Perspectives on weak interactions in complex materials at different length scales.

Nanocomposite materials consist of nanometer-sized quantum objects such as atoms, molecules, voids or nanoparticles embedded in a host material. These quantum objects can be exploited as a super-structure, which can be designed to create material properties targeted for specific applications. For electromagnetism, such targeted properties include field enhancements around the bandgap of a semiconductor used for solar cells, directional decay in topological insulators, high kinetic inductance in superconducting circuits, and many more. Despite very different application areas, all of these properties are united by the common aim of exploiting collective interaction effects between quantum objects. The literature on the topic spreads over very many different disciplines and scientific communities. In this review, we present a cross-disciplinary overview of different approaches for the creation, analysis and theoretical description of nanocomposites with applications related to electromagnetic properties.

Premelting of ice adsorbed on a rock surface.

Considering ice-premelting on a quartz rock surface (i.e. silica) we calculate the Lifshitz excess pressures in a four layer system with rock-ice-water-air. Our calculations give excess pressures across (1) ice layer, (2) water layer, and (3) ice-water interface for different ice and water layer thicknesses. We analyse equilibrium conditions where the different excess pressures take zero value, stabilized in part by repulsive Lifshitz interactions. In contrast to previous investigations which considered varying thickness of only one layer (ice or water), here we present theory allowing for simultaneous variation of both layer thicknesses. For a given total thickness of ice and water, this allows multiple alternative equilibrium solutions. Consequently the final state of a system will depend on initial conditions and may explain variation in experimental measurements of the thicknesses of water and ice layers.

Trapping of Gas Bubbles in Water at a Finite Distance below a Water-Solid Interface.

Gas bubbles in a water-filled cavity move upward because of buoyancy. Near the roof, additional forces come into play, such as Lifshitz, double layer, and hydrodynamic forces. Below uncharged metallic surfaces, repulsive Lifshitz forces combined with buoyancy forces provide a way to trap micrometer-sized bubbles. We demonstrate how bubbles of this size can be stably trapped at experimentally accessible distances, the distances being tunable with the surface material. By contrast, large bubbles (≥100 µm) are usually pushed toward the roof by buoyancy forces and adhere to the surface. Gas bubbles with radii ranging from 1 to 10 µm can be trapped at equilibrium distances from 190 to 35 nm. As a model for rock, sand grains, and biosurfaces, we consider dielectric materials such as silica and polystyrene, whereas aluminium, gold, and silver are the examples of metal surfaces. Finally, we demonstrate that the presence of surface charges further strengthens the trapping by inducing ion adsorption forces.

Why direct or reversed Hofmeister series? Interplay of hydration, non-electrostatic potentials, and ion size.

A modified Poisson-Boltzmann analysis is made of the double layer interaction between two silica surfaces and two alumina surfaces in chloride electrolyte. The analysis incorporates nonelectrostatic ion-surface dispersion interactions based on ab initio ionic excess polarizabilities with finite ion sizes. A hydration model for the tightly held hydration shell of kosmotropic ions is introduced. A direct Hofmeister series (K > Na > Li) is found at the silica surface while the reversed series (Li > Na > K) is found at alumina, bringing theory in line with experiment for the first time. Calculations with unhydrated ions also suggest that surface-induced dehydration may be occurring at the alumina surface.

Structure of wet specimens in electron microscopy. Improved environmental chambers make it possible to examine wet specimens easily.

