Efficient NiII2LnIII2 electrocyclization catalysts for the synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary or secondary amines

A series of heterometallic coordination clusters (CCs) [NiII2LnIII2(L1)4Cl2(CH3CN)2] 2CH3CN [Ln = Y (1Y), Sm (1Sm), Eu (1Eu), Gd (1Gd), or Tb (1Tb)] were synthesized by the reaction of (E)-2-(2-hydroxy-3-methoxybenzylidene-amino)phenol) (H2L1) with NiCl2·6(H2O) and LnCl3·x(H2O) in the presence of Et3N at room temperature. These air-stable CCs can be obtained in very high yields from commercially available materials and are efficient catalysts for the room-temperature domino ring-opening electrocyclization synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary or secondary amines under a non-inert atmosphere. Structural modification of the catalyst to achieve immobilization or photosensitivity is possible without deterioration in catalytic activity

Deconstructing the Late Phase of Vimentin Assembly by Total Internal Reflection Fluorescence Microscopy (TIRFM)

Quantitative imaging of intermediate filaments (IF) during the advanced phase of the assembly process is technically difficult, since the structures are several µm long and therefore they exceed the field of view of many electron (EM) or atomic force microscopy (AFM) techniques. Thereby quantitative studies become extremely laborious and time-consuming. To overcome these difficulties, we prepared fluorescently labeled vimentin for visualization by total internal reflection fluorescence microscopy (TIRFM). In order to investigate if the labeling influences the assembly properties of the protein, we first determined the association state of unlabeled vimentin mixed with increasing amounts of labeled vimentin under low ionic conditions by analytical ultracentrifugation. We found that bona fide tetrameric complexes were formed even when half of the vimentin was labeled. Moreover, we demonstrate by quantitative atomic force microscopy and electron microscopy that the morphology and the assembly properties of filaments were not affected when the fraction of labeled vimentin was below 10%. Using fast frame rates we observed the rapid deposition of fluorescently labeled IFs on glass supports by TIRFM in real time. By tracing their contours, we have calculated the persistence length of long immobilized vimentin IFs to 1 µm, a value that is identical to those determined for shorter unlabeled vimentin. These results indicate that the structural properties of the filaments were not affected significantly by the dye. Furthermore, in order to analyze the late elongation phase, we mixed long filaments containing either Alexa 488- or Alexa 647-labeled vimentin. The ‘patchy’ structure of the filaments obtained unambiguously showed the elongation of long IFs through direct end-to-end annealing of individual filaments

Unique Phase Transition on Spin-2 Triangular Lattice of Ag2MnO2

Ag2MnO2 is studied as a possible candidate compound for an antiferromagnetic XY spin model on a triangular lattice. In spite of the large Curie-Weiss temperature of -430 K found in magnetic susceptibi-lity, Mn3+ spins with S = 2 do not undergo a conventional long-range order down to 2 K probably owing to the geometrical frustration and two dimensionality in the system. Instead, a unique phase transition is found at 80 K, where specific heat exhibits a clear sign of a second-order phase transition, while magnetic susceptibility changes smoothly without a distinct anomaly. We think that this transition is related to the chirality degree of freedom associated with a short-range order, which has been expected for the classical XY spin model on a triangular lattice. On further cooling, spin-glass-like behavior is observed below 22 K, possibly corresponding to a quasi-long-range order.Comment: to appear in J. Phys. Soc. Jpn, Vol. 77, No.

Synthesis, characterization, and bonding properties of polymeric fullerides AC70·nNH3 (A = Ca, Sr, Ba, Eu, Yb)

Reduction of C-70 with alkaline earth and rare earth metals dissolved in liquid ammonia results in metal fulleride solvates AC(70).nNH(3) (A = Ca, Sr, Ba, Eu, Yb) containing linear polymeric, anionic chains (1)(infinity)[C-70(2-)] The compounds were characterised by means of Raman spectroscopy and single- crystal structure determination. The accurate crystal structure of [Sr(NH3)(8)]C-70.3NH(3), determined with atomic resolution, allowed for a comparison with results of quantum chemical calculations. The nature of the C-C bonds in the fulleride is analysed in detail leading to a model explaining the unexpected polymerisation of C-70(2-)

Geometric variations and electron localizations in intermetallics: PbFCl type compounds

The structural relations of the intermetallic compounds Cu2Sb, Mn2Sb, Fe2As, Mn2As, Cr2As, Sc2Sb as well as of YTiSi and ZrSiS, all adopting the PbFCl structure, are discussed. In the course of these investigations, the crystal structures of Mn2Sb, Mn2As and Fe2As have been redetermined and refined from single crystal data. Bandstructures have been calculated in the framework of Density Functional Theory. The bonding properties are compared on the basis of partial densities of states, of the Crystal Orbital Hamilton Population (COHP) and of the Electron Localization Function (ELF). The trend of the d electrons to become more localized with increasing number leads to different bonding conditions in the compounds discussed