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Biomedical subjects

Gerald Brezesinski

Publications and source records attributed to Gerald Brezesinski.

At least 19 recordsLinked to original sources
PubMed2006

Modifying dipalmitoylphosphatidylcholine monolayers by n-hexadecanol and dipalmitoylglycerol.

The monolayer structure of pure dipalmitoylphosphatidylcholine (DPPC) and equimolar mixtures of DPPC/n-hexadecanol (C(16)OH) and DPPC/dipalmitoylglycerol (DPG) are studied by the film balance technique and grazing incidence X-ray diffraction measurements. At 20 degrees C, the binary systems exhibit complete miscibility. In contrast to pure DPPC monolayers, a condensing effect is observed in the presence of both non-phospholipid additives; but the phase transition behavior differs. The tilt angle of the hydrocarbon chains in the DPPC/C(16)OH mixture is significantly smaller than in pure DPPC monolayers. The tilt of the chains is even further reduced in the mixed monolayer of DPPC/DPG. A comparison of the three systems reveals distinct structural features such as phase state, chain tilt, and molecular area over a wide range of surface pressures. Therefore, these monolayers provide a highly suitable model to investigate the influence of structural parameters on biological processes occurring at the membrane surface, e.g. enzymatic reactions and adsorption events.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2006

Weak first-order tilting transition in monolayers of mono- and bipolar docosanol derivatives.

A systematic analysis of pressure-area isotherms and grazing incidence X-ray diffraction (GIXD) data of 22-methoxydocosan-1-ol (H3C-O-(CH2)22-OH, MDO), docosan-1-ol (H3C-(CH2)21-OH, DO), and docosyl methyl ether (H3C-(CH2)21-O-CH3, DME) monolayers on pure water between 10 and 35 degrees C is presented. All monolayers form fully condensed phases in the investigated temperature region. The GIXD data reveal that the monolayers exhibit the phase sequence -S at lower temperature and -LS at higher temperature. Phase diagrams have been established. Inserting a second hydrophilic group at the opposite end of the molecule (bipolar MDO) shifts the S/LS boundary to higher temperatures. All monolayers exhibit herringbone (HB) packing at lower temperatures. The "kink" in the isotherms observed at lower temperatures is replaced by a very small plateau region at higher temperatures. The entropy changes connected with this weak first-order tilting transition are much smaller compared with the first-order transition from liquid-expanded (LE) to condensed (LC). Additionally, this transition is endothermic in contrast to the LE/LC transition. The reason for the endothermic transition is the weaker positional correlation in the nontilted state compared with the tilted one. The appearance of the weak first-order endothermic transition can be connected with the changed phase sequence. X-ray photoelectron spectroscopy (XPS) measurements provide information about the polar group orientation. Considerations based on GIXD and XPS data as well as adhesion energy of the different terminal end groups lead to the conclusion that the hydroxyl group of the bipolar MDO is attached to the water surface while the methoxy group is in contact with air. The presented results show that the second hydrophilic group influences the monolayer properties in a mild way.

Fatty Alcohols↗
PubMed2006

Characterization of anomalous flow and phase behavior in a Langmuir monolayer of 2-hydroxy-tetracosanoic acid.

Langmuir monolayers of long-chain fatty acids display a wide range of interesting flow and phase behaviors, but the correlation between these behaviors varies. In this paper, we report two interesting behaviors in a Langmuir monolayer of 2-hydroxy-tetracosanoic acid: phase coexistence between the L(2h) and L(2)' phases over a large pressure range and a peak in the viscosity and elastic modulus of the material as a function of pressure. The two behaviors are confirmed over a range of temperatures for which the location of the undistorted lattice appears to vary relative to the range of coexistence for the two phases. Evidence for a correlation between the phase behavior and the peak in the mechanical properties is presented.

Journal Article↗
PubMed2006

Interactions of a fungistatic antibiotic, griseofulvin, with phospholipid monolayers used as models of biological membranes.

