Importance of the polarization forces in He-metal surface interaction potential

In this paper we describe coupled channel calculation for atom-surface scattering for arbitrary potentials. We study, for the first time, the effect of the polarization-van der Waals forces. It is concluded that these forces are important for defining the repulsive part of the atom-metal surface potential. We study the He-Ni (110) system and present good agreement with experimental data for energies between 20 and 250 meV.     

Bestimmung von Corticosteroiden im Blut durch Doppelmarkierung und Messung von 14C und 3H in der Gasphase

Ohne ZusammenfassungAuszug aus der Dissertation Reinhard Ködding, Technische Hochschule München 1961.     

Die basenkatalysierte Umlagerung von N-Aryl-S,S-dialkylsulfimiden zu o-Alkylthioalkylanilinen

Zusammenfassung Die Umlagerung von N-Aryl-S,S-dimethylsulfimiden in Toluol/Triäthylamin liefert in hohen Ausbeuten o-Methylthiomethylaniline. In Alkohol verläuft die Umlagerung ohne Zusatz von Basen rascher, als Nebenreaktion läuft aber die Spaltung zu dem zugrunde liegenden aromatischen Amin ab. 2,6-Di-substituierte N-Arylsulfimide ergeben durch analoge Umlagerung Cyclohexadienimine. Die Umlagerung von N-Aryl-S,S-dialkylsulfimiden erfolgt langsamer als die der S-Methylderivate; sie führte in einem Fall in hohen Ausbeuten zu einem durch 1,2-Wanderung entstandenen N-Alkylthioalkylprodukt. Die Ergebnisse liefern Aufschlüsse über den Mechanismus von Methylthiomethylierungen von anilinen und Phenolen.

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Methylthiomethylation of anilines and phenols, VII: Basecatalysed rearrangement of N-aryl-S.S-dialkyl sulfimides to o-methylthiomethyl anilines

Rearrangement of N-aryl-S.S-dimethyl sulfimides in toluene/triethyl amine yields high amounts of o-methylthiomethylated anilines. Rearrangement in ethanol without addition of base proceeds faster, but yields also the original aniline as by-product. 2.6-Di-substituted N-aryl sulfimides yielded on analogous rearrangement cyclohexadiene imines. The rearrangement of N-aryl-S.S-dialkyl sulfimides is slower than that of the S-methyl derivatives, and yielded in one case high amounts of N-alkylthioalkyl product formed via 1.2-migration. The results offer some informations on the mechanism of methylthiomethylations of anilines and phenols.

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Herrn Prof. Dr.H. Nowotny gewidmet.

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6. Mitt.:P. Claus, N. Vavra undP. Schilling, Mh. Chem.102, 1072 (1971).     

Mechanism of enzymatic Birch reduction: stereochemical course and exchange reactions of benzoyl-CoA reductase

Dearomatizing benzoyl-coenzyme A reductases (BCR) from facultatively anaerobic bacteria are key enzymes in the anaerobic degradation of aromatic compounds. They catalyze the ATP-dependent reduction of benzoyl-CoA (BCoA) to cyclohexa-1,5-diene-1-carboxyl-CoA (dienoyl-CoA). A Birch reduction mechanism involving alternate electron transfer and protonation steps has been proposed for BCR. In this work we reacted BCoA in H2O and D2O, and d5-BCoA in H2O with BCR and the second enzyme of the pathway, dienoyl-CoA hydratase (DCH). The 1,4 hydration product formed from the dienoyl-CoA, 6-hydroxycyclohex-1-ene-1-carbonyl-CoA, was analyzed by several NMR techniques. The results obtained indicate that BCR stereoselectively forms the trans-dienoyl-CoA product, and DCH stereoselectively catalyzes a trans-1,4 water addition. Moreover, unexpected proton exchanges at C-2 and C-6 were observed. They indicate that a free radical intermediate with an unusual low pKa is formed during BCR catalysis. This finding provides evidence for the proposed Birch reduction mechanism of BCR and is in agreement with the established radical mechanism of homologous alpha-hydroxyacyl-CoA dehydratases.     