Several recent technological advances have increased the practicality and usefulness of the technique of electron microscopy of wet objects. (i) There have been gains in the effective penetration of high-voltage microscopes, scanning transmission microscopes, and high-voltage scanning microscopes. The extra effective penetration gives more scope for obtaining good images through film windows, gas, and liquid layers. (ii) Improved methods of obtaining contrast are available (especially dark field and inelastic filtering) that often make it possible to obtain sufficient contrast with wet unstained objects. (iii) Improved environmental chamber design makes it possible to insert and examine wet specimens as easily as dry specimens. The ultimate achievable resolution for wet objects in an environmental chamber will gradually become clear experimentally. Resolution is mainly a function of gas path, liquid and wet specimen thickness, specimen stage stability, acceleration voltage, and image mode (fixed or scanning beam) (13). Much depends on the development of the technique for controlling the thickness of extraneous water film around wet objects or the technique for depositing wet objects onto dry, hydrophobic support films. Although some loss of resolution due to water or gas scattering will always occur, an effective gain is anticipated in preserving the shape of individual molecules and preventing the partial collapse that usually occurs on drying or negative staining. The most basic question for biological electron microscopy is probably whether any living functions of cells can be observed so that the capabilities of the phase contrast and interference light microscopes can be extended. Investigators are now rapidly approaching a final answer to this question. The two limiting factors are (i) maintaining cell motility in spread cells immersed in thin layers of media and (ii) reducing beam radiation damage to an acceptable level. The use of sensitive emulsions and image intensifiers can bring the observation dose below that required to stop cell motility. Use of a timed, pulsed deflector system enables sufficiently short exposures to be obtained to eliminate blurring due to Brownian motion. Environmental chambers have enhanced the possibilities of electron diffraction analysis of minute crystals and ordered biological structures. High-resolution electron diffraction patterns (especially kinematic) of protein crystals can only be obtained in a wet environment. Hence, it may now be possible to obtain undistorted images of protein molecules. Moreover, by subjecting diffraction patterns to image-iterative techniques (56), it will be possible to phase the electron diffraction patterns to give a calculated image with a higher resolution than that which can be produced by electron microscope objective lenses. Environmental chambers offer exciting prospects for the determination of water structure and water and ice nucleation (atmospheric science). Nucleation data near the molecular level have been badly needed for some time. The application of environmental chambers in industrial chemistry, for example, in studies of polymerization, catalysis, and corrosion, are awaiting exploration. They offer an unusual approach to measurements of reaction kinetics through images that should be both sensitive and rapid.

Direct observation of domains in wet lipid bilayers.

Domain structure and phase separation in hydrated lipid bilayers have been imaged directly by selected reflection dark-field electron microscopy. Domains in multicomponent bilayers are much smaller than those in single component bilayers, in agreement with results obtained by selected area electron diffraction.

Electron diffraction of wet biological membranes.

Electron diffraction patterns were obtained for the first time from single wet phospholipid bilayers and from wet human erythrocyte membranes by using a temperature-controlled electron microscope hydration stage. Selective area diffraction showed the existence of semicrystalline domains. A structural transition was observed at the transition temperature of the wet dipalmitoyl lecithin bilayer.

Neutron diffraction of cell membranes (myelin).

Small-angle neutron diffraction (wavelength 4.05 angstroms) of human and rabbit sciatic nerve has been carried out by means of the Brookhaven high flux beam reactor with an automated slit camera. Most of the free water of the nerves was substituted in order to minimize incoherent scatter of hydrogen atoms. The differences in amplitude and phase shifts between neutrons and x-rays resulted in a neutron diffraction pattern that was completely different from the x-ray pattern. The neutron pattern consisted of a single peak of about 89-angstrom spacing in the region examined (up to 6-angstrom spacing). The strong third, fourth, and fifth order reflections (about 60, 45, and 36 angstroms) seen in the x-ray pattern were suppressed. The neutron data indicated a strong scattering from one portion of the membrane.

Electron diffraction of wet proteins: catalase.

Electron diffraction patterns having 3500 reflections out to 2 angstromns were obtained from wet microcrystals of catalase. No diffraction was obtained if the water vapor pressure was set below 90 percent of the equilibrium value.

Anion-specific partitioning in two-phase finite volume systems: possible implications for mechanisms of ion pumps.

In two-phase finite volume systems of electroneutral phospholipids, the electrolyte concentration is different in the two phases. The partitioning is highly anion-specific, a phenomenon not accounted for by classical electrolyte theories. It is explained if ionic dispersion forces that lead to specific ion binding are taken into account. The mechanism provides a contribution to active ion pumps not previously considered.

Phase transition of plasma membranes of rat hepatocyte and hepatoma cells by electron diffraction.

