ray diffraction (GIXD). Increasing chain length corresponds to a temperature effect, which was quantified for different lipids, depending on the head group structure using isotherm (two-dimensional systems) and DSC (three-dimensional systems) measurements. The combination of structure investigations revealed generic phase diagrams, which describe the phase behavior of multiple-chain lipids in two dimensions. For the 1-acyl-2-O-alkyl phospholipids, the generic phase diagram exhibits only L(2d), LS and LE phases while the exchange of the position of the branched acyl and the non-branched alkyl chains at the glycerol backbone leads to a much richer polymorphism (L(2h), L(2d), Ov, LS, S, tau, LE). Here we present the first experimental evidence of the unusual tau phase for multiple-chain lipid monolayers. This phase exhibits an undistorted in-plane lattice despite of tilted chains.

Micelles↗
PubMed2001

Organization of two-dimensional phospholipid monolayers on a gel-forming substrate.

The formation and structural evolution of two-dimensional amphiphilic monolayers on a liquid mineral sol undergoing a sol-gel transition have been studied by surface x-ray scattering techniques. The gelation process is accompanied by the formation of a single layer of mineral particles beneath the surface, inducing a reorganization of the lipidic monolayers.

Gels↗