Increasing the Structural Span of Alkyne Metathesis

A new generation of alkyne metathesis catalysts, which are distinguished by high activity and an exquisite functional group tolerance, allows the scope of this transformation to be extended beyond its traditional range. They accept substrates that were previously found problematic or unreactive, such as propargyl alcohol derivatives, electron‐deficient and electron‐rich acetylenes of various types, and even terminal alkynes. Moreover, post‐metathetic transformations other than semi‐reduction increase the structural portfolio, as witnessed by the synthesis of a annulated phenol derivative via ring‐closing alkyne metathesis (RCAM) followed by a transannular gold‐catalyzed Conia‐ene reaction. Further examples encompass a post‐metathetic transannular ketone–alkyne cyclization with formation of a trisubstituted furan, a ruthenium‐catalyzed redox isomerization, and a Meyer–Schuster rearrangement/oxa‐Michael cascade. These reaction modes fueled model studies toward salicylate macrolides, furanocembranolides, and the cytotoxic macrolides acutiphycin and enigmazole A; moreover, they served as the key design elements of concise total syntheses of dehydrocurvularin ( 27 ) and the antibiotic agent A26771B ( 36 ).     

Asymmetric orientational writing dependence on polarization and direction in Li2O–Nb2O5–SiO2 glass with femtosecond laser irradiation

Strong birefringence photo-induced by the femtosecond laser irradiation and a sensitivity to the orientation of the laser movement versus the laboratory reference (i.e., difference between rightward and leftward or between upward and downward) have been demonstrated in 32.5Li₂O–27.5Nb₂O₅–40SiO₂ glass. An asymmetry with the orientation of the laser scanning was firstly observed by one of the authors in 2003 in pure silica (Poumellec et al. in Opt Express 11:1070, 2003). Here, we show in addition that this asymmetric orientational sensitivity is dependent on the direction of laser polarization and the laser scanning (i.e., when the direction is horizontal or vertical). In particular, no asymmetric writing is detected when both laser scanning and polarization directions are vertical. These observations are not explained by the available model.     

Properties ofΛ-hypernuclei from p+A reactions

We study the production ofΛ hyperons inp+A reactions on the basis of a BUU transport approach for³² S,⁶⁵ Cu,¹²⁰ Sn,¹⁹⁷ Au,²⁰⁸ Pb and²³⁸ U from 1.1 to 1.7 GeV beam energy and evaluate the properties of the hypernuclei produced with respect to excitation energy, transverse and longitudinal momentum, angular momentum and mass. Furthermore, the decay of the hypernuclei by particle emission in competition with fission channels is followed by a statistical model calculation. We find the systemp+¹⁹⁷ Au at about 1.5 GeV to be optimally suited for the production of heavy hypernuclei, where theΛ-decay is expected to be dominated by nonmesonic decay channels.     

Excitation of theΔ (1232)-resonance in proton-nucleus collisions

The excitation of theΔ resonance is observed in proton collisions on C, Nb and Pb targets at 0.8 and 1.6 GeV incident energies. The mass E₀ and widthΓ of the resonance are determined from the invariant mass spectra of correlated (p, π^±)-pairs in the final state of the collision: The mass E₀ is smaller than that of the free resonance, however by comparing to intra-nuclear cascade calculations, this reduction is traced back to the effects of Fermi motion, NN scattering and pion reabsorption in nuclear matter.     

"Acid extractable" metal concentrations in solid matrices: a comparison and evaluation of operationally defined extraction procedures and leaching tests

Different frequently used methods to determine the influence of acid conditions on heavy metal release from soils, sediments and waste materials, namely pH_stat leaching tests and acid extractions with acetic acid (HOAc) (0.11 M and 0.43 M) and sodium acetate (NaOAc) (1 M) were compared for 30 samples (soils, sediments and waste materials) with different physico-chemical properties and a different degree of contamination. However, no distinct relationship was found between physico-chemical sample characteristics, total element concentrations and acid-extractable metal concentrations in the presented dataset.

pH played an important role in explaining the release of metals from the contaminated soils, sediments and waste materials. The pH-shift after extraction with the different acetic acid solutions (0.11 M and 0.43 M) was both explained by the initial pH of the sample and its acid neutralizing capacity. The pH of the NaOAc extract was well buffered and the release of elements from solid matrices by NaOAc was both the result of the complexation with acetate and pH (pH 5). Generally, a linear correlation was found between the amount of Zn and Cd extracted by 0.11 M HOAc, 0.43 M HOAc and 1 M NaOAc. The amounts of Zn and Cd extracted with HOAc (0.11 M and 0.43 M) were comparable with amounts of respectively Zn and Cd released during pH_stat leaching at pH 4. However, for Cu, Pb and As, it was often not possible to relate the results of a pH_stat leaching test to the results of single extractions with acetic acid solutions.     

Rational Synthesis of Molybdenum(V) Tetramers Consisting of [Mo2O4]2+ Dimers Held Together by Bridging Phosphinate Ligands and the Tungsten(VI) Dimer [(CH3O)2(O)W(μ-O)(μ-O2PPh2)2W(O)(CH3O)2]: Structural and Theoretical Considerations

Reacting MoO₂(acac)₂ with Ph₂POOH or Me₂POOH in EtOH results in the formation of the tetranuclear molybdenum (V) clusters Mo₄(μ ₃-O)₄(μ-O₂PR₂)₄O₄, PR₂ = PPh₂, 1, or PMe₂, 2, in functional yields (>90% and 55% respectively). The reaction of WO₂(acac)₂ with Ph₂POOH in MeOH affords the tungsten dimer [(CH₃O)₂(O)W(μ-O)(μ-O₂PPh₂)₂W(O)(CH₃O)₂], 3. The single crystal X-ray determined structures of complexes 1–3 are reported. In 1 and 2, the four Mo=O units are interconnected by four triply bridging oxygen atoms, resulting in a distorted cubic-like structure for the Mo₄(μ ₃-O)₄O₄ units. Each molybdenum atom forms two additional Mo–O bonds with two oxygen atoms from different adjacent phosphinato ligands. Complex 3, a tungsten dimer, contains packing disorder and consists of bridging oxo and diphenylphosphinato ligands. The bonding of 1 and 2 assessed by density-functional methods showed that bonding between the Mo(V) centers occurs through σ overlap of the d _xy orbitals. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Dedicated to the memory of Professor F. A. Cotton. Veritas numquam perit.     

Isometric Group Actions on Banach Spaces and Representations Vanishing at Infinity

Our main result is that the simple Lie group G = Sp(n, 1) acts metrically properly isometrically on L ^p (G) if p > 4n + 2. To prove this, we introduce Property , with V being a Banach space: a locally compact group G has Property if every affine isometric action of G on V, such that the linear part is a C ₀-representation of G, either has a fixed point or is metrically proper. We prove that solvable groups, connected Lie groups, and linear algebraic groups over a local field of characteristic zero, have Property . As a consequence, for unitary representations, we characterize those groups in the latter classes for which the first cohomology with respect to the left regular representation on L ²(G) is nonzero; and we characterize uniform lattices in those groups for which the first L2-Betti number is nonzero.