Synthesis,solution dynamics and chemical vapour deposition of heteroleptic zinc complexes via ethyl and amide zinc thioureides

Ethyl and amide zinc thioureides [L¹ZnEt]₂ (1), [L¹*ZnEt]₂ (2) and [L¹Zn(N(SiMe₃)₂)]₂ (3) have been synthesised from the equimolar reaction of thiourea ligands (HL¹ = ⁱPrN(H)CSNMe₂ and HL¹* = PhN(H)CSNMe₂) with diethyl zinc and zinc bis[bis(trimethylsilyl)amide] respectively. New routes towards heteroleptic complexes have been investigated through reactions of 1, 2 and 3 with β-ketoiminates (HL² = [(Me)CN(H){ⁱPr}–CHC(Me) O]), bulky aryl substituted β-diiminates (HL³ = [(Me)CN(H){Dipp}–CHC(Me) N{Dipp}] (Dipp = diisopropylphenyl) and HL³* = [(Me)CN(H){Dep}–CHC(Me) N{Dep}] (Dep = diethylphenyl)) and donor-functionalised alcohols (HL⁴ = Et₂N(CH₂)₃OH and HL⁴* = Me₂N(CH₂)₃OH) and have led to the formation of the heteroleptic complexes [L¹*ZnL³*] (5), [L¹ZnL⁴]₂ (6), [L¹ZnL⁴*]₂ (7), [L¹*ZnL⁴] (8) and [L¹*ZnL⁴*] (9). All complexes have been characterised by ¹H and ¹³C NMR, elemental analysis, and the X-ray structures of HL¹*, 1, 2, 6 and 7 have been determined via single crystal X-ray diffraction. Variable temperature ¹H, COSY and NOESY NMR experiments investigating the dynamic behaviour of 5, 6 and 7 have shown these molecules to be fluxional. On the basis of solution state fluxionality and thermogravimetric analysis (TGA), alkoxyzinc thioureides 6 and 7 were investigated as single-source precursors for the deposition of the ternary material zinc oxysulfide, Zn(O,S), a buffer layer used in thin film photovoltaic devices. The aerosol-assisted chemical vapour deposition (AACVD) reaction of 7 at 400 °C led to the deposition of the heterodichalcogenide material Zn(O,S), which was confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX), with optical properties investigated using UV/vis spectroscopy, and surface morphology and film thickness examined using scanning electron microscopy (SEM).

This work investigates the synthesis and solution dynamics of heteroleptic alkoxyzinc thioureides for the chemical vapour deposition of the heterochalcogenide material Zn(O,S).     

Structural phase transitions in CaC2

Pure CaC2, free of CaO impurities, was obtained by the reaction of elemental calcium with graphite at 1,070 K. By means of laboratory X-ray and synchrotron powder diffraction experiments, the phase diagram was investigated in the temperature range from 10 K to 823 K; this confirmed the literature data that reported the partial coexistence of up to four modifications. Aside from a cubic high-temperature modification CaC2 IV (Fm3m, Z = 4) and the well-known tetragonal modification CaC2 I (I4/mmm, Z = 2), a low-temperature modification CaC2 II (C2/c, Z =4) that crystallizes in the ThC2 structure type and a metastable modification CaC2 III (C2/m, Z = 4) that crystallizes in a new structure type were found. It was shown that phase transition temperatures as well as the relative amounts of the various CaC2 modifications depend upon the size of the crystallites, the thermal treatment. and the purity of the sample, as a comparison with technical CaC2 confirmed.     

Hydrogen transfer reaction on the surface of an oxide catalyst

RuO2(110) exposes two kinds of active surface species (acidic and basic centers) that govern the interaction of the gas phase in contact with the catalyst's surface. Here we will elucidate the cooperative interplay of these two active surface sites for a simple model reaction, namely the water formation over RuO2 catalysts when supplying hydrogen and oxygen from the gas phase. The bridging O atoms harvest the hydrogen from the gas phase, while the on-top O atoms pick up those adsorbed hydrogen atoms from the bridging O atoms to form water. This mechanism of hydrogen transfer is mediated by a strong hydrogen bond. Hydrogen transfer is expected to play a vital role for the whole class of catalyzed hydrogenation and dehydrogenation reactions of hydrocarbons over RuO2.     

Ru(0001) model catalyst under oxidizing and reducing reaction conditions: in-situ high-pressure surface X-ray diffraction study

With surface X-ray diffraction (SXRD) using a high-pressure reaction chamber we investigated in-situ the oxidation of the Ru(0001) model catalyst under various reaction conditions, starting from a strongly oxidizing environment to reaction conditions typical for CO oxidation. With a mixture of O(2) and CO (stoichiometry, 2:1) the partial pressure of oxygen has to be increased to 20 mbar to form the catalytically active RuO(2)(110) oxide film, while in pure oxygen environment a pressure of 10(-5) mbar is already sufficient to oxidize the Ru(0001) surface. For preparation temperatures in the range of 550-630 K a self-limiting RuO(2)(110) film is produced with a thickness of 1.6 nm. The RuO(2)(110) film grows self-acceleratedly after an induction period. The RuO(2) films on Ru(0001) can readily be reduced by H(2) and CO exposures at 415 K, without an induction period.     