Griseofulvin (GF) is an oral antibiotic for widely occurring superficial mycosis in man and animals caused by dermaphyte fungi; it is also used in agriculture as a fungicide. The mechanism of the biological activity of GF is poorly understood. Here, the interactions of griseofulvin with lipid membranes were studied using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), and 1,2-myristoyl-sn-glycero-3-phosphoethanolamine (DMPE) monolayers spread at the air/water interface. Surface pressure (Pi), electric surface potential (Delta V), grazing incidence X-ray diffraction (GIXD), and Brewster angle microscopy (BAM) were used for studying pure phospholipid monolayers spread on GF aqueous solutions, as well as mixed phospholipid/GF monolayers spread on pure water subphase. Moreover, phospholipase A2 (PLA2) activity toward DLPC monolayers and molecular modeling of the GF surface and lipophilic properties were used to get more insight into the mechanisms of GF-membrane interactions. The results obtained show that GF has a meaningful impact on the film properties; we propose that nonpolar interactions are by and large responsible for GF retention in the monolayers. The modification of membrane properties can be detected using both physicochemical and enzymatic methods. The results obtained may be relevant for elaborating GF preparations with increased bioavailability.

Air↗
PubMed2006

Analytical investigation of the interactions between SC3 hydrophobin and lipid layers: elaborating of nanostructured matrixes for immobilizing redox systems.

Hydrophobins are highly tensioactive fungal proteins with a pronounced affinity for interfaces and a propensity for self-assembly. Recently, these proteins were shown to be useful in retaining different molecules on solid surfaces. This finding offers a possibility for developing new functional materials, while creating the necessity of further research at a deeper mechanistic level. In this work, the mechanisms governing the surface phenomena were studied using native Schizophyllum commune hydrophobin (SC3) and lipid mono- and bilayers; the soft matter systems were used to get a handle on the interactive protein/interface effects at a molecular level. The results obtained indicated that the SC3/lipid membrane interactions were adjusted by protein conformational adaptation, allowing its incorporation into lipid matrixes; the incorporation of a chelating SC3 hydrophobin (PFA-SC3) in a monoolein cubic phase yielded a biomimetic, cell-like system of Cu(II) cation immobilization. This system, which is suitable for modifying electrode surface and monitoring the Cu(II)/Cu(0) redox process, may be of practical interest in switching and sensing.

Fungal Proteins↗
PubMed2006

DNA condensation and interaction with zwitterionic phospholipids mediated by divalent cations.

Artificial viruses are considered to be a promising tool in gene therapy. To find lipid-DNA complexes with high transfection efficiency but without toxicity is a fundamental aim. Although cationic lipids are frequently toxic for cells, neutral lipids are completely nontoxic. Zwitterionic lipids do not interact with DNA directly; however, the interaction can be mediated by divalent cations. Langmuir monolayers represent a well-defined model system to study the DNA-lipid complexes at the air/water interface (quasi-2D systems). In this work, isotherms, infrared reflection absorption spectroscopy (IRRAS), X-ray reflectivity (XR), grazing incidence X-ray diffraction (GIXD), and Brewster angle microscopy (BAM) measurements are used to study the interaction of calf thymus DNA with DMPE (1,2-dimyristoyl-phosphatidylethanolamine) monolayers mediated by Ca2+ or Mg2+ ions. DNA adsorption is observed only in the presence of divalent cations. At low lateral pressure, the DNA partially penetrates into the lipid monolayer but is squeezed out at high pressure. The adsorption layer has a thickness of 18-19 A. Additionally, GIXD provides information about a one-dimensional ordering of adsorbed DNA. The periodic distance between DNA strands depends on the type of the divalent cation.

Adsorption↗
PubMed2006

Breakdown of the Gouy-Chapman model for highly charged Langmuir monolayers: counterion size effect.

Deviations from the classic Gouy-Chapman (GC) model due to the finite size of hydrated counterions were tested for negatively charged Langmuir monolayers with different surface charge densities. Monolayers with the largest charge density (>0.6 C.m(-2)) show an increase of the surface potential for a series of alkali metal cations from Li(+) to Cs(+) by 200-250 mV. The increase is similar for different monolayers and suggests that this effect is independent of the particular type of headgroup. The magnitude of variation is comparable with model estimations of the electrical double layer (EDL) potential implying that the deviation from the GC model is drastic. Deviations from the GC model rapidly vanish with decreasing monolayer charge density and become hardly observable below 0.3 C.m(-2). For monolayers with a high charge density on subphases containing different sized counterions, preferential participation of the smallest ions in the EDL should be favorable in terms of electrostatic free energy because of packing density limitations. This effect was demonstrated for behenyl sulfate (BS) monolayers (0.64 C.m(-2)) with the X-ray reflectivity technique. For the Cs(+)-Li(+) system, the fraction of Cs(+) in the EDL is 50-60% compared with only 10% of Cs(+) in the subphase. Providing high surface charge density, a small univalent Cs(+) is capable to compete even with a bulky divalent Mg(2+). For equal concentrations of Cs(+) and Mg(2+) in the subphase, the Cs(+)/Mg(2+) ratio in EDL of BS monolayer is 1.3 to 2.0 (in contrast to 0.04, predicted by the GC model). All experimental results of this study are described in terms of packing density limitations for hydrated counterions in the EDL.

