377 research outputs found
Circularly polarised luminescence spectroscopy of chiral europium (III) complexes
Circularly Polarised Luminescence (CPL) spectroscopy detects the differential emission of left and right circularly polarised light from luminescent chiral species, and so can be thought of as the emission analogue of circular dichroism spectroscopy. The circularly polarised emission of chiral europium complexes derived from the 12-ane-4 macrocycle cyclen, (examples of which are shown below) have been recorded using this technique. (Fig. 10701)
These and similar complexes have shown an ability to bind to biologically important anions such as carbonate and phosphate in aqueous media and are able to report this event by a change in luminescence. These interactions have been investigated by monitoring the emitted circularly polarised light using the technique described and the binding of the substrate is clearly signalled. Typical CPL spectra of the europium complexes will be presented as will the binding study results and a detailed account of how the spectra is obtained
A Second Double-Stranded RNA Virus from Yeast
AbstractTwo double-stranded RNA viruses exist as permanent persistent infections of the yeastSaccharomyces cerevisiae:ScVL1 and ScVLa. Both belong to the Totiviridae, which include a number of fungal and protozoan double-stranded RNA viruses. Although ScVL1 and ScVLa share the same genomic organization and mode of expression and coexist in the same cells, they show no evidence of recombination: with one limited exception, sequence conservation is detectable only in regions conserved in all totiviruses. Both have two open reading frames on their single essential RNAs:cap(encoding a capsid polypeptide) andpol(encoding an RNA-dependent RNA polymerase). The ScVLa virus, like ScVL1, appears to express its Pol domain by a −1 translational frameshift
Adsorption of benzene on Si(100) from first principles
Adsorption of benzene on the Si(100) surface is studied from first
principles. We find that the most stable configuration is a
tetra--bonded structure characterized by one C-C double bond and four
C-Si bonds. A similar structure, obtained by rotating the benzene molecule by
90 degrees, lies slightly higher in energy. However, rather narrow wells on the
potential energy surface characterize these adsorption configurations. A
benzene molecule impinging on the Si surface is most likely to be adsorbed in
one of three different di--bonded, metastable structures, characterized
by two C-Si bonds, and eventually converts into the lowest-energy
configurations. These results are consistent with recent experiments.Comment: 4 pages, RevTex, 2 PostScript gzipped figure
Prevalence of oxygen defects in an in-plane anisotropic transition metal dichalcogenide
Atomic scale defects in semiconductors enable their technological
applications and realization of novel quantum states. Using scanning tunneling
microscopy and spectroscopy complemented by ab-initio calculations we determine
the nature of defects in the anisotropic van der Waals layered semiconductor
ReS. We demonstrate the in-plane anisotropy of the lattice by directly
visualizing chains of rhenium atoms forming diamond-shaped clusters. Using
scanning tunneling spectroscopy we measure the semiconducting gap in the
density of states. We reveal the presence of lattice defects and by comparison
of their topographic and spectroscopic signatures with ab initio calculations
we determine their origin as oxygen atoms absorbed at lattice point defect
sites. These results provide an atomic-scale view into the semiconducting
transition metal dichalcogenides, paving the way toward understanding and
engineering their properties.Comment: 9 pages, 4 figures; Supp 5 pages, 4 figure
Spontaneous magnetization of aluminum nanowires deposited on the NaCl(100) surface
We investigate electronic structures of Al quantum wires, both unsupported
and supported on the (100) NaCl surface, using the density-functional theory.
We confirm that unsupported nanowires, constrained to be linear, show
magnetization when elongated beyond the equilibrium length. Allowing ions to
relax, the wires deform to zig-zag structures with lower magnetization but no
dimerization occurs. When an Al wire is deposited on the NaCl surface, a
zig-zag geometry emerges again. The magnetization changes moderately from that
for the corresponding unsupported wire. We analyse the findings using electron
band structures and simple model wires.Comment: submitted to PHys. Rev.
Folded cavity SOI microring sensors for high sensitivity and real time measurement of biomolecular binding.
We demonstrate folded waveguide ring resonators for biomolecular sensing. We show that extending the ring cavity length increases the resonator quality factor, and thereby enhances the sensor resolution and minimum level of detection, while at the same time relaxing the tolerance on the coupling conditions to provide stable and large resonance contrast. The folded spiral path geometry allows a 1.2 mm long ring waveguide to be enclosed in a 150 microm diameter sensor area. The spiral cavity resonator is used to monitor the streptavidin protein binding with a detection limit of approximately 3 pg/mm(2), or a total mass of approximately 5 fg. The real time measurements are used to analyze the kinetics of biotin-streptavidin binding
Silicon Atomic Quantum Dots Enable Beyond-CMOS Electronics
We review our recent efforts in building atom-scale quantum-dot cellular
automata circuits on a silicon surface. Our building block consists of silicon
dangling bond on a H-Si(001) surface, which has been shown to act as a quantum
dot. First the fabrication, experimental imaging, and charging character of the
dangling bond are discussed. We then show how precise assemblies of such dots
can be created to form artificial molecules. Such complex structures can be
used as systems with custom optical properties, circuit elements for
quantum-dot cellular automata, and quantum computing. Considerations on
macro-to-atom connections are discussed.Comment: 28 pages, 19 figure
Electronic Transport in a Three-dimensional Network of 1-D Bismuth Quantum Wires
The resistance R of a high density network of 6 nm diameter Bi wires in
porous Vycor glass is studied in order to observe its expected semiconductor
behavior. R increases from 300 K down to 0.3 K. Below 4 K, where R varies
approximately as ln(1/T), the order-of-magnitude of the resistance rise, as
well as the behavior of the magnetoresistance are consistent with localization
and electron-electron interaction theories of a one-dimensional disordered
conductor in the presence of strong spin-orbit scattering. We show that this
behaviour and the surface-enhanced carrier density may mask the proposed
semimetal-to-semiconductor transition for quantum Bi wires.Comment: 19 pages total, 4 figures; accepted for publication in Phys. Rev.
Functional analysis of the SRV-1 RNA frameshifting pseudoknot
Simian retrovirus type-1 uses programmed ribosomal frameshifting to control expression of the Gag-Pol polyprotein from overlapping gag and pol open-reading frames. The frameshifting signal consists of a heptanucleotide slippery sequence and a downstream-located 12-base pair pseudoknot. The solution structure of this pseudoknot, previously solved by NMR [Michiels,P.J., Versleijen,A.A., Verlaan,P.W., Pleij,C.W., Hilbers,C.W. and Heus,H.A. (2001) Solution structure of the pseudoknot of SRV-1 RNA, involved in ribosomal frameshifting. J. Mol. Biol., 310, 1109–1123] has a classical H-type fold and forms an extended triple helix by interactions between loop 2 and the minor groove of stem 1 involving base–base and base–sugar contacts. A mutational analysis was performed to test the functional importance of the triple helix for −1 frameshifting in vitro. Changing bases in L2 or base pairs in S1 involved in a base triple resulted in a 2- to 5-fold decrease in frameshifting efficiency. Alterations in the length of L2 had adverse effects on frameshifting. The in vitro effects were well reproduced in vivo, although the effect of enlarging L2 was more dramatic in vivo. The putative role of refolding kinetics of frameshifter pseudoknots is discussed. Overall, the data emphasize the role of the triple helix in −1 frameshifting
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