Full automation of derivatization--solid-phase microextraction-gas chromatography-mass spectrometry with a dual-arm system for the determination of organometallic compounds in aqueous samples

The determination of organometallic compounds in aqueous samples by in-vial derivatization and headspace solid-phase microextraction (SPME)-gas chromatography (GC)-mass spectrometry (MS) has been fully automated using a Twin PAL dual-arm robotic system. Linearity, accuracy, sensitivity for a series of n-methyl, n-ethyl, and n-phenyl metal substituted chloride compounds of tin, lead, and mercury were investigated. The automated method was compared to similar manual methods and improved precision, speed and throughput was achieved. By originally programming the Twin PAL dual-arm system with the supplier's software (Cycle Composer, Version 1.5.0) the arms on the robot were only able to work in sequence. However, in order to have a flexible system and exploit time efficiently the robotic arms must work simultaneously. This was accomplished by programming the robot with the new software package called Cruise Control 4-2 for Twin PALs. Compared to Cycle Composer, Cruise Control 4-2 enhanced the speed and throughput of the automated system further. In addition, with a built-in crash prevention protocol and an improved user interface a more user-friendly system was obtained.     

Quantitative 13C-NMR spectroscopy of coals using 200 MHz-spectrometers

Summary A technique is described for recording all carbons in coals almost quantitatively using 200 MHz NMR-spectrometers. A spinning rate of 8 kHz and single pulse excitation are employed to achieve this aim. The determined aromaticities obtained by means of single-pulse excitation and cross-polarisation experiments are compared. Furthermore, dipolar dephasing experiments are applied to illustrate that a great part of Cq-carbon cannot be observed using the cross-polarisation technique.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Ein Kriterium für die Richtigkeit der Milnor-Vermutung

Let F denote a field of characteristic ≠2. The Witt ring WF (i.e. the ring of similarity classes of quadratic forms with coefficients in F) will be characterized by taking the similarity classes of certain Pfister forms [2] as generators and using suitable relations among them (theorem 1). In order to characterize GF, the graded ring associated to WF, in terms of generators and relations Milnor [4] constructed a homomorphism from his ring k_*F onto GF and conjectured this homomorphism to be an isomorphism. This conjecture turns out to be equivalent to a problem on ideals in a commutative ring (theorem 2).     

PORPHYRIN-INDUCED PHOTODAMAGE TO ISOLATED HUMAN NEUTROPHILS

Abstract— Human neutrophils were irradiated with light at 340–380 nm in the presence of low concentrations of protoporphyrin or uroporphyrin. At increasing light doses or increasing concentrations of protoporphyrin, the neutrophils rapidly lost the ability of locomotion. Also, neutrophil chemiluminescence and hexose-monophosphate shunt activity rapidly declined. An early event was leakage of endogenous K⁺ followed by lactate dehydrogenase and at a later stage leakage of particle-bound acid phosphatase. A number of cellular enzymes were inactivated, the susceptibility to inactivation decreased in the order: succinate dehydrogenase > lactate dehydrogenase > glutamate dehydrogenase > acid phosphatase. Uroporphyrin had no effect on neutrophil functions, leakage of K⁺, or cellular enzymes. The results suggest that photodamage to the plasma membrane and the mitochondria are earlier events than photodamage to lysosomes.     

Al3Li4(BH4)13: A Complex Double‐Cation Borohydride with a New Structure

The new double‐cation Al–Li–borohydride is an attractive candidate material for hydrogen storage due to a very low hydrogen desorption temperature (～70 °C) combined with a high hydrogen density (17.2 wt %). It was synthesised by high‐energy ball milling of AlCl₃ and LiBH₄. The structure of the compound was determined from image‐plate synchrotron powder diffraction supported by DFT calculations. The material shows a unique 3D framework structure within the borohydrides (space group=P‐43n, a=11.3640(3) Å). The unexpected composition Al₃Li₄(BH₄)₁₃ can be rationalized on the basis of a complex cation [(BH₄)Li₄]³⁺ and a complex anion [Al(BH₄)₄]^?. The refinements from synchrotron powder diffraction of different samples revealed the presence of limited amounts of chloride ions replacing the borohydride on one site. In situ Raman spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TG) and thermal desorption measurements were used to study the decomposition pathway of the compound. Al–Li–borohydride decomposes at ～70 °C, forming LiBH₄. The high mass loss of about 20 % during the decomposition indicates the release of not only hydrogen but also diborane.     

The inverse sandwich complex [(K(18-crown-6))2Cp][CpFe(CO)2]--unpredictable redox reactions of [CpFe(CO)2]I with the silanides Na[SiRtBu2] (R = Me, tBu) and the isoelectronic phosphanyl borohydride K[PtBu2BH3

The dimeric iron carbonyl [CpFe(CO)(2)](2) and the iodosilanes tBu(2)RSiI were obtained from the reaction of [CpFe(CO)(2)]I with the silanides Na[SiRtBu(2)] (R = Me, tBu) in THF. By the reactions of [CpFe(CO)(2)]I and Na[SiRtBu(2)] (R = Me, tBu) the disilanes tBu(2)RSiSiRtBu(2) (R = Me, tBu) were additionally formed using more than one equivalent of the silanide. In this context it should be noted that reduction of [CpFe(CO)(2)](2) with Na[SitBu(3)] gives the disilanes tBu(3)SiSitBu(3) along with the sodium ferrate [(Na(18-crown-6))(2)Cp][CpFe(CO)(2)]. The potassium analogue [(K(18-crown-6))(2)Cp][CpFe(CO)(2)] (orthorhombic, space group Pmc2(1)), however, could be isolated as a minor product from the reaction of [CpFe(CO)(2)]I with [K(18-crown-6)][PtBu(2)BH(3)]. The reaction of [CpFe(CO)(2)](2) with the potassium benzophenone ketyl radical and subsequent treatment with 18-crown-6 yielded the ferrate [K(18-crown-6)][CpFe(CO)(2)] in THF at room temperature. The crown ether complex [K(18-crown-6)][CpFe(CO)(2)] was analyzed using X-ray crystallography (orthorhombic, space group Pna2(1)) and its thermal behaviour was investigated.