Omega-halonitriles: domino cyclizations to oxa- and carbocyclic nitriles

t-BuOK-induced deprotonation of omega-haloalkylnitriles generates remarkably stable potassiated nitriles. In situ deprotonation and alkylation of omega-chloroalkylnitriles with aldehyde electrophiles trigger sequential nucleophilic-electrophilic alkylations generating substituted tetrahydrofuranyl and tetrahydropyranyl nitriles. Redirecting the cyclization manifold with 5-iodopentanenitrile and a ketone causes a complementary electrophilic-nucleophilic cyclization to the corresponding carbonitrile. Collectively these cyclizations provide rapid assembly of five- and six-membered oxa- and carbocyclic nitriles demonstrating the utility of omega-halonitriles in domino alkylations.     

Reexamination of CeCl3 and InCl3 as activators in the diastereoselective Mukaiyama aldol reaction in aqueous media

A search for suitable reaction conditions in Mukaiyama-type aldol condensations activated by CeCl(3) and InCl(3) revealed that the reaction proceeds best in i-PrOH/H(2)O (95:5). Contrary to literature precedent, no reaction was observed in pure water, and the encountered destruction of the starting silyl enol ether can be ascribed to initial hydrolysis of the Lewis acid. As anticipated from the dual parameter (pK(h), WERC value) characteristics of CeCl(3) and InCl(3), the former proved more efficient as Lewis acid-promoter, in terms of reaction speed and yield. Nevertheless, InCl(3) was a superior catalyst during evaluation of the diastereoselectivity of the process. In this regard, determination of diastereoselectivity as a function of time showed that the InCl(3)-catalyzed reaction is irreversible, whereas the CeCl(3)-catalyzed reaction is a reversible process. In both cases, formation of the syn product is kinetically preferred, although DeltaDeltaG(++)273K(InCl(3)) = 1.50 kcal/mol versus DeltaDeltaG(++)273K (CeCl(3)) = 0.38 kcal/mol. Molecular modeling (semiempirical PM3, ab initio HF/3-21G*, hybrid B3LYP/3-21G*, and B3LYP/LANL2DZ) of the diastereoselective aldol reaction promoted by InCl(3) supports a "closed", Zimmermann-Traxler transition state.     

Efficient asymmetric synthesis of the vasopeptidase inhibitor BMS-189921

[reaction: see text] An efficient asymmetric synthesis of the vasopeptidase inhibitor BMS-189921 was accomplished. Two short enantioselective syntheses of the common key intermediate (S)-alpha-aminoazepinone 6b were developed. Olefin 3 was converted to 6b via asymmetric hydrogenation. Alternatively, enyne 12 was converted to racemic alpha-aminoazepinone 15b, which was transformed to 6b by a practical dynamic resolution.     

Surfactant driven flows overlying a hydrophobic epithelium: film rupture in the presence of slip

Both for tear films and along the airways within the lung, one has an extremely thin fluid layer overlying a biological substrate; in both cases surfactants either of natural origin, or artificially introduced, are important in driving fluid flows. There is evidence that slip can occur when hydrophilic liquids, similar to mucus or aqueous tear films, overlie hydrophobic epithelium. Utilizing results from recent experimental findings we examine the possible influence of slip upon tear film rupture, important in so-called dry eye, and upon surfactant-induced flows within the lung, used in surfactant replacement therapy.     

Interchange of infimum and integral

We prove a new interchange theorem of infimum and integral. Its distinguishing feature is, on the one hand, to establish a general framework to deal with interchange problems for nonconvex integrands and nondecomposable sets, and, on the other hand, to link the theorems of Rockafellar and Hiai-Umegaki with the one of Bouchitté-Valadier. We give an application to relaxation of nonconvex geometric integrals of Calculus of Variations.Received: 20 March 2002, Accepted: 12 March 2003, Published online: 16 May 2003     

Energy Levels of Neutral Atoms Via a New Perturbation Method

The energy levels of neutral atoms supported by potential V (r) = -Zexp(-ar)/r (Yukawa potential) are studied, using both dimensional and dimensionless quantities, via a new analytical methodical proposal (devised to solve for nonexactly solvable Schrödinger equation). Using dimensionless quantities, by scaling the radial Hamiltonian through y = Zr and = /Z, we report that the scaled screening parameter is restricted to have values ranging from zero to less than 0.4. On the other hand, working with the scaled Hamiltonian enhances the accuracy and extremely speeds up the convergence of the energy eigenvalues. The energy levels of several new eligible scaled screening parameter values are also reported.     

Low-energy effects in brane worlds: Liennard–Wiechert potentials and Hydrogen Lamb shift

Testing extra dimensions at low-energies may lead to interesting effects. In this work a test point charge is taken to move uniformly in the 3D subspace of a (3 + n)-brane embedded in a (3 + n + 1)-space with n compact and one warped infinite spatial extra dimensions. We found that the electromagnetic potentials of the point charge match standard Liennard–Wiechert’s at large distances but differ from them close to it. These are finite at the position of the charge and produce finite self-energies. We also studied a localized Hydrogen atom and take the deviation from the standard Coulomb potential as a perturbation. This produces a Lamb shift that is compared with known experimental data to set bounds for the parameter of the model. This work provides details and extends results reported in a previous Letter. We are pleased to dedicate this work to Professor Octavio Obregón on occasion of his 60th birthday. H. A. Morales-Técotl is an associate member of the Abdus Salam ICTP, Trieste Italy.     

Unconditionally Stable Complex Envelope Wave Equation PML Algorithm for Band Limited FDTD Simulations

Unconditionally stable complex envelope (CE) perfectly matched layer (PML) absorbing boundary conditions (ABCs) are presented for truncating the scalar wave-equation finite difference time domain (WE-FDTD) grids. The formulations are based on incorporating the alternating direction implicit (ADI) scheme into the CE FDTD implementations of the scalar wave-equation derived in the PML region at the domain boundaries. Numerical example carried out in two dimensional domain shows that the proposed formulations are more accurate than the classical ADI scalar wave equation PML formulations when it is used for modelling band limited electromagnetic applications.     

Pretreatment effects on the electrochemical responses for aluminium–magnesium alloy AA5083 corrosion behaviour

Electrochemical investigations on aluminium alloy corrosion in a sodium chloride solution have been performed by potentiostatic and potentiodynamic (electrochemical impedance spectroscopy) methods. Measurements have been obtained after mechanical polishing or electrochemical stripping in deaerated or not solution. All the results are strongly depending on the pretreatments that are undergone in the laboratory before the experimental measurements. Mechanical polishing induces huge effects on the surface of the analysed samples and a long time is necessary to avoid the effects of this treatment; instead, an electrochemical cleaning does not modify the surface and results can be regarded more rapidly as significant of the surface with higher reproducibility.