Temperature dependence of electric field noise above gold surfaces

Electric field noise from fluctuating patch potentials is a significant problem for a broad range of precision experiments, including trapped ion quantum computation and single spin detection. Recent results demonstrated strong suppression of this noise by cryogenic cooling, suggesting an underlying thermal process. We present measurements characterizing the temperature and frequency dependence of the noise from 7 to 100 K, using a single Sr+ ion trapped 75 mum above the surface of a gold plated surface electrode ion trap. The noise amplitude is observed to have an approximate 1/f spectrum around 1 MHz, and grows rapidly with temperature as T;{beta} for beta from 2 to 4. The data are consistent with microfabricated cantilever measurements of noncontact friction but do not extrapolate to the dc measurements with neutral atoms or contact potential probes.     

The preparation of monitors and comparators for k0-INAA using standard solutions

Journal of Radioanalytical and Nuclear Chemistry - The methodology adopted at the Laboratory of Analytical Techniques of Instituto Peruano de Energía Nuclear for preparation of monitors and...     

A comparison of 2-D chromatography separations using UV and (18)O quantification of proteins in similar proteomes

Proteins present in two mitochondria preparations were separated by 2-D chromatography using the ProteomeLab PF-2D Protein Fractional System, protein fractionation in two dimensions (PF-2D). The proteins in each first-dimension fraction were determined by trypsinization and LC-MS/MS. Chromatography peaks were quantified by UV detection using the "Mapping Tools" software (Beckman). The proteins present in UV detected peaks were trypsinized and identified by automated MS/MS sequencing. Relative amounts of the proteins present in the equivalent peak for each sample were assessed by comparison of the intensities of the constituent peptides and a predicted PF-2D value was calculated from the total ion count (TIC) for each peptide. Relative quantification for (18)O labeled peptides was performed using the ZoomQuant (v1.43b) software [1, 2]. We found that the chromatography peaks detected by UV generally contained several proteins. Using (18)O labeling we determined that in each peak the ratios of the constituent proteins were different. When these ratios were normalized using the TIC to account for abundance, the resulting ratio corresponded to that determined by UV. The predicted value for the PF-2D score corresponded to the observed value for each peak irrespective of the number or proteins detected.     

Direct syntheses of Lan+1NinO3n+1 phases (n=1, 2, 3 and ∞) from nanosized co-crystallites

A new direct route for the “bottom up” syntheses of phases in the La_n+1Ni_nO_3n+1 series (n=1, 2, 3 and ∞) has been achieved via single-step heat treatments of nanosized co-crystallized precursors. The co-crystallized precursors were prepared using a continuous hydrothermal flow synthesis system that uses a superheated water flow at ca. 400 °C and 24.1 MPa to produce nanoparticulate slurries. Overall, a significant reduction in time and number of steps for the syntheses of La₃Ni₂O₇ and La₄Ni₃O₁₀ was achieved compared with more conventional synthesis methods, which typically require multiple homogenization and reheating steps over several days.     

Sampling in Paley-Wiener spaces on combinatorial graphs

A notion of Paley-Wiener spaces on combinatorial graphs is introduced. It is shown that functions from some of these spaces are uniquely determined by their values on some sets of vertices which are called the uniqueness sets. Such uniqueness sets are described in terms of Poincare-Wirtinger-type inequalities. A reconstruction algorithm of Paley-Wiener functions from uniqueness sets which uses the idea of frames in Hilbert spaces is developed. Special consideration is given to the -dimensional lattice, homogeneous trees, and eigenvalue and eigenfunction problems on finite graphs.

     

Near IR luminescent rare earth 3,4,5,6-tetrafluoro-2-nitrophenoxide complexes: Synthesis,X-ray crystallography and spectroscopy

3,4,5,6-Tetrafluoro-2-nitrophenoxide (L⁻) forms complexes with rare earth M³⁺ ions. X-ray crystal structures of substances with the stoichiometry Cs₂ML₅ · mEt₂O (M = Er, m = 0; M = Er, m = 1; M = Y, m = 1.5; M = Yb, m = 1) have been determined. Each M³⁺ ion is coordinated to two bidentate and three monodentate L⁻ ions; Et₂O does not coordinate to M³⁺. The complexes absorb both visible and ultraviolet light. The solid Er³⁺ and Yb³⁺ complexes have unusually long lifetimes (τ = 20.2 μs and 142 μs, respectively) for the decay of their luminescence in the near-infrared region following photoexcitation; this is attributed to the lack of C–H bonds and other high frequency oscillators that could cause vibrational quenching.     

Chemoselective modification of proteins: hitting the target

The use of synthetic molecules to modulate and track biological events is a central component of chemical biology. As a result, the precise, covalent modification of biomolecules is a key goal for this field. Several strategies have emerged that allow specific tailoring of polypeptides through either endogenous residues or introduced functionality. This tutorial review discusses these recent advances in the context of in vitro and in vivo applications.     

Chiral manganese complexes with pinene appended tetradentate ligands as stereoselective epoxidation catalysts

A novel family of chiral manganese complexes Lambda-1(CF(3)SO(3)) and Delta-2(CF(3)SO(3)), have been stereoselectively prepared, characterized and studied as epoxidation catalysts. The complexes are structurally related to [Mn(II)(CF(3)SO(3))(2)(alpha-MCP)] (MCP=N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)cyclohexane-trans-1,2-diamine), recently reported as a very efficient epoxidation catalyst in combination with peracetic acid. Pinene rings have been fused to the 4 and 5 positions of the two pyridine groups of the ligand, giving rise to complexes where the two labile binding sites of the manganese ion are confined in a better-defined chiral pocket than in the parent [Mn(II)(CF(3)SO(3))(2)(alpha-MCP)]. Chirality in these complexes arises from the stereochemistry of the trans-diaminocyclohexane ring, from the pinene ring and also from the topological chirality adopted by the ligand upon binding to the manganese ion. While previous studies have demonstrated that small modifications in the structure of the MCP ligand result in a dramatic loss of efficiency, Lambda-1(CF(3)SO(3)) and Delta-2(CF(3)SO(3)) exhibit comparable catalytic activity to [Mn(II)(CF(3)SO(3))(2)(alpha-MCP)]. In addition, the complexes exhibit a remarkable stereoselectivity (up to 46% ee) in the epoxidation of selected substrates. The results reported in this work point towards modification of the 4 and 5 positions of the pyridine groups as a new strategy towards the design of stereoselective versions of this family of highly active and environmentally benign epoxidation catalysts.