The transition temperatures (Tc) of the plasma membranes of Reuber H-35 hepatoma and normal ACl rat hepatocytes were measured by electron diffraction under physiological conditions. Diffraction rings below Tc indicate the existence of solid lipid domains. The Tc of both membranes increase to a plateau value of 17.5 degrees during the storage period of 4 days at 4 degrees, the rate of increase being slower for normal liver membranes. The extrapolations to zero storage suggest an innate difference of Tc for these two membranes. Storage in oxygen-reduced media slows down the initial increase in Tc in normal liver membranes, while the depletion of divalent cations accelerates the increase. Differences in lipid composition are partly responsible for this behavior.

Organ-cultured epithelial tissue as an in vitro model for invasion: quantitation and high-voltage electron microscopy of tumor cell attachment.

An invasion model designed specifically for studying mechanisms of invasion of squamous-cell carcinomas was developed with murine buccal mucosa as the host tissue. The mucosal explants were destratified by growth in low-calcium medium (less than 0.07 mM), which results in a dorsal surface composed of one or two layers of basal epithelial cells. The explant has a three-dimensional histoarchitecture similar to in vivo mucosa. A spontaneously transformed epithelial cell line (Pam 27; Yuspa , S. H., Hawley -Nelson, P., Koehler , B., and Stanley, J. R. Cancer Res., 40: 4694-4703, 1980) was used to seed explants. Attachment and subsequent growth and invasion were monitored. The morphology of attachment was examined by conventional and high-voltage electron microscopy. In addition, attachment was quantitated by using [125I]iododeoxyuridine-labeled tumor cells. Attachment was shown to be an active process which involves an interdigitation of tumor-host cell processes. Junctional complexes were also observed between tumor and host epithelial cells. By 24 hr, tumor cells were spread on the basal cells and were in the process of replacing host cells. Long-term growth of explants showed that tumor cells can repopulate the epithelial surface and invade the stromal region.

Ascites tumor invasion of mouse peritoneum studied by high-voltage electron microscope stereoscopy.

Interaction of Krebs-2 and Ehrlich tetraploid cells with NYLR/Nya mouse peritoneum mesothelium and penetration of basal lamina and elastic reticulum were studied. Invasion of abdominal viscera was rare. Invading cells had a shrunken nucleus and cytoplasm like the "dark cells" of hyperplastic epithelia. High-voltage electron microscope stereoscopy showed that invasive cells pass through small holes in the elastic reticulum by adherence to the reticulum and by constriction of the cells. High voltage electron microscopy stereoscopy of collagen fibers near tumor cells indicated that fragmentation and loss of collagen is minimal. Rapid progression by ascites transfer appears to produce anchorage-independent cells adapted to ascites fluid growth, but new selection steps must be adopted to concentrate strongly invasive subpopulations.

Establishment and characterization of two new squamous cell carcinoma cell lines derived from tumors of the head and neck.

Two human cell lines were established from untreated squamous cell carcinomas of the head and neck. Line 183 was derived from a head and neck squamous cell carcinoma of the tonsil and 1483 from a head and neck squamous cell carcinoma of the retromolar trigone. Both lines grow in a cobblestone pattern demonstrating their epithelial heritage. Immunofluorescence studies and one-dimensional polyacrylamide gel electrophoresis indicated that both lines contain cytokeratins. Line 1483 is more aggressive in nude mice, has a higher efficiency for anchorage-independent growth, expresses p21ras (product of the ras oncogene) at a higher level, and is more aneuploid than 183. 1483 also grows as a multicellular tumor spheroid. Line 1483, which was established from the primary tumor of a patient with nodal metastasis, thus displays more progressed characteristics than line 183, which was established from a patient with no clinically positive nodes.

Small-angle X-ray scattering from mitochondria.

