Enantioselective acylation of silyl ketene acetals through fluoride anion-binding catalysis

A highly enantioselective acylation of silyl ketene acetals with acyl fluorides has been developed to generate useful α,α-disubstituted butyrolactone products. This transformation is promoted by a new thiourea catalyst and 4-pyrrolidinopyridine and represents the first example of enantioselective thiourea anion-binding catalysis with fluoride.     

Determination of steroid hormones in blood by GC–MS/MS

This paper presents the development, optimization and validation of a methodology to determine nine key steroid hormones (viz. pregnenolone, progesterone, dehydroepiandrosterone, androstenedione, testosterone, dihydrotestosterone, estrone, 17α-estradiol and 17β-estradiol) expressed in the steroidogenesis in biological fluids. The analytical method allows for the determination of steroid hormones in blood plasma and serum down to 0.08–0.16 ng/mL for estrogens, 0.20–0.36 ng/mL for androgens and 0.36–0.43 ng/mL for progestagens. These limits of detection were obtainable using a two-step solid-phase clean-up for fractionation and elimination of interfering lipids (fatty acids, phospholipids, glycerides and sterols) from the steroid hormones. The accuracy of the method was 50–112% in the range 0.10 to 2.00 ng/mL.     

Catalytic deuteration of silanes mediated by N-heterocyclic carbene-Ir(III) complexes

The catalytic activity of a series of coordinatively unsaturated NHC-M(III) (M = Rh, Ir; NHC = N-heterocyclic carbene) complexes was tested in the deuteration of secondary and tertiary silanes. Among these, [IrCl(I(t)Bu')(2)] provides the highest conversions to the deuterated species. Mechanistic studies highlight the reversible nature of the ortho-metalation reaction.     

Organic conductors: Electrical and magnetic properties of tetrathiafulvalenium-methyl-tetracyano-p-quinodimethanide (TTF-MTCNQ)

The metal-insulator transition in TTF-MTCNQ is broadened and shifted to a higher temperature compared to the transition in TTF-TCNQ. Tetramethyl-TTF-MTCNQ is found to display a similar behaviour, while tetramethyl-TSF-MTCNQ is insulating. The paramagnetic susceptibility of TTF-MTCNQ is comparable to that of TTF-TCNQ above the transition.     

Anomalous magnetoresistance in an organic conductor: (TMTSF)2PF6

The effect of a transverse magnetic field on the chain axis resistivity of the new organic conductor (TMTSF)₂PF₆ is found to be substantial near the transition point. δρ/ρ₀ is + 20% at B=6Vsm^-2 just above the transition. An interpretation based on curvature in the Fermi surface is proposed.     

An algorithm for the minimax weber problem

The paper presents an algorithm for finding the weighted absolute center of a given set of points in the Euclidean plane.The algorithm is a specialized implementation of the method of feasible directions.The presentation includes a proof of convergence as well as computational experience.     

First-principles modelling of scanning tunneling microscopy using non-equilibrium Green’s functions

The investigation of electron transport processes in nano-scale architectures plays a crucial role in the development of surface chemistry and nano-technology. Experimentally, an important driving force within this research area has been the concurrent refinements of scanning tunneling microscopy (STM) techniques. The theoretical treatment of the STM operation has traditionally been based on the Bardeen and Tersoff-Hamann methods which take as input the single-particle wave functions and eigenvalues obtained from finite cluster or slabs models of the surface-tip interface. Here, we present a novel STM simulation scheme based on non-equilibrium Green’s functions (NEGF) and Wannier functions which is both accurate and very efficient. The main novelty of the scheme compared to the Bardeen and Tersoff-Hamann approaches is that the coupling to the infinite (macroscopic) electrodes is taken into account. As an illustrating example we apply the NEGF-STM method to the Si(001)-(2×1):H surface with sub-surface P doping and discuss the results in comparison to the Bardeen and Tersoff-Hamann methods.