Algorithms↗
PubMed2006

Ionization state and structure of l-1,2-dipalmitoylphosphatidylglycerol monolayers at the liquid/air interface.

Phosphatidylglycerols are components of biological membranes. The phase behavior of these phospholipids was extensively investigated. However, there is still no definite picture about the dependence of the ionization state and monolayer structure on subphase composition. The major problem of previous investigations is that none of the methods used allow obtaining the ionization degree directly. In the present work we apply techniques developed in the past decades for Langmuir monolayers: infrared reflection absorption spectroscopy (IRRAS) as well as X-ray diffraction and reflectivity techniques, which provide straightforward information about structure and ionization state of a L-1,2-dipalmitoylphosphatidylglycerol (DPPG) monolayer. The Gouy-Chapman model is applied to evaluate the intrinsic pKa. Therewith, the ionization degree can be determined even at low pH values. The experimental titration curves are in good agreement with theoretical curves based on the Gouy-Chapman model. The obtained instrinic pKa amounts to 1. The ionization degree of a DPPG monolayer is independent of the monovalent cation size. In contrast, the structure of a DPPG monolayer is strongly affected by the type of divalent cations.

Air↗
PubMed2005

Adsorption of amyloid beta-peptide at polymer surfaces: a neutron reflectivity study.

The adsorption of amyloid beta-peptide at hydrophilic and hydrophobic modified silicon-liquid interfaces was characterized by neutron reflectometry. Distinct polymeric films were used to obtain noncharged (Formvar), negatively (sodium poly(styrene sulfonate)) and positively charged (poly(allylamine hydrochloride)) hydrophilic as well as hydrophobic surfaces (polystyrene and a polysiloxane-dodecanoic acid complex). Amyloid beta-peptide was found to adsorb at positively charged hydrophilic and hydrophobic surfaces, whereas no adsorbed layer was detected on hydrophilic noncharged and negatively charged films. The peptide adsorbed at the positively charged film as patches, which were dispersed on the surface, whereas a uniform layer was observed at hydrophobic surfaces. The thickness of the adsorbed peptide layer was estimated to be approximately 20 A. The peptide formed a tightly packed layer, which did not contain water. These studies provide information about the affinity of the amyloid beta-peptide to different substrates in aqueous solution and suggest that the amyloid fibril formation may be driven by interactions with surfaces.

Adsorption↗
PubMed2005

Unconventional air-stable interdigitated bilayer formed by 2,3-disubstituted fatty acid methyl esters.

A single-chain fatty acid methyl ester, racemic anti-3-fluoro-2-hydroxyeicosanoic acid methyl ester (beta-FHE), forms an unconventional air-stable interdigitated bilayer at the air-water interface. The interdigitated bilayer transferred onto solid substrate by the Langmuir-Blodgett (LB) technique keeps air-stable without any substrate modification or protein inclusion. There are two visible plateaus in the surface pressure-molecular area (pi-A) isotherms of beta-FHE Langmuir film during continuous compression. According to Brewster angle microscopy (BAM), grazing incidence X-ray diffraction (GIXD), X-ray reflectivity (XR), fluorescence microscopy (FM), and atomic force microscopy (AFM) measurements, the first plateau is attributed to the coexistence of liquid expanded (LE) and liquid condensed (LC) phases in the monolayer, while the second plateau is interpreted as the transition from LC monolayer to interdigitated bilayer. The coupling between tilt and curvature associated with the packing mismatch between headgroup and chain gives rise to buckling and folding of the monolayer, leading to the transition of the LC monolayer to a bilayer structure. The diffusion-limited aggregation (DLA) model is applied to describe the formation of the fractal structures of the bilayer as observed in the second plateau. In addition, the transition between monolayer and bilayer is reversible. The present works are interesting for understanding biological processes, for example, the behavior of lung surfactants.

Air↗
PubMed2005

Langmuir and langmuir-blodgett films of metallosupramolecular polyelectrolyte-amphiphile complexes.

