High-valent organometallic copper and palladium in catalysis

Copper and palladium catalysts are critically important in numerous commercial chemical processes. Improvements in the activity, selectivity and scope of these catalysts could drastically reduce the environmental impact, and increase the sustainability, of chemical reactions. One rapidly developing strategy for achieving these goals is to use 'high-valent' organometallic copper and palladium intermediates in catalysis. Here we describe recent advances involving both the fundamental chemistry and the applications of these high-valent metal complexes in numerous synthetically useful catalytic transformations.     

Microring-Assisted Coupling Between Dissimilar Waveguides

The use of microring resonators to assist in the evanescent field coupling between dissimilar waveguides is proposed and analyzed. Theoretical analysis based on the coupled mode theory and nu-merical example show that complete cross power transfers can be obtained near the microring resonances. Applications of the device include power dividers, low-power thermo-optic or electro-optic switches, and modulators.     

Low strength of deep San Andreas fault gouge from SAFOD core

The San Andreas fault accommodates 28-34 mm?yr(-1) of right lateral motion of the Pacific crustal plate northwestward past the North American plate. In California, the fault is composed of two distinct locked segments that have produced great earthquakes in historical times, separated by a 150-km-long creeping zone. The San Andreas Fault Observatory at Depth (SAFOD) is a scientific borehole located northwest of Parkfield, California, near the southern end of the creeping zone. Core was recovered from across the actively deforming San Andreas fault at a vertical depth of 2.7 km (ref. 1). Here we report laboratory strength measurements of these fault core materials at in situ conditions, demonstrating that at this locality and this depth the San Andreas fault is profoundly weak (coefficient of friction, 0.15) owing to the presence of the smectite clay mineral saponite, which is one of the weakest phyllosilicates known. This Mg-rich clay is the low-temperature product of metasomatic reactions between the quartzofeldspathic wall rocks and serpentinite blocks in the fault. These findings provide strong evidence that deformation of the mechanically unusual creeping portions of the San Andreas fault system is controlled by the presence of weak minerals rather than by high fluid pressure or other proposed mechanisms. The combination of these measurements of fault core strength with borehole observations yields a self-consistent picture of the stress state of the San Andreas fault at the SAFOD site, in which the fault is intrinsically weak in an otherwise strong crust.     

Current status of cutthroat trout subspecies in the western Bonneville Basin

Recent discoveries of native cutthroat trout populations in desert mountain ranges on the western fringe of the Bonneville Basin have prompted intensified management efforts by state and federal agencies. Analysis of Snake Valley cutthroat specimens in Trout Creek, Deep Creek Mountain Range, Utah, indicate this is a pure strain of the trout which once inhabited Pleistocene Lake Bonneville and which was thought to be extinct in Utah. The Snake Valley cutthroat is similar to Salmo clarki utah of the eastern Bonneville Basin; however, electrophoretic and morphomeristic analysis show unique genetic differences brought about by long - term isolation (8,000 years) from the remainder of the Bonneville Basin cutthroat. This cutthroat is a common ancestor to several other limited cutthroat populations within the basin in Nevada. In May 1977 the BLM withdrew from mineral entry about 27,000 acres within the Deep Creek Mountains for protection of this salmonid cutthroat and other unique resources on the range. Results of 1977 stream surveys on the Pilot Peak Mountain Range, Utah, indicate the presence of the threatened Lahontan cutthroat, Salmo clarki henshawi, in one isolated stream.     

Transposition of hAT elements links transposable elements and V(D)J recombination

Transposons are DNA sequences that encode functions that promote their movement to new locations in the genome. If unregulated, such movement could potentially insert additional DNA into genes, thereby disrupting gene expression and compromising an organism's viability. Transposable elements are classified by their transposition mechanisms and by the transposases that mediate their movement. The mechanism of movement of the eukaryotic hAT superfamily elements was previously unknown, but the divergent sequence of hAT transposases from other elements suggested that these elements might use a distinct mechanism. Here we have analysed transposition of the insect hAT element Hermes in vitro. Like other transposons, Hermes excises from DNA via double-strand breaks between the donor-site DNA and the transposon ends, and the newly exposed transposon ends join to the target DNA. Interestingly, the ends of the donor double-strand breaks form hairpin intermediates, as observed during V(D)J recombination, the process which underlies the combinatorial formation of antigen receptor genes. Significant similarities exist in the catalytic amino acids of Hermes transposase, the V(D)J recombinase RAG, and retroviral integrase superfamily transposases, thereby linking the movement of transposable elements and V(D)J recombination.