Synthese,Struktur und Eigenschaften von drei Tetranatrium-tetrametaphosphimat-Hydraten

Synthesis, Structure, and Properties of Three Tetrasodium Tetrametaphosphimate Hydrates Single crystals of three tetrasodium tetrametaphosphimate hydrates Na₄(PO₂NH)₄ · x H₂O with x = 2 and 3, respectively, have been obtained and characterized by single crystal X-ray diffraction. Dimorphous Na₄(PO₂NH)₄ · 3 H₂O is formed at RT. It crystallizes monoclinic ( 1 ) or triclinic ( 2 ) (α-Na₄(PO₂NH)₄ · 3 H₂O ( 1 ): P2₁, a = 1002.7(2), b = 1189.7(2), c=1193.1(2)pm, β=104.93(1)°, Z=4; β-Na₄(PO₂NH)₄ · 3 H₂O ( 2 ): P 1¯, a = 843.64(9), b = 848.54(10), c = 994.7(2) pm, α = 83.07(1), β = 76.31(1), γ = 87.46(1)°, Z = 2). Compound 2 is formed in the presence of NaCl during the crystallization from aqueous solution. Tetrasodium tetrametaphosphimate dihydrate ( 3 ) is formed at 60 °C (Na₄(PO₂NH)₄ · 2 H₂O ( 3 ): C2/c, a = 2225.6(3), b = 513.0(1), c = 1566.7(2) pm, β = 134.21(1)°, Z = 4). In 1 and 2 the P₄N₄ ring of the tetrametaphosphimate ions attains a saddle and in 3 a twistboat conformation. The conformations of the anions have been analysed using torsion angles, displacement asymmetry parameters, and puckering parameters. The (PO₂NH)₄^4– rings of the compounds 1 , 2 , and 3 are linked by N–H · · &mid     

MAD: practical implementation of MCAO concepts

The European Southern Observatory (ESO) together with external research institutes have built a Multi-Conjugate Adaptive Optics (MCAO) Demonstrator (MAD) to perform wide field-of-view adaptive optics correction (2′ in K band). The aim of MAD is to demonstrate the on-sky feasibility of the MCAO technique and to evaluate its critical aspects in the framework of both the 2nd generation instrumentation for the Very Large Telescope (VLT) and the Overwhelmingly Large Telescope (OWL). The MAD module will be installed on the VLT to perform on-sky observations. MAD comprises two deformable mirrors and two different multi-reference wavefront sensors with natural guide stars. In this article we present the MAD design, some aspects of the MAD calibration and the first closed-loop results in the laboratory in Single Conjugated Adaptive Optics (SCAO) and Ground Layer Adaptive Optics (GLAO) configurations. To cite this article: E. Marchetti et al., C. R. Physique 6 (2005).     

Triazolo-linked cinchona alkaloid carbamate anion exchange-type chiral stationary phases: Synthesis by click chemistry and evaluation

Immobilization strategy based on Huisgen 1,3-dipolar cycloaddition (click chemistry) of 10,11-didehydrocinchona tert-butylcarbamates to azido-grafted silica gels has been evaluated for preparation of novel chiral stationary phases (CSP 1-3). The resultant 1,2,3-triazole-linked CSPs were tested under various mobile phase conditions (polar organic and reversed phase mode) with a representative set of structurally diverse racemic acids including N-protected aminoacids, aromatic and aryloxycarboxylic acids as well as binaphthol phosphate. The chiral recognition performance of the C3-triazole-linked CSPs was found to mirror largely that of the known C3-thioether-linked CSP in terms of elution order, enantioselectivity and retention behavior. In an effort to assess the non-specific binding expressed as retention increment of these triazole-linked CSPs, the parent azidopropyl- and triazole-modified silica materials (thus not containing the chiral head ligand) were studied independently. Compared with the corresponding CSPs, the analyte retention on the azidopropyl control column was very low, and practically negligible on the corresponding triazole-modified reference column. Only minor losses in analyte retention behavior (<5%) were observed with triazole-linked CSPs after two month of continuous use with polar-organic and reversed-phase-type mobile phases, highlighting the excellent stability of the 1,2,3-triazole linker.     

