ent-Homoabyssomicins A and B, two new spirotetronate metabolites from Streptomyces sp. Ank 210

ent-Homoabyssomicins A (1) and B (2) are new complex polycyclic spirotetronate metabolites isolated from Streptomyces sp. isolate Ank 210. The structures of 1 and 2 were elucidated by detailed spectroscopic analyses of 1D and 2D NMR data. The absolute configuration of 1 was established by subsequent single-crystal X-ray diffraction studies.     

SYNTHESE UND STEREOCHEMIE DER 1-AMINO- UND 1-PHENYLAMINO-1,3-AZAPHOSPHOLAN-5-ONE

Abstract

Die Titelverbindungen werden durch Kondensation von Carboxymethyl- und 1-Carboxyethylphenylphosphin mit dem Hydrazon oder Phenylhydrazon des Benzaldehyds dargestellt. Die 1-Benzoylamino- und 1-Benzylidenamino-derivate des 1,3-Azaphospholan-5-ons sind auf unterschiedlichem Wege zugänglich, indem einmal das 1-Amino-1,3-azaphospholan-5-on mit Benzoylchlorid oder Benzaldehyd umgesetzt oder die Carboxyalkylphosphine mit N-Benzoyl-benzaldehydhydrazon bzw. Benzalazin zur Reaktion gebracht werden. Die Reaktionen verlaufen unter stark bevorzugter Bildung sterisch einheitlicher Diastereomere deren relative Konfiguration ¹H-NMR-spektroskopisch bestimmt wird. Vorstellungen über die Ursachen des stereospezifischen Reaktionsablaufs werden entwickelt.

The title compounds are prepared by condensation of carboxymethylphenylphosphine or 1-carboxyethylphenyl-phosphine with the hydrazone or phenylhydrazone of benzaldehyde. The 1-benzoylamino- and 1-benzylidenamino-derivatives of the basic compounds are made by two routes, by reaction of 1-amino-1,3-azaphospholan-5-ones with benzoylchloride or benzaldehyde or by interaction of the carboxyalkylphosphines with N-benzoyl-benzaldehyde-hydrazone or benzalazine, respectively. All the reactions proceed under stereospecific formation of certain diastereomers, the relative configuration of which is elucidated by investigating their ¹H-nmr-spectra. Suggestions concerning the stereospecifity of the reactions are discussed.     

Surface state charge dynamics of a high-mobility three-dimensional topological insulator

We present a magneto-optical study of the three-dimensional topological insulator, strained HgTe, using a technique which capitalizes on advantages of time-domain spectroscopy to amplify the signal from the surface states. This measurement delivers valuable and precise information regarding the surface-state dispersion within <1 meV of the Fermi level. The technique is highly suitable for the pursuit of the topological magnetoelectric effect and axion electrodynamics.     

Synthesis of tailored WO3 and WOx (2.9 < x < 3) nanoparticles by adjusting the combustion conditions in a H2/O2/Ar premixed flame reactor

Flame synthesis of WO₃ and WO_x (2.9 < x < 3) nanoparticles is carried out by adding a dilute concentration of WF₆ as precursor in a low-pressure H₂/O₂/Ar premixed flame reactor. The reactor is equipped with molecular-beam sampling and particle mass spectroscopy (PMS) to determine particle composition and sizes as a function of height above burner. Varying the H₂/O₂ ratio allowed us to tune the stoichiometry of the product. With a H₂/O₂ ratio of 0.67 white colored stoichiometric WO₃ is formed, whereas the H₂/O₂ ratio >0.8 yields blue colored non-stoichiometric WO_x (2.9 < x < 3) nanoparticles. The size of nanoparticles can be controlled by varying the residence time in the high-temperature zone of the reactor as observed by molecular-beam sampling with subsequent analysis using PMS. Transmission electron microscopy (TEM) images of as-synthesized nanoparticles show that particles are non-agglomerated and have an almost spherical morphology. The X-ray diffraction (XRD) pattern of the as-synthesized material indicates that the powders exhibit poor crystallinity, however, subsequent thermal annealing of the sample in air changes its structure from amorphous to crystalline phase. It is observed that particles with sub-stoichiometric composition (WO_x) show higher conductivity compared to the stoichiometric WO₃ sample.     

Azo‐group labelled polyesters by end‐capping with 2‐oxazoline derivatives – photochemical properties

Two azobenzene containing 2‐oxazolines were used for labeling of a polyester with carboxylic end groups by the end‐capping method. The modification was performed under the conditions of either reactive processing or in a solution. Photochemical activity of the prepared polymers, as well as that of the modifiers was studied. The polymers prepared represent new photosensitive materials that undergo photochemical trans‐cis isomerizations and reverse cis‐trans reactions.     

The generation of amplified spontaneous emission in high‐power CPA laser systems

An analytical model is presented describing the temporal intensity contrast determined by amplified spontaneous emission in high‐intensity laser systems which are based on the principle of chirped pulse amplification. The model describes both the generation and the amplification of the amplified spontaneous emission for each type of laser amplifier. This model is applied to different solid state laser materials which can support the amplification of pulse durations . The results are compared to intensity and fluence thresholds, e.g. determined by damage thresholds of a certain target material to be used in high‐intensity applications. This allows determining if additional means for contrast improvement, e.g. plasma mirrors, are required for a certain type of laser system and application. Using this model, the requirements for an optimized high‐contrast front‐end design are derived regarding the necessary contrast improvement and the amplified “clean” output energy for a desired focussed peak intensity. Finally, the model is compared to measurements at three different high‐intensity laser systems based on Ti:Sapphire and Yb:glass. These measurements show an excellent agreement with the model.

     

On The Potential of Dynamic Nuclear Polarization Enhanced Diamonds in Solid‐State and Dissolution 13C NMR Spectroscopy

Dynamic nuclear polarization (DNP) is a versatile option to improve the sensitivity of NMR and MRI. This versatility has elicited interest for overcoming potential limitations of these techniques, including the achievement of solid‐state polarization enhancement at ambient conditions, and the maximization of ¹³C signal lifetimes for performing in vivo MRI scans. This study explores whether diamond's ¹³C behavior in nano‐ and micro‐particles could be used to achieve these ends. The characteristics of diamond's DNP enhancement were analyzed for different magnetic fields, grain sizes, and sample environments ranging from cryogenic to ambient temperatures, in both solution and solid‐state experiments. It was found that ¹³C NMR signals could be boosted by orders of magnitude in either low‐ or room‐temperature solid‐state DNP experiments by utilizing naturally occurring paramagnetic P₁ substitutional nitrogen defects. We attribute this behavior to the unusually long electronic/nuclear spin‐lattice relaxation times characteristic of diamond, coupled with a time‐independent cross‐effect‐like polarization transfer mechanism facilitated by a matching of the nitrogen‐related hyperfine coupling and the ¹³C Zeeman splitting. The efficiency of this solid‐state polarization process, however, is harder to exploit in dissolution DNP‐enhanced MRI contexts. The prospects for utilizing polarized diamond approaching nanoscale dimensions for both solid and solution applications are briefly discussed.