X-ray (CuKalpha) scattering curves of rat liver mitochondria are characterized by continuously decreasing intensity from 0.5 to 5 mrad and a broad maximum centered near 20 mrad. The condensed-to-orthodox morphological transition of the inner membranes of intact mitochondria causes a dramatic decrease in scattering at very small angle and a marked shift of the 20 mrad maximum to smaller angle. A similar small-angle scattering maximum is observed with inner mitochondrial membrane fractions prepared by digitonin treatment and osmotic shock/step gradient centrifugation procedures. However, the small-angle X-ray scattering curves of mitochondria after acetone treatment and osmoticlysis/sonication are essentially continuous. These characteristics of mitochondrial X-ray scattering are discussed in terms of known structural features of the organelle.

Uncoupled-induced changes in mitochondrial structure detected by small-angle x-ray scattering.

Small-angle X-ray scattering data suggest that major but reversible rearrangements of mitochondrial inner membrane structure are induced by uncouplers. Low levels of 2,4-dinitrophenol (10 micronM) cause a perceptible wide-angle shift of the 20 mrad X-ray scattering maximum characteristic of intact liver mitochondria. Higher dinitrophenol concentrations (greater than 25 micronM) reduce this scattering maximum to one-third its initial intensity. In terms of mitochondrial function, the former scattering change appears to correlate with the uncoupling of oxidative phosphorylation while the latter occurs in the course of dinitrophenol stimulation of mitochondrial ATPase activity.

Electron diffraction study of hydrated phospholipid single bilayers. Effects of temperature hydration and surface pressure of the "precursor" monolayer.

The molecular packing and phase transition of hydrated dipalmitoylphosphatidylcholine single bilayers are studied by electron diffraction, using an electron microscope equipped with a hydration stage. The phase transition and area per molecule are measured as functions of temperature, hydration and the surface pressure of the monolayer from which the bilayer is formed. The transition temperature of a bilayer agrees with calorimetric measurements on bulk lipid/water mixtures. The molecular packing of a bilayer corresponds to that of the precursor monolyer at a surface pressure of 47 dyne/cm.

"Dark cells" in normal, hyperplastic, and promoter-treated mouse epidermis studied by conventional and high-voltage electron microscopy.

Dark cells (DC) could be reproducibly demonstrated by differential toluidine-blue staining and electron microscopy (EM) of NYLR/Nya 16- to 19-day embryo and new born skin and phorbol ester-treated or untreated young adult skin. High-voltage electron microscopy on the same or adjacent sections showed that toluidine-blue staining picks out some but not all the DC seen by EM. The ultrastructure of DC was similar in all the above situations, except that phorbol ester-induced DC showed a less contracted nucleus. No support was obtained for DC as stem cells either for basal-cell hyperplasia or for development of hair follicle or gland outgrowths. Most of the severely contracted DC (Types 3 and 4) were assumed to have undergone an apoptotic type of cell death. Two phenomena that may have caused the contraction and apoptosis were observed. Formation of a "contraction vacuole" adjacent to the DC probably led to a loss of intercellular communication. An apparent necrosis of dermal capillaries in areas of abundant follicle downgrowth probably produced local anoxia. Further characterization of DC requires a search for cytochemical or immunologic markers, analysis of intracellular calcium and other elements, and the cloning of subpopulations of basal cells that can be selectively induced to form DC.

The usefulness of the high voltage electron microscope in biomedical ultrastructure analysis.

We now have the tools to quantitate and correctly interpret the size, shape, and distribution of organelles in cells. It appears likely that the results will require some changes in some basic assumptions of ultrastructural cytology. This should also result in some new biochemical hypotheses about control of cell metabolism.

Reproducibility of electron diffraction intensity data obtained from hydrated microcrystals of rat hemoglobin.

Analysis of electron diffraction patterns from rat hemoglobin taken at 200 kV on a wet stage yields intensity data to a resolution of 2-3 A which are as reproducible as those from typical X-ray diffraction. Some crystals were so similar that the differences in measured intensities were insignificant (R = 0.056), but in other cases real differences between crystals were observed (R = 0.33). Dynamic scattering was insignificant under our diffraction conditions; however, exposures to electron doses as low as 10(-2) e/A2 produced detectable changes in measured intensities. Limits to the reproducibility of the data are set by radiation damage and errors in microdensitometry.