UV irradiation of polycyclic aromatic hydrocarbons in ices: production of alcohols, quinones, and ethers.
Polycyclic aromatic hydrocarbons (PAHs) in water ice were exposed to ultraviolet (UV) radiation under astrophysical conditions, and the products were analyzed by infrared spectroscopy and mass spectrometry. Peripheral carbon atoms were oxidized, producing aromatic alcohols, ketones, and ethers, and reduced, producing partially hydrogenated aromatic hydrocarbons, molecules that account for the interstellar 3.4-micrometer emission feature. These classes of compounds are all present in carbonaceous meteorites. Hydrogen and deuterium atoms exchange readily between the PAHs and the ice, which may explain the deuterium enrichments found in certain meteoritic molecules. This work has important implications for extraterrestrial organics in biogenesis. (+info)
Freeze-fracture replication of organized tissue without cryoprotection.
Fresh pieces of rat liver and pancreas were rapidly frozen without prior chemical fixation or cryoprotection, and replicated folloing freeze-fracture. Replicas revealed small peripheral areas free of ice crystals or damage and, within such areas, general ultrastructural morphology was essentially similar to that seen in conventionally processed material. On fracture faces of plasma and nuclear membranes a population of less prominent particles in addition to conventional membrane-associated particles was seen, and smooth areas devoid of particles of any type were seen on some nuclear membranes. These smooth areas did not appear to be similar to smooth areas allegedly arising as artifacts of conventional processing. Tight junctions and gap junctions appeared as they do in cryoprotected specimens. The results provide a base-line for assessing the possible effects of processing steps or agents on the ultrastructure of organized tissues as revealed in freeze-fracture replicas. (+info)
Cryoelectron microscopy of a nucleating model bile in vitreous ice: formation of primordial vesicles.
Because gallstones form so frequently in human bile, pathophysiologically relevant supersaturated model biles are commonly employed to study cholesterol crystal formation. We used cryo-transmission electron microscopy, complemented by polarizing light microscopy, to investigate early stages of cholesterol nucleation in model bile. In the system studied, the proposed microscopic sequence involves the evolution of small unilamellar to multilamellar vesicles to lamellar liquid crystals and finally to cholesterol crystals. Small aliquots of a concentrated (total lipid concentration = 29.2 g/dl) model bile containing 8.5% cholesterol, 22.9% egg yolk lecithin, and 68.6% taurocholate (all mole %) were vitrified at 2 min to 20 days after fourfold dilution to induce supersaturation. Mixed micelles together with a category of vesicles denoted primordial, small unilamellar vesicles of two distinct morphologies (sphere/ellipsoid and cylinder/arachoid), large unilamellar vesicles, multilamellar vesicles, and cholesterol monohydrate crystals were imaged. No evidence of aggregation/fusion of small unilamellar vesicles to form multilamellar vesicles was detected. Low numbers of multilamellar vesicles were present, some of which were sufficiently large to be identified as liquid crystals by polarizing light microscopy. Dimensions, surface areas, and volumes of spherical/ellipsoidal and cylindrical/arachoidal vesicles were quantified. Early stages in the separation of vesicles from micelles, referred to as primordial vesicles, were imaged 23-31 min after dilution. Observed structures such as enlarged micelles in primordial vesicle interiors, segments of bilayer, and faceted edges at primordial vesicle peripheries are probably early stages of small unilamellar vesicle assembly. A decrease in the mean surface area of spherical/ellipsoidal vesicles was correlated with the increased production of cholesterol crystals at 10-20 days after supersaturation by dilution, supporting the role of small unilamellar vesicles as key players in cholesterol nucleation and as cholesterol donors to crystals. This is the first visualization of an intermediate structure that has been temporally linked to the development of small unilamellar vesicles in the separation of vesicles from micelles in a model bile and suggests a time-resolved system for further investigation. (+info)
Hydrogen peroxide on the surface of Europa.
Spatially resolved infrared and ultraviolet wavelength spectra of Europa's leading, anti-jovian quadrant observed from the Galileo spacecraft show absorption features resulting from hydrogen peroxide. Comparisons with laboratory measurements indicate surface hydrogen peroxide concentrations of about 0.13 percent, by number, relative to water ice. The inferred abundance is consistent with radiolytic production of hydrogen peroxide by intense energetic particle bombardment and demonstrates that Europa's surface chemistry is dominated by radiolysis. (+info)
The global topography of Mars and implications for surface evolution.
Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The topography of Tharsis consists of two broad rises. Material excavated from Hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary. The present topography has three major drainage centers, with the northern lowlands being the largest. The two polar cap volumes yield an upper limit of the present surface water inventory of 3.2 to 4.7 million cubic kilometers. (+info)
Topography of the lunar poles from radar interferometry: a survey of cold trap locations.
Detailed topographic maps of the lunar poles have been obtained by Earth-based radar interferometry with the 3.5-centimeter wavelength Goldstone Solar System Radar. The interferometer provided maps 300 kilometers by 1000 kilometers of both polar regions at 150-meter spatial resolution and 50-meter height resolution. Using ray tracing, these digital elevation models were used to locate regions that are in permanent shadow from solar illumination and may harbor ice deposits. Estimates of the total extent of shadowed areas poleward of 87.5 degrees latitude are 1030 and 2550 square kilometers for the north and south poles, respectively. (+info)
Effects of cryoprotectants and ice-seeding temperature on intracellular freezing and survival of human oocytes.
The accurate determination of the freezing conditions that promote intracellular ice formation (IIF) is crucial for designing cryopreservation protocols for cells. In this paper, the range of temperatures at which IIF occurs in human oocytes was determined. Fresh oocytes with a germinal vesicle, failed-to-fertilize (metaphase I and metaphase II stages) and polyspermic eggs were used for this study. The occurrence of IIF was first visualized at a cooling rate of 120 degrees C/min using a programmable thermal microscope stage connected to a videomicroscope. Then, with a cooling rate of 0.2 degrees C/min, the seeding temperature of the extracellular ice was modified to decrease the incidence of IIF and increase the survival rate of frozen-thawed human oocytes. After adding different cryoprotectants, the median temperature of IIF (TMED) was decreased by approximately 23 degrees C in mouse and only by approximately 6.5 degrees C in human oocytes. Using 1.5 M propylene glycol and seeding temperatures of -8.0, -6.0 and -4.5 degrees C, the incidence of IIF was 22/28 (78%), 8/24 (33%) and 0/33 (0%) and the 24 h post-thaw survival rate was 10/31(32%), 19/34 (56%) and 52/56 (93%) respectively. The results show that IIF occurs more readily in human oocytes, and that ice seeding between -6 degrees C and -8 degrees C triggers IIF in a large number of human oocytes. Undesirable IIF can be prevented and survival rates maximized by raising the seeding temperature as close as possible to the melting point of the solution, which in our instrument was -4.5 degrees C. (+info)
Diversity of Holocene life forms in fossil glacier ice.
Studies of biotic remains of polar ice caps have been limited to morphological identification of plant pollen and spores. By using sensitive molecular techniques, we now demonstrate a much greater range of detectable organisms; from 2000- and 4000-year-old ice-core samples, we obtained and characterized 120 clones that represent at least 57 distinct taxa and reveal a diversity of fungi, plants, algae, and protists. The organisms derive from distant sources as well as from the local arctic environment. Our results suggest that additional taxa may soon be readily identified, providing a plank for future studies of deep ice cores and yielding valuable information about ancient communities and their change over time. (+info)