A detailed analysis of a metallosupramolecular polyelectrolyte-amphiphile complex (PAC) at the air-water interface is presented. Langmuir isotherms, Brewster angle microscopy, and X-ray reflectance and diffraction methods are employed to investigate the structure of the Langmuir monolayers. The PAC is self-assembled from 1,3-bis[4'-oxa-(2,2':6',2' '-terpyridinyl)]propane, iron acetate, and dihexadecyl phosphate (DHP). Spreading the PAC at the air-water interface results in a monolayer that consists of two strata. DHP forms a monolayer at the top of the interface, while the metallosupramolecular polyelectrolyte is immersed in the aqueous subphase. Both strata are coupled to each other through electrostatic interactions. The monolayers can be transferred onto solid substrates, resulting in well-ordered multilayers. Such multilayers are model systems for well-ordered metal ions in two dimensions.

Journal Article↗
PubMed2005

Modifying calf lung surfactant by hexadecanol.

Monolayer properties such as phase behavior, collapse pressure, and surface viscosity are determined by monolayer composition. Learning how to control these properties through simple additives is important to understanding lung surfactant monolayers and to designing optimal replacement surfactants for treatment of disease. The properties of Infasurf, a replacement lung surfactant derived from calf lung lavage organic extract, can be modified in a controlled fashion by adding hexadecanol (HD). Grazing incidence X-ray diffraction shows that the HD preferentially interacts with dipalmitoylphosphatidylcholine (DPPC), the main phospholipid component of Infasurf, in the same way as in binary mixtures of DPPC and HD. HD intercalates between the DPPC chains, which leads to a tighter packing of the two-dimensional lattice and greater stability of the solid phase. This molecular reorganization triggers changes at the macroscopic scale, leading to a greatly increased solid-phase fraction at a given surface pressure and order of magnitude increases in the surface shear viscosity. However, the collapse pressure decreases, and, hence, the minimum surface tension of the film increases.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2005

Hydrolysis reaction analysis of L-alpha-distearoylphosphatidylcholine monolayer catalyzed by phospholipase A2 with polarization-modulated infrared reflection absorption spectroscopy.

The hydrolysis reaction of L-alpha-distearoylphosphatidylcholine (DSPC) monolayers catalyzed by phospholipase A2 (PLA(2)) has been studied using polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) with film balance measurements. The PM-IRRAS analysis provides quantitative information about the reaction efficiency at different surface pressures. It was found that the reaction efficiency of L-DSPC monolayer hydrolysis catalyzed by PLA(2) decreased with increasing surface pressure. At zero pressure (lift-off point), the hydrolysis reaction efficiency has the highest value of 45%. Increasing surface pressure leads to the decrease of the hydrolysis efficiency. Since the surface pressure is above 20 mN/m, the hydrolysis reaction nearly stopped. PM-IRRAS technique provides a powerful means to study the hydrolysis process catalyzed by phospholipase A2 at the air/water interface.

Hydrolysis↗
PubMed2005

Adsorption of amyloid beta (1-40) peptide at phospholipid monolayers.

The folding of amyloid beta (1-40) peptide into beta-sheet-containing fibrils is thought to play a causative role in Alzheimer's disease. Because of its amphiphilic character, the peptide can interact with phospholipid membranes. Langmuir monolayers of negatively charged DPPS, DPPG, and DMPG, and also of zwitterionic DPPC and DMPC, have been used to study the influence of the peptide on the lipid packing and, vice versa, the influence of phospholipid monolayers on the peptide secondary structure by infrared reflection absorption spectroscopy and grazing incidence X-ray diffraction. The peptide adsorbs at the air/water (buffer) interface, and also inserts into uncompressed phospholipid monolayers. When adsorbed at the interface, the peptide adopts a beta-sheet conformation, with the long axis of these beta-sheets oriented almost parallel to the surface. If the lipid exhibits a condensed monolayer phase, then compression of the complex monolayer with the inserted peptide leads to the squeezing out of the peptide at higher surface pressures (above 30 mN m(-1)). The peptide desorbs completely from zwitterionic monolayers and negatively charged DPPG and DPPS monolayers on buffer, but remains adsorbed in the beta-sheet conformation at negatively charged monolayers on water. This can be explained in terms of electrostatic interactions with the lipid head groups. It also remains adsorbed at, or penetrating into, disordered anionic monolayers on buffer. Additionally, the peptide does not influence the condensed monolayer structure at physiological pH and modest ionic strength.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2005

Small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) studies of amide phospholipids.

