Au Substitution Research Articles

Identification of a protein complex that binds to a dodecamer sequence found at the 3' ends of yeast mitochondrial mRNAs.

An activity from Saccharomyces cerevisiae mitochondria was identified that specifically bound to a 12-nucleotide sequence, AAUAA(U/C)AUUCUU, that is a site for processing of pre-mRNAs so as to generate the mature 3' ends of mRNAs. Because processing occurs 3' to the end of the dodecamer site, all mRNAs in yeast mitochondria terminate with that sequence. RNase T1 digestion fragments which terminated precisely at their 3' ends with the dodecamer sequence bound the activity, indicating that mRNAs in vivo would be capable of binding. Gel mobility shift analyses using RNA oligonucleotides showed that binding was reduced by a U-to-A substitution at position 3 of the dodecamer sequence; a C-to-A substitution at position 10 eliminated binding. UV cross-linking identified three polypeptides with approximate molecular masses of 19, 60, and 70 kDa as constituents of the binding activity. These estimates included the contribution of the 32P-labeled RNA oligonucleotide used to tag these polypeptides. An oligonucleotide with a UA-->AU substitution at positions 3 and 4 of the dodecamer site formed complexes deficient in the 19-kDa species, suggesting that binding specificity was inherent to the higher-molecular-weight polypeptides. Assembly of the complex at a dodecamer site on an RNA protected sequences located 5' to the dodecamer site from digestion by a nucleoside triphosphate-dependent 3' exoribonuclease found in yeast mitochondria. Since mitochondrial mRNAs terminate with an intact dodecamer sequence, the binding activity may function in the stabilization of mRNAs in addition to 3'-end formation of mRNAs.

Magnetic and NMR study of valence phase transition in YbIn 1− xT xCu 4 (T = Ag and Au)

The magnetic susceptibility, 115In Knight shift and 63Cu NQR frequency ν Q in YbIn 1− x T x Cu 4 (T = Ag and Au) with x≤0.1 have been measured in order to investigate the valence phase transition at T 4=40 K. For x=0 they exhibit drastic changes at T v. The Ag or Au substitution increases T v and also decreases ν Q, which is mainly ascribed to an increase in its electronic contribution and suggests a change in the 4f and conduction electron hybridization. The effect of the Ag substitution on T v and ν Q is more remarkable, probably because of a heavy fermion character of YbAgCu 4.

Effects of alloying in the Ce(Pt1−xAux)Si heavy fermion, dense Kondo system

Abstract We report the effects of Au substitution in the Heavy Fermion system Ce(Pt 1−x Au x )Si (0≤x≤0.10), invetigated by x-ray diffraction, electrical resistivity, and dc magnetic susceptibility measurements. CePtSi crystallizes in the LaPtSi-type tetragonal structure with 14 1 md space group and with lattice parameters a =0.4197 nm, and c =1.447 nm. The unit cell volume increases with increasing Au concentration, mainly due to an increase in the c lattice parameter. Electrical resistivity and dc magnetic susceptibility are presented for the temperature range 2 to 350K. We find the possibility of additional electronic mass enhancement in Ce(Pt 0.94 Au 0.06 )Si and a strongly compensated moment (1.3ω B ) for x≥0.08, which we attribute to Kondo compensation.

X-ray-diffraction study of a thermomechanically detwinned single crystal of YBa2Cu3O6+x.

A twin-free single crystal of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ has been studied at room temperature and 115 K by x-ray-diffraction analysis. The crystal was grown from an Y-Ba-Cu-O melt in a gold crucible, leading to a 2% substitution of Au for Cu. Twins were removed from the as-grown crystal by a novel thermomechanical process, resulting in an orthorhombic (Pmmm), single-domain crystal. Oxygen positions and occupancies in the Cu-O basal plane have been refined, showing that the O(5) site is completely vacant, and the O(4) atoms are offset from the crystallographic mirror plane positions by 0.15 \AA{} in a zig-zag fashion. Gold, which is a common impurity in crystals grown by the present technique, was found to occupy Cu(1) sites only. Weak superlattice reflections suggest a possible three-dimensional ordering of O and/or Au. To our knowledge, this paper reports the first high-resolution x-ray study of an intentionally detwinned, superconducting ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ single crystal.

Electrical and magnetic properties of U( Pt1− xAux) 3(0 ⩽ x ⩽ 1)

The effect of Au substitution for Pt in the heavy fermion compound UPt 3 is studied with respect to the electronic and magnetic properties. A dramatic increase of ϱ 0 is found as well as the appearence of antiferromagnetism, reminiscent of the Pd or Th substituted systems. Above about 10 at%Au, the resistivity behavior is significantly different from the Pd and Th cases. Resistivity, specific heat and magnetic susceptibility data are also reported for UAu 3

Activation of a ruthenium cluster by a gold centre

Substitution of Au(PPH3) for hydrogen in [Ru4H4(cO)12] incrases the rate of catalytic pent-1-ene isomerisation.

Transformation behavior of PdAuSi metallic glasses

The transformation behavior of roller-quenched amorphous Pd 0.82− x Au x Si 0.18 and Pd 0.835− x Au x Si 0.165 alloys, where x ⩽ 0.10, after rapid heating to temperatures near to or above T g, is reported. The calorimetrically determined glass ( T g) and kinetic crystallization ( T c) temperatures both increased with x up to x ≈ 0.04. With increasing x, at x ⩾ 0.04, T c decreased rapidly while T g varied little. Binary Pd 0.82Si 0.18 alloys crystallized to an fcc phase without apparent composition segregation. The tendency to phase separate at T near T g, as manifested by small- (SAXS) and large-angle X-ray scattering and calorimetry, increased with increasing Au substitution. Pd 0.8Au 0.035Si 0.165 alloy apparently phase separated by a nucleation and growth mechanism, with a growth rate limited by the melt viscosity, to form an fcc phase dispersed in an amorphous phase which later crystallized. Pd 0.74Au 0.08Si 0.18 alloy phase separated initially to two melts, each of which later crystallized in turn. The initial separation behavior was generally consistent with the predictions of the spinodal theory but with some deviation from Cahn's linear relation.