Critical field for complete vortex expulsion from narrow superconducting strips

We have measured the maximum field for which vortices are completely expelled from a thin-film superconducting strip. Niobium strips of width W were field cooled and imaged with a scanning Hall-probe microscope. Below a critical field B(m) approximately Phi(0)/W(2) all flux was expelled; above this field vortices were observed with a density increasing approximately linearly with field. The small value of the critical field, which is orders of magnitude less than in the bulk, implies that superconducting devices should be designed with narrow wires to eliminate the generation of noise from vortex motion.     

Hydrogen bonding-based 3D supramolecular architecture of [Cu(CHA)2][TCM]·11H2O

Reaction of Na₄TCM (1) (H₄TCM = tetra[4-(carboxyphenyl)oxamethyl]methane) with [Cu(CHA)](ClO₄)₂ (2)(CHA = 1,3,6,8,11,14-hexaaz atricyclo[12.2.1.1.^8,11] octadecane) in a DMF-water mixture yields [Cu(CHA)]₂[TCM] (3). Structural analysis of [Cu(CHA)]₂[TCM]·11H₂O (3·11H₂O) by single crystal X-ray diffraction reveals strong copper-oxygen bonds between two complex cations and the tetraanion leading to a 3D coordination network (zwitterionic structure), consolidated through additional NH...O=C hydrogen bonding within the cation/anion association. The resulting coordination geometry around a copper atom is a distorted square pyramidal with an oxygen atom of the anionic ligand in the apical position. A 3D supramolecular network is developed in the crystal based only on NH...OC hydrogen bonds between the macrocyclic metallic tecton and the carboxylate groups of neighboring 3D coordinated (zwitterionic) moieties. The pseudotetrahedral TCM^4? tetraanionic ligand induces a diamondoid architecture formed of large distorted adamantanoid cages.      

Protein–Inorganic Array Construction: Design and Synthesis of the Building Blocks

Herein we describe the design and synthesis of the first series of di‐functional ligands for the directed construction of inorganic‐protein frameworks. The synthesized ligands are composed of a metal‐ion binding moiety (terpyridine‐based) conjugated to an epoxysuccinyl peptide, known to covalently bind active cysteine proteases through the active‐site cysteine. We explore and optimize two different conjugation chemistries between the di‐functionalized metal‐ion ligand and the epoxysuccinyl‐containing peptide moiety: peptide‐bond formation (with limited success) and Cu^I‐catalysed click chemistry (with good results). Further, the complexation of the synthesized ligands with Fe^II and Ni^II ions is investigated: the di‐functional ligands are confirmed to behave similarly to the parent terpyridine. As designed, the peptidic moiety does not interfere with the complexation reaction, in spite of the presence of two triazole rings that result from the click reaction. ES‐MS together with NMR and UV/Vis studies establish the structure, the stoichiometry of the complexation reactions, as well as the conditions under which chemically sensitive peptide‐containing polypyridine ligands can undergo the self‐assembly process. These results establish the versatility of our approach and open the way to the synthesis of di‐functional ligands containing more elaborated polypyridine ligands as well as affinity labels for different enzyme families. As such, this paper is the first step towards the construction of robust supramolecular species that cover a size‐regime and organization level previously unexplored.     

Involvement of cyan and ester groups in surface interactions of aerosil–cyanophenyl alkyl benzoate systems with high silica density: Infrared investigations

Composites prepared from aerosil A380 and liquid crystals (LCs) of 4-n-alkyl-4′-cyanophenyl benzoate type, with four to six carbon atoms in the alkyl chain were investigated by infrared spectroscopy. Their high silica content (of 2–7 g aerosil/1 g of LC) was given by thermogravimetric investigations and allows the observation of a rather thin LC layer on the silica particles. Several surface species onto the external surface of the grains were demonstrated. Arguments are given that monomer and dimer species are present in the bulk cyanophenyl benzoate materials while bulk-like species along with hydrogen-bonded ones coexist in the so-called surface layer of the composites. The main interaction of LC molecules with the aerosil surface is by hydrogen bonding taking place with the involvement of the cyan group. There is a contribution of ester carbonyl group to these surface interactions but this cannot be well quantified.     