High-throughput NMR-based screening with competition binding experiments

The Achilles heel of ligand-based NMR screening methods is their failure to detect high-affinity ligands and molecules that bind covalently to the receptor. We have developed a novel approach for performing high-throughput screening with NMR spectroscopy that overcomes this limitation. The method also permits detection of potential high-affinity molecules that are only marginally soluble, thus significantly enlarging the diversity of compounds amenable to NMR screening. The techniques developed utilize transverse and/or selective longitudinal relaxation parameters in combination with competition binding experiments. Mathematical expressions are derived for proper setup of the NMR experiments and for extracting an approximate value of the binding constant for the identified ligand from a single-point measurement. With this approach it is possible to screen thousands of compounds in a short period of time against protein or DNA and RNA fragments. The methodology can also be applied for screening plant and fungi extracts.     

Potential cerebral perfusion agents. Synthesis and evaluation of new radioiodinated barbituric acid analogs

Two new ¹²⁵I-labeled barbituric acid analogs, 5-ethyl-5-(E-1-iodo-1-penten-5-yl)2-thiobarbituric acid ( 4 ) and 5-ethyl-5-( m -iodophenyl)barbituric acid ( 7 ), have been prepared and evaluated in rats as potential cerebral perfusion agents. Annulation of 2-ethyl-2-(E-1-iodo-1-penten-5-yl)malonate ( 3 ) with thiourea in the presence of sodium ethoxide gave the 5-ethyl-5-(E-1-iodo-1-penten-5-y1)-thiobarbituric acid ( 4 ). Diethyl 2-ethyl-2-phenyl-malonate was treated with thallium(III) trifluoroacetate followed by addition of aqueous potassium iodide to provide diethyl 2-ethyl-2-(m-iodophenyl)malonate ( 10 ). The malonic ester derivative 10 was condensed with urea in the presence of sodium hydride to give the desired 5-ethyl-5-(m-iodophenyl)barbituric acid ( 7 ), and a decarbethoxylation product, 2-(m-iodophenyl)butyric acid ( 11 ). Iodine-125-labeled 4 and 7 were synthesized in the same manner and the tissue distribution of these new agents evaluated in rats. Both [¹²⁵I] 4 and [¹²⁵I] 7 showed high brain uptake. Significant in vivo deiodination was detected with [¹²⁵I] 4 whereas [¹²⁵I] 7 was found to be stable to deiodination.     

香豆素类化合物的一种新合成方法

香豆素类化合物是一类重要的有生物活性的天然产物,也可用作香料、阻凝剂和三线态光敏剂。用 Meldrum 酸合成该类化合物,已有一些报道。我们在研究 Meldrum 酸系列     

十二烯基丁二酸改性氧化锆色谱固定相性能研究

本文用十二烯基丁二酸（DSA）改性氧化锆得到一种新的锆基质色谱固定相。改性前后的红外光谱的差异表明，DSA以两个羧基与氧化锆结合，由于多位点结合方式提高了固定相的稳定性，因此固定相可以在碱性（pH8．5）条件下稳定使用。锆基质色谱固定相具有较强的疏水性，用于中性及碱性化合物的分离取得了满意的结果。     

龙爪芦荟和库拉索芦荟中微量锗的测定与红外光谱区别

采用吸光光度法对龙爪芦荟和库拉索芦荟中的微量锗进行了测定,并探讨了两种芦荟的红外光谱的区别。结果表明,龙爪芦荟中含锗量在26.1～28.6μg·g-1,回收率为91.6%～97 5%。库拉索芦荟中含锗量在16.8～20.0μg·g-1,回收率为87.1%～94.5%。两种芦荟的FT IR光谱图在2100cm-1处有明显差异,由此可区别两种芦荟。     

Reactor production and processing of therapeutic radioisotopes for applications in nuclear medicine

In this paper the reactor production of a variety of therapeutic radionuclides of current clinical interest are discussed. Examples include radioisotopes produced by single neutron capture and those which are available from –/decay of reactor-produced parent radioisotopes. Two examples of generator parents produced by double neutron capture of targets are also discussed. One key example in this category is¹⁸⁸W, produced from irradiation of enriched¹⁸⁶W. The production of¹⁸⁸W in the ORNL High Flux Isotope Reactor and the fabrication and performance of the first production level large-scale clinical prototype¹⁸⁸W/¹⁸⁸Re generators are also described.