Surface behaviour and lipid interaction of Alzheimer beta-amyloid peptide 1-42: a membrane-disrupting peptide

Amyloid aggregates, found in patients that suffer from Alzheimer's disease, are composed of fibril-forming peptides in a β-sheet conformation. One of the most abundant components in amyloid aggregates is the β-amyloid peptide 1–42 (Aβ 1–42). Membrane alterations may proceed to cell death by either an oxidative stress mechanism, caused by the peptide and synergized by transition metal ions, or through formation of ion channels by peptide interfacial self-aggregation. Here we demonstrate that Langmuir films of Aβ 1–42, either in pure form or mixed with lipids, develop stable monomolecular arrays with a high surface stability. By using micropipette aspiration technique and confocal microscopy we show that Aβ 1–42 induces a strong membrane destabilization in giant unilamellar vesicles composed of palmitoyloleoyl-phosphatidylcholine, sphingomyelin, and cholesterol, lowering the critical tension of vesicle rupture. Additionally, Aβ 1–42 triggers the induction of a sequential leakage of low- and high-molecular-weight markers trapped inside the giant unilamellar vesicles, but preserving the vesicle shape. Consequently, the Aβ 1–42 sequence confers particular molecular properties to the peptide that, in turn, influence supramolecular properties associated to membranes that may result in toxicity, including: 1), an ability of the peptide to strongly associate with the membrane; 2), a reduction of lateral membrane cohesive forces; and 3), a capacity to break the transbilayer gradient and puncture sealed vesicles.

Neurotoxic, redox-competent Alzheimer's --amyloid is released from lipid membrane by methionine oxidation

The amyloid β peptide is toxic to neurons, and it is believed that this toxicity plays a central role in the progression of Alzheimer's disease. The mechanism of this toxicity is contentious. Here we report that an Aβ peptide with the sulfur atom of Met-35 oxidized to a sulfoxide (Met(O)Aβ) is toxic to neuronal cells, and this toxicity is attenuated by the metal chelator clioquinol and completely rescued by catalase implicating the same toxicity mechanism as reduced Aβ. However, unlike the unoxidized peptide, Met(O)Aβ is unable to penetrate lipid membranes to form ion channel-like structures, and β-sheet formation is inhibited, phenomena that are central to some theories for Aβ toxicity. Our results show that, like the unoxidized peptide, Met(O)Aβ will coordinate Cu₂₊ and reduce the oxidation state of the metal and still produce H2O2. We hypothesize that Met(O)Aβ production contributes to the elevation of soluble Aβ seen in the brain in Alzheimer's disease.

Plasmodium falciparum induces reorganization of host membrane proteins during intraerythrocytic growth

The virulence of the malaria parasite, Plasmodium falciparum, is due in large part to the way in which it modifies the membrane of its erythrocyte host. In this work we have used confocal microscopy and fluorescence recovery after photo-bleaching to examine the lateral mobility of host membrane proteins in erythrocytes infected with P falciparum at different stages of parasite growth. The erythrocyte membrane proteins band 3 and glycophorin show a marked decrease in mobility during the trophozoite stage of growth. Erythrocytes infected with a parasite strain that does not express the knob-associated histidine-rich protein show similar effects, indicating that this parasite protein does not contribute to the immobilization of the host proteins. Erythrocytes infected with ring-stage parasites exhibit intermediate mobility indicating that the parasite is able to modify its host prior to its active feeding stage.

Improved extraction of heavy metal ions using membrane technology

Investigates tha application of polymer membranes in industrial wastewater treatment. Several novel membrane systems have been developed. The new systems overcome the problems of low extractant capacity and slow rate of extraction of the traditional membrane system. These new systems offer significant scope for the treatment of industrial wastewater containing heavy metal ions.

Platinum electrodeposition for polymer electrolyte membrane fuel cells

A novel electrodeposition technique for preparing the catalyst layer in polymer electrolyte membrane fuel cells has been designed, which may enable an increase in the level of platinum utilisation currently achieved in these systems. This method consists of a two-step procedure involving the impregnation of platinum ions into a preformed catalyst layer (via an ion-exchange into the Nafion polymer electrolyte), followed by a potentiostatic reduction. The concentration of Nafion within the catalyst layer was found to have a significant bearing on the size of the platinum deposits. The preparation of catalyst layers containing a desired platinum loading should also be possible using this method. Surface areas of the platinum deposits were determined using cyclic voltammetry. The prepared catalyst was compared with a conventional electrode made from E-TEK Pt/C. Scanning electron microscopy was used to investigate the dispersion of the platinum particles. Platinum loadings were determined quantitatively by atomic absorption spectroscopy.

