An unprecedented alpha-C-C agostic interaction in a cyclopropyl tris(pyrazolyl)boratoniobium complex

Structural, spectroscopic and theoretical evidence indicate that an unusual alpha-C-C agostic interaction is preferred over both alpha- and beta-C-H agostic alternatives in the title compound, TpMe2NbCl(c-C3H5)(MeCCMe).     

The preparation and intra- and intermolecular addition reactions of acyclic N-acylimines: application to the synthesis of (+/-)-sertraline

Intramolecular endo-cyclization reactions of N-acyliminium ions have seen wide application for the synthesis of heterocyclic compounds. The corresponding exocyclic variant, which would provide 1-aminotetralin derivatives, for example, has little precedent. We have discovered that acyclic N-acylcarbamates can be readily reduced to the corresponding N-acylhemiaminal derivatives in high yield using DIBAL as the reducing agent. These intermediates are remarkably stable and, if desired, can be purified and stored. The acyclic N-acylhemiaminals undergo both intra- and intermolecular nucleophilic addition reactions mediated by strong Lewis acids, such as TiCl(4). Diastereoselectivity, induced either by a substituent on the newly formed ring, or by utilizing a chiral ester on the carbamic acid, was disappointingly low. This methodology was successfully applied to the synthesis of the racemic form of the marketed antidepressant sertraline.     

Optimal acoustic fields in compact thermoacoustic refrigerators

Thermoacoustic refrigerators have been developed during the last 15 years, employing quasi-standing resonant acoustic waves inside fluid-filled cavities to transfer heat along a stack region. Because higher efficiency can be reached when a significant travelling wave component exists in the resonator, specific resonant thermoacoustic devices have been designed allowing to adjust more or less the ratio of travelling and standing wave components. However, the acoustic pressure field and the particle velocity field do not appear to be the optimal ones, for the thermal quantities of interest. Thus, it is the aim of the paper to present a new kind of thermoacoustic standing wave-like device which allows to control easily and independently the pressure field and the particle velocity field, after investigating the optimal acoustic field, in the stack region, for the main parameters of interest, i.e. the temperature gradient, the thermoacoustic heat flow and the coefficient of performance.     

Novel polyesteramide-based di- and triblock copolymers: From thermo-mechanical properties to hydrolytic degradation

Two types of biodegradable poly(ε-caprolactone (CLo))-co-poly(ε-caprolactam (CLa)) copolymers were prepared by catalyzed hydrolytic ring-opening polymerization. For the first type of materials, the respective cyclic comonomers were added simultaneously in the reaction medium leading to the formation of copolymers having a random distribution of co-units within the polyesteramide sequence, as evidenced by ¹H and ¹³C NMR. For the second type of copolymers, the cyclic comonomers were added sequentially in the reaction medium yielding diblock polyesteramides, again evidenced by NMR. The thermal and thermo-mechanical properties of the copolymers were investigated by DSC and DMA and correlated with the copolymer topology and composition. The copolymers were characterized by a storage modulus and α transition temperature intermediate to the modulus and T_g of the corresponding homopolymers. The chemical composition and molecular weight of the copolymers proved to have only a limited effect on the thermo-mechanical properties of the materials. The hydrolytic degradation of random copolymers was studied in a phosphate buffer at 60 °C and discussed in terms of chemical composition and molecular weight of the copolymers.     

Synthesis of vinylindoles and vinylpyrroles by the Peterson olefination or by use of the Nysted reagent

Vinylindoles and vinylpyrroles were prepared from their corresponding aldehydes or ketones using the Peterson olefination, or by use of the Nysted reagent, a commercially available gem‐dimetallic compound. The two methods provide efficient and convenient access to these useful heterocyclic 1,3‐diene systems. J. Heterocyclic Chem., (2011).     

Homogenization of periodic linear degenerate PDEs

It is well known under the name of ‘periodic homogenization’ that, under a centering condition of the drift, a periodic diffusion process on Rd converges, under diffusive rescaling, to a d-dimensional Brownian motion. Existing proofs of this result all rely on uniform ellipticity or hypoellipticity assumptions on the diffusion. In this paper, we considerably weaken these assumptions in order to allow for the diffusion coefficient to even vanish on an open set. As a consequence, it is no longer the case that the effective diffusivity matrix is necessarily non-degenerate. It turns out that, provided that some very weak regularity conditions are met, the range of the effective diffusivity matrix can be read off the shape of the support of the invariant measure for the periodic diffusion. In particular, this gives some easily verifiable conditions for the effective diffusivity matrix to be of full rank. We also discuss the application of our results to the homogenization of a class of elliptic and parabolic PDEs.     

Exploiting special structure in semidefinite programming: A survey of theory and applications

Semidefinite programming (SDP) may be seen as a generalization of linear programming (LP). In particular, one may extend interior point algorithms for LP to SDP, but it has proven much more difficult to exploit structure in the SDP data during computation.     

Inertia and damping effects on the damage-dependent burst size distribution of fiber bundles

Distributions of simultaneous fiber failures—bursts—in loaded fiber bundles are studied considering inertia and damping. Resulting burst size distributions have universal properties: all approach the power law D_ΔΔ^−2.5 for larger burst sizes Δ. Momentary burst size distributions evolve with increasing damage and do not follow power laws but are still universal. Finally, it is briefly outlined how to use distribution progression to assess damage state.     

Surface characterization of a cross‐linked cytochrome c film on cysteamine‐modified gold electrodes

The aim of the present paper is to characterize a cross‐linked horse heart cytochrome c (HHC) film on cysteamine‐modified gold electrodes. The HHC film was deposited using 1‐ethyl‐3‐(3‐dimethylaminopropyl)‐carbodiimide (EDC) as a coupling agent. Attenuated total reflection infrared (ATR‐IR) spectroscopic analyses were performed to characterize the newly formed surface on a qualitative and conformational level. The film thickness was measured using a noncontact optical surface profiler, while quantitative data and information on the heterogeneity of the film were obtained by means of synchrotron radiation X‐ray micro fluorescence (SR micro‐XRF). Results indicate that, in addition to electrochemical studies, spectroscopic analysis methods are essential to gain insight in the effect of immobilization strategies on protein conformations. The latter is of relevance in the development and optimization of biosensors. Copyright © 2009 John Wiley & Sons, Ltd.