Hydroamination of Dihapto-Coordinated Benzene and Diene Complexes of Tungsten: Fundamental Studies and the Synthesis of γ-Lycorane

Reactions are described for complexes of the form WTp(NO)(PMe₃)(η²-arene) and various amines, where the arene is benzene or benzene with an electron-withdrawing substituent (CF₃, SO₂Ph, SO₂Me). The arene complex is first protonated to form an η²-arenium species, which then selectively adds the amine. The resulting η²-5-amino-1,3-cyclohexadiene complexes can then be subjected to the same sequence with a second nucleophile to form 3-aminocyclohexene complexes, where up to three stereocenters originate from the arene carbons. Alternatively, 1,3-cyclohexadiene complexes containing an ester group at the 5 position (also prepared from an arene) can be treated with acid followed by an amine to form trisubstituted 3-aminocyclohexenes. When the amine is primary, ring closure can occur to form a cis-fused bicyclic γ-lactam. Highly functionalized cyclohexenes can be liberated from the tungsten through oxidative decomplexation. The potential utility of this methodology is demonstrated in the synthesis of the alkaloid γ-lycorane. An enantioenriched synthesis of a lactam precursor to γ-lycorane is also described. This compound is prepared from an enantioenriched version of the tungsten benzene complex. Regio- and stereochemical assignments for the reported compounds are supported by detailed 2D-NMR analysis and 13 molecular structure determinations (SC-XRD).     

On‐bead combinatorial synthesis and imaging of europium(III)‐based paraCEST agents aids in identification of chemical features that enhance CEST sensitivity

The rate of water exchange between the inner sphere of a paramagnetic ion and bulk water is an important parameter in determining the magnitude of the chemical exchange saturation transfer signal from paramagnetic CEST agents (paraCEST). This is governed by various geometric, steric and ligand field factors created by macrocyclic ligands surrounding the paramagnetic metal ion. Our previous on‐bead combinatorial studies of di‐peptoid–europium(III)–1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA)–tetraamide complexes revealed that negatively charged groups in the immediate vicinity of the metal center strongly enhances the CEST signal. Here, we report a solid phase synthesis and on‐bead imaging of 76 new DOTA derivatives that are developed by coupling with a single residue onto each of the three arms of a DOTA–tetraamide scaffold attached to resin beads. This single residue predominantly carries negatively charged groups blended with various physico‐chemical characteristics. We found that non‐bulky negatively charged groups are best suited at the immediate vicinity of the metal ion, while positive, bulky and halogen containing moieties suppress the CEST signal. Copyright © 2017 John Wiley & Sons, Ltd.     

4-Hydroxy-3,5-pyridinedicarboxylic Acids: Synthesis,Complexation Properties Towards Fe(III), Al(III), Cu(II), Zn(II), Human Serum Albumin,and Cellular Toxicity

4-hydroxy-3,5-pyridinedicarboxylic acid (DQ58) and 4-hydroxy-1-methyl-3,5-pyridinedicarboxylic acid (DQ71508) have been synthesized, and their Fe(III), Al(III), Cu(II), and Zn(II) coordination properties have been studied by potentiometry, UV–Vis spectroscopy (in the case of Fe(III), Al(III), Cu(II)), ¹H-NMR (for Al(III)) and EPR (for Cu(II)). The thermodynamic results were used to model the extent of the toxic metal ions decorporation (Fe(III) or Al(III)) in the presence of the essential metal ions (Cu(II) or Zn(II)). DQ58 and DQ71508 were demonstrated to interact with human serum albumin (HSA), which is assumed to be the main serum transporter of the chelators, and binding constants have been obtained by ultrafiltration. IC₅₀ values of 5.185 × 10^?3 and 1.033 × 10^?3 mol·L^?1 were collected after 24 and 48 h of treatment with DQ71508 towards human embryonic kidney HEK-293 cells, demonstrating the relatively low cytotoxicity of this compound. According to these results, both DQ58 and DQ71508 seem to be potential candidates for Fe chelation therapy, and DQ58 is a better Fe(III) chelator than DQ71508.     

