Magnetic penetration depth of 585-01585-01585-01: Tc ∼ σ0 in the overdoped region

We report transverse field muon spin rotation experiments carried out on Tl₂Ba₂CuO₆₊. This system spans the whole overdoped regime, in which T_c is reduced by excess oxygen doping despite an increasing normal state carrier concentration. In the heavily overdoped regime the extrapolated low temperature depolarization rate(0) is found to scale linearly with the superconducting critical temperature T_c similar to the behavior previously observed for other cuprates in the underdoped regime. In the framework of the clean limit London model,(0) ^–2 n _s (0)/m _s ^* , suggesting that the depression of T_c by overdoping is associated with a decrease of the superconducting condensate density. This needs to be understood in view of the observed increase in the normal state carrier density. We discuss some possible explanations for this behavior.     

Cationic tetrakis(nucleobase)complexes of PtII as metalloligands and potential building blocks for molecular architectures

Three cationic tetrakis(nucleobase) complexes of Pt(II) have been synthesized: [Pt(Hmhyp-N7)4](NO3)2.H2O 1, [Pt(Hegua-N7)4](NO3)2.2KNO(3).5H2O and trans-[Pt(Hmcyt-N3)2(Hegua-N7)2](NO3)2 3 (Hmhyp = 9-methylhypoxanthine, Hegua = 9-ethylguanine, Hmcyt = 1-methylcytosine). The X-ray crystal structure of has been determined. All three cationic compounds rapidly react with Hg(II), but gel formation prevented an adequate characterization of the products formed. However, a Cu(II) adduct of was isolated in crystalline form and characterized crystallographically. [{(H2O)Cu(Hmhyp)4Pt}2Cu(ClO4)4)](ClO4)2(NO3)4.6H2O crystallizes in a centrosymmetric Cu-Pt-Cu-Pt-Cu chain structure with Cu-Pt separations of 2.791(1)A(outside) and 3.8980(9)A(inside). Two of the three Cu(II) ions are bound via exocyclic O(6) sites of the Hmhyp nucleobases. At neutral and moderate alkaline pH both and form virtually insoluble precipitates, which redissolve at strongly alkaline pH to give eventually anionic [Pt(L)4]2- species (L = mhyp, egua). Finally, interacts with complementary Hmcyt to give Watson-Crick associates, as demonstrated by 1H NMR spectroscopy in DMSO-d(6).     

Polarographische Bestimmung kleiner Wolframmengen

Zusammenfassung Sehr kleine Wolframkonzentrationen von etwa 0,1–20 g/ml werden am besten in Grundlösungen mit 9–10 m PerchlorsÄure + 0,6–0,7 m WeinsÄure polarographisch bestimmt. Für höhere Konzentrationen von etwa 20–100 g/ml sind Lösungen mit 9–10 m SalzsÄure + 0,3 m WeinsÄure (oder 0,1 m CitronensÄure) + 0,01% Gelatine vorzuziehen.

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Summary For the determination of very small concentrations of tungsten (0.1 to 20 g/ml) solutions with 9–10 M perchloric + 0.6–0.7 M tartaric acid are especially suitable. The determination of higher concentrations (20–100 g/ml) should be preferably performed in solutions with 9–10 M hydrochloric + 0.3 M tartaric acid (or 0.1 M citric acid) + 0.01% gelatin.

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Herrn Prof. Dr., Dr. h.c. Dr. h.c. Dr. h.c. Wilhelm Klemm zum 70. Geburtstag gewidmet.     

Separation of radionuclides from a fission product solution by ion exchange on alumina

The distribution of different radionuclides depends on their speciation in the real fission product solution and the electric charge of the alumina. The pH-value is the main parameter that influences the disyribution coefficient. By combination of an acidic adsorption and an alkaline desorption process, the interesting fission molybdenum can be separated. The distribution ratios of the relevant radionuclides are described.     

Synthesis of Carbo- and Heterocyclic Aldehydes Bearing an Adjacent Donor Group – Ozonolysis versus OsO4/KIO4-Oxidation

Summary. The synthesis of carbo- and heterocyclic aldehydes bearing an ipso-methoxy group is investigated. The synthetic sequence is based on an initial Grignard addition of an olefin to a cyclic ketone followed by methylation of the resulting tertiary alcohol. The terminal olefin serves as precursor for the aldehyde functionality. Oxidation by ozonolysis turned out to depend significantly on the distance of the donor methoxy group. The observed side reactions could be circumvented by applying a one-pot OsO₄ mediated diol formation followed by Malaprade oxidation using KIO₄. A series of carbo- and heterocyclic precursors were successfully converted to the title products.     