Varying chemically the structure of phospholipids in the region between hydrophobic and hydrophilic segments is expected to have a strong influence on the interaction with water and the phase behavior. This is studied in this work with the motivation to investigate these lipids as potential inhibitors of phospholipase A2. Thus the amide phospholipids L-ether-amide-PC (1-O-hexadecyl-2-N-palmitoyl-2-amino-2-deoxy-sn-glycero-3-phosphocholine), L-ester-amide-PC (1-palmitoyl-2-N-palmitoyl-2-amino-2-deoxy-sn-glycero-3-phosphocholine) and L-ether-amide-PE (1-O-hexadecyl-2-N-palmitoyl-2-deoxy-sn-glycero-3-phosphoethanolamine) have been synthesized and characterized. The phase behavior and thermal transitions in buffer dispersions are examined by a combination of high-sensitivity differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS) experiments between 10 and 80 degrees C at pH 8.9. The onset temperatures determined from DSC measurements agree well with the starting temperatures of changes in the repeat distance obtained by SAXS measurements. The phases observed are lamellar both below and above the main phase transition. The phase transition temperatures and enthalpies depend strongly on the substitutions in sn-1 position and head group structure. The lamellar repeat distance in gel and liquid-crystalline phases increases with increasing temperature for L-ester-amide-PC and L-ether-amide-PC, whereas the temperature dependence is opposite for the L-ether-amide-PE. The observed behavior is discussed and compared with that of DPPC and DPPE, indicating the strong dependence of hydration and phase behavior on head group structure.

Amides↗
PubMed2005

Hydration properties of N-(alpha-hydroxyacyl)-sphingosine: X-ray powder diffraction and FT-Raman spectroscopic studies.

The thermotropic properties of N-(alpha-hydroxyacyl)-sphingosine (CER[AS]) in dry and hydrated state were studied by means of X-ray powder diffraction and FT-Raman spectroscopy. The polymorphic states of the CER[AS]/water mixture (lamellar crystalline, lamellar hexagonal gel, liquid crystalline) depend on the thermal pre-treatment of the sample. Only by heating the CER[AS]/water mixture above the melting chain transition can the system be hydrated. At room temperature, both dry and hydrated states form lamellar structures, which differ in their repeat distance and packing of hydrocarbon chains. Above the melting chain transition, hydrated CER[AS] forms a liquid crystalline hexagonal phase, whereas anhydrous CER[AS] forms an isotropic liquid phase. The various phases of hydrated CER[AS] are distinguished on the basis of the corresponding Raman spectra.

Ceramides↗
PubMed2004

Adsorption of amyloid beta (1-40) peptide to phosphatidylethanolamine monolayers.

The aggregation of soluble, nontoxic amyloid beta (Abeta) peptide to beta-sheet containing fibrils is assumed to be a major step in the development of Alzheimer's disease. Interactions of Abeta with neuronal membranes could play a key role in the pathogenesis of the disease. Herein, we study the adsorption of synthetic Abeta peptide to DPPE and DMPE monolayers (dipalmitoyl- and dimyristoylphosphatidylethanolamine). Both lipids exhibit a condensed monolayer state at 20 degrees C and form a similar lattice. However, at low packing densities (at large area per molecule), the length of the acyl chains determines the phase behavior, therefore DPPE is fully condensed whereas DMPE exhibits a liquid-expanded state with a phase transition at approximately 5-6 mNm(-1). Adsorption of Abeta to DPPE and DMPE monolayers at low surface pressure leads to an increase of the surface pressure to approximately 17 mNm(-1). The same was observed during adsorption of the peptide to a pure air-water interface. Grazing incidence X-ray diffraction (GIXD) experiments show no influence of Abeta on the lipid structure. The adsorption kinetics of Abeta to a DMPE monolayer followed by IRRAS (infrared reflection absorption spectroscopy) reveals the phase transition of DMPE molecules from liquid-expanded to condensed states at the same surface pressure as for DMPE on pure water. These facts indicate no specific interactions of the peptide with either lipid. In addition, no adsorption or penetration of the peptide into the lipid monolayers was observed at surface pressures above 30 mNm(-1). IRRAS allows the measurement of the conformation and orientation of the peptide adsorbed to the air-water interface and to a lipid monolayer. In both cases, with lipids at surface pressures below 20 mNm(-1) and at the air-water interface, adsorbed Abeta has a beta-sheet conformation and these beta-sheets are oriented parallel to the interface.

Adsorption↗