4 research outputs found
Discovery of a nanodiamond-rich layer in the Greenland ice sheet
We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5!106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or high-explosive detonation. This morphology has not been reported previously in cosmic material, but has been observed in terrestrial impact material. This is the first highly enriched, discrete layer of NDs observed in glacial ice anywhere, and its presence indicates that ice caps are important archives of ET events of varying magnitudes. Using a preliminary ice chronology based on oxygen isotopes and dust stratigraphy, the ND-rich layer appears to be coeval with ND abundance peaks reported at numerous North American sites in a sedimentary layer, the Younger Dryas boundary layer (YDB), dating to 12.9 0.1 ka. However, more investigation is needed to confirm this association
Evidence of Cosmic Impact at Abu Hureyra, Syria at the Younger Dryas Onset (similar to 12.8 ka): High-temperature melting at > 2200 degrees C
Investigation of 1,3,5-Triaza-7-phosphaadamantane-Stabilized Silver Nanoparticles as Catalysts for the Hydration of Benzonitriles and Acetone Cyanohydrin
A straightforward
synthesis of water-soluble silver nanoparticles
stabilized by PTA (1,3,5-triaza-7-phosphaadamantane, a water-soluble
phosphine ligand) ligands was developed. The nanoparticles were thoroughly
characterized by ultraviolet–visible spectroscopy, <sup>31</sup>P nuclear magnetic resonance spectroscopy, transmission electron
microscopy,
and energy dispersive X-ray spectroscopy. The effectiveness of the
Ag–PTA nanoparticles as catalysts for the hydration of nitriles
to amides in water under mild conditions was explored using a series
of substituted benzonitriles and cyanohydrins. In comparison to all
previously investigated homogeneous catalysts, the Ag–PTA system
excels at cyanohydrin hydration, including acetone cyanohydrin hydration.
Cyanohydrins are in equilibrium with small amounts of cyanide, and
experiments revealed that the Ag–PTA nanoparticles disassemble
in the presence of cyanide. The catalyst solution, which is proposed
to contain a soluble AgÂ(CN)<sub><i>n</i></sub><sup>1–<i>n</i></sup> complex (with <i>n</i> likely equal to
2),
remained unpoisoned even in the presence of 10 equiv of cyanide.
It is suggested that no cyanide poisoning occurs because the AgÂ(I)
complex is labile. Overall, the Ag–PTA catalyst system (a)
is not poisoned by cyanide, (b) catalyzes hydration reactions under
mild conditions (in air and at relatively low temperatures), (c) is
easily synthesized from cheap starting materials, and (d) can hydrate
heteroaromatics in good yields. The recognition of the importance
of labile metal cyanide bonding represents an important step forward
in catalyst design for improving the catalytic hydration of acetone
cyanohydrin