Three-Dimensional Transmission Electron Microscopy: A Novel Imaging and Characterization Technique with Nanometer Scale Resolution for Materials Science

Three-dimensional transmission electron microscopy (3D-TEM), effectuated by multiple imaging of a sample combined with image analysis, offers a new approach in materials science to obtain 3D information of complex solid materials. Here we report first-of-its-kind results that have been obtained with zeolite materials. Virtual cross-sections and volume rendering of the 3D reconstruction of a metal/zeolite crystal (Ag/NaY) give unequivocal information on the location of the silver particles (10-40 nm in diameter). Virtual cross-sections of the 3D reconstruction of an acid-leached mordenite show the three-dimensional mesoporous channel system (3-20 nm in diameter) with a clarity and definition not seen before

Development and Application of 3-Dimensional Transmission Electron Microscopy (3D-TEM) for the Characterization of Metal-Zeolite Catalyst Systems

With electron tomography (3D-TEM) a 3D-reconstruction is calculated from a series of TEM images taken at a tilt angle range (tilting range) of +70° to -70°. The reconstruction can be visualized with contour surfaces that give information about the surface of the sample as well as with slices through the reconstruction that give detailed information on the interior of the sample. Electron tomography gives much more information than Scanning Electron Microscopy (SEM), since SEM gives only information about the surface of a sample. As a case study, the imaging of silver clusters on zeolite NaY is given. The reconstruction shows silver particles at the external surface as well as a silver particle in a mesopore of the zeolite crystallite. It is concluded that 3D-TEM comprises a breakthrough in the characterization of nano-structured solid catalysts

Lipidic intramembranous particles

In 1979 we described for the first time the phenomenon of 'lipidic intramembranous particles' or 'lipidic particles' in model membranes. These particles have been called 'lipidic particles' since they were found in pure lipid systems, and thus must originate from a specific lipid organization. Such lipidic particles have been found in a variety of lipid mixtures and in total lipid extracts under physiological conditions in excess water. A common feature of these lipid systems is that at least one of the lipids prefers to adopt the hexagonal II (Hn) phase when dispersed in pure form. n this review I will try to evaluate all the data concerning the phenomenon of 'lipidic particles'

Modulation of membrane structure by Ca2+ and dibucaine as detected by 31P NMR

The polymorphic phase behaviour of model membrane systems consisting of 20 mol% bovine brain phosphatidylserine and 80 mol% egg yolk phosphatidylethanolamine has been examined employing 31P NMR techniques. It is shown that the addition of Ca2+ to such systems can trigger isothermal bilayer to hexagonal (HII) phase transitions, and that such effects can be reversed by the subsequent incorporation of the local anaesthetic dibucaine. These results are discussed in terms of a recent model for membrane fusion (Cullis, P.R. and Hope, M.J. (1978) Nature 271, 672–674) and mechanisms of anaesthesia

Possible role of non-bilayer lipids in the structure of mitochondria. A freeze-fracture electron microscopy study

The possible role of non-bilayer phospholipids on the structure of isolated rat liver mitochondria has been morphologically studied. Freshly isolated freeze-fractured mitochondria show smooth fracture faces with particles, representing the limiting membranes. The frequency and size of the particles is representative for the various membrane faces. Distinctly large particles and pits represent the attachment sites of cristae to the inner membrane. Liposome-like structures in the matrix are found upon incubation with Ca2+ and Mn2+. At 5 mM Mn2+ and more, curved hexagonal (HII) phase tubes are observed. Subsequent addition of 1 mM EDTA results in disappearance of the HII tubes, and liposomal structures can again be seen. These findings are interpreted in terms of an Mn2+-induced lamellar to HII phase transition. Patchwork-like structures characterize the membranes of mitochondria, quenched from 37°C, as well as those incubated with Ca2+, Mn2+, Mg2+ and apo- or cytochrome c. This phenomenon is interpreted as being the result of the fracture plane, jumping from the outer to the inner limiting membrane and vice versa at sites of contact. A semi-fusion model, in which non-bilayer lipids are involved, is proposed for these contact sites

The lateral distribution of intramembrane particles in the erythrocyte membrane and recombinant vesicles

Triton X-100 (in concentrations which did not cause a significant solubilization of membrane material) caused aggregation of the intramembrane particles of human erythrocyte ghosts. Ghosts from which the extrinsic proteins had been removed by alkali treatment showed a temperature-induced aggregation of the particles. With virtually no spectrin present, the particles in these stripped ghosts could still be aggregated by manipulations with ionic strength and pH, or by the addition of calcium. Recombinant vesicles were made from a Triton X-100 extract and a mixture of phospholipids with a composition which resembled that of the inner monolayer of erythrocyte membrane. In these recombinants the same manipulations with ionic strength and pH and the addition of calcium caused a rearrangement of the particles, resulting in the appearance of particle-free areas. In recombinants prepared from a Trixon X-100 extract and egg phosphatidylcholine the lateral distribution of the particles was not altered by these manipulations. It is concluded that in the erythrocyte membrane the intramembrane particles can be aggregated by effects of external agents on lipid components. In this light the role of spectrin in stabilizing the membrane by interactions with lipids in the inner monolayer is discussed

Prevention of calcium-induced membrane structural alterations in erythrocyte membranes by flunarizine

The calcium antagonist flunarizine is shown to be able to prevent particle aggregation, membrane aggregation and blebbing resulting from elevated calcium concentrations. The anti-ischemic effects of flunarizine may therefore result in part from its ability to directly interfere with calcium-membrane interactions and thus prevent the lethal membrane reorganizations which occur after a period of ischemia during intracellular calcium overload