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991.
Bifunctional Cyclam‐Based Ligands with Phosphorus Acid Pendant Moieties for Radiocopper Separation: Thermodynamic and Kinetic Studies
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Monika Paúrová Jana Havlíčková Aneta Pospíšilová Miroslav Vetrík Dr. Ivana Císařová Dr. Holger Stephan Dr. Hans‐Jürgen Pietzsch Dr. Martin Hrubý Prof. Petr Hermann Prof. Jan Kotek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4671-4687
Two macrocyclic ligands based on cyclam with trans‐disposed N‐methyl and N‐(4‐aminobenzyl) substituents as well as two methylphosphinic (H2 L1 ) or methylphosphonic (H4 L2 ) acid pendant arms were synthesised and investigated in solution. The ligands form stable complexes with transition metal ions. Both ligands show high thermodynamic selectivity for divalent copper over nickel(II) and zinc(II)—K(CuL) is larger than K(Ni/ZnL) by about seven orders of magnitude. Complexation is significantly faster for the phosphonate ligand H4 L2 , probably due to the stronger coordination ability of the more basic phosphonate groups, which efficiently bind the metal ion in an “out‐of‐cage” complex and thus accelerate its “in‐cage” binding. The rate of CuII complexation by the phosphinate ligand H2 L1 is comparable to that of cyclam itself and its derivatives with non‐coordinating substituents. Acid‐assisted decomplexation of the copper(II) complexes is relatively fast (τ1/2=44 and 42 s in 1 M aq. HClO4 at 25 °C for H2 L1 and H4 L2 , respectively). This combination of properties is convenient for selective copper removal/purification. Thus, the title ligands were employed in the preparation of ion‐selective resins for radiocopper(II) separation. Glycidyl methacrylate copolymer beads were modified with the ligands through a diazotisation reaction. The separation ability of the modified polymers was tested with cold copper(II) and non‐carrier‐added 64Cu in the presence of a large excess of both nickel(II) and zinc(II). The experiments exhibited high overall separation efficiency leading to 60–70 % recovery of radiocopper with high selectivity over the other metal ions, which were originally present in 900‐fold molar excess. The results showed that chelating resins with properly tuned selectivity of their complexing moieties can be employed for radiocopper separation. 相似文献
992.
In Situ Solid‐State Reactions Monitored by X‐ray Absorption Spectroscopy: Temperature‐Induced Proton Transfer Leads to Chemical Shifts
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Dr. Joanna S. Stevens Dr. Monika Walczak Dr. Cherno Jaye Dr. Daniel A. Fischer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15600-15604
The dramatic colour and phase alteration with the solid‐state, temperature‐dependent reaction between squaric acid and 4,4′‐bipyridine has been probed in situ with X‐ray absorption spectroscopy. The electronic and chemical sensitivity to the local atomic environment through chemical shifts in the near‐edge X‐ray absorption fine structure (NEXAFS) revealed proton transfer from the acid to the bipyridine base through the change in nitrogen protonation state in the high‐temperature form. Direct detection of proton transfer coupled with structural analysis elucidates the nature of the solid‐state process, with intermolecular proton transfer occurring along an acid‐base chain followed by a domino effect to the subsequent acid‐base chains, leading to the rapid migration along the length of the crystal. NEXAFS thereby conveys the ability to monitor the nature of solid‐state chemical reactions in situ, without the need for a priori information or long‐range order. 相似文献
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Virgil Percec Monika J. Sienkowska 《Journal of polymer science. Part A, Polymer chemistry》2009,47(2):628-634
Pentaerythritol tetrakis(2‐iodopropionate) was used as a tetrafunctional initiator for the Na2S2O4 catalyzed SET‐DTLRP of n‐butyl acrylate in water at room temperature. The resulting tetrafunctional poly(n‐butyl acrylate) macroinitiator with Mn = 14,864 or Mn = 3627 per arm was used to initiate the SET‐DTLRP of vinyl chloride and provide the first examples of four‐arm star‐block copolymers [PVC‐b‐PBA‐CH(CH3)? CO? O? CH2]4C. The Mn of the PVC segment from each arm of the four‐arm star‐block copolymer varied between 353 and 33,622. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 628–634, 2009 相似文献
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Monika Winklmeier 《Journal of Differential Equations》2008,245(8):2145-2175
The operator associated to the angular part of the Dirac equation in the Kerr-Newman background metric is a block operator matrix with bounded diagonal and unbounded off-diagonal entries. The aim of this paper is to establish a variational principle for block operator matrices of this type and to derive thereof upper and lower bounds for the angular operator mentioned above. In the last section, these analytic bounds are compared with numerical values from the literature. 相似文献
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