Effects of backwashing on PVDF membrane fouling by organic foulants

Membrane is usually subject to fouling by various organic foulants, such as yeast, protein and sodium alginate during filtration. Backwashing is a common practice to reduce membrane fouling. It is essential to evaluate the effects of backwashing on fouling in order to optimize operational parameters. In this experiment, poly(vinylidene fluoride) (PVDF) membranes were used to filter organic foulants from suspensions in a dead-end stirred cell. Three types of organic foulants including yeast, protein and sodium alginate which were stained with fluorescent dyes before filtration were used with different combinations in the experiments. After filtration, the PVDF membrane was backwashed.

Consequently, a stack of images, instrumental data and sample data were captured from the fouling layers on the PVDF membrane surface using confocal laser scanning microscope (CLSM) and its associated image acquisition software LAS AF. Then, the quality of the images was enhanced for better visualization and a set of quantitative fouling data were derived by using the software code developed by the project team at Deakin University.

This collection contains raw image data of poly(vinylidene fluoride) (PVDF) membrane’s fouling layer when three types of organic foulants present, which are captured by confocal laser scanning microscopy (CLSM) and its software, and the instrumental and sample metadata, the processed image data and the geometrical structure properties of the fouling layer. By comparing with the same membrane without backwashing, the efficiency of backwashing was computed.

This data collection would be useful to evaluate the backwashing efficiency of PVDF membrane in order to optimize frequency and operational conditions of backwashing by membrane materials researchers and water researchers.

Polycarbonate (PC) membrane fouling by protein and sodium alginate

This data was obtained from an experiment, where polycarbonate (PC) membranes were used to filter two types of organic foulants, including protein and sodium alginate, from suspension in a dead-end filtration cell. These model foulants were stained with fluorescent dyes before filtration. Consequently, a stack of images were captured from the fouling layers on the PC membrane surface using confocal laser scanning microscope (CLSM). This data collection contains 105 2D images of polycarbonate (PC) membranes fouling layer. This data collection would be useful to investigate membrane fouling mechanism by membrane materials researchers and water researchers.

Polycarbonate (PC) membrane fouling by protein and yeast

This data collection contains 126 images of polycarbonate (PC) membranes fouling layer where two types of organic foulants including protein and yeast present.

This data collection would be useful to investigate membrane fouling mechanism by membrane materials researchers and water researchers.

Polycarbonate (PC) membrane fouling by yeast, protein and sodium alginate

This data collection contains 110 images of polycarbonate (PC) membranes fouling layer where three types of organic foulants including yeast, protein and sodium alginate present.

This data collection would be useful to investigate membrane fouling mechanism by membrane materials researchers and water researchers.

Immobilized artificial membrane chromatography : quantitative structure-retention relationships of structurally diverse drugs

The chromatographic capacity factors (log k‘) for 32 structurally diverse drugs were determined by high performance liquid chromatography (HPLC) on a stationary phase composed of phospholipids, the so-called immobilized artificial membrane (IAM). In addition, quantitative structure-retention relationships (QSRR) were developed in order to explain the dependence of retention on the chemical structure of the neutral, acidic, and basic drugs considered in this study. The obtained retention data were modeled by means of multiple regression analysis (MLR) and partial least squares (PLS) techniques. The structures of the compounds under study were characterized by means of calculated physicochemical properties and several nonempirical descriptors. For the carboxylic compounds included in the analysis, the obtained results suggest that the IAM-retention is governed by hydrophobicity factors followed by electronic effects due to polarizability in second place. Further, from the analysis of the results obtained of two developed quantitative structure-permeability studies for 20 miscellaneous carboxylic compounds, it may be concluded that the balance between polarizability and hydrophobic effects is not the same toward IAM phases and biological membranes. These results suggest that the IAM phases could not be a suitable model in assessing the acid-membrane interactions. However, it is not possible to generalize this observation, and further work in this area needs to be done to obtain a full understanding of the partitioning of carboxylic compounds in biological membranes. For the non-carboxylic compounds included in the analysis, this work shows that the hydrophobic factors are of prime importance for the IAM-retention of these compounds, while the specific polar interactions, such as electron pair donor−acceptor interactions and electrostatic interactions, are also involved, but they are not dominant.