Evaluation of pI Marker Sources for cIEF Characterization of a Therapeutic Antibody

Isoelectric point markers from five sources have been compared and evaluated to replace the Bio-Rad brand markers (pI 6.2 and 7.5) used for pI determination of the charge isoforms of a therapeutic monoclonal cancer antibody (pI range of 6.3–7.2) in a capillary isoelectric focusing (cIEF) identity assay. Two of the five sources were found to be optimal replacement markers for the antibody molecule. Isoelectric point markers manufactured by Fluka (pI 5.5 and 7.6) and synthetic peptide markers prepared in-house (pI 5.91 and 7.27) produced antibody cIEF profiles, pI values, and percent corrected peak areas most comparable to the Bio-Rad marker results. Marker robustness was demonstrated by evaluating the markers using different CE instruments, marker lots, and capillary lots, as well as evaluating the markers at multiple Amgen sites.     

Studies on the drift properties and spatial resolution using a microMEGAS-equipped time projection chamber

R&D studies on the performance as well as on the gas properties of the microMEGAS-based time projection chamber with standard readout were carried out in June 2005 using 4 GeV/c pion beam in a magnetic field from 0 to 1 T at the proton synchrotron beam line at KEK, Japan. Analysis of the electron drift velocity, diffusion constant and point resolution of padrow measurement for MicroMEGAS TPC filled with 95% argon and 5% isobutane gas are presented. The underlying physical mechanism which determines the optimal TPC performance are briefly discussed. Preliminary measurements of gas properties and spatial resolution in close agreement with the analytical calculation and MAGBOLTZ simulation are summarized and presented in this paper.      

RhCl_3/CH_3I催化醋酸甲酯羰基化制醋酐——Ⅱ.LiOAc存在下的动力学和机理

1.前言 在醋酸甲酯羰基化高活性均相铑催化体系中,CH_3I和锂化合物及含氮、膦有机物是最常用的助催剂。Schrod等首先对RhCl_3—CH_3I—有机碱—络合物体系催化醋酸甲酯羰基化反应动力学及红外光谱进行了研究,发现反应对醋酸甲酯为零级;CO的反应级数在压力1.5MPa以上也为零级;铑和CH_3I反应级数为一级;膦的反应级数随浓度增加由一级变为零级;Cr(CO)_6对反应速率影响不大,同时发现存在着中间反应物Rh(CO)_2I_2~-。根据这些实验事实,他们提出了类似于甲醇羰基化制醋酸的催化反应机理,认为速率控制步骤是CH_3I与Rh(CO)l-2~-的氧化加成,但他们没有报导有关锂化物助催剂的作用。Eastman公司的研究人员Polichnowski研究了RhCl_3—CH_3I—Lil体系催化醋酸甲酯羰基化动力学和原位红外光谱,也发现当反应总压在3.0MPa以上时,反应初速与CO压力无关,但RhCl_3,CH_3I和LiI等浓度     

Optically detected electron resonance in phosphorus-doped ZnTe

Samples of ZnTe showing near gap edge luminescence predominantly due to exciton recombination at shallow neutral acceptors and donor- acceptor pair recombination have been investigated using optically detected magnetic resonance (ODMR). Emission polarization changes at 2.318 eV were observed due to magnetic resonance of electrons at g_e = + 0.401 ± 0.004. The observations are consistent with the donor trapped electron resonance resulting from microwave induced changes in donor-acceptor pair photoluminescence.     

Determination of the strain distribution in a circular plate under uniform pressure for biaxial stress tests

A simple apparatus is described for generating a biaxial stress at the surface of a plastics testpiece in the form of a circular plate. A theory is developed for the calculation of the strain distribution in situations where the deflection of the centre of the plate is comparable with its thickness. Theoretical predictions are compared with strain values determined by a moiré fringe method and using strain gauges. These comparisons are made on two plates of different thickness loaded to pressure levels which produce similar maximum strains in the two plates but different deflection-to-thickness ratios. Conclusions are drawn on the applicability of the theory, and recommendations are made for the testing of plastics plates for failure studies.     

New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.     

A topological approach to evasiveness

The complexity of a digraph property is the number of entries of the vertex adjacency matrix of a digraph which must be examined in worst case to determine whether the graph has the property. Rivest and Vuillemin proved the result (conjectured by Aanderaa and Rosenberg) that every graph property that is monotone (preserved by addition of edges) and nontrivial (holds for some but not all graphs) has complexity Ω(v ²) wherev is the number of vertices. Karp conjectured that every such property is evasive, i.e., requires that every entry of the incidence matrix be examined. In this paper the truth of Karp’s conjecture is shown to follow from another conjecture concerning group actions on topological spaces. A special case of the conjecture is proved which is applied to prove Karp’s conjecture for the case of properties of graphs on a prime power number of vertices. Supported in part by an NSF postdoctoral fellowship Supported in part by NSF under grant No. MCS-8102248