Ultrafast bond softening in bismuth: mapping a solid's interatomic potential with X-rays

Intense femtosecond laser excitation can produce transient states of matter that would otherwise be inaccessible to laboratory investigation. At high excitation densities, the interatomic forces that bind solids and determine many of their properties can be substantially altered. Here, we present the detailed mapping of the carrier density-dependent interatomic potential of bismuth approaching a solid-solid phase transition. Our experiments combine stroboscopic techniques that use a high-brightness linear electron accelerator-based x-ray source with pulse-by-pulse timing reconstruction for femtosecond resolution, allowing quantitative characterization of the interatomic potential energy surface of the highly excited solid.     

Receptors: localization and specificity of binding of serotonin in the central nervous system

Formation of a Schiff base between the ethylamine residue of serotonin and an appropriate carbonyl residue at the receptor site may be among the forces holding serotonin onto the receptor. Reduction of this imine may provide a means of permanently labeling receptors as a preliminary to their isolation.     

Striatal nondopaminergic neurons: possible involvement in feeding and drinking behavior

Intracaudate injections of kainic acid destroy striatal neurons containing acetylcholine and gamma-aminobutyric acid but leave dopaminergic nerve terminals in this brain region intact. Rats injected with the drug are aphagic and adipsic, and have other behavioral abnormalities strikingly similar to those seen in animals with lesions in the dopaminergic nigrostriatal bundle.     

Primary structure of the beta subunit of the DHP-sensitive calcium channel from skeletal muscle

Complementary DNAs for the beta subunit of the dihydropyridine-sensitive calcium channel of rabbit skeletal muscle were isolated on the basis of peptide sequences derived from the purified protein. The deduced primary structure is without homology to other known protein sequences and is consistent with the beta subunit being a peripheral membrane protein associated with the cytoplasmic aspect of the sarcolemma. The protein contains sites that might be expected to be preferentially phosphorylated by protein kinase C and guanosine 3',5'-monophosphate-dependent protein kinase. A messenger RNA for this protein appears to be expressed in brain.     

Mineral inclusions in diamond: temperature and pressure of equilibration

Two distinct suites of minerals included in natural diamond occur and probably represent different physical and chemical conditions during diamond growth. Minerals of the ultramafic suite appear to have equilibrated in the range 1000 degrees to 1300 degrees C between 45 and 65 kilobars, whereas the temperature range for minerals of the eclogitic suite is 850 degrees to 1250 degrees C. At present, models relating the partitioning of magnesium and iron between coexisting phases are not sufficiently rigorous to determine a value for the pressure of equilibration of these eclogitic suite inclusions.     

Optically active carbon: kinetic resolution of c76 by asymmetric osmylation

The chiral fullerene C(76) was kinetically resolved by asymmetric osmylation providing an example of an optically active allotrope of a pure element. C(76) recovered from the treatment of racemic C(76) with OsO(4) and a chiral alkaloid ligand, showed a specific rotation [alpha](D) of -4000 degrees (> 97 percent enantiomeric excess) and a circular dichroism spectrum corresponding to the ultraviolet spectrum. Regenerated C(76) formed by reducing the asymmetrically osmylated C(76) with SnCl(2) was enriched in the opposite enantiomer. Analysis of the local curvature of the C(76) molecule indicated that OsO(4) should selectively add to 2 of the 30 types of bonds in C(76). This regioselectivity was supported chromatographically and interpreted in terms of the kinetic resolution.     

Ore metals through geologic history

The ores of chromite, nickel, copper, and zinc show a wide distribution over geologic time, but those of iron, titanium, lead, uranium, gold, silver, molybdenum, tungsten, and tin are more restricted. Many of the limitations to specific time intervals are probably imposed by the evolving tectonic history of Earth interacting with the effects of the biomass on the evolution of the earth's s surface chemistry. Photosynthetic generation of free oxygen and "carbon" contributes significantlly to the diversity of redox potentials in both sedimentary and igneous-related processes of ore formation, influencing the selection of metals at the source, during transport, and at the site of ore deposition.