Nature of the packing of ribosomes within chromatoid bodies

Optical Fourier transformns, made of electron mnicrographs of the crystalline array of ribonucleoprotein known as chromatoid bodies of Entamoeba invadens, have been interpreted as the transforms of a helix of 12 nodes in five turns. A model shows that this helix may be built of spheres 180 angstroms in diameter, placed at a radius of 150 angstroms. The optical transform of the model is very similar to the transform of the original electron micrograph.     

Ultrastructure of gamma-M immunoglobulin and alpha macroglobulin: electron-microscopic study

Electron microscopy of purified Waldenstr?m macroglobulins and normal human and rabbit gammaM immunoglobulins revealed spider-like structures with five legs varying in length and often joining a central ring. Usually only the central more rigid part of this structure (about 150 by 170 angstroms) was clearly visible, but occasionally particles were seen with longer very flexible legs having a total span of about 350 angstroms. Molecules of gammaM antibody retained antibody activity during preparation for electron microscopy. Human and rabbit alpha macroglobulins revealed more rigid symmetric structures (100 by 200 angstroms) which resembled the Russian letter .     

Particle Formation during Water-Vapor Photolysis

Micrometer-sized particles have been produced by the photolysis of water vapor at wavelengths between 1500 and 1700 angstroms. Although the composition of the particles was not determined, the rate of particle production is consistent with the efficient conversion of water photolysis products to particulate matter. Such a process may be of importance in planetary atmospheres.     

Magnetite: Behavior near the Single-Domain Threshold

Maximum values for the single-domain threshold d(0) and superpara-magnetic threshold d(8) in pure magnetite are found to be 570+/-50 and 350+/-50 angstroms, respectively. Particles larger than do but smaller than about 0.25 micron have size-dependent saturation remanences and coercive forces like those of multidomain particles, but intense and stable thermoremanent magnetization like that of single-domain particles. The presence of magnetite grains in this size range could account for the essentially single-domain character of stable natural remanence in many volcanic and intrusive rocks.     

Soft X-ray Images of the Solar Corona with a Normal-Incidence Cassegrain Multilayer Telescope

High-resolution images of the sun in the soft x-ray to extreme ultraviolet(EUV) regime have been obtained with normal-incidence Cassegrain multilayer telescopes operated from a sounding rocket in space. The inherent energy-selective property of multilayer-coated optics allowed distinct groups of emission lines to be isolated in the solar corona and the transition region. The Cassegrain telescopes provided images in bands centered at 173 and 256 angstroms. The bandpass centered at 173 angstroms is dominated by emission from the ions Fe IX Fe X. This emission is from coronal plasma in the temperature range 0.8 x 10(6) to 1.4 x 10(6)K. The images have angular resolution of about 1.0 to 1.5 arc seconds, and show no degradation because of x-ray scattering. Many features of coronal structure, including magnetically confined loops of hot plasma, coronal plumes, polar coronal holes, faint structures on the size scale of supergranulation and smaller, and features due to overlying cool prominences are visible in the images. The density structure of polar plumes, which are thought to contribute to the solar wind, has been derived from the observations out to 1.7 solar radii.     

Cometary particles: thin sectioning and electron beam analysis

Thin sections (500 to 1000 angstroms thick) of individual micrometeorites (5 to 15 micrometers) have been prepared with an ultramicrotome equipped with a diamond knife. Electron microscopic examination of these sections has revealed the internal structures of chondritic micrometeorites, and a subset of highly porous, fragile particles has been identified. Delicate meteoritic materials such as these are characteristic of debris from cometary meteors.     

Determination of the pore size of cell walls of living plant cells

The limiting diameter of pores in the walls of living plant cells through which molecules can freely pass has been determined by a solute exclusion technique to be 35 to 38 angstroms for hair cells of Raphanus sativus roots and fibers of Gossypium hirsutum, 38 to 40 angstroms for cultured cells of Acer pseudoplatanus, and 45 to 52 angstroms for isolated palisade parenchyma cells of the leaves of Xanthium strumarium and Commelina communis. These results indicate that molecules with diameters larger than these pores would be restricted in their ability to penetrate such a cell wall, and that such a wall may represent a more significant barrier to cellular communication than has been previously assumed.     

