Bayesian reconstruction of the density of states

A Bayesian framework is developed to reconstruct the density of states from multiple canonical simulations. The framework encompasses the histogram reweighting method of Ferrenberg and Swendsen. The new approach applies to nonparametric as well as parametric models and does not require simulation data to be discretized. It offers a means to assess the precision of the reconstructed density of states and of derived thermodynamic quantities.     

Untersuchungen zur Dynamik von Magnetschwebefahrzeugen auf elastischen Fahrwegen

Übersicht Es werden Methoden entwickelt, mit deren Hilfe man das dynamische Verhalten von Magnetschwebefahrzeugen auf elastischen Fahrwegen untersuchen kann. Ausgehend von einer Analyse des Fahrzeugs, der Magnetstellglieder und des Fahrwegs wird in systematischer Weise das mathematische Modell des Gesamtsystems aufgebaut. Es ergeben sich lineare Zustandsgleichungen mit periodisch zeitvariablen Koeffizienten und springenden Zustandsgrößen. Sie bilden die Grundlage für die Berechnung der Stabilitätsbedingungen und der stationären Lösung sowie für eine numerische Simulation. Die Leistungsfähigkeit der Methoden wird anhand eines Beispiels demonstriert.

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Summary Methods are developed to investigate the dynamical behaviour of magnetically levitated vehicles on flexible guideways. Starting with the analysis of vehicle, suspension and guideway the mathematical model of the closed-loop system is obtained in a systematic way. The results are linear state equations with periodically time-varying coefficients and jumping states. They underlie the evaluation of stability conditions and steady-state responses as well as numerical simulation procedures. The efficiency of the methods is demonstrated by an example.

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Die Untersuchungen wurden mit Mitteln des Bundesministeriums für Forschung und Technologie gefördert.     

Addition reactions and redox esterifications of carbonyl compounds by N-heterocyclic carbenes of indazole

Thermal decarboxylation converts 1,2-dimethylindazolium-3-carboxylate into indazol-3-ylidene, which reacts in situ with ketones to form stable 1:1 adducts. When the reaction is conducted with aromatic aldehydes in alcohols, redox esterifications to benzoates are observed. Model reactions such as redox esterifications of aromatic aldehydes with sodium alcoholates in the presence of 1,2-dimethylindazolium salt and oxidations of sodium benzylates by 1,2-dimethylindazolium salt to aldehydes lend support to a Cannizzaro-type mechanism of this reaction.     

Solid‐state NMR Study of the YadA Membrane‐Anchor Domain in the Bacterial Outer Membrane

MAS‐NMR was used to study the structure and dynamics at ambient temperatures of the membrane‐anchor domain of YadA (YadA‐M) in a pellet of the outer membrane of E. coli in which it was expressed. YadA is an adhesin from the pathogen Yersinia enterocolitica that is involved in interactions with the host cell, and it is a model protein for studying the autotransport process. Existing assignments were sucessfully transferred to a large part of the YadA‐M protein in the E. coli lipid environment by using ¹³C‐¹³C DARR and PDSD spectra at different mixing times. The chemical shifts in most regions of YadA‐M are unchanged relative to those in microcrystalline YadA‐M preparations from which a structure has previously been solved, including the ASSA region that is proposed to be involved in transition‐state hairpin formation for transport of the soluble domain. Comparisons of the dynamics between the microcrystalline and membrane‐embedded samples indicate greater flexibility of the ASSA region in the outer‐membrane preparation at physiological temperatures. This study will pave the way towards MAS‐NMR structure determination of membrane proteins, and a better understanding of functionally important dynamic residues in native membrane environments.     

Hybrid Structure of the Type 1 Pilus of Uropathogenic Escherichia coli

Type 1 pili are filamentous protein assemblies on the surface of Gram‐negative bacteria that mediate adhesion to host cells during the infection process. The molecular structure of type 1 pili remains elusive on the atomic scale owing to their insolubility and noncrystallinity. Herein we describe an approach for hybrid‐structure determination that is based on data from solution‐state NMR spectroscopy on the soluble subunit and solid‐state NMR spectroscopy and STEM data on the assembled pilus. Our approach is based on iterative modeling driven by structural information extracted from different sources and provides a general tool to access pseudo atomic structures of protein assemblies with complex subunit folds. By using this methodology, we determined the local conformation of the FimA pilus subunit in the context of the assembled type 1 pilus, determined the exact helical pilus architecture, and elucidated the intermolecular interfaces contributing to pilus assembly and stability with atomic detail.     

Synthesis of new pyridines with oligocations and oxygen nucleophiles

Nucleophilic substitution of 4-(dimethylamino)pyridine on pentachloropyridine yielded pentakis(pyridine-2,3,4,5,6-pentayl)pyridinium, tris-(3,5-dichloropyridine-2,4,6-triyl)pyridinium, or (tetrachloropyridin-4-yl)pyridinium depending on the reaction conditions. Nucleophilic substitution with water, hydroxides, and alcoholates resulted in new betaines and highly substituted pyridines. [structure: see text]