High-temperature reversed-phase liquid chromatography coupled to isotope ratio mass spectrometry

Compound‐specific isotope analysis (CSIA) by liquid chromatography coupled to isotope ratio mass spectrometry (LC/IRMS) has until now been based on ion‐exchange separation. In this work, high‐temperature reversed‐phase liquid chromatography was coupled to, and for the first time carefully evaluated for, isotope ratio mass spectrometry (HT‐LC/IRMS) with four different stationary phases. Under isothermal and temperature gradient conditions, the column bleed of XBridge C₁₈ (up to 180 °C), Acquity C₁₈ (up to 200 °C), Triart C₁₈ (up to 150 °C), and Zirchrom PBD (up to 150 °C) had no influence on the precision and accuracy of δ¹³C measurements, demonstrating the suitability of these columns for HT‐LC/IRMS analysis. Increasing the temperature during the LC/IRMS analysis of caffeine on two C₁₈ columns was observed to result in shortened analysis time. The detection limit of HT‐RPLC/IRMS obtained for caffeine was 30 mg L^–1 (corresponding to 12.4 nmol carbon on‐column). Temperature‐programmed LC/IRMS (i) accomplished complete separation of a mixture of caffeine derivatives and a mixture of phenols and (ii) did not affect the precision and accuracy of δ¹³C measurements compared with flow injection analysis without a column. With temperature‐programmed LC/IRMS, some compounds that coelute at room temperature could be baseline resolved and analyzed for their individual δ¹³C values, leading to an important extension of the application range of CSIA. Copyright © 2011 John Wiley & Sons, Ltd.     

Completely connected clustered graphs

Planar drawings of clustered graphs are considered. We introduce the notion of completely connected clustered graphs, i.e., hierarchically clustered graphs that have the property that not only every cluster but also each complement of a cluster induces a connected subgraph. As a main result, we prove that a completely connected clustered graph is c-planar if and only if the underlying graph is planar. Further, we investigate the influence of the root of the inclusion tree to the choice of the outer face of the underlying graph and vice versa.     

Descartes,Cardiac Heat,and Alchemy

René Descartes (1596–1650) insisted on a heat and light theory to explain cardiac movement, and used concepts such as distillation of the vital spirits, fermentation in the digestive process, and fermentation in the circulation of the blood. I argue that his theory of the body as a heat-exchange system was based on alchemical and natural philosophical notions of fire and light expounded by precursors and contemporaries who included Jean D'Espagnet, Jean Fernel, Jan Baptist van Helmont, and Andreas Libavius. Descartes endeavoured to mechanise their approaches, creating a theory in which fire and heat, a legacy from thermal explanations of physiology, were transformed into alchemical fire, and then into mechanistic or physicalist heat.     

Fictitious play in coordination games

We study the Fictitious Play process with bounded and unbounded recall in pure coordination games for which failing to coordinate yields a payoff of zero for both players. It is shown that every Fictitious Play player with bounded recall may fail to coordinate against his own type. On the other hand, players with unbounded recall are shown to coordinate (almost surely) against their own type as well as against players with bounded recall. In particular, this implies that a FP player's realized average utility is (almost surely) at least as large as his minmax payoff in 2×2 coordination games. Received: December 1997/Final version: November 1998     

Über die aldehydselektivität von alkylkomplexen von scandium,yttrium, lanthan und lanthaniden aldehyd/keton-konkurrenzversuchen

In-situ prepared alkyl complexes Hal₂M-Alk (Alk = Me, Bu) of the f-metals Ce, Pr, Nd, Sm, Gd exhibit very low selectivity in competition experiments between heptanal and diethylketone in THF, whereas the selectivity of complexes Hal₂M-Me (M = Sc, Y, La) is distinctly higher with decreasing tendency in the sequence Sc>Y>La. These and previously reported¹ results led to a general working hypothesis about the reasons of the aldehyde-selectivity of transition metal alkyls.     

Untersuchung von Kakao,Schokolade, Kaffee und Tee

Analytical and Bioanalytical Chemistry -     

Combining magnetic resonance measurements with numerical simulations – Extracting blood flow physiology information relevant to the investigation of intracranial aneurysms in the circle of Willis

Cerebral aneurysms in the region of the circle of Willis have an incidence of 3–6% in western populations and involve the risk of rupture with subsequent subarachnoidal bleeding. The patient specific blood flow patterns are of substantial importance for understanding the pathogenesis of the lesions and may eventually contribute to deciding on the most efficient treatment procedure for a specific patient.A non-invasive method for performing in vivo measurements on blood velocity is 4D phase-contrast magnetic resonance angiography (PC-MRA), on the basis of which a flow field with all its parameters can be simulated. We are using this approach to investigate the hemodynamic parameters in the circle of Willis and, by analyzing the values at common locations of aneurysms, trying to find potential parameters to predict the development of aneurysms. Methodologically, we are acquiring the artery geometry with 3D-time-of-flight magnetic resonance (TOF) measurements and the blood velocity in the feeding arteries with 4D PC-MRA measurements in a healthy volunteer. These measurements are combined with computational fluid dynamics (CFD) to describe detailed hemodynamic patterns within the circle of Willis.     

Delivery of myo-Inositol Hexakisphosphate to the Cell Nucleus with a Proline-Based Cell-Penetrating Peptide

Inositol hexakisphosphate (InsP₆) is a central member of the inositol phosphate messengers in eukaryotic cells. Tools to manipulate the level of InsP₆, particularly with compartment selectivity, are needed to enable functional cellular studies. We present cationic octa-(4S)guanidiniumproline ( Z8 ) for the delivery of InsP₆ into the cell nucleus. CD spectroscopy, binding affinity, dynamic light scattering, and computational studies revealed that Z8 binds tightly to InsP₆ and upon binding undergoes a conformational change from a PPII-helical structure to a structure that forms aggregates. The unique conformational features of the cationic oligoproline enable complex formation and cellular delivery of InsP₆ with considerably greater efficacy than the flexible counterpart octaarginine.