NMR studies of simple molecules on metal surfaces

In recent years, improvements in the sensitivity of nuclear magnetic resonance have made it possible to detect progressively smaller numbers of nuclei. Experiments and studies previously thought to be impractical can now be undertaken, for example, the study of phenomena at surfaces. Nuclear magnetic resonance has been applied to study simple molecules (carbon monoxide, acetylene, and ethylene) adsorbed on metal surfaces (ruthenium, rhodium, palladium, osmium, iridium, and platinum). The metals, in the form of clusters 10 to 50 angstroms in diameter, supported on alumina, are typical of real catalysts. The experiments provide information about the bonding of the molecules to the metal, the structures the molecules assume after adsorption, the motion of molecules on the surface, the breakup of molecules induced by heating, and the products of such breakup.     

Palladium: preparation and catalytic properties of particles of uniform size

A method has been developed for the preparation of uniform palladium particles of diameter from 55 to 450 angstroms. Uniform particles of gold layered on palladium were also synthesized. Hydrothermal treatment of aluminum hydroxide sol was used to prepare rods of alumina with uniform cross section from 100 to 500 angstroms and of varying lengths. The palladium was adsorbed as individual particles on alumina rods, both present in aqueous suspension. Then the suspension was dried to give a catalyst containing metal particles of uniform size dispersed in open pores produced by the intermeshing of the alumina rods. This procedure guaranteed the absence of diffusion control in the rate of reactions observed experimentally. All stages of the preparation were monitored with the electron microscope. The kinetics of the ethylene-hydrogen reaction were examined by means of a pulse technique. The number of active sites determined by carbon monoxide titration of the surface was equal to the number of surface atoms as determined by the calculation of the quantities of compounds involved in the synthesis and electron microscope examination. Furthermore, the activity per site depended on the method of preparation, being four times smaller when sodium formate was used as a reducing agent instead of sodium citrate. This may be due to the fact that the shape of particles makes certain crystallographic planes more favorable. Decrease in the size of particles to 56 angstroms produced no effect on catalytic activity beyond that due to the increase in the number of surface atoms. The activity of commercial 5 percent palladium on alumina diluted 100-fold with alumina gave 80.4 percent conversion with propylene and 82.7 percent conversion with ethylene. Thus there was little difference in the behavior of the two olefins.     

Photolytic cleavage of sulfonamide bonds

It has been found that the sulfonamide bond is relatively susceptible to photolytic cleavage. The breakdown was effected either by irradiation with a source having a continuous emission above the wavelengths of 1800 angstroms or by another source emitting principally at 2537 angstroms. Less destruction of the amino acids was seen with the latter relative to the sulfonamide bond cleavage. The cleavage was not effected by irradiation at wavelengths greater than about 3000 angstroms. Side reactions were noted involving decarboxylation, demination, and destruction of certain susceptible amino acids such as tryptophan. In only one case was a product found that arose from cleavage of a carboxamide bond; glycyltyrosine gave glycine and tyrosine upon irradiation. A yield of 75 percent of the corresponding amino acid has been obtained by irradiation of tosylhistidine; yields of 75 to 100 percent have been obtained from sulfamic acid (NH(2)SO(3)H). A qualitative method for identifying sulfonylated amino acids is described.     

Tabashir: an opal of plant origin

A specimen of tabashir, a variety of opal found in bamboo, contained more water but smaller amounts of alkalis and alkaline earths than most opals. It consisted of particles of about 100 angstroms in diameter, linked together in clumps, which appeared in fractured surfaces as irregularities. The tabashir was amorphous, but its microstructure differed from that of silicagel and amorphous opal of inorganic origin.     

Single crystals of transfer RNA: an x-ray diffraction study

Large single crystals of formylmethionyl transfer RNA have been prepared. An x-ray diffraction study shows that the material crystallizes in a hexagonal lattice with a equal to 170 angstroms, c equal to 234 angstroms. The diffraction pattern extends to spacings just under 20 angstroms at present. The crystals are heavily hydrated, containing 88 percent water.     

Crystalline transfer RNA: the three-dimensional Patterson function at 12-angstrom resolution

An orthorhombic form of crystalline formylmethionine transter RNA has been obtained which contains one molecule as the asymmetric unit of the unit cell. Three-dimensional x-ray diffraction data have been collected up to a resolution of 12 angstroms, and from this a Patterson function has been calculated. The function contains an elongated ridge of interatomic vectors parallel to the c-axis of the crystal. Analysis of the function suggests that the molecules are elogated and dimerized in an overlapping antiparrael fashion along the c-axis. The dimer has a length near 109 angstroms and a width of 35 angstroms in one direction. The individual molecular length is approximately 80 angstroms with an irregular cross section measuring 25 by 35 angstrms.     

