WIN-DAISY: Application to oriented molecules. Analysis and simulation of NEMA-NMR spectra

The¹H-NMR spectra of 3-methyl-3-cyano-cyclopropene and¹⁹F-NMR spectra of bis-trifluoromethyl-mercury have been measured in nematic liquid crystal EBBA and in mixture of EBBA+M MBBA, respectively. The novel program systemWIN-DAISY was used for automated analysis and simulation of NMR spectra, and optimised parameters for dipolar coupling constants extracted.     

Point sets with distinct distances

For positive integersd andn letf _d (n) denote the maximum cardinality of a subset of then ^d -gird {1,2,...,n} ^d with distinct mutual euclidean distances. Improving earlier results of Erds and Guy, it will be shown thatf ₂ (n)c·n ^2/3 and, ford3, thatf _d (n)c _d ·n ^2/3 ·(lnn)^1/3, wherec, c _d >0 are constants. Also improvements of lower bounds of Erds and Alon on the size of Sidon-sets in {1²,22²,...,n ²} are given.Furthermore, it will be proven that any set ofn points in the plane contains a subset with distinct mutual distances of sizec ₁·n ^1/4, and for point sets in genral position, i.e. no three points on a line, of sizec ₂·n ^1/3 with constantsc ₁,c ₂>0. To do so, it will be shown that forn points in ² with distinct distancesd ₁,d ₂,...,d _t , whered _i has multiplicitym _i , one has _i=1 ^t m _i ² c·n _3.25 for a positive constantc. If then points are in general position, then we prove _i=1 ^t m _i ² c·n ₃ for a positive constantc and this bound is tight.Moreover, we give an efficient sequential algorithm for finding a subset of a given set with the desired properties, for example with distinct distances, of size as guaranteed by the probabilistic method under a more general setting.     

Orientational Properties of Poly‐γ‐benzyl‐L‐glutamate: Influence of Molecular Weight and Solvent on Order Parameters of the Solute

Residual dipolar couplings (RDCs) have recently become increasingly important in organic structure determination due to their unique information content. One main limitation for the use of RDCs in organic compounds, however, is that the compound in question needs to be oriented with respect to the magnetic field in order to measure RDCs. So far, there are very few possibilities for modulating the induced degree of orientation. The situation is even worse when chiral orienting media are considered, which could allow absolute configuration determination in the future. We have conducted a systematic investigation into modulating the orientation induced by one chiral orienting medium, namely organic solutions of PBLG (poly‐γ‐benzyl‐L ‐glutamate), as a function of its molecular weight and the organic co‐solvent used, and have obtained significant insights into factors that influence the order induced. With increasing molecular weight of the polypeptide the orientation of the solutes decreases, leading to well‐resolved spectra with improved line shapes. This can be attributed exclusively to the fact that the critical concentration of the liquid‐crystalline phase decreases with increasing molecular weight (pure dilution effect). Any influence of increasing flexibility on the orientation can be ruled out.     

Enantioselective Phenol Coupling by Laccases in the Biosynthesis of Fungal Dimeric Naphthopyrones

Biaryl compounds are ubiquitous metabolites that are often formed by dimerization through oxidative phenol coupling. Hindered rotation around the biaryl bond can cause axial chirality. In nature, dimerizations are catalyzed by oxidative enzymes such as laccases. This class of enzymes is known for non‐specific oxidase reactions while inherent enantioselectivity is hitherto unknown. Here, we describe four related fungal laccases that catalyze γ‐naphthopyrone dimerization in a regio‐ and atropselective manner. In vitro assays revealed that three enzymes were highly P‐selective (ee >95 %), while one enzyme showed remarkable flexibility. Its selectivity for M‐ or P‐configured dimers varied depending on the reaction conditions. For example, a lower enzyme concentration yielded primarily (P)‐ustilaginoidin A, whereas the M atropisomer was favored at higher concentration. These results demonstrate inherent enantioselectivity in an enzyme class that was previously thought to comprise only non‐selective oxidases.     

Coherent and turbulent process analysis in the flow past a circular cylinder at high Reynolds number

This article presents an experimental study of the turbulent flow past a circular cylinder at high Reynolds number by means of advanced optical measurements techniques. Following previous studies using standard PIV and stereoscopic PIV (3C PIV), TRPIV and 3C-TRPIV have been employed in low subsonic wind tunnel environment. The database consisting of statistical and time-dependent fields aims at providing a physical analysis of the coherent and turbulent part, as well as a proper basis for validation and improvement of recent turbulence modelling approaches for strongly detached flow at high Reynolds number. As the nonlinear interaction between the coherent and turbulent dynamics have to be taken into account in a model, particular attention is paid to a decomposition of the flow into a coherent and a turbulent part, and to the analysis of their dynamics. This is achieved both using phase averaging and Proper Orthogonal Decomposition. For phase averaging, the two first POD coefficients are used for the evaluation of the vortex shedding phase angle. Furthermore, selected results of a Detached Eddy Simulation which had been validated by means of the experiment, are also presented to contribute to the physical analysis. The present study's experimental data resolved in space and time allow the confirmation of the conditional averaging for the turbulent stresses evaluation, by alleviating their overestimation due to phase jitter that occurs between the trigger signal and the velocity, when the phase angle is determined from a wall pressure signal. A more accurate physical analysis of the flow is achieved, particularly regarding the occurrence of irregular vortex shedding.     

Konzentrationseffekte in Isocyanat-Alkohol-Systemen

Summary The reaction between aromatic isocyanate and alcohol in nonpolar solvents at different alcohol and isocyanate concentrations and the effect of the presence of urethane in this solution at the start of the reaction have been examined. The results indicate that the rate constants of the observed second-order equation are dependent on the concentration of the reactants and of the urethane.

     

Ein Beitrag zur Existenz von Allylberyllium- und Allylaluminiumverbindungen

A Contribution to the Existence of Allyl Beryllium and Allyl Aluminium Compounds Diethyl beryllium reacts with triallyl boron with fast exchange of the ethyl and allyl groups. Diallyl beryllium formed in this reaction is transferred in oligomer organoberyllium products. – Similar reactions take place between aluminium trialkyls and triallyl, trimethallyl and tricrotyl boron.     

Ionotrope Gele von Polyuronsäuren

Ohne Zusammenfassung vgl. I. Bildung und Verhalten. Kolloid-Z.140, 76, ff (1955) Diese Arbeit wurde zum Teil mit Mitteln der Deutschen Forschungsgemeinschaft und des Fonds zur F?rderung der Chemie durchgeführt.     

Contributions to the chemistry of organo-transition metal compounds. 51. Preparation and characterization of the organomanganese(III) compound Na[Mn(C5H5)4]

At reaction of Mn(acac)₃ with NaC₅H₅ in tetrahydrofuran solution Na[Mn(η¹?C₅H₅)_4?n(η⁵ -C₅H₅)_n] was obtained as a crystalline, red-violet, diamagnetic organomanganese(III) compound, which was characterized by n.m.r., i.r., and electronic spectra and by conductivity measurements.