Cover Picture: Nanoscale Chemical Imaging of the Reduction Behavior of a Single Catalyst Particle (Angew. Chem. Int. Ed. 20/2009)

Iron‐based catalysts for the Fischer–Tropsch synthesis bring about the conversion of synthesis gas (CO/H₂) derived from coal or biomass into liquid transportation fuels. In their Communication on page 3632 ff., B. M. Weckhuysen, F. M. F. de Groot, and co‐workers provide insights into the difference in behavior of the catalyst precursors during pretreatment in H₂ on both the nanoscopic and the bulk scale. These findings enable further understanding of how the activated catalyst works.

     

Aging of cholinesterases phosphylated by tabun proceeds through O-dealkylation

Human butyrylcholinesterase (hBChE) hydrolyzes or scavenges a wide range of toxic esters, including heroin, cocaine, carbamate pesticides, organophosphorus pesticides, and nerve agents. Organophosphates (OPs) exert their acute toxicity through inhibition of acetylcholinesterase (AChE) by phosphorylation of the catalytic serine. Phosphylated cholinesterase (ChE) can undergo a spontaneous, time-dependent process called "aging", during which the OP-ChE conjugate is dealkylated. This leads to irreversible inhibition of the enzyme. The inhibition of ChEs by tabun and the subsequent aging reaction are of particular interest, because tabun-ChE conjugates display an extraordinary resistance toward most current oxime reactivators. We investigated the structural basis of oxime resistance for phosphoramidated ChE conjugates by determining the crystal structures of the non-aged and aged forms of hBChE inhibited by tabun, and by updating the refinement of non-aged and aged tabun-inhibited mouse AChE (mAChE). Structures for non-aged and aged tabun-hBChE were refined to 2.3 and 2.1 A, respectively. The refined structures of aged ChE conjugates clearly show that the aging reaction proceeds through O-dealkylation of the P(R) enantiomer of tabun. After dealkylation, the negatively charged oxygen forms a strong salt bridge with protonated His438N epsilon2 that prevents reactivation. Mass spectrometric analysis of the aged tabun-inhibited hBChE showed that both the dimethylamine and ethoxy side chains were missing from the phosphorus. Loss of the ethoxy is consistent with the crystallography results. Loss of the dimethylamine is consistent with acid-catalyzed deamidation during the preparation of the aged adduct for mass spectrometry. The reported 3D data will help in the design of new oximes capable of reactivating tabun-ChE conjugates.     

Superparamagnetic Fe3O4SiO2 nanocomposites: enabling the tuning of both the iron oxide load and the size of the nanoparticles

Using a water-in-oil microemulsion system, silica nanoparticles containing superparamagnetic iron oxide (SPIO) crystals have been prepared and characterized. With this method, the loading of iron oxide crystals, the thickness of the silica shells, and the overall particle sizes are tunable. Moving from low to high water concentration, within the microemulsion region, resulted in a gradual shift from larger particles, ca. 100 nm and fully loaded with SPIOs, to smaller particles, ca. 30 nm containing only one or a few SPIOs. By varying the amount of silica precursor, the thickness of the silica shell was altered. Field dependent magnetization measurements showed the magnetic properties of the SPIOs were preserved after the synthesis.     

Tagging alcohols with cyclic carbonate: a versatile equivalent of (meth)acrylate for ring-opening polymerization

Cyclic carbonate monomers based on a single biocompatible scaffold allow for incorporation of a wide range of functional groups into macromolecules via ring-opening polymerization.     

A cation-exchange material for protein separations based on grafting of thiol-terminated sulfopropyl methacrylate telomers onto hydrophilized monodisperse divinylbenzene particles

A strong cation-exchange separation material has been prepared from monodisperse divinylbenzene particles modified by a "grafting to" approach, utilizing as anchoring points epoxy groups introduced onto the surface of the particles via oxidation of residual vinyl groups. The grafted chains consisted of thiol-terminated telomers of sulfopropyl methacrylate prepared by iniferter mediated polymerization, and grafting was performed by reaction of the corresponding thiolate anion with the surface epoxy groups. Attachment through epoxy moieties that were subsequently converted into 2,3-propanediol groups increased the hydrophilicity of the polymeric particles and incubation experiments showed no signs of the proteins denaturing on the column during an extended contact time of 1 h at room temperature. The performance of the grafted material was demonstrated by the chromatographic separation of cytochrome C, lysozyme, myoglobin, and ribonuclease A, in a cation-exchange mode.     