Ein symmetrisches Tetrasulfolenoporphyrin als Reaktivbaustein,Vorläufige Mitteilung

A Symmetrical Tetrasulfolenoporphyrin as Reactive Building Block The efficient preparation of the symmetric tetrasulfolenoporphyrin 1 is reported, which shows good solubility in a variety of solvents. In 1 , four sulfone groups that symmetrically bridge the eight methylene groups in β‐position at the pyrrole rings provide four sulfolene (=2,5‐dihydrothiophene 1,1‐dioxide) units which are prone to cleavage by thermally induced extrusion of sulfur dioxide. The tetrasulfolenoporphyrin, accordingly, is indicated to lend itself to specific and multiple refunctionalization by the replacement of the sulfone groups by other functionalities in SO₂ extrusion/cycloaddition sequences. The predicted reactivity and the potential of a zinc complex of the tetrasulfolenoporphyrin as a reactive porphyrin module (see 5 b ) is tested in exploratory experiments. To this end, thermolysis of the tetrasulfolenoporphyrinatozinc 5 b in dichlorobenzene solution (at 140°) and in the presence of [5,6]fullerene‐C₆₀‐I_h gives the (fullereno‐porphyrinato)zinc 6 still having three sulfolene units and a `diagonal' (difullerenoporphyrinato)zinc 7 that still has two sulfolene units, in 14 and in 43% yield, respectively.     

Optimal control of Markovian jump processes with partial information and applications to a parallel queueing model

We consider a stochastic control problem over an infinite horizon where the state process is influenced by an unobservable environment process. In particular, the Hidden-Markov-model and the Bayesian model are included. This model under partial information is transformed into an equivalent one with complete information by using the well-known filter technique. In particular, the optimal controls and the value functions of the original and the transformed problem are the same. An explicit representation of the filter process which is a piecewise-deterministic process, is also given. Then we propose two solution techniques for the transformed model. First, a generalized verification technique (with a generalized Hamilton–Jacobi–Bellman equation) is formulated where the strict differentiability of the value function is weaken to local Lipschitz continuity. Second, we present a discrete-time Markovian decision model by which we are able to compute an optimal control of our given problem. In this context we are also able to state a general existence result for optimal controls. The power of both solution techniques is finally demonstrated for a parallel queueing model with unknown service rates. In particular, the filter process is discussed in detail, the value function is explicitly computed and the optimal control is completely characterized in the symmetric case.     

Electric field-induced isomerization of azobenzene by STM

The electric field applied between the tip of a scanning tunneling microscope and a metallic surface is shown to induce the reversible trans-cis isomerization of single azobenzene derivatives adsorbed on a Au(111) surface. The investigated molecule is symmetrically equipped with four tert-butyl groups, which decouple the azobenzene core from the metallic surface, facilitating the formation of highly ordered islands. Due to the spatial extension of the electric field, it is possible to switch many molecules within the same island simultaneously.     

Robust consumption-investment problems with random market coefficients

We consider consumption-investment problems in a financial market with general random coefficients where the market price of risk process is unknown. The investor tries to maximize his expected utility under the worst-case parameter configuration. To solve robust consumption-investment problems, we make use of stochastic Bellman?CIsaac equations. These equations can be explicitly solved for power, exponential and logarithmic utility. This enables us to characterize a robust optimal consumption-investment strategy and a worst-case market price of risk process in terms of the solution of a backward stochastic differential equation.     

Alkene–Tetrazine Ligation for Imaging Cellular DNA

5‐Vinyl‐2′‐deoxyuridine (VdU) is the first reported metabolic probe for cellular DNA synthesis that can be visualized by using an inverse electron demand Diels–Alder reaction with a fluorescent tetrazine. VdU is incorporated by endogenous enzymes into the genomes of replicating cells, where it exhibits reduced genotoxicity compared to 5‐ethynyl‐2′‐deoxyuridine (EdU). The VdU–tetrazine ligation reaction is rapid (k≈0.02 M ^?1 s^?1) and chemically orthogonal to the alkyne–azide “click” reaction of EdU‐modified DNA. Alkene–tetrazine ligation reactions provide the first alternative to azide–alkyne click reactions for the bioorthogonal chemical labeling of nucleic acids in cells and facilitate time‐resolved, multicolor labeling of DNA synthesis.