Imaging from monostatic scattered intensities

This paper is about inverse scattering from monostatic intensity‐only measurements. We first formally rederive the geometrical optics approximation for a penetrable convex target. We then derive two direct imaging methods. The first one finds the point that best maps measurements over one circle onto a second one, due to amplitude decay of the scattered wave. The second one is a linearization of the problem, based on estimating the curvature of the object as a function of the measurements, due to the geometrical optics approximation. The first method aims at estimating the position of the target, whereas the second one aims at reconstructing the shape. The paper finishes with numerical tests showing the relevance and the limits of the proposed methods. Copyright © 2013 John Wiley & Sons, Ltd.     

A Chemoenzymatic Approach to Enantiomerically Pure Amines Using Dynamic Kinetic Resolution: Application to the Synthesis of Norsertraline

Dynamic transformation : A racemization catalyst and the enzyme Candida antarctica lipase B (CALB) were combined in a one‐pot dynamic kinetic resolution (DKR) of primary amines, which were transformed to their corresponding amides in up to 95 % yield and >99 % ee. This chemoenzymatic DKR was also applied to the synthesis of norsertraline (see scheme).

     

17-Diazo pristinamycin IIB preparation and synthetic applications

We report hereafter the preparation of 17-diazo pristinamycin II_B and its synthetic applications based on the generation of the corresponding carbene/carbenoid. In particular, we describe rhodium-catalyzed insertion reactions and the Wolff rearrangement of this α-diazo-ketone.     

New synthesis of imidazole derivatives from cyanobenzenes

An efficient access to 4-aryl imidazole scaffolds is described in two steps and one operation. Cyanoaryl-imidazolines are easily obtained by a (3?+?2) heterocyloaddition involving cyanobenzenes as dipolarophiles and a non-stabilized azomethine ylide as an electron-rich 1,3-dipole. Oxidation of the crude mixture affords an efficient two-steps access to the corresponding imidazoles.     

‘Bis-ornithine’ (2,2-bis(aminopropyl)glycine): a new tetravalent template for assembling different functional peptides

Synthesis of bis-ornithine, a new C^α,α-disubstituted α-amino acid bearing orthogonally protected α and δ amine groups is reported. Bis-ornithine (bisOrn) and dipeptides containing bis-ornithine have been synthesized in solution up to multigram scale. As a first example, one of these compounds Boc-βAla-bisOrn(Alloc)₂-OH has been attached to a solid support and used as template for the synthesis of a symmetrical assemblage of peptides.     

Metallic mesh properties and design of submillimeter filters

By using a Michelson interferometer in the asymmetric mode with helium cooled bolometer, we have measured with precision the complex transmittance and reflectance of metallic meshes in the wavelength region 0.7–4 at normal incidence. The important variations of the transmittance with the angle of incidence have been thoroughly investigated. Changes around the maximum transmittance are explained by the propagation of diffracted modes. Phase measurements show that a sharp dip appearing at _d with 1<_d/g<1.8 is related to the finite thickness of the mesh. From our measurements as well as other data precedently published it appears that there is a linear dependance between _d/g and the relative width of the slots of the mesh. All these deviations from classical models must absolutely be taken in account when designing high performances far infrared filters.     

The Unexpected Helical Supramolecular Assembly of a Simple Achiral Acetamide Tecton Generates Selective Water Channels

Achiral 2-hydroxy-N-(diphenylmethyl)acetamide (HNDPA) crystallizes in the P6₁ chiral space group as a hydrate, building up permeable chiral crystalline helical water channels. The crystallization-driven chiral self-resolution process is highly robust, with the same air-stable crystalline form readily obtained under a variety of conditions. Interestingly, the HNDPA supramolecular helix inner pore is filled by a helical water wire. The whole edifice is mainly stabilized by robust hydrogen bonds involving the HNDPA amide bonds and CH^…π interactions between the HNDPA phenyl groups. The crystalline structure shows breathing behavior, with completely reversible release and re-uptake of water inside the chiral channel under ambient conditions. Importantly, the HNDPA channel is able to transport water very efficiently and selectively under biomimetic conditions. With a permeability per channel of 3.3 million water molecules per second in large unilamellar vesicles (LUV) and total selectivity against NaCl, the HNDPA channel is a very promising functional nanomaterial for future applications.     

Anisotropic nonlinear optical absorption of gold nanorods in a silica matrix

Nanocomposite films consisting of gold nanospheres or gold nanorods embedded in a silica matrix have been prepared using a hybrid deposition technique consisting of plasma-enhanced chemical vapor deposition of SiO₂ and co-sputtering of gold, followed by annealing at 900 °C. Subsequent irradiation with 30 MeV heavy ions (Cu⁵⁺) was used to form gold nanorods. Linear and nonlinear optical properties of this material are closely related with the surface plasmon resonance in the visible. The nonlinear absorption coefficient (α₂@532 nm) for the films containing gold nanospheres was measured by Z-scan and P-scan techniques, and it was found to be isotropic and equal to −4.8 × 10⁻² cm/W. On the contrary, gold nanorods films exhibited two distinct surface plasmon resonance absorption bands giving rise to a strong anisotropic behavior, namely a polarization-dependent linear absorption and saturable absorption. Z-scan and P-scan measurements using various light polarization directions yielded nonlinear absorption coefficient (α₂@532 nm) values varying from −0.9 × 10⁻² cm/W up to −3.0 × 10⁻² cm/W. Linearity of the P-scan method in the context of nanocomposite saturable absorption is also discussed.     

Stereoselective Double Functionalization of Geminated C(sp3)-Organodimetallic Linchpins

Geminated C(sp³)-organodimetallics can serve as dinucleophilic linchpins for the rapid assembly of complex molecular structures through two consecutive electrophilic substitution reactions with two different electrophiles. Implementation of these double functionalization sequences in a stereoselective manner to develop tools for asymmetric synthesis has attracted considerable interest from the synthetic community over the last decade. The focus has been put mostly on 1,1-bimetallic reagents containing boron, zinc or zirconium, and different strategies have been applied for such a purpose, including the diastereoselective transformation of enantioenriched chiral reagents or the enantioselective conversion of achiral or racemic derivatives. Asymmetric catalysis is at stake in most of the approaches developed. In this review article, we highlight the key advances in the development of 1,1-bimetallic linchpins as tools for asymmetric synthesis, emphasizing the underlying general concepts.     

Crossing of the Cystic Barriers of Toxoplasma gondii by the Fluorescent Coumarin Tetra-Cyclopeptide

{"type":"entrez-nucleotide","attrs":{"text":"FR235222","term_id":"258291874","term_text":"FR235222"}}FR235222 is a natural tetra-cyclopeptide with a strong inhibition effect on histone deacetylases, effective on mammalian cells as well as on intracellular apicomplexan parasites, such as Toxoplasma gondii, in the tachyzoite and bradyzoite stages. This molecule is characterized by two parts: the zinc-binding group, responsible for the binding to the histone deacetylase, and the cyclic tetrapeptide moiety, which plays a crucial role in cell permeability. Recently, we have shown that the cyclic tetrapeptide coupled with a fluorescent diethyl-amino-coumarin was able to maintain properties of cellular penetration on human cells. Here, we show that this property can be extended to the crossing of the Toxoplasma gondii cystic cell wall and the cell membrane of the parasite in its bradyzoite form, while maintaining a high efficacy as a histone deacetylase inhibitor. The investigation by molecular modeling allows a better understanding of the penetration mechanism.