Temperature dependence of the flux line lattice transition into square symmetry in superconducting LuNi2B2C

We have investigated the temperature dependence of the H parallel to c flux line lattice structural phase transition from square to hexagonal symmetry, in the tetragonal superconductor LuNi2B2C ( T(c) = 16.6 K). At temperatures below 10 K the transition onset field, H2(T), is only weakly temperature dependent. Above 10 K, H2(T) rises sharply, bending away from the upper critical field. This contradicts theoretical predictions of H2(T) merging with the upper critical field and suggests that just below the H(c2)(T) curve the flux line lattice might be hexagonal.     

Magnetic ground state of pure and doped CeFe2

A combination of neutron elastic and inelastic, resonant x-ray scattering, and 57Fe M?ssbauer experiments are used to determine the unusual magnetic ground state of CeFe2. The complementarities between different time-scale techniques may allow one to understand the dynamic features of the ground state in CeFe2 and its pseudobinary compounds, and how the frustration of Fe tetrahedra leads the appearance of antiferromagnetic fluctuations in the presence of ferrimagnetism. The resulting model can be used to rationalize many of the unusual and conflicting experimental results reported for this material in the literature.     

A novel electrophoretic technique designed to modify the ratio of magnesium isotopes inside the creatine kinase active sites. A preliminary report

A simple and efficient preparative electrophoretic technique has been proposed to obtain a modified creatine kinase (CK, E.C.2.7.3.2) molecule with an increased content of 25Mg in the active site. A key point of the method is the special design of a 0.9 x 12.0 cm column for ascendent electrophoresis, packed consecutively, from the bottom to the top, with layers of 30 % PAAG (polyacrylamide grade), 25Mg2+ -containing 7.5 % PAAG, enzyme-binding ADP Sepharose and 2.2 % agarose gels, based on different tris-glycine and tris-HCl separation buffer systems. The isotope substitution process was a result of simultaneous desorption of enzyme from ADP Sepharose and electrically directed extensive flow of 25Mg2+ cations through the porous gel matrix. Greater than 8-fold 25Mg enrichment, i.e. a 10.2-86.3 % increase of 25Mg contribution to total enzyme magnesium, has been reached. The modified 25Mg-rich CK samples manifest higher (2.4-fold increase) values of specific catalytic activity when compared with intact (control) ones.     

A PFG NMR experiment for translational diffusion measurements in low-viscosity solvents containing multiple resonances

Pulsed gradient simulated-echo (PGSE) NMR diffusion measurements provide a facile and accurate means for determining the self-diffusion coefficients for molecules over a wide range of sizes and conditions. The measurement of diffusion in solvents of low intrinsic viscosity is particularly challenging, due to the persistent presence of convection. Although convection can occur in most solvent systems at elevated temperatures, in lower viscosity solvents (e.g., short chain alkanes), convection may manifest itself even at ambient laboratory temperatures. In most circumstances, solvent suppression will also be required, and for solvents that have multiple resonances, effective suppression can likewise represent a substantial challenge. In this article, we report an NMR experiment that combines a double-stimulated echo PFG approach with a WET-based solvent suppression scheme that effectively and simultaneously address the issues of dynamic range and the deleterious effects of convection. The experiment described will be of general benefit to studies aimed at the characterization of diffusion of single molecules directly dissolved in low-viscosity solvents, and should also be of substantial utility in studies of supramolecular assemblies such as reverse-micelles dissolved in apolar solvents.     

Interdependence of magnetism and superconductivity in the borocarbide TmNi2B2C

We have discovered a new antiferromagnetic phase in TmNi2B2C by neutron diffraction. The ordering vector is Q(A) = (0.48,0,0) and the phase appears above a critical in-plane magnetic field of 0.9 T. The field was applied in order to test the assumption that the zero-field magnetic structure at Q(F) = (0.094,0.094,0) would change into a c-axis ferromagnet if superconductivity were destroyed. We present theoretical calculations which show that two effects are important: a suppression of the ferromagnetic component of the RKKY exchange interaction in the superconducting phase and a reduction of the superconducting condensation energy due to the periodic modulation of the moments at Q(A).     

Verification of the selectivity of a liquid chromatography method for determination of stilbenes and flavonols in red wines by mass spectrometry

Quantification of bioactive phenols, like stilbenes and flavonols (SaF), has been conducted to evaluate the nutraceutical potential of red wines. However, there is still a lack of full validated, fast and accessible liquid chromatography methods offering high selectivity and a simple procedure. We present here the use of a high-resolution mass spectrometer to evaluate the selectivity of a feasible and traditional liquid chromatography technique (HPLC–DAD) to analyze markers of aglycone SaF in red wines. The SaF compounds were tested: trans-resveratrol, trans-ε-viniferin, quercetin, myricetin, and kaempferol, as well as trans-cinnamic acid, one of their precursors. System suitability and validation tests were employed for the selected conditions (octylsilane column, methanol mobile phase, and gradient elution). The validation process ensured the HPLC–DAD method was selective, linear, sensitive, precise, accurate and robust. The method was then applied to red wine samples from the Campanha Gaúcha region, Southern Brazil. The real samples contained different SaF levels, showing that the method is applicable to routine use. Furthermore, this was the first SaF characterization of red wines from the Campanha Gaúcha, contributing to regional and product development.     

Heat-Free Biomimetic Metal Molding on Soft Substrates

Fabrication of bio-templated metallic structures is limited by differences in properties, processing conditions, packing, and material state(s). Herein, by using undercooled metal particles, differences in modulus and processing temperatures can be overcome. Adoption of autonomous processes such as self-filtration, capillary pressure, and evaporative concentration leads to enhanced packing, stabilization (jamming) and point sintering with phase change to create solid metal replicas of complex bio-based features. Differentiation of subtle differences between cultivars of the rose flower with reproduction over large areas shows that this biomimetic metal patterning (BIOMAP) is a versatile method to replicate biological features either as positive or negative reliefs irrespective of the substrate. Using rose petal patterns, we illustrate the versatility of bio-templated mapping with undercooled metal particles at ambient conditions, and with unprecedented efficiency for metal structures.     

Nickel(0)-catalyzed isomerization of an aryne complex: formation of a dinuclear Ni(I) complex via C-H rather than C-F bond activation

The reaction of the aryne complex (PEt3)2Ni(eta2-C6H2-4,5-F2) with a catalytic amount of Ni(PEt3)2 results in a dinuclear Ni(I) complex from the coupling of the isomer (PEt3)2Ni(eta2-C6H2-3,4-F2), obtained via rearrangement of the aromatic C-H bonds, which demonstrates that Ni(PEt3)2 is kinetically capable of C-H bond activation, even in the presence of C-F bonds. The intermediate [(PEt3)2Ni]2(mu-eta2:eta2-C6H2-4,5-F2) was isolated and crystallographically characterized; the mu-eta2:eta2-bonding mode observed is unprecedented in aryne chemistry.     

Local superconducting density of States of ErNi2B2C

We present local tunneling microscopy and spectroscopy measurements at low temperatures in single crystalline samples of the magnetic superconductor ErNi2B2C . The electronic local density of states shows a striking departure from s-wave BCS theory with a finite value at the Fermi level, which amounts to half of the normal phase density of states.