Dimensionality switching through a thermally induced reversible single-crystal-to-single-crystal phase transition in a cyanide complex

The heterometallic hexanuclear cyanide-bridged complex {[Mn(bpym)(H(2)O)](2)[Fe(HB(pz)(3))(CN)(3)](4)} (1), its C(15)N and D(2)O enriched forms {[Mn(bpym)(H(2)O)](2)[Fe(HB(pz)(3))(C(15)N)(3)](4)} (2) and {[Mn(bpym)(D(2)O)](2)[Fe(HB(pz)(3))(CN)(3)](4)} (3), and the hexanuclear derivative complex {[Mn(bpym)(H(2)O)](2)[Fe(B(pz)(4))(CN)(3)](4)}·4H(2)O (4) [bpym = 2,2'-bipyrimidine, HB(pz)(3)(-) = hydrotris(1-pyrazolyl)borate, B(pz)(4)(-) = tetra(1-pyrazolyl)borate] have been synthesized. Their structures have been determined through single-crystal X-ray crystallography at different temperatures. Whereas 3 and 4 maintain a discrete hexanuclear motif during the entire temperature range investigated (down to 95 K), 1 and 2 exhibit a thermally induced reversible single-crystal to single-crystal phase transition driven by a remarkable concerted rearrangement of hydrogen and cyanide coordination bonds. While hexanuclear complexes are observed in the high temperature phases (noted 1a and 2a) above 200 K, the low temperature phases are composed of one-dimensional coordination polymers noted 1b and 2b. The magnetic properties of the four compounds have been investigated in the 2-300 K range, and they reveal the occurrence of an overall antiferromagnetic behavior. The thermal dependence of the optical reflectivity and the FT-IR absorbance have been studied for 1 in the range 10-300 K and 130-300 K, respectively. A comparative analysis of the structural and electronic properties for 1-4 clearly underlines the major role of the intermolecular interactions in the topological and dimensional rearrangement observed during the structural phase transition. This result opens new perspectives in the design of cyanide-based switchable magnetic materials using coordination bonds rearrangements.     

Thermal behavior of Ni,Co and Fe succinates embedded in silica matrix

This paper presents the thermal behavior of Co, Ni and Fe succinates obtained by sol-gel synthesis using Co(II), Ni(II) and Fe(III) nitrates, 1,4-butanediol and tetraethyl orthosilicate as reactants. The thermal analysis revealed the formation of succinates at 413–453 K and their decomposition to ferrites at 503–623 K. The rate constants for the decomposition of succinates to ferrites, calculated using the isotherms at 473, 523, 573 and 623 K, were used to determine the activation energy of each ferrite (NiFe₂O₄, Ni_0.3Co_0.7Fe₂O₄, Ni_0.7Co_0.3Fe₂O₄ and CoFe₂O₄) embedded in the silica matrix. By increasing the Ni content in the mixed Ni–Co ferrites, the activation energy decreases from 13.530 to 1.944 kJ mol^?1. The formation and decomposition of succinate precursors and the formation of silica matrix were confirmed by FT-IR spectroscopy, while the formation of CoFe₂O₄ and NiFe₂O₄ single-phases embedded in the silica matrix was confirmed by X-ray diffraction analysis. The nanocrystallites size decreases from 31.7 (CoFe₂O₄) to 18.5 nm (NiFe₂O₄). The optical band gap of mixed Co–Ni ferrites was significantly higher than that corresponding to CoFe₂O₄. The photocatalytic activity of the samples was evaluated against Rhodamine B under visible light. All the samples have photocatalytic activities, the best performance being obtained in the case of Ni_0.7Co_0.3Fe₂O₄.

     

Interplay between composition,structural dynamics and thermodynamic data in amino acid nitrates

Journal of Thermal Analysis and Calorimetry - A systematic thermodynamic study has been performed for a series of nitrates having cations derived from the α-amino acids glycine (Gly),...