Publications

Abstract The three‐component gold‐catalyzed coupling of terminal alkenes with arylboronic acids and oxygen nucleophiles is described.

Syntheses of high-valent open-chain metallostannylene hydride complexes from transition metal polyhydride complexes and aryl-substituted amidostannylenes are reported. The reaction of (^MeBDI^Dipp)IrH₄ (^MeBDI^Dipp = (Dipp)NC(Me)CH(Me)CN(Dipp); Dipp = 2,6-diisopropylphenyl) with DMPSnN(SiMe₃)₂ (DMP = C₆H₃-2,6-Mes₂, Mes = mesityl) gives access to metallostannylene (^MeBDI^Dipp)IrH₃SnDMP (<b>1</b>) with HN(SiMe₃)₂ as the byproduct. Similarly, treatment of Cp*IrH₄ (Cp* = η⁵-C₅Me₅) with DMPSnN(SiMe₃)₂ leads to the formation of Cp*IrH₃SnDMP (<b>2</b>). In contrast to <b>1</b>, <b>2</b> cleanly reacts with a second equivalent of DMPSnN(SiMe₃)₂, allowing for the synthesis of bis(metallostannylene) Cp*IrH₂(SnDMP)₂ (<b>3</b>). Additionally, the synthesis and characterization of two new amidostannylenes DMPSn[N(Dipp)(SiMe₃)] (<b>4</b>) and TripSn[N(Dipp)(SiMe₃)] (<b>5</b>; Trip = 2,4,6-triisopropylphenyl) is presented. While the reaction of Cp*IrH₄ with <b>4</b> represents an alternative route to <b>2</b>, treatment of (^MeBDI^Dipp)IrH₄ with <b>5</b> yields the amidostannylene complex (^MeBDI^Dipp)(H)₂Ir═Sn(Trip){N(Dipp)(SiMe₃)} (<b>6</b>) with concomitant release of H₂, rendering stannylene coordination a reaction pathway that competes with Sn-N bond cleavage and metallostannylene formation. Within the broader context of transition metal-main group element compounds, metallostannylene formation is characterized as a formal deprotonation of the transition metal polyhydride complex by the amidostannylene. Notably, the ambiphilicity of amidostannylenes, which distinguishes them from tetravalent amidostannanes, appears to be essential for efficient Ir-Sn bond formation.

Summary The gravitropism defective 2 ( grv2 ) mutants of Arabidopsis thaliana were previously characterized as exhibiting shoot agravitropism resulting from mutations in a homolog of the Caenorhabditis elegans RECEPTOR‐MEDIATED ENDOCYTOSIS‐8 ( RME‐8 ) gene, which is required in C. elegans for endocytosis. A fluorescent protein fusion to the GRV2 protein localized to endosomes in transgenic plants, and vacuolar morphology was altered in grv2 mutants. A defect in vacuolar membrane dynamics provides a mechanistic explanation for the gravitropic defect, and may also account for the presence of an enlarged vacuole in early embryos, together with a nutrient requirement during seedling establishment. The GRV2‐positive endosomes were sensitive to Wortmannin but not brefeldin A (BFA), consistent with GRV2 operating late in the endocytic pathway, prior to delivery of vesicles to the central vacuole. The specific enlargement of GRV2:YFP structures by Wortmannin, together with biochemical data showing that GRV2 co‐fractionates with pre‐vacuolar markers such as PEP12/SYP21, leads us to conclude that in plants GRV2/RME‐8 functions in vesicle trafficking from the multivesicular body/pre‐vacuolar compartment to the lytic vacuole.

We present a comprehensive multiwavelength temporal and spectral analysis of the `fast rise exponential decay' GRB 070419A. The early-time emission in the γ-ray and X-ray bands can be explained by a central engine active for at least 250 s, while at late times the X-ray light curve displays a simple power-law decay. In contrast, the observed behaviour in the optical band is complex (from 102 up to 106 s). We investigate the light-curve behaviour in the context of the standard forward/reverse shock model; associating the peak in the optical light curve at ~450 s with the fireball deceleration time results in a Lorenz factor Γ ~ 350 at this time. In contrast, the shallow optical decay between 450 and 1500 s remains problematic, requiring a reverse shock component whose typical frequency is above the optical band at the optical peak time for it to be explained within the standard model. This predicts an increasing flux density for the forward shock component until t ~ 4 × 106 s, inconsistent with the observed decay of the optical emission from t ~ 104 s. A highly magnetized fireball is also ruled out due to unrealistic microphysic parameters and predicted light-curve behaviour that is not observed. We conclude that a long-lived central engine with a finely tuned energy injection rate and a sudden cessation of the injection is required to create the observed light curves, consistent with the same conditions that are invoked to explain the plateau phase of canonical X-ray light curves of γ-ray bursts.

The manipulation of photons in structures smaller than the wavelength of light is central to the development of nanoscale integrated photonic systems for computing, communications, and sensing. We assemble small groups of freestanding, chemically synthesized nanoribbons and nanowires into model structures that illustrate how light is exchanged between subwavelength cavities made of three different semiconductors. The coupling strength of the optical linkages formed when nanowires are brought into contact depends both on their volume of interaction and angle of intersection. With simple coupling schemes, lasing nanowires can launch coherent pulses of light through ribbon waveguides that are up to a millimeter in length. Also, interwire coupling losses are low enough to allow light to propagate across several right-angle bends in a grid of crossed ribbons. The fraction of the guided wave traveling outside the wire/ribbon cavities is used to link nanowires through space and to separate colors within multiribbon networks. In addition, we find that nanoribbons function efficiently as waveguides in liquid media and provide a unique means for probing molecules in solution or in proximity to the waveguide surface. Our results lay the spadework for photonic devices based on assemblies of active and passive nanowire elements and presage the use of nanowire waveguides in microfluidics and biology.

Abstract — The electron–hole (EH) bilayer tunneling field-effect transistor promises to eliminate heavy-doping band tails enabling a smaller subthreshold swing voltage. Nevertheless, the electrostatics of a thin structure must be optimized for gate efficiency. We analyze the tradeoff between gate efficiency versus ON-state conductance to find the optimal device design. Once the EH bilayer is optimized for a given ON-state conductance, Si, Ge, and InAs all have similar gate efficiency, around 40%–50%. Unlike Si and Ge, only the InAs case allows a manageable work function difference for EH bilayer transistor operation. Index Terms — Electron–hole (EH) bilayer, quantization, semiconductor device modeling, tunneling, tunneling field-effect transistor (TFET). I.