Relaxometric and solution NMR structural studies on ditopic lanthanide(III) complexes of a phosphinate analogue of DOTA with a fast rate of water exchange

A novel "ditopic" ligand containing two monophosphinate triacetate DOTA-like units linked by a thiourea bridge has been synthesized and its complexes with Ln3+ ions (Ln = Y, Eu, Gd, Dy) investigated by NMR spectroscopy and relaxometry. The presence of one water molecule in the first coordination sphere has been determined by the measurement of the dysprosium(III)-induced 17O NMR shifts. The 1H and 31P NMR spectra of the Eu(III) derivative indicate a higher abundance of the fast-exchanging twisted square antiprismatic (m) isomer than the isomeric square antiprismatic (M; m/M = 3:2) complex. The analysis of the 89Y and 13C T1 NMR relaxation times in the Gd(III)/Y(III) mixed complex have provided useful structural information. Values of ca. 6.3 and 8.2 A for the Gd...Y and Gd...C distances, respectively, have been estimated which indicate a rather compact solution structure. This result finds support in the value of the relaxivity whose increase (at 20 MHz and 298 K) on passing from the monomeric (5.7 s(-1) mM(-1)) to the ditopic complex (8.2 s(-1) mM(-1)) can be attributed to the doubling of the inner-sphere term following the doubling of the molecular size. The structural and dynamic relaxivity-controlling parameters were assessed by a simultaneous fitting of the variable temperature 17O NMR and 1H NMRD relaxometric data. The mean water residence lifetime (298tauM) has been found to be 53 ns, one of the shortest values reported for ditopic complexes. The reorientational correlation time is two times longer (298tauR = 183 ps) than the corresponding value of the parent monomeric Gd(III) complex, thus supporting the view of a limited degree of internal rotation. The possible influence of magnetic Gd-Gd coupling has been excluded by a comparison of the 1H NMRD profiles of the homodinuclear Gd(III)/Gd(III) and the heterodinuclear Gd(III)/Y(III) complexes.     

Ideal convergence of continuous functions

For a given ideal I⊆P(ω), IC(I) denotes the class of separable metric spaces X such that whenever is a sequence of continuous functions convergent to zero with respect to the ideal I then there exists a set of integers {m₀<m₁<?} from the dual filter F(I) such that limi→∞fmi(x)=0 for all x∈X. We prove that for the most interesting ideals I, IC(I) contains only singular spaces. For example, if I=Id is the asymptotic density zero ideal, all IC(Id) spaces are perfectly meager while if I=Ib is the bounded ideal then IC(Ib) spaces are σ-sets.     

Conformational behavior of simple furanosides studied by optical rotation

Experimental and theoretical specific optical rotations (OR) of anhydro, epithio, and epiminoderivatives of methyl tetrofuranosides in chloroform solutions have been compared and used as a tool for exploring their conformational behavior. The potential energy surfaces of these saccharides with reduced flexibility were examined with the density functional theory and the MP2 and CCSD(T) wavefunctions methods. Theoretical ORs were obtained by Boltzmann averaging of values calculated for local minima. Resultant rotations could be used to assess the quality of the DFT and MP2 relative conformer energies. OR values calculated for equilibrium geometries in vacuum were significantly improved when the solvent was accounted for by a polarizable continuum model and first and diagonal second OR derivatives were used for an anharmonic vibrational averaging. The DFT used as a default method reproduced the experimental data fairly well. A modified B3LYP functional containing 70% of HF exchange further improved the results. Because of the strong dependence of OR on the conformation, not only the absolute configuration could be determined, but also the conformational populations were estimated. Likewise, the predicted dependence of OR on the light wavelength well agreed with experiment. The increasing precision of the contemporary computational methods thus makes it possible to relate the specific rotation to more detailed features in molecular structure. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

On 2-walks in chordal planar graphs

A 2-walk is a closed spanning trail which uses every vertex at most twice. A graph is said to be chordal if each cycle different from a 3-cycle has a chord. We prove that every chordal planar graph G with toughness has a 2-walk.     