Effect of Zn...Zn separation on the hydrolytic activity of model dizinc phosphodiesterases

From the study of highly preorganized model systems, experimental support has been obtained for a possible functional role of the Zn-(H)O...HO(H)-Zn motif in oligozinc hydrolases. The mechanistic relevance of such an array, which may be described as a hydrated form of a pseudo-terminal Zn-bound hydroxide, has recently been supported by DFT calculations on various metallohydrolase active sites. In the present targeted approach, the Zn...Zn distance in two related dizinc complexes has been controlled through the use of multifunctional pyrazolate-based ligand scaffolds, giving either a tightly bridged Zn-O(H)-Zn or a more loosely bridged Zn-(H)O...HO(H)-Zn species in the solid state. Zn-bound water has been found to exhibit comparable acidity irrespective of whether the resulting hydroxide is supported by strong hydrogen-bonding in the O(2)H(3) moiety or is in a bridging position between two zinc ions, indicating that water does not necessarily have to adopt a bridging position in order for its pK(a) to be sufficiently lowered so as to provide a Zn-bound hydroxide at physiological pH. Comparative reactivity studies on the cleavage of bis(4-nitrophenyl)phosphate (BNPP) mediated by the two dizinc complexes have revealed that the system with the larger Zn...Zn separation is hydrolytically more potent, both in the hydrolysis and the transesterification of BNPP. The extent of active site inhibition by the reaction products has also been found to be governed by the Zn...Zn distance, since phosphate diester coordination in a bridging mode within the clamp of two zinc ions is only favored for Zn...Zn distances well above 4 A. Different binding affinities are rationalized in terms of the structural characteristics of the product-inhibited complexes for the two different ligand scaffolds, with dimethyl phosphate found as a bridging ligand within the bimetallic pocket.     

Complex formation of uranium(VI) with the amino acids l-glycine and l-cysteine: A fluorescence emission and UV–Vis absorption study

The complexation of uranium(VI) with the amino acids l-glycine and l-cysteine has been investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and UV–Vis spectroscopy at a low pH range. The identified 1:1 and 1:2 uranyl-l-glycine complexes fluoresce and have similar absorbance properties. In contrast to the glycine system, uranyl forms two different non-fluorescent 1:1 complexes with l-cysteine, showing individual absorbance properties under the given experimental conditions. The corresponding complex formation constants were calculated using the spectroscopic data.     

Enantioselective Synthesis of Pseudomonic Acids. I. Synthesis of Key Intermediates

An enantioselective synthesis of key intermediates for the synthesis of the anti-microbially active pseudomonic acids A ( 1 ), B ( 2 ) and C ( 3 ) is described. D -Ribose ( 4 ) was used as starting material.     

Electrothermal atomic absorption spectrometric determination of lead in high-purity reagents with flow-injection on-line microcolumn preconcentration and separation using a macrocycle immobilized silica gel sorbent

A fully automated procedure for the determination of ng l⁻¹ amounts of lead has been developed using flow injection (FI) online column preconcentration coupled with electrothermal atomic absorption spectrometry (ETAAS). The proposed FI manifold and its operation make possible the introduction of the total eluate volume into the graphite atomizer, avoiding the necessity for optimization of subsampling the eluate. The interference of other heavy metal ions due to competition for active sites of the sorbent is overcome using a highly selective macrocycle immobilized on silica gel (Pb-02). Lead is adsorbed on a microcolumn (50 μl) packed with Pb-02, and after washing the column with dilute nitric acid, air is introduced to remove all solution from the column and connecting tubing. The sorbed analyte is then eluted quantitatively into the graphite tube atomizer, preheated to 100°C, with 36 μl of ETDA solution (0.035 mol l⁻¹, pH 10.5), propelled by air in order to minimize dispersion. The collection efficiency was 77% and with a sample loading flow rate of 3 ml min⁻¹ and a 60 s preconcentration time, the enhancement factor was 77 and the throughput was 17 samples per hour. The relative standard deviation (n = 10) at the 300 ng l⁻¹ level was 2.7%, and the detection limit (3σ) was 0.4 ng l⁻¹. No interference from heavy metals was observed, but ions of Ba²⁺, Sr²⁺ and K⁺ were found to interfere when the concentration ratios of interferent to lead exceeded values of 2000, 20 000 and 200 000, respectively. Quantitative recovery of lead was achieved from sodium, magnesium, aluminum, lanthanum and heavy metal salt solutions. The high selectivity and sensitivity, combined with extremely low blank values, make the proposed technique particularly attractive for the analysis of high-purity reagents, semiconductors and other high-purity materials. Results are presented for the determination of lead in some high-purity reagents.