Fluorometric assay of histamine in tissues and body fluids: Choice of the purification procedure and identification in the nanogram range

Summary Several procedures for the isolation of histamine from tissues and body fluids were examined. For the fluorometric assay of histamine concentrations higher than 1 g/g tissue or ml blood the extraction into n-butanol as well as the cation-exchange chromatography on Dowex 50W-X8 proved suitable. The determination of histamine in whole blood of dogs gave valid results only after chromatography on Dowex 50, in human plasma and gastric juice only after the combined application of both purification methods. Histamine was identified by thin-layer chromatography on cellulose, by inactivation in the presence of purified diamine oxidase from pig kidney and purified histamine methyltransferase from guinea-pig brain, by the biological activities and by the fluorescence spectra of the condensation product between histamine and o-phthaldialdehyde. Histamine concentrations in tissues and body fluids of man and some laboratory animals are reported.

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Fluorimetrische Bestimmung von Histamin in Geweben und Körperflüssigkeiten: Wahl eines geeigneten Reinigungsverfahrens und Identifizierung im ng-Bereich

Zusammenfassung Verschiedene Isolierungsverfahren für Histamin zur fluorimetrischen Bestimmung wurden geprüft. Für Histamingehalte von mehr als 1 g/g Gewebe oder Milliliter Vollblut eignet sich sowohl die Butanolextraktion als auch die Ionenaustausch-Chromatographie an Dowex 50W-X8, für Vollblut des Hundes nur das letztere Verfahren, für Plasma und Magensaft des Menschen nur die Kombination der beiden Isolierungsmethoden. Histamin wurde identifiziert durch Dünnschicht-Chromatographie auf Cellulose, Umsatz durch angereicherte Diaminoxydase und Histaminmethyltransferase, durch die Fluorescenzspektren nach Kondensation mit o-Phthaldialdehyd und durch seine biologische Aktivität. Die Histamingehalte in Geweben und Körperflüssigkeiten des Menschen und einiger Versuchstiere werden mitgeteilt.

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Members of SFB 37 (Restitution und Substitution innerer Organe of Deutsche Forschungsgemeinschaft).     

Analysis of methoxypyrazines in wine using headspace solid phase microextraction with isotope dilution and comprehensive two-dimensional gas chromatography

This study reports an optimized headspace-solid phase microextraction (HS-SPME) method for the determination of methoxypyrazines in wine. Analysis was performed by using comprehensive two-dimensional gas chromatography with novel detection capabilities, including nitrogen phosphorus detection (GC x GC-NPD) and time-of-flight mass spectrometry (GC x GC-TOFMS). In the latter, stable isotope dilution was performed for the quantitation of 2-methoxy-3-(2-methylpropyl) pyrazine (IBMP), using labelled 2-(2H3)methoxy-3-(2-methylpropyl)pyrazine (d3-IBMP) as the internal standard, and resolution of the two analogues was facilitated using the deconvolution capabilities of the TOFMS. This research represents the first report of HS-SPME with isotope dilution and GC x GC-TOFMS (GC x GC-IDTOFMS). Analysis by GC x GC-NPD enabled detection limits of 0.5 ng/L for the quantitation of IBMP, which was superior to that obtained using GC x GC-IDTOFMS (1.95 ng/L). Nevertheless, both methods were adequately sensitive for real wine analysis, yielding highly comparable IBMP concentrations of 26.1 and 27.8 ng/L, respectively, from a Sauvignon blanc wine. The complexity of the real wine headspace was simplified as a result of selective detection using GC x GC-NPD and, in the case of GC x GC-IDTOFMS, the use of extracted ion chromatograms (EICs).     

Strain relaxation in the epitaxy of La2/3Sr1/3MnO3 grown by pulsed-laser deposition on SrTiO3(001)

With a Curie point at 370?K, the half-metal (La_0.7Sr_0.3)MnO₃ (LSMO) is one of the most interesting candidates for electronic devices based on tunnel magnetoresistance. SrTiO₃ (STO) is up to now the best substrate for the epitaxy of suitable thin films of LSMO. The pseudocubic unit cell of rhombohedral LSMO has a parameter a _LSMO such that (a _STO ? a _LSMO)/a _LSMO = +?0.83% (where a _STO is the parameter of cubic STO) and an angle of 90.26°. As strained growth is tetragonal, relaxation implies recovery of both the pseudocubic parameter and of the original angle. In the LSMO layers that we prepare by pulsed-laser deposition, we show that these two processes are quite independent. The angular distortion is partially recovered by twinning in films 25?nm thick, while recovery of the parameter never occurs in the thickness range that we explored (up to 432?nm). A relaxation, however, takes place above a thickness of 100?nm, associated with a transition from two-dimensional to three-dimensional columnar growth. It is accompanied by chemical fluctuations. Our magnetic measurements exhibit Curie temperatures and magnetic moments very close to the bulk values in those layers where the crystal parameter is strained but the angle partially relaxed.     