Chiral recognition applications of molecularly imprinted polymers: a critical review

Molecular imprinting technology offers the unique opportunity to tailor chiral stationary phases with predefined chiral recognition properties by employing the enantiomers of interest as binding-site-forming templates. Added advantages, such as ease of preparation, chemical robustness, low-cost production, and the possibility of shaping molecularly imprinted polymers (MIPs) in various self-supporting formats, render them attractive materials for a broad range of chiral recognition applications. In this review a critical overview on recent developments in the field of MIP-based chiral recognition applications is given, focusing on separation techniques and molecular sensing. Inherent limitations associated with the use of enantioselective MIP materials in high-performance separation techniques are outlined, including binding site heterogeneity and slow mass transfer characteristics. The prospects of MIP materials as versatile recognition elements for the design of enantioselective sensor systems are highlighted.     

Single-crystal characterization of Co7(OH)6(H2O)3(C4H4O4)47H2O; A new cobalt succinate identified through high-throughput synthesis

A new form of cobalt succinate has been discovered using high-throughput methods and its structure was solved by single crystal X-ray diffraction. Co₇(C₄H₄O₄)₄(OH)₆(H₂O)₃7H₂O crystallizes in the monoclinic space group P2₁/c with cell parameters: a=7.888(2) Å, b=19.082(6) Å, c=23.630(7) Å, β=91.700(5)°, V=3555(2) Å³, R₁=0.0469. This complex structure, containing 55 crystallographically distinct non-hydrogen atoms, is compared to the previously reported nickel phase, characterized using ab initio structure solution from synchrotron powder diffraction data.     

Polymerization of Cyclic Monomers, 10,

Methyl 2‐(bicyclo[3.1.0]hex‐1‐yl)acrylate ( 1 ) was synthesized from methyl 2‐(cyclopentene‐1‐yl)‐2‐hydroxyacetate by cyclopropanation, followed by oxidation to the corresponding bicyclic 2‐oxoacetate and Wittig olefination with methyltriphenylphosphonium bromide. Initiated with 2,2′‐azoisobutyronitrile at 65 °C in chlorobenzene, the radical homopolymerization of 1 occurred with opening of the cyclopropane ring leading to a polymer with a glass transition temperature of 90 °C. The reactivity of 1 in radical copolymerization was higher than that of methyl methacrylate.

     

Synthesis and Biological Characterization of Monomeric and Tetrameric RGD-Cryptophycin Conjugates

The effective delivery of cytotoxic agents to tumor cells is a key challenge in anticancer therapy. Multivalent integrinspecific ligands are considered a promising tool to increase the binding affinity, selectivity, and internalization efficiency of small-molecule drug conjugates. Herein, we report the synthesis and biological evaluation of a multimeric conjugate containing the high-affinity integrin α_vβ₃ binding ligand RAFT-c(RGDfK)₄, a lysosomally cleavable Val-Cit linker, and cryptophycin-55 glycinate, a potent inhibitor of tubulin polymerization. In vitro cytotoxicity assays verified that the multimeric RGD-cryptophycin conjugate displays improved potency compared to the monomeric analogue in integrin α_vβ₃ overexpressing tumor cell lines, while significantly reduced activity was observed in the integrin-negative cell line.     

Localizing nearby sound sources in a classroom: binaural room impulse responses

Binaural room impulse responses (BRIRs) were measured in a classroom for sources at different azimuths and distances (up to 1 m) relative to a manikin located in four positions in a classroom. When the listener is far from all walls, reverberant energy distorts signal magnitude and phase independently at each frequency, altering monaural spectral cues, interaural phase differences, and interaural level differences. For the tested conditions, systematic distortion (comb-filtering) from an early intense reflection is only evident when a listener is very close to a wall, and then only in the ear facing the wall. Especially for a nearby source, interaural cues grow less reliable with increasing source laterality and monaural spectral cues are less reliable in the ear farther from the sound source. Reverberation reduces the magnitude of interaural level differences at all frequencies; however, the direct-sound interaural time difference can still be recovered from the BRIRs measured in these experiments. Results suggest that bias and variability in sound localization behavior may vary systematically with listener location in a room as well as source location relative to the listener, even for nearby sources where there is relatively little reverberant energy.     

State of order in blends of poly(butylene terephthalate) with poly(ethylene terephthalate) or polycarbonate

Blends of PBT with PET or PC were studied by X-ray diffraction and DSC for different conditions of crystallization. PBT and PET crystallize very similarly, though they are recognized as partially compatible in the melt. In the PBT/PC blends X-ray diffraction examinations show crystallization of PC after 4 h of annealing. In the melt, both components are compatible. T_g-calculations indicate a plasticizing effect. In both kinds of blends, PBT crystallizes faster than PC or PET. Fast crystallization processes were examined by X-ray diffraction measurements with synchrotron radiation.