A characterization of semisimple plane polynomial automorphisms

It is well-known that an element of the linear group is semisimple if and only if its conjugacy class is Zariski closed. The aim of this paper is to show that the same result holds for the group of complex plane polynomial automorphisms.     

First synthesis of 2-aminosubstituted-2-perfluoroalkyl-3,6-dihydro-2H-thiopyrans by hetero-Diels-Alder reactions of fluorinated thioamides under microwave heating

This Letter presents the first examples of hetero-Diels-Alder reactions of polyfluoroalkanethiocarboxylic acid amides and 2,3-dimethylbutadiene under microwave heating. Cycloaddition reactions proved to be dependent on the nature of perfluoroalkyl chain and on the substituents attached to the nitrogen atom. Formation of ammonium salts was also performed by simple treatment of the corresponding cycloadducts with trifluoromethanesulfonic acid. In the case of octafluorobutyl-substituted derivative, one spontaneous desamination reaction took place leading to new 2H-thiopyran.     

Creating carbon-carbon bonds with samarium diiodide for the synthesis of modified amino acids and peptides

In this perspective, an overview of our experiences on the application of samarium diiodide in organic synthesis for the preparation of amino acid and peptide analogues is presented. Three different carbon-carbon bond forming reactions are discussed, including side chain introductions, gamma-amino acid synthesis and acyl-like radical additions for the construction of C-C mimics of the peptidic bonds.     

Probing microstructure evolution during the hardening of gypsum by proton NMR relaxometry

We report a comprehensive proton NMR relaxation study of the water confined in the evolving porous structure of hardened gypsum prepared with different water-to-plaster ratios (w/p) and increasing additions of crushed gypsum. This study gives some new information on the microstructure, the water distribution, and the hydration kinetics without any drying or perturbing preparation. The bi-exponential transverse magnetization decay reveals the existence of two water populations in slow exchange. However, the different behaviors of these populations during saturation and desaturation experiments show evidence of a fast exchange of each population with the surface. Two modes of organization of the microstructure of this material are identified through an original model of exchange as a function of the water-to-plaster ratio (0.4 < or = w/p < or = 0.6 and 0.7 < or = w/p < or = 1). A clear gap is shown in the exchange rate value above w/p = 0.6 that could be representative of a percolation threshold. Both the method and the theory presented can be applied more widely to other porous media with reactive surface areas.     

Multi-scale approach continuously relating the microstructure and the macroscopic mechanical properties of plaster pastes during their settings

A new multi-scale experimental approach is proposed to continuously relate the microstructure and the macroscopic mechanical properties of plaster pastes during their settings. (1)H NMR relaxometry is used to follow continuously and not destructively, the degree of hydration and the microstructure evolution during the setting and hardening of plaster paste. Transmission of shear and compressional ultrasonic velocities enable the determination of macroscopic mechanical properties of the material during the setting. On the basis of similar behaviors of Young's modulus and NMR-population of confined water as function of the degree of hydration, we conclude that NMR gives a better understanding of the evolution of the microstructure at the origin of a better control of the macroscopic mechanical properties.     

Modulating the activity of membrane-active peptides through Zn(II) complexation

Seeking to increase the selectivity of antimicrobial peptides for prokaryotic cells, we incorporated a bis-dipicolyl amine (bis-DPA) ligand at the N-terminus of de novo designed model peptides. The Zn₂·bisDPA complex increases the interaction of peptides with anionic model membranes, while decreasing interactions with zwitterionic model membranes. Further, it improves the peptides’ antimicrobial activity and decreases their hemolytic activity without substantial changes to their secondary structure. Therefore, incorporating a Zn₂·bisDPA complex is a useful strategy to enhance the selectivity of antimicrobial peptides.     

Macrophage Activation by a Lipophilic Derivative of Muramyldipeptide within Nanocapsules: Investigation of the Mechanism of Drug Delivery

Different colloidal formulations: nanocapsules (NC), emulsion and micelles, containing the lipophilic immunomodulator muramyltripeptide cholesterol (MTP-Chol) induce nitric oxide synthase activity in the RAW 264.7 cell line. The use of cytochalasin B, an inhibitor of cell movements, showed that phagocytosis was an important mechanism as far as NC and the emulsion were concerned. However, when the cells were separated from particles containing the immunomodulator by a membrane of 100nm pore size, significant activity could still be obtained, provided that serum was included in the medium. To determine whether low-density lipoprotein (LDL) might act as an intermediate carrier for MTP-Chol, the transfer of the immunomodulator from NC to LDL was studied by an ultrafiltration/centrifugation method followed by HPLC analysis. Although MTP-Chol could be transferred to LDL, when purified human LDL was added to serum-free medium, activation by MTP-Chol NC was reduced, rather than increased. This suggests that intact LDL carrying MTP-Chol is not taken up to a great extent by these macrophages.     

Disulfide- and thiol-incorporating copper catenanes: synthesis, deposition onto gold, and surface studies

Two new copper-complexed [2]catenanes have been prepared, both of which consist of two different interlocking rings. In both cases, one of the rings incorporates a disulfide bridge. The other ring contains either a single chelate (phen=1,10-phenanthroline, a bidentate ligand) or two different chelates (phen and terpy, 2,2',6',2"-terpyridine, a tridentate chelate). Deposition of these two complexes on a gold electrode surface was carried out by standard procedures, leading to reductive cleavage of the S-S bridge. The adsorbed species can be viewed as [2]catenanes for which the gold atoms of the electrode surface are an integral fragment of one of the two rings. They yield clear electrochemical responses, but no motion is observed for the catenane incorporating a phen unit and a terpy fragment in one of the two rings, regardless of the metal oxidation state. This is at odds with the behavior of the parent compound in solution, which undergoes ring-gliding motions upon electrochemical reduction or oxidation of the copper center. Near-field microscopy was used to study the deposited layers (STM and AFM). STM images suggest that the molecules do not tend to order at long range on the surface. Polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS) led to promising results: the two catenanes deposited are likely to be oriented perpendicular to the gold surface. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2111/2002/f3636_s.pdf or from the author. 1: Infrared spectra of [Cu.2]+ as a powder (black line, transmission IR spectroscopy) and as a SAM on gold (dotted line, PM-IRRAS). (Spectra offset and scaled for clarity; significant peaks marked with an asterisk.) 2: STM image (819x819 nm2) of a monolayer of [Cu.3]+ on Au(111) on mica.