Oxygen evolution on Ru1 − x Ni x O2 − y nanocrystalline electrodes

Nanocrystalline Ru_1 − x Ni _x O_2 − y with 0.02 < x < 0.30 were prepared by a sol–gel approach at temperatures between 300 and 600 °C. XRD patterns of the prepared materials indicate a single-phase character conforming to a tetragonal syngony. All prepared materials are sufficiently stable in acid media and show activity towards oxygen evolution. The activity towards oxygen evolution reaction of the materials with constant chemical composition decreases with increasing particle size. The increasing Ni content enhances the electrocatalytic activity in a stepwise manner with abrupt changes for materials containing approximately 5% or 15% of the cationic sites substituted by Ni.     

Molecular Dynamisc Simulation of Polyelectrolites

We carried out simulations of a polymer chain using molecular dynamics algorythm. As a model we used a three-dimensional set monomers (electrically charged material points) connected with its nearest neighbours by harmonic potential. Additionally all pairs of segments interacts by the Lennard-Jones (LJ) and Coulomb forces. The aim of the simulation was to determine chain conformation and other basic properties like radius of gyration and moment of inertia for various polymer length and electric charge distribution.Presented model could be alternative tool for structure prediction to typically used ones based on AMBER 99 [1] or another advanced force field.     

Effect of Processing Treatment and Modified Atmosphere Packing on Carrot’s Microbial Community Structure by Illumina MiSeq Sequencing

The aim of this study was to analyze the microbiome of carrot (Daucus carota subsp. sativus) subjected to minimal pre-treatment (rinsing in organic acid solution) and packaging in a high-oxygen modified atmosphere, and then stored for 17 days under refrigeration conditions (4 °C). The highest levels of bacteria in the carrot microbiome were characterized, at almost 78%, by bacteria belonging to the Enterobacteriaceae and Pseudomonadaceae families. Rinsing in a solution of ascorbic and citric acids resulted in the improvement of microbiological quality in the first day of storage. However, the use of a high-oxygen modified atmosphere extended the shelf life of the minimally processed product. Compared to carrots stored in air, those stored in high oxygen concentration were characterized by a greater ratio of bacteria belonging to the Serratia and Enterobacter genera, and a lower ratio belonging to the Pseudomonas and Pantoea genera. Moreover, the β-biodiversity analysis confirmed that the oxygen concentration was the main factor influencing the differentiation of the metabiomes of the stored carrots. The bacterial strains isolated from carrots identified by molecular methods were mostly pathogenic or potentially pathogenic microorganisms. Neither the minimal pre-treatment nor packaging in high-oxygen atmosphere was able to eliminate the threat of pathogenic bacteria emerging in the product.     

Anodic and Cathodic Platinum Dissolution Processes Involve Different Oxide Species

The degradation of Pt-containing oxygen reduction catalysts for fuel cell applications is strongly linked to the electrochemical surface oxidation and reduction of Pt. Here, we study the surface restructuring and Pt dissolution mechanisms during oxidation/reduction for the case of Pt(100) in 0.1 M HClO₄ by combining operando high-energy surface X-ray diffraction, online mass spectrometry, and density functional theory. Our atomic-scale structural studies reveal that anodic dissolution, detected during oxidation, and cathodic dissolution, observed during the subsequent reduction, are linked to two different oxide phases. Anodic dissolution occurs predominantly during nucleation and growth of the first, stripe-like oxide. Cathodic dissolution is linked to a second, amorphous Pt oxide phase that resembles bulk PtO₂ and starts to grow when the coverage of the stripe-like oxide saturates. In addition, we find the amount of surface restructuring after an oxidation/reduction cycle to be potential-independent after the stripe-like oxide has reached its saturation coverage.     

Facile One-Step Oxidation of N-Boc-Protected Diarylhydrazines to Diaryldiazenes with (Diacetoxyiodo)benzene under Mild Conditions

A study on the oxidation of N-Boc- and N,N'-bis-Boc-protected 1,2-diarylhydrazines with (diacetoxyiodo)benzene is reported. The reactions proceed quickly in acetic acid at slightly elevated temperatures, giving diaryldiazenes in good to excellent yields. Electron-donating and electron-withdrawing groups are well tolerated. This synthetic protocol also applies to synthesising (aryldiazenyl)pyridines and unsymmetrical 1,3,5-tris(arylazo)benzenes.