Single‐pulse pulsed laser polymerization–electron paramagnetic resonance investigations into the termination kinetics of n‐butyl acrylate macromonomers

The termination of model mid‐chain radicals (MCRs), which mimic radicals that occur in acrylate polymerization over a broad range of reaction conditions, has been studied by single‐pulse pulsed laser polymerization (SP‐PLP) in conjunction with electron paramagnetic resonance spectroscopy. The model radicals were generated by initiator‐fragment addition to acrylic macromonomers that were preformed prior to the kinetic experiments, thus enabling separation of termination from the propagation reaction, for these model radicals propagate sparingly, if at all, on the timescale of SP‐PLP experiments. Termination rate coefficients of the MCRs were determined in the temperature range of 0–60°C in acetonitrile and butyl propionate solution as well as in bulk macromonomer over the range of 0–100 °C. Termination rate coefficients slightly below those of the corresponding secondary radicals were deduced, demonstrating the relatively high termination activity of this species, even when undergoing MCR–MCR termination. For chain length of 10, a reduction by a factor of 6 is observed. Unusually high activation energies were found for the termination rate coefficient in these systems, with 35 kJ mol^?1 being determined for bulk macromonomer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Broadband excitation pulses for high‐field solid‐state nuclear magnetic resonance spectroscopy

In nuclear magnetic resonance spectroscopy, experimental limits due to the radiofrequency transmitter and/or coil means that conventional radiofrequency pulses (“hard pulses”) are sometimes not sufficiently powerful to excite magnetization uniformly over a desired range of frequencies. Effects due to nonuniform excitation are most frequently encountered at high magnetic fields for nuclei with a large range of chemical shifts. Using optimal control theory, we have designed broadband excitation pulses that are suitable for solid‐state samples under magic‐angle‐spinning conditions. These pulses are easy to implement, robust to spinning frequency variations, and radiofrequency inhomogeneities, and only four times as long as a corresponding hard pulse. The utility of these pulses for uniformly exciting ¹³C nuclei is demonstrated on a 900 MHz (21.1 T) spectrometer. Copyright © 2012 John Wiley & Sons, Ltd.     

A Class of Non-associated Materials: n-Monotone Materials—Hooke’s Law of Elasticity Revisited

Generalized Standard Materials are governed by maximal cyclically monotone operators and modeled by convex potentials. Géry de Saxcé’s Implicit Standard Materials are modeled by biconvex bipotentials. We analyze the intermediate class of n-monotone materials governed by maximal n-monotone operators and modeled by Fitzpatrick’s functions. Revisiting the model of elastic materials initiated by Robert Hooke, and insisting on the linearity, coaxiality and monotonicity properties of the constitutive law, we illustrate that Fitzpatrick’s representation of n-monotone operators coming from convex analysis provides a constructive method to discover the best bipotential modeling a n-monotone material. Giving up the symmetry of the linear constitutive laws, we find out that n-monotonicity is a relevant criterion for the materials characterization and classification.     

Martingales and buffer overflow for the symmetric shortest queue model

Queueing Systems - A variant of the standard symmetric system of two parallel queues under the join-the-shortest-queue policy is introduced. Here, the shortest queue has service rate $$\mu _1$$ ,...     

Optical Spectroscopy as a Method for Skin Cancer Risk Assessment

Skin cancer is the most prevalent cancer, and its assessment remains a challenge for physicians. This study reports the application of an optical sensing method, elastic scattering spectroscopy (ESS), coupled with a classifier that was developed with machine learning, to assist in the discrimination of skin lesions that are concerning for malignancy. The method requires no special skin preparation, is non‐invasive, easy to administer with minimal training, and allows rapid lesion classification. This novel approach was tested for all common forms of skin cancer. ESS spectra from a total of 1307 lesions were analyzed in a multi‐center, non‐randomized clinical trial. The classification algorithm was developed on a 950‐lesion training dataset, and its diagnostic performance was evaluated against a 357‐lesion testing dataset that was independent of the training dataset. The observed sensitivity was 100% (14/14) for melanoma and 94% (105/112) for non‐melanoma skin cancer. The overall observed specificity was 36% (84/231). ESS has potential, as an adjunctive assessment tool, to assist physicians to differentiate between common benign and malignant skin lesions.     

Boronate Ligands in Materials: Determining Their Local Environment by Using a Combination of IR/Solid‐State NMR Spectroscopies and DFT Calculations

Boronic acids (R‐B(OH)₂) are a family of molecules that have found a large number of applications in materials science. In contrast, boronate anions (R‐B(OH)₃^?) have hardly been used so far for the preparation of novel materials. Here, a new crystalline phase involving a boronate ligand is described, Ca[C₄H₉‐B(OH)₃]₂, which is then used as a basis for the establishment of the spectroscopic signatures of boronates in the solid state. The phase was characterized by IR and multinuclear solid‐state NMR spectroscopy (¹H, ¹³C, ¹¹B and ⁴³Ca), and then modeled by periodic DFT calculations. Anharmonic OH vibration frequencies were calculated as well as NMR parameters (by using the Gauge Including Projector Augmented Wave—GIPAW—method). These data allow relationships between the geometry around the OH groups in boronates and the IR and ¹H NMR spectroscopic data to be established, which will be key to the future interpretation of the spectra of more complex organic–inorganic materials containing boronate building blocks.     

Direct Comparison of Subvalent,Polycationic Group 13 Cluster Compounds: Lessons learned on Isoelectronic DMPE Substituted Gallium and Indium Tetracation Salts

The tetracationic, univalent cluster compounds [{M(dmpe)}₄]⁴⁺ (M=Ga, In; dmpe=bis(dimethylphosphino)ethane) were synthesized as their pf salts ([pf]⁻=[Al(OR^F)₄]⁻; R^F=C(CF₃)₃). The four-membered ring in [{M(dmpe)}₄]⁴⁺ is slightly puckered for M=Ga and almost square planar for M=In. Yet, although structurally similar, only the gallium cluster is prevalent in solution, while the indium cluster forms temperature dependent equilibria that include even the monomeric cation [In(dmpe)]⁺. This system is the first report of one and the same ligand inducing formation of isoelectronic and isostructural gallium/indium cluster cations. The system allows to study systematically analogies and differences with thermodynamic considerations and bonding analyses, but also to outline perspectives for bond activation using cationic, subvalent group 13 clusters.