EINIGE NEUE THIOPHOSPHINSÄUREAMIDE R2P(S)NHR': SYNTHESE UND KERNRESONANZSPEKTROSKOPISCHE UNTERSUCHUNGEN

Abstract

P.P-Dialkylthiophosphinsäureamide R₂P(S)NHR' (R=Me, 'Pr, 'Bu; R'=Me, Et, ⁱPr. ^cHex. ^tBu. Ph. etc.) wurden erhalten durch Umsetzung von R₂PNHR' mit Schwefel oder durch Reaktion von Me₂P(S)CI mit primaren Aminen. Ihre ³¹P- und ¹³C-NMR-Spektren werden diskutiert. Insbesondere die Di-t-butylthiophosphinsäureamide sind auszilg;ergewöhnlich stabil gegen Hydrolyse und Luftsauerstoff. P,P-Dialkylthiophosphinic acid amides R₂P(S)NHR' (R=Me. ⁱPr. ^tBu; R'=Me, Et, ⁱPr, ^cHex. ^tBu, Ph. etc.) have been obtained by reaction of the corresponding aminophosphines with sulfur or by reaction of dimethylthiophosphorylhalides with primary amines. Their ³¹P- and ¹³C-NMR spectra are discussed. The di-t-butylthiophosphinic compounds proved to be remarkably stable against moisture and oxygen.     

CNDO/2-CALCULATIONS ON THE STABILIZATION OF CARBANIONS BY σ-BIVALENT SULFUR

Abstract

The significantly enhanced acidity of C[sbnd]H bonds attached to a σ-bivalent sulfur atom can be explained without taking into account the octet expansion of sulfur. The higher carbanion stabilization effect of sulfur in comparison to oxygen has been related to the greater capability of the σ-bivalent sulfur to take up excess charge into the sp-valence shell.     

Fragmentation of deuterated rhodamine B derivates by laser and collisional activation in an FT-ICR mass spectrometer

Xanthene dyes such as rhodamine B undergo an interesting mass-spectrometric fragmentation reaction that eliminates small neutral alkanes such as propane. This fragmentation reaction has been investigated in a Fourier transform ion cyclotron mass spectrometer by means of laser photodissociation with visible light as well as by collision-induced dissociation. Different isotopically labeled decarboxyrhodamine B compounds were used to investigate the fragmentation mechanism. The results support a concerted mechanism for the formation of the alkanes instead of a two-step radical mechanism.     

A d10 Ni–(H2) Adduct as an Intermediate in H?H Oxidative Addition across a Ni?B Bond

Bifunctional E H activation offers a promising approach for the design of two‐electron‐reduction catalysts with late first‐row metals, such as Ni. To this end, we have been pursuing H₂ activation reactions at late‐metal boratranes and herein describe a diphosphine–borane‐supported Ni—(H₂) complex, [(^PhDPB^iPr)Ni(H₂)], which has been characterized in solution. ¹H NMR spectroscopy confirms the presence of an intact H₂ ligand. A range of data, including electronic‐structure calculations, suggests a d¹⁰ configuration for [(^PhDPB^iPr)Ni(H₂)] as most appropriate. Such a configuration is highly unusual among transition‐metal H₂ adducts. The nonclassical H₂ adduct is an intermediate in the complete activation of H₂ across the Ni B interaction. Reaction‐coordinate analysis suggests synergistic activation of the H₂ ligand by both the Ni and B centers of the nickel boratrane subunit, thus highlighting an important role of the borane ligand both in stabilizing the d¹⁰ Ni—(H₂) interaction and in the H—H cleavage step.     

Laminate structures in plastic composite materials with rigid layers

A variational model for composite materials with rigid horizontal layers is introduced within the framework of geometrically nonlinear single-slip plasticity. Considering the orientation of the slip system, we discuss the effective material response in the case of vanishing layer thickness and give explicit examples of possible macroscopic deformations which are realized by simple laminate constructions. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Natural products as DNA methyltransferase inhibitors: a computer-aided discovery approach

DNA methyltransferases (DNMTs) represent promising targets for the development of unique anticancer drugs. However, all DNMT inhibitors currently in clinical use are nonselective cytosine analogs with significant cytotoxic side-effects. Several natural products, covering diverse chemical classes, have indicated DNMT inhibitory activity, but these effects have yet to be systematically evaluated. In this study, we provide experimental data suggesting that two of the most prominent natural products associated with DNA methylation inhibition, (−)-epigallocathechin-3-gallate (EGCG) and curcumin, have little or no pharmacologically relevant inhibitory activity. We therefore conducted a virtual screen of a large database of natural products with a validated homology model of the catalytic domain of DNMT1. The virtual screening focused on a lead-like subset of the natural products docked with DNMT1, using three docking programs, following a multistep docking approach. Prior to docking, the lead-like subset was characterized in terms of chemical space coverage and scaffold content. Consensus hits with high predicted docking affinity for DNMT1 by all three docking programs were identified. One hit showed DNMT1 inhibitory activity in a previous study. The virtual screening hits were located within the biological-relevant chemical space of drugs, and represent potential unique DNMT inhibitors of natural origin. Validation of these virtual screening hits is warranted.     

How geometry controls the tearing of adhesive thin films on curved surfaces

Flaps can be detached from a thin film glued on a solid substrate by tearing and peeling. For flat substrates, it has been shown that these flaps spontaneously narrow and collapse in pointy triangular shapes. Here we show that various shapes, triangular, elliptic, acuminate, or spatulate, can be observed for the tears by adjusting the curvature of the substrate. From combined experiments and theoretical models, we show that the flap morphology is governed by simple geometric rules.     

Proposal for an optical laser producing light at half the Josephson frequency

We describe a superconducting device capable of producing laser light in the visible range at half of the Josephson generation frequency with the optical phase of the light locked to the superconducting phase difference. It consists of two single-level quantum dots embedded in a p-n semiconducting heterostructure and surrounded by a cavity supporting a resonant optical mode. We study decoherence and spontaneous switching in the device.     

Theory of the ac spin-valve effect

The spin-valve complex magnetoimpedance of symmetric ferromagnet-normal-metal-ferromagnet junctions is investigated within the drift-diffusion (standard) model of spin injection. The ac magnetoresistance-the real part difference of the impedances of the parallel and antiparallel magnetization configurations-exhibits an overall damped oscillatory behavior, as an interplay of the diffusion and spin relaxation times. In wide junctions the ac magnetoresistance oscillates between positive and negative values, reflecting resonant amplification and depletion of the spin accumulation, while the line shape for thin tunnel junctions is predicted to be purely Lorentzian. The ac spin-valve effect could be a technique to extract spin transport and spin relaxation parameters in the absence of a magnetic field and for a fixed sample size.