The crystal and magnetic structure of the magnetocaloric compound FeMnP0.5Si0.5

The crystal and magnetic structure of the magnetocaloric compound FeMnP_0.5Si_0.5 has been studied by means of neutron and X-ray powder diffraction. Single phase samples of nominal composition FeMnP_0.5Si_0.5 have been prepared by the drop synthesis method. The compound crystallizes in the Fe₂P-type structure () with the magnetic moments aligned along the a-axis. It is found that the Fe atoms are mainly situated in the tetrahedral 3g site while the Mn atoms prefer the pyramidal 3f position. The material is ferromagnetic (T_C=382 K) and at 296 K the total magnetic moment is . It is shown that the magnetic moment in the 3f site is larger () than in the 3g site ().     

The road to gravitational-wave astronomy

Gravitational-wave astronomy is an area of great promise, yet to be realized. While we are waiting for the first (undisputed!) direct detection of these elusive waves it is useful to take stock and consider the challenges that need to be met if we want this field to reach its full potential. This write-up provides a brief introduction to some of the key ideas and the current state-of-play, and lists a range of modelling questions that need to be considered in the future.     

Mass transfer to blood flowing through arterial stenosis

The present investigation deals with a mathematical model representing the mass transfer to blood streaming through the arteries under stenotic condition. The mass transport refers to the movement of atherogenic molecules, that is, blood-borne components, such as oxygen and low-density lipoproteins from flowing blood into the arterial walls or vice versa. The blood flowing through the artery is treated to be Newtonian and the arterial wall is considered to be rigid having differently shaped stenoses in its lumen arising from various types of abnormal growth or plaque formation. The nonlinear unsteady pulsatile flow phenomenon unaffected by concentration-field of the macromolecules is governed by the Navier–Stokes equations together with the equation of continuity while that of mass transfer is controlled by the convection-diffusion equation. The governing equations of motion accompanied by appropriate choice of the boundary conditions are solved numerically by MAC(Marker and Cell) method and checked numerical stability with desired degree of accuracy. The quantitative analysis carried out finally includes the respective profiles of the flow-field and concentration along with their distributions over the entire arterial segment as well. The key factors like the wall shear stress and Sherwood number are also examined for further qualitative insight into the flow and mass transport phenomena through arterial stenosis. The present results show quite consistency with several existing results in the literature which substantiate sufficiently to validate the applicability of the model under consideration.      

Preconditioning by inverting the Laplacian: an analysis of the eigenvalues

Wolfgang Hackbusch ^{We study the eigenvalues of the operator generated by usingthe inverse of the Laplacian as a preconditioner for self-adjointsecond-order elliptic partial differential equations with smoothcoefficients. It is well-known that the spectral condition numberof the preconditioned operator can be bounded by , where k is the uniformly positive coefficientof the second-order elliptic equation. The purpose of this paperis to study the spectrum of the preconditioned operator. Wewill show that there is a strong relation between the spectrumof this operator and the range of the coefficient function.In the continuous case, we prove, both for mappings definedon Sobolev spaces and in terms of generalized functions, thatthe spectrum of the preconditioned operator contains the rangeof the coefficient function k. In the discrete case, we indicateby numerical examples that the entire discrete spectrum is approximatelygiven by values of k.}     

Formate stability and carbonate hydrogenation on strained Cu overlayers on Pt(1 1 1)

Formate (HCOO) synthesis, decomposition and the hydrogenation of carbonate (CO₃) on Cu overlayers deposited on a Pt(1 1 1) single crystal are investigated to examine the reactivity of a Cu surface under tensile strain with defects present.Formate is synthesized from a 0.5 bar mixture of 70% CO₂ and 30% H₂ at varying temperatures, and the evolution is followed with polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). Subsequent TPD reveals decomposition of the formate species into CO₂ and H₂ at 420 ± 5 K for strained Cu at sub-monolayer to monolayer coverages. This is a significantly lower decomposition temperature than obtained earlier on pristine Cu(1 1 1) (460 K), as well as for thicker Cu layers where we assign an observed decomposition peak at 440 ± 5 K to relaxed, but defect-rich Cu(1 1 1). However, the thermal stability of formate on strained and defect-rich Cu is similar to previous results obtained for supported, and lattice-strained, Cu nanoparticles.The hydrogenation of carbonate produced by 0.3 bar CO₂ exposure at room temperature was monitored with XPS and TPD showing a significant loss of carbonate when subjected to 0.2 bar H₂ at room temperature. However, the presence of formate on the surface, or any other hydrogenation product, could not be established during or after H₂ exposure by PM-IRRAS, EELS or TPD. Even so, the results suggest that carbonate and its hydrogenation may constitute a relevant pathway to methanol production.