β‐Elimination of an aziridine to an allylic amine: a mechanistic study

The base‐induced rearrangement of aziridines has been examined using a combination of calculations and experiment. The calculations show that the substituent on nitrogen is a critical feature that greatly affects the favorability of both α‐deprotonation, and β‐elimination to form an allylic amine. Experiments were carried out to determine whether E2‐like rearrangement to the allylic amine with lithium diisopropyl amide (LDA) is possible. N‐tosyl aziridines were found to deprotonate on the tosyl group, preventing further reaction. A variety of N‐benzenesulfonyl aziridines having both α‐ and β‐protons decomposed when treated with LDA in either tetrahydrofuran or hexamethylphosphoramide. However, when α‐protons were not present, allylic amine was formed, presumably via β‐elimination. Copyright © 2011 John Wiley & Sons, Ltd.     

An improved weighted essentially non-oscillatory scheme for hyperbolic conservation laws

In this article we develop an improved version of the classical fifth-order weighted essentially non-oscillatory finite difference scheme of [G.S. Jiang, C.W. Shu, Efficient implementation of weighted ENO schemes, J. Comput. Phys. 126 (1996) 202–228] (WENO-JS) for hyperbolic conservation laws. Through the novel use of a linear combination of the low order smoothness indicators already present in the framework of WENO-JS, a new smoothness indicator of higher order is devised and new non-oscillatory weights are built, providing a new WENO scheme (WENO-Z) with less dissipation and higher resolution than the classical WENO. This new scheme generates solutions that are sharp as the ones of the mapped WENO scheme (WENO-M) of Henrick et al. [A.K. Henrick, T.D. Aslam, J.M. Powers, Mapped weighted essentially non-oscillatory schemes: achieving optimal order near critical points, J. Comput. Phys. 207 (2005) 542–567], however with a 25% reduction in CPU costs, since no mapping is necessary. We also provide a detailed analysis of the convergence of the WENO-Z scheme at critical points of smooth solutions and show that the solution enhancements of WENO-Z and WENO-M at problems with shocks comes from their ability to assign substantially larger weights to discontinuous stencils than the WENO-JS scheme, not from their superior order of convergence at critical points. Numerical solutions of the linear advection of discontinuous functions and nonlinear hyperbolic conservation laws as the one dimensional Euler equations with Riemann initial value problems, the Mach 3 shock–density wave interaction and the blastwave problems are compared with the ones generated by the WENO-JS and WENO-M schemes. The good performance of the WENO-Z scheme is also demonstrated in the simulation of two dimensional problems as the shock–vortex interaction and a Mach 4.46 Richtmyer–Meshkov Instability (RMI) modeled via the two dimensional Euler equations.     

A Pro-Fluorescent Ubiquitin-Based Probe to Monitor Cysteine-Based E3 Ligase Activity

Protein post-translational modification with ubiquitin (Ub) is a versatile signal regulating almost all aspects of cell biology, and an increasing range of diseases is associated with impaired Ub modification. In this light, the Ub system offers an attractive, yet underexplored route to the development of novel targeted treatments. A promising strategy for small molecule intervention is posed by the final components of the enzymatic ubiquitination cascade, E3 ligases, as they determine the specificity of the protein ubiquitination pathway. Here, we present UbSRhodol, an autoimmolative Ub-based probe, which upon E3 processing liberates the pro-fluorescent dye, amenable to profile the E3 transthiolation activity for recombinant and in cell-extract E3 ligases. UbSRhodol enabled detection of changes in transthiolation efficacy evoked by enzyme key point mutations or conformational changes, and offers an excellent assay reagent amenable to a high-throughput screening setup allowing the identification of small molecules modulating E3 activity.     

ChemInform Abstract: Icosahedron Oligomerization and Condensation in Intermetallic Compounds. Bonding and Electronic Requirements

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