On the fate of biliverdin-IIIα-dimethyl ester formed by scrambling during syntheses of biliverdin-IXα-dimethyl ester from bilirubin

Summary In preparations of biliverdin-IX-dimethyl ester (2 b) from bilirubin-IX (1) the ratio of the XIII- and III-isomers3 b and4 b, formed via intermolecular scrambling, should be unity. However, irrespective of the synthetic variant considered, the amount of4 b obtained usually is exceptionally low. This is partly ascribed to a consecutive reaction of4 b in acidic methanol affording the chiral diastereomeric bridged biliverdins5 (a undb) and6 (a andb), respectively.

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Zum Verbleib des durch Scrambling gebildeten Biliverdin-III-dimethylethers bei Synthesen des IX-Isomeren aus Bilirubin

Zusammenfassung Bei der Darstellung von Biliverdin-IX-dimethylester (2 b) aus Bilirubin-IX (1) sollte das Verhältnis der durch intermolekulares Scrambling gebildeten XIII- und III-Isomeren3 b bzw.4 b eins betragen. Tatsächlich aber ist die Ausbeute an4 b, unabhängig von der verwendeten synthetischen Variante, immer sehr klein. Dieser Umstand läßt sich zumindest teilweise auf eine spezifische Reaktion von4 b in saurem Methanol zurückführen, in deren Verlauf die chiralen diastereoisomeren überbrückten Biliverdine5 (a undb) sowie6 (a undb) gebildet werden.

     

Evidence for a cyclonic regime in a precessing cylindrical container

We report experimental observations obtained by particle image velocimetry of the behavior of a flow driven by rotation and precession of a cylindrical container. Various hydrodynamical regimes are identified according to the value of the control parameter which is the ratio ?? of the precession frequency to the rotation frequency. In particular, when ?? is increased from small values, we have observed an induced differential rotation followed by the apparition of permanent cyclonic vortices.     

Benefits and Malefits of Solvent Vent Mode in Combination with Tandem Mass Spectrometry for Static Headspace Analysis of Organic Solvents by Gas Chromatography

Chromatographia - Static headspace analysis is of value for the detection of volatile compounds present in biological and environmental samples in trace amounts. However, trace compound detection...     

Production of reference materials for the detection and size determination of silica nanoparticles in tomato soup

A set of four reference materials for the detection and quantification of silica nanoparticles (NPs) in food was produced as a proof of principle exercise. Neat silica suspensions were ampouled, tested for homogeneity and stability, and characterized for total silica content as well as particle diameter by dynamic light scattering (DLS), electron microscopy (EM), gas-phase electrophoretic molecular mobility analysis (GEMMA), and field-flow fractionation coupled with an inductively coupled mass spectrometer (FFF-ICPMS). Tomato soup was prepared from ingredients free of engineered nanoparticles and was spiked at two concentration levels with the silica NP suspension. Homogeneity of these materials was found sufficient to act as reference materials and the materials are sufficiently stable to allow long-term storage and distribution at ambient temperature, providing proof of principle of the feasibility of producing liquid food reference materials for the detection of nanoparticles. The spiked soups were characterized for particle diameter by EM and FFF-ICPMS (one material only), as well as for the total silica content. Although questions regarding the trueness of the results from EM and FFF-ICPMS procedures remain, the data obtained indicate that even assigning values should eventually be feasible. The materials can therefore be regarded as the first step towards certified reference materials for silica nanoparticles in a food matrix.     

Hydration and hemiacetal formation in oxo-[m . n]metacyclophanes

[m . 2]Metacyclophanes with an oxo-function in the C₂ bridge exhibit an enhanced carbonyl reactivity towards nucleophiles. The equilibrium constants for hydration and hemiacetal formation markedly decrease asm increases and qualitatively correlate with the ring strain present in the parent hydrocarbon. [m . n]Metacyclophanes withm,n 3 are almost free from intraanular steric strain. Accordingly, oxo-functions in the bridges do not exhibit an appreciable enhancement of reactivity.

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Hydrat- und Hemiacetalbildung bei Oxo-[m . n]metacyclophanen

Zusammenfassung [m . 2]Metacyclophane mit einer Oxo-Funktion in der C₂-Brücke zeigen eine erhöhte Carbonylreaktivität gegenüber Nucleophilen. Die Gleichgewichtskonstanten für die Hydratisierung und Hemiacetalbildung nehmen mit steigendemm ab und korrelieren qualitativ mit der Ringspannung des entsprechenden Kohlenwasserstoffs. Dagegen sind [m . n]Metacyclophane mitm,n 3 weitgehend frei von intraanularen sterischen Spannungen. Oxo-Funktionen in den Brücken besitzen deshalb keine nennenswert erhöhte Carbonylreaktivität.

     

Cumulants in noncommutative probability theory II

We continue the investigation of noncommutative cumulants. In this paper various characterizations of generalized Gaussian random variables are proved. Supported by the European Network No. HPRN-CT-2000-00116 and the Austrian Science Fund (FWF) Project No. R2-MAT.     

Microlensing of Kepler stars as a method of detecting primordial black hole dark matter

If the dark matter consists of primordial black holes (PBHs), we show that gravitational lensing of stars being monitored by NASA's Kepler search for extrasolar planets can cause significant numbers of detectable microlensing events. A search through the roughly 150,000 light curves would result in large numbers of detectable events for PBHs in the mass range 5×10(-10) M(⊙) to 10(-4) M(⊙). Nondetection of these events would close almost 2 orders of magnitude of the mass window for PBH dark matter. The microlensing rate is higher than previously noticed due to a combination of the exceptional photometric precision of the Kepler mission and the increase in cross section due to the large angular sizes of the relatively nearby Kepler field stars. We also present a new formalism for calculating optical depth and microlensing rates in the presence of large finite-source effects.     

Intrinsic Artefacts in Optical Oxygen Sensors—How Reliable are our Measurements?

Optical oxygen sensing is of broad interest in many areas of research, such as medicine, food processing, and micro‐ and marine biology. The operation principle of optical oxygen sensors is well established and these sensors are routinely employed in lab and field experiments. Ultratrace oxygen sensors, which enable measurements in the sub‐nanomolar region (dissolved oxygen), are becoming increasingly important. Such sensors prominently exhibit phenomena that complicate calibration and measurements. However, these phenomena are not constrained to ultratrace sensors; rather, these effects are inherent to the way optical oxygen sensors work and may influence any optical oxygen measurement when certain conditions are met. This scenario is especially true for applications that deal with high‐excitation light intensities, such as microscopy and microfluidic applications. Herein, we present various effects that we could observe in our studies with ultratrace oxygen sensors and discuss the reasons for their appearance, the mechanism by which they influence measurements, and how to best reduce their impact. The phenomena discussed are oxygen photoconsumption in the sensor material; depletion of the dye ground state by high‐excitation photon‐flux values, which can compromise both intensity and ratiometric‐based measurements; triplet–triplet annihilation; and singlet‐oxygen accumulation, which affects measurements at very low oxygen concentrations.