A Different Approach to Enantioselective Organic Synthesis: Absolute Asymmetric Synthesis of Organometallic Reagents

Voilà, optical activity : Both enantiomers of 1‐chloroindene have been synthesized in high selectivity from solely achiral starting materials, and without using optically active catalysts (see scheme). These symmetry‐breaking syntheses provide a proof‐of‐concept for a new approach to asymmetric synthesis. NCS=N‐chlorosuccinimide.

     

On small tension p-branes

This Letter deals with p-branes with small but non-zero tension. We prove the existence of canonical transformations, within a perturbation theory, that link specific geometries of p  -branes to solvable theories, namely string-like and particle-like theories. The specific shapes correspond to stretched configurations. For configurations linked to string-like theories one will upon quantization get a critical dimension of (25+p$25+p$).     

On the block counting process and the fixation line of the Bolthausen–Sznitman coalescent

The block counting process and the fixation line of the Bolthausen–Sznitman coalescent are analyzed. It is shown that these processes, properly scaled, converge in the Skorohod topology to the Mittag-Leffler process and to Neveu’s continuous-state branching process respectively as the initial state tends to infinity. Strong relations to Siegmund duality, Mehler semigroups and self-decomposability are pointed out. Furthermore, spectral decompositions for the generators and transition probabilities of the block counting process and the fixation line of the Bolthausen–Sznitman coalescent are provided leading to explicit expressions for functionals such as hitting probabilities and absorption times.     

Studies of oxidation of iron nanowires encased in porous aluminium oxide template

The transformations of phase composition of iron nanowires deposited into porous alumina template when annealing in the air were studied. The samples of iron nanowires of different diameter (8, 13, 15, 30 nm) were annealed for 1.5 h at temperature up to 600°C. In addition, for nanowires of 15 nm diameter the dependence of phase composition on annealing time was investigated. The phases were determined by applying Mössbauer spectroscopy. New Fe(II) and Fe(III) contributions to Mössbauer spectra were found and those were indentified as caused by the formation of hercynite FeAl₂O₄ and (Fe _x Al_1???x )₂O₃ with small x values (x?≤?0.15). It has been found that though initially the Fe(II) compound forms rapidly, afterwards its formation rate becomes lower than that of Fe(III) and after longer annealing time the Fe(III) content exceeds Fe(II) one.     

On the unitarity of gauged non-compact world-sheet supersymmetric WZNW models

In this paper we generalize our investigation of the unitarity of non-compact WZNW models connected to Hermitian symmetric spaces to the N=1$N=1$ world-sheet supersymmetric extension of these models. We will prove that these models have a unitary spectrum in a BRST approach for antidominant highest weight representations if the level and weights of the gauged subalgebra are integers. We will find new critical string theories in 7 and 9 space–time dimensions.     

γ‐Azaproline Confers pH Responsiveness and Functionalizability on Collagen Triple Helices

Proline derivatives bearing substituents at Cγ are valuable tools for biological and materials investigations. However, the stereochemistry at Cγ can produce undesired steric or stereoelectronic interactions. Here, we introduce γ‐azaproline (γ‐azPro), which lacks a stereogenic center at Cγ, as a pH‐responsive and functionalizable proline analogue that can adapt to its environment. Conformational analyses by NMR spectroscopy and DFT calculations revealed that the imidazolidine ring of γ‐azPro is flexible. Incorporation of γ‐azPro into collagen model peptides (CMPs) produced pH‐responsive triples helices and triple helices that can be easily functionalized.     

On the Evaporation of Colloidal Suspensions in Confined Pillar Arrays

The thermal and electrical transport capabilities of materials in electronic packaging are key to supporting high-performance microelectronic systems. In composite and hybrid materials, both of these transport capabilities are limited by contact resistances. We propose a directed nanoparticle assembly method to reduce contact resistances by transforming point contacts between micrometer-sized objects into quasi-areal contacts. The nanoparticle assembly is directed by the formation of liquid bridges in contact points during the evaporation of a colloidal suspension. In this work, we experimentally study the evaporation of colloidal suspensions in confined porous media to yield uniform nanoparticle assembly, as required for electronic packaging. The evaporation pattern of liquids in confined pillar arrays is either branched or straight, depending on the surface tension of the liquid and on the pore size defined by the pillar size and spacing. Stable evaporation fronts result in uniform nanoparticle deposition above a bond number threshold of 10\(^{-3}\). However, at reduced evaporation dynamics, liquid pinning results from colloidal particle accumulations at the liquid–vapor interface, ultimately leading to undesired colloidal bridging between pillars.     

Particle Creation at a Point Source by Means of Interior-Boundary Conditions

We consider a way of defining quantum Hamiltonians involving particle creation and annihilation based on an interior-boundary condition (IBC) on the wave function, where the wave function is the particle-position representation of a vector in Fock space, and the IBC relates (essentially) the values of the wave function at any two configurations that differ only by the creation of a particle. Here we prove, for a model of particle creation at one or more point sources using the Laplace operator as the free Hamiltonian, that a Hamiltonian can indeed be rigorously defined in this way without the need for any ultraviolet regularization, and that it is self-adjoint. We prove further that introducing an ultraviolet cut-off (thus smearing out particles over a positive radius) and applying a certain known renormalization procedure (taking the limit of removing the cut-off while subtracting a constant that tends to infinity) yields, up to addition of a finite constant, the Hamiltonian defined by the IBC.     

Zerovalent Rhodium and Iridium Silatranes Featuring Two‐Center,Three‐Electron Polar σ Bonds

Species with 2‐center, 3‐electron (2c/3e^?) σ bonds are of interest owing to their fascinating electronic structures and potential for interesting reactivity patterns. Report here is the synthesis and characterization of a pair of zerovalent (d⁹) trigonal pyramidal Rh and Ir complexes that feature 2c/3e^? σ bonds to the Si atom of a tripodal tris(phosphine)silatrane ligand. X‐ray diffraction, continuous wave and pulse electron paramagnetic resonance, density‐functional theory calculations, and reactivity studies have been used to characterize these electronically distinctive compounds. The data available highlight a 2c/3e^? bonding framework with a σ*‐SOMO of metal 4‐ or 5d_z² parentage that is partially stabilized by significant mixing with Si (3p_z) and metal (5‐ or 6p_z) orbitals. Metal‐ligand covalency thus buffers the expected destabilization of transition‐metal (TM)‐silyl σ*‐orbitals by d–p mixing, affording well‐characterized examples of TM–main group, and hence polar, 2c/3e^? σ “half‐bonds”.