Visible‐Light‐Enabled Direct Decarboxylative N‐Alkylation

The development of efficient and selective C?N bond‐forming reactions from abundant feedstock chemicals remains a central theme in organic chemistry owing to the key roles of amines in synthesis, drug discovery, and materials science. Herein, we present a dual catalytic system for the N‐alkylation of diverse aromatic carbocyclic and heterocyclic amines directly with carboxylic acids, by‐passing their preactivation as redox‐active esters. The reaction, which is enabled by visible‐light‐driven, acridine‐catalyzed decarboxylation, provides access to N‐alkylated secondary and tertiary anilines and N‐heterocycles. Additional examples, including double alkylation, the installation of metabolically robust deuterated methyl groups, and tandem ring formation, further demonstrate the potential of the direct decarboxylative alkylation (DDA) reaction.     

A fluorescence lifetime-based binding assay for acetylpolyamine amidohydrolases from Pseudomonas aeruginosa using a [1,3]dioxolo[4,5-f][1,3]benzodioxole (DBD) ligand probe

High-throughput assays for drug screening applications have to fulfill particular specifications. Besides the capability to identify even compounds with low potency, one of the major issues is to minimize the number of false-positive hits in a screening campaign in order to reduce the logistic effort for the subsequent cherry picking and confirmation procedure. In this respect, fluorescence lifetime (FLT) appears as an ideal readout parameter that is supposed to be robust against autofluorescent and light-absorbing compounds, the most common source of systematic false positives. The extraordinary fluorescence features of the recently discovered [1,3]dioxolo[4,5-f][1,3] benzodioxole dyes were exploited to develop an FLT-based binding assay with exceptionally robust readout. The assay setup was comprehensively validated and shown to comply not only with all requirements for a powerful high-throughput screening assay but also to be suitable to determine accurate binding constants for inhibitors against enzymes of the histone deacetylase family. Using the described binding assay, the first inhibitors against three members of this enzyme family from Pseudomonas aeruginosa were identified. The compounds were characterized in terms of potency and selectivity profile. The novel ligand probe should also be applicable to other homologues of the histone deacetylase family that are inhibited by N-hydroxy-N′-phenyloctandiamide.

Magnetocapacitance study of the fractional-quantum-Hall effect: Quasiparticle charge and spin polarization

By the method of capacitance spectroscopy and of magnetotransport we have investigated the and fractional-quantum-Hall-effect (FQHE) states in gated GaAs AlGaAs heterojunctions with tuned electron areal density. Our experimental results confirm the theoretical prediction of the fractional quasiparticle charge in the FQHE state and of the existence of spin-aligned quasiholes and spin-reversed quasielectrons in the fully spin-polarized FQHE state.     

On stable torsion-free nilpotent groups

Summary We show that an infinite field is interpretable in a stable torsion-free nilpotent groupG of classk, k>1. Furthermore we prove thatG/Z _k-1 (G) must be divisible. By generalising methods of Belegradek we classify some stable torsion-free nilpotent groups modulo isomorphism and elementary equivalence.Supported by the Deutsche Forschungsgemeinschaft     

A Dynamic Mixture Model for Unsupervised Tail Estimation without Threshold Selection

Exceedances over high thresholds are often modeled by fitting a generalized Pareto distribution (GPD) on R⁺. It is difficult to select the threshold, above which the GPD assumption is enough solid and enough data is available for inference. We suggest a new dynamically weighted mixture model, where one term of the mixture is the GPD, and the other is a light-tailed density distribution. The weight function varies on R⁺ in such a way that for large values the GPD component is predominant and thus takes the role of threshold selection. The full data set is used for inference on the parameters present in the two component distributions and in the weight function. Maximum likelihood provides estimates with approximate standard deviations. Our approach has been successfully applied to simulated data and to the (previously studied) Danish fire loss data set. We compare the new dynamic mixture method to Dupuis' robust thresholding approach in peaks-over-threshold inference. We discuss robustness with respect to the choice of the light-tailed component and the form of the weight function. We present encouraging simulation results that indicate that the new approach can be useful in unsupervised tail estimation, especially in heavy tailed situations and for small percentiles.     

Multimode-Eigenschaften verschiedener Halbleiterlasermodelle. II

The influence of electron intraband scattering processes on the semiconductor laser behaviour is investigated. These processes thermalize the electrons in each band in a very short time. For the example of optical band to band transitions withk-selection rule it is shown, that no holeburning is possible, if the scattering relaxation time is much shorter than the radiative lifetime. We show for this limit that in a linear approximation only one running laser mode is stable. In order to include both band and localisation effects the model of optical transitions between an impurity level and a band is treated. Diffusion processes between the impurities and scattering processes in the band are taken into account. The treatment shows that usually the local inhomogenity of the inversion produced by standing modes is more important than the energetic one for the stabilisation of different laser modes. The model of full energetic homogenisation in the presence of diffusion processes was introduced byStatz andTang. We discuss in a qualitative manner which deviations should be expected if this limit is not fully realized.     

Domino reactions consisting of heterocyclization and 1,2-migration-redox-neutral and oxidative transition-metal catalysis

Two cats, two paths: Two novel domino reactions starting from 6-hydroxy-2-alkyl-2-alkynylcyclohexanones have been discovered. While redox-neutral platinum catalysis gives rise to furans through a sequence of cyclization, 1,2-shift, and Grob fragmentation, oxidative copper catalysis provides an entry to bicyclic 2,3-dihydrofurans. Upon cyclization and oxidation, an unusual benzilic acid rearrangement can take place in this case.     

Origin of the Voc enhancement with a p-doped nc-SiOx:H window layer in n-i-p solar cells

The introduction of a nc-SiOx:H material as window layer in single junction a-Si:H n-i-p solar cell leads to a V_oc enhancement of 80 mV compared to a μc-Si:H p-layer. According to numerical modeling of the V_oc, both the higher work function p-layer and the conduction band offset (CBO) at the i/p interface match well with the experimental V_oc increase with the oxygen content. Using the differential temperature method, the built-in voltage (V_bi) of the cells with the two different p-layers is measured to be similar, agreeing well with the CBO model. Thus we attribute the improvement of the V_oc to the reduction of recombination at the i/p interface, as a consequence of the CBO in this region.