Water-based Synthesis and Properties of a Scandium 1,4-Naphthalenedicarboxylate

A new scandium naphthalenedicarboxylate with the framework composition [Sc₂(1,4-NDC)₃] (H₂-1,4-NDC = 1,4-naphthalenedicarboxylic acid) was obtained under hydrothermal synthesis conditions. A structure model could be developed by a combination of 3D electron diffraction measurements and computationally assisted structure determination, which was further validated by a good agreement with the experimental powder X-ray diffraction pattern. The structure consists of isolated ScO₆ octahedra interconnected by the carboxylate groups of linker molecules to form chains. These chains are connected by the naphthalene-moieties to form a three-dimensional framework with square-shaped pores and the organic group pointing into the pores. Although very similar synthesis conditions were chosen, [Sc₂(1,4-NDC)₃] is not isostructural to aluminum naphthalenedicarboxylate [Al(OH)(1,4-NDC)], which crystallizes in a MIL-53 type structure. This can be traced back to the different inorganic building units that are observed. The compound was thoroughly characterized by elemental analysis, IR spectroscopy, sorption measurements, thermogravimetric analysis and luminescence measurements. [Sc₂(1,4-NDC)₃] exhibits a high thermal stability and a ligand-based blue luminescence in the solid state at room temperature.     

Sulle equazioni di una curva monomiale proiettiva

Riassunto Si dà una costruzione di un insieme minimale di generatori omogenei per l'ideale di una curva monomiale proiettiva e una limitazione per il grado delle equazioni che la definiscono.

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Summary A construction of a minimal system of homogeneous generators for the ideal of a monomial projective curve and a degree bound for its defining equations are given.

     

Sintering of a bcc structure of spherical particles of equal and different sizes

Solid-state sintering of a bcc structure of spherical particles has been studied numerically by use of simple shape parameters to describe the state of the unit cell. Both free and pressure-assisted sintering of particles of equal and different sizes for various ratios of boundary and surface diffusion have been considered. At low relative densities, the evolution of particle radius, interparticle junction radius and shrinkage predicted by the bcc model are rather similar to sintering of a simple row of particles. At higher densities, the porosity closes up; that is, the junctions start to interact, or the next-nearest neighbours in the particle structure attain contact. Quantative measures of the density at the transition from open pore space between the particles to closed porosity as well as the density at which the next-nearest neighbours start to touch are derived. Furthermore, different dihedral angles and the evolution of relative density and sintering stresses are studied.     

Electronic Transitions in Different Redox States of Trinuclear 5,6,11,12,17,18-Hexaazatrinaphthylene-Bridged Titanium Complexes: Spectroelectrochemistry and Quantum Chemistry

Multinuclear transition metal complexes bridged by ligands with extended π-electronic systems show a variety of complex electronic transitions and electron transfer reactions. While a systematic understanding of the photochemistry and electrochemistry has been attained for binuclear complexes, much less is known about trinuclear complexes such as hexaphenyl-5,6,11,12,17,18-hexaazatrinaphthylene-tristitanocene [(Cp₂Ti)₃HATN(Ph)₆]. The voltammogram of [(Cp₂Ti)₃HATN(Ph)₆] shows six oxidation and three reduction waves. Solution spectra of [(Cp₂Ti)₃HATN(Ph)₆] and of the electrochemically formed oxidation products show electronic transitions in the UV, visible and the NIR ranges. Density functional theory (DFT) and linear response time-dependent DFT show that the three formally titanium(II) centers transfer an electron to the HATN ligand in the ground state. The optically excited transitions occur exclusively between ligand-centered orbitals. The charged titanium centers only provide an electrostatic frame to the extended π-electronic system. Complete active self-consistent field (CASSCF) calculation on a structurally simplified model compound, which considers the multi-reference character imposed by the three titanium centers, can provide an interpretation of the experimentally observed temperature-dependent magnetic behavior of the different redox states of the title compound in full consistency with the interpretation of the electronic spectra.     

Genetic microheterogeneity of human transthyretin detected by IEF

Mutations of the human transthyretin (TTR) gene have attracted medical interest as a cause of amyloidosis. Recently, we have described in detail an electrophoretic procedure with PAGE followed by IEF in urea gradients for the study of the microheterogeneity of TTR monomers (Altland, K., Winter, P., Sauerborn, M. K., Electrophoresis 1999, 20, 1349-1364). In this paper, we present a study on 49 different mutations of TTR including 33 that result in electrically neutral amino acid substitutions. The aims of the investigation were to test the sensitivity of the procedure to detect TTR variants in patients with TTR amyloidosis and their relatives and to identify some common characteristics that could explain the amyloidogenicity of these variants. We found that all tested amyloidogenic mutations could be detected by our method with the exception of those for which the corresponding variant was absent in plasma samples. Most of the electrically neutral amyloidogenic TTR variants had in common a reduced conformational stability of monomers by the activity of protons and urea. For three variants, e.g. TTR-F64L, TTR-I107V and TTR-V122I, the monomers had a conformational stability close to that of normal monomers but we found experimental and structural arguments for a weakening of the monomer-monomer contact. All types of amyloidogenic mutations affected the stability of TTR tetramers.     

Water-protein and ligand-protein interactions as determined by selective NMR relaxation studies

Water-macromolecules and ligand-macromolecules interactions were investigated considering the effects induced by the presence of a macromolecule on both the water and the ligand NMR selective (R₁^SE) and non-selective (R₁^NS) spin-lattice relaxation rates. The results obtained from the solvent studies were used to describe the solvent dynamics at the macromolecule-solvent interface. On the other hand, ligand R₁^SE and (R₁^NS) analysis allowed the definition of the “affinity index”, [A]_L^T, an index related to the extent of the macromolecule-ligand recognition process.     

On the blowing up of solutions to quantum hydrodynamic models on bounded domains

The blow-up in finite time for the solutions to the initial-boundary value problem associated to the multi-dimensional quantum hydrodynamic model in a bounded domain is proved. The model consists on conservation of mass equation and a momentum balance equation equivalent to a compressible Euler equations corrected by a dispersion term of the third order in the momentum balance. The proof is based on a priori estimates for the energy functional for a new observable constructed with an auxiliary function, and it is shown that, under suitable boundary conditions and assumptions on the initial data, the solution blows up after a finite time. I.M. Gamba is supported by NSF-DMS0507038. M.P. Gualdani acknowledges partial support from the Deutsche Forschungsgemeinschaft, grants JU359/5 and was partially supported under the Feodor Lynen Research fellowship. P. Zhang is partially supported by the NSF of China under Grant 10525101 and 10421101, and the innovation grant from the Chinese Academy of Sciences. Part of the work was done when P. Zhang visited the Department of Mathematics of Texas University at Austin, the author would like to thank the hospitality of the department. Support from the Institute for Computational Engineering and Sciences at the University of Texas at Austin is also gratefully acknowledged.     

New hybrid [2]catenanes based on a 4,4'-bipyridinium ligand

The self-assembly-mediated synthesis of metallomacrocycles 4a and 4b from (en)M(NO3)2 (M = Pd, Pt) and bipyridinium ligand 3 is described. The reaction is templated by disodium p-phenyldiacetic dicarboxylate, which is inserted into the macrocyclic cavity. Similarly, the self-assembly process between ligand 3, (en)M(NO3)2 (M = Pd, Pt), and the macrocyclic polyether 6 resulted in the formation of hybrid catenanes 7a and 7b. In the [2]catenanes, the circumrotation of the macrocyclic polyether through the cavity of the metallocycle is slow on the 1H NMR time scale.