Polymeric particles of protein insoluble at pH5 from rat liver

A procedure is given for approximating the volumes of small particles of protein insoluble at pH 5. Among particles smaller than 2.08 x 10(7) cubic angstroms the change in size was linear. The distribution of sizes indicated a polymeric relationship among the particles.     

Very heavy solar cosmic rays: energy spectrum and implications for lunar erosion

The energy spectrum of solar cosmic-ray particles of the iron group has been determined for the first time over the energy range from 1 to 100 million electron volts per nucleon by the use of glass removed from the Surveyor 3 spacecraft. The difference between the observed (energy)(-3) spectrum and the limiting spectrum derived previously from tracks in lunar rocks gives an erosion rate of 0 to 2 angstroms per year. High-energy fission of lead, induced by galactic cosmicray protons and alpha particles, has also been observed.     

Crystallography of some lunar plagioclases

Crystals of calcic bytownite from type B rocks have space group I1 with c approximately 14 angstroms. Bytownite crystals from type A rocks are more sodic and have space group C1, c approximately 7 angstroms. Cell parameters of eight bulk feldspar separates from crystalline rocks indicate that the range of angle gamma is about 23 times the standard error of measurement, and its value might be useful for estimation of composition. Cell parameters of seven ilmenites are close to those of pure FeTiO(3).     

Garnet-like structures of high-pressure cadmium germanate and calcium germanate

Crystals of CdGeO(3) grown at a pressure of 65 kilobars are tetragonal and have an ordered, garnet-like crystal structure with cadmium occupying the dodecahedral and octahedral sites, and germanium the octahedral and tetrahedral sites. The crystal structure (a = 12.406 +/- 1 angstroms, c = 12.256 +/- 1 angstroms, and space group 14,/a) has been refined by least-squares analysis to an R (discrepancy index) of 0.073. Two high-pressure phases of CaGeO(3) were synthesized, one isotypic with tetragonal CdGeO(3) (a = 12.514 +/- 3 angstroms, c = 12.358 +/- 3 angstroms), and the other isotypic with perovskite.     

Freeze-fractured Acholeplasma laidlawii membranes: nature of particles observed

Freeze-fracture of Acholeplasma laidlawii membranes from cells incubated in the presence of puromycin or omission of amino acids reveals a decrease in the number of particles between 50 and 100 angstroms in the hydrophobic fracture plane, which strongly suggests that these particles are protein. Additional evidence indicates that they may be involved in substrate transport.     

A Fluorite Isotype of SnO2 and a New Modification of TiO2: Implications for the Earth's Lower Mantle

The existence of a cubic fluorite-type SnO(2) and a hexagonal TiO(2) (which may be related to the fluorite structure) have been demonstrated by an in situ x-ray diffraction study in which a diamond-anvil pressure cell was used after the samples had been heated by a continuous yttrium-aluminum-garnet laser. At room temperature, the lattice parameter for SnO(2) (fluorite) is a = 4.925 +/- 0.005 angstroms and those for TiO(2) (fluorite-related) are a = 9.22 +/- 0.01 angstroms and c = 5.685 +/- 0.006 angstroms at about 250 kilobars. The volume change associated with the transition from rutile to fluorite (or related structure) is about -8 percent for SnO(2) and -10.5 percent for TiO(2) at transition. Upon release of pressure, both the fluorite-type SnO(2) and the TiO(2) reverted to the alpha-PbO(2) structure at room temperature. The hypothesis that the earth's lower mantle is composed of oxide phases might be feasible if it were possible for SiO(2) to possess the fluorite structure or its related forms at high pressure, as shown for SnO(2) and TiO(2) in this study. The oxide hypothesis proposed here differs from that postulated by Birch in that the primary coordination of silicon is 6 for Birch's hypothesis and 8 for the hypothesis presented here.     

Garnet: first occurrence in the lunar rocks

Three grains of almandine-rich garnet isolated from lunar sample 12021 have the composition Alm(70.7)Gro(25.0)Sp(2.7)Pyr(1.6), with cell edge of 11.624 angstroms and refractive index of 1.81. The garnet probably formed late in the crystallization sequence.