A highly selective catalytic method for the oxidative functionalization of C-H bonds

This communication describes a new and highly practical Pd(II)-catalyzed method for the regio- and chemoselective oxidative functionalization of arenes and alkanes. Carbon-hydrogen bonds of substrates that contain a variety of directing groups (e.g., pyridine, azobenzene, pyrazole, and imine derivatives) are selectively transformed into esters, ethers, and aryl-halides under mild conditions. The scope of this reaction in terms of substrate, directing group, and oxidant is described, and a preliminary catalytic cycle is proposed.     

Direct wiring of cytochrome c's heme unit to an electrode: electrochemical studies

A novel strategy for the immobilization of cytochrome c on the surface of chemically modified electrodes is demonstrated and used to investigate the protein's electron-transfer kinetics. Mixed monolayer films of alkanethiols and omega-terminated alkanethiols (terminated with pyridine, imidazole, or nitrile groups that are able to ligate with the heme) are used to adsorb cytochrome c to the surface of gold electrodes. The use of mixed films, as opposed to pure films, allows the concentration of adsorbed cytochrome to remain dilute and ensures a higher degree of homogeneity in their environment. The adsorbed protein is studied using electrochemical methods and scanning tunneling microscopy.     

Enantio- and diastereoselective reductive aldol reactions with iridium-pybox catalysts

[see reaction]. A catalytic amount of [(cod)IrCl]2 and indane-pybox converts diethylmethylsilane, methyl acrylate, and certain aldehydes to the derived reductive aldol adduct with good enantio- and diastereocontrol.     

Precise Measurement of Muon Capture on the Proton

The aim of the μCap experiment is a 1% measurement of the singlet capture rate Λ _S for the basic electro-weak reaction μ + p → n + ν_μ. This observable is sensitive to the weak form-factors of the nucleon, in particular to the induced pseudoscalar coupling constant g _P . It will provide a rigorous test of theoretical predictions based on the Standard Model and effective theories of QCD. The present method is based on high precision lifetime measurements of μ⁻ in hydrogen gas and the comparison with the free μ⁺ lifetime. The μ⁻ experiment will be performed in ultra-clean, deuterium-depleted H₂ gas at 10 bar. Low density compared to liquid H₂ is chosen to avoid uncertainties due to ppμ formation. A time projection chamber acts as a pure hydrogen active target. It defines the muon stop position in 3D and detects rare background reactions. Decay electrons are tracked in cylindrical wire-chambers and a scintillator array covering 75% of 4π. This revised version was published online in August 2006 with corrections to the Cover Date.     

Smolyak algorithms based on digital (t, α, d)-sequences for multivariate integration

We use so-called (t, α, d)-sequences and Smolyak's algorithm to construct d × l -dimensional integration rules with optimal convergence rates in a suitable function space. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Amphiphilic ESIPT benzoxazole derivatives as prospective fluorescent membrane probes

Fluorescent amphiphilic benzoxazole derivatives were synthesized and used to produce photoactive phosphatidylcholine (PC) liposomes by reserve-phase evaporation. The dyes absorbed in the UV region and were fluorescent in the blue-green region (determined by solvent polarity). The alkyl chain length seemed to play a fundamental role in the photophysics of the benzoxazole fluorophore in reverse liposomes, and despite the same ESIPT core and phospholipid building block, each amphiphilic dye had a particular emission profile related to the dye location in the liposome. The fluorescence emission spectra from dye 5 showed that its fluorophore experienced a polar environment, due to the single normal emission, while dyes 6–7 had (in part) a normal emission, and the main fluorescent band ascribed to the ESIPT emission indicated a more hydrophobic environment. Despite the complex fluorescent profiles, the benzoxazole derivatives could be successfully introduced into the reverse liposome structure due to the interaction between the alkyl chain and PC bilayer.     

Relations Between Seepage Velocities in Immiscible,Incompressible Two-Phase Flow in Porous Media

Based on thermodynamic considerations, we derive a set of equations relating the seepage velocities of the fluid components in immiscible and incompressible two-phase flow in porous media. They necessitate the introduction of a new velocity function, the co-moving velocity. This velocity function is a characteristic of the porous medium. Together with a constitutive relation between the velocities and the driving forces, such as the pressure gradient, these equations form a closed set. We solve four versions of the capillary tube model analytically using this theory. We test the theory numerically on a network model.     

Analysis of the occurrence of stick-slip in AFM-based nano-pushing

The use of the Atomic Force Microscope (AFM) as a tool to manipulate matter at the nanoscale is promising. However, the complexity of the corresponding physics and mechanics makes such nanomanipulation difficult and not very accurate. In the present paper, we analyze the dynamics of AFM-based nano-pushing manipulation. Simulation results show that the choice of the manipulation speed and loading force highly affect the manipulation outcome. In addition, simulations predict the existence of several threshold manipulation speeds. These thresholds mark the transitions between no stick-slip motion and either unique or multiple coexisting stick-slip. The obtained results bear significant implications and help get more insight into AFM-based nano-pushing.