Synthesis of Linear Acetylenic Carbon: The "sp" Carbon Allotrope

A carbon allotrope based on "sp" hybridization containing alternating triple and single bonds (an acetylenic or linear carbon allotrope) has been prepared. Studies of small (8 to 28 carbon atoms) acetylenic carbon model compounds show that such species are quite stable (130 degrees to 140 degrees C) provided that nonreactive terminal groups or end caps (such as tert-butyl or trifluoromethyl) are present to stabilize these molecules against further reactions. In the presence of end capping groups, laser-based synthetic techniques similar to those normally used to generate fullerenes, produce thermally stable acetylenic carbon species capped with trifluoromethyl or nitrile groups with chain lengths in excess of 300 carbon atoms. Under these conditions, only a negligible quantity of fullerenes is produced. Acetylenic carbon compounds are not particularly moisture or oxygen sensitive but are moderately light sensitive.     

Irreversible inhibition of nuclear exoribonuclease by thymidine-3'-fluorophosphate and p-haloacetamidophenyl nucleotides

Exoribonuclease purified from Ehrlich ascites tumor cell nuclei and in intact HeLa cell nuclei is irreversibly inactivated by tow concentrations of p-bromo- and p-iodoacetamidophenyl nucleotides and by thymidine-3'-fluorophosphate. Iodoacetate, bromoacetate, and thymidine-5'-fluorophosphate do not affect the enzyme. Although p-haloacetamidophenyl nucleotides inactivate ribonucleic acid polymerase of isolated HeLa cell nuclei, thymidine-3'-fluorophosphate does not affect the activity of this enzyme in vitro.     

Mitochondrial-satellite and circular DNA filaments in yeast

Mitochondrial DNA of Saccharomyces cerevisiae contains a satellite DNA (density, 1.682) that appears to exist as open-ended filaments at least 5 microns long. DNA from intact cells contains circular filaments whose lengths vary from 0.5 to 7 microns, with a great majority at 1.95 microns. The circular DNA has a density similar to that of the major nuclear peak (1.697). When heat-denatured mitochondrial-satellite DNA is renatured, it cross-links to form a molecule that is larger than the native molecule. The formation of cross-links results in hypersharpening of the density profiles in cesium chloride and also leads to failure to pass Millipore filter paper.     

The structure and receptor binding properties of the 1918 influenza hemagglutinin

The 1918 influenza pandemic resulted in about 20 million deaths. This enormous impact, coupled with renewed interest in emerging infections, makes characterization of the virus involved a priority. Receptor binding, the initial event in virus infection, is a major determinant of virus transmissibility that, for influenza viruses, is mediated by the hemagglutinin (HA) membrane glycoprotein. We have determined the crystal structures of the HA from the 1918 virus and two closely related HAs in complex with receptor analogs. They explain how the 1918 HA, while retaining receptor binding site amino acids characteristic of an avian precursor HA, is able to bind human receptors and how, as a consequence, the virus was able to spread in the human population.     

Organic Glasses: A New Class of Photorefractive Materials

The performance of amorphous organic photorefractive (PR) materials in applications such as optical data storage is generally limited by the concentration of active molecules (chromophores) that can be incorporated into the host without forming a crystalline material with poor optical quality. In polymeric PR systems described previously, performance has been limited by the necessity of devoting a large fraction of the material to inert polymer and plasticizing components in order to ensure compositional stability. A new class of organic PR materials composed of multifunctional glass-forming organic chromophores is described that have long-term stability and greatly improved PR properties.     

The Origin of the Great Bend of the Nile from SIR-C/X-SAR Imagery

The course of the Nile in northern Sudan follows a contorted path through Precambrian bedrock. Radar imagery shows that basement structures control the river's course in this region. Northward-flowing segments follow Precambrian fabrics, whereas east-west segments follow faults of much younger age. These faults may reflect recent uplift of the Nubian Swell and deflection of the river to the southwest to form the great bend of the Nile.