Enantiospecific C?H Activation Using Ruthenium Nanocatalysts

The activation of C H bonds has revolutionized modern synthetic chemistry. However, no general strategy for enantiospecific C H activation has been developed to date. We herein report an enantiospecific C H activation reaction followed by deuterium incorporation at stereogenic centers. Mechanistic studies suggest that the selectivity for the α‐position of the directing heteroatom results from a four‐membered dimetallacycle as the key intermediate. This work paves the way to novel molecular chemistry on nanoparticles.     

Synthesis of Unprecedented Sulfonylated Phosphono‐exo‐Glycals Designed as Inhibitors of the Three Mycobacterial Galactofuranose Processing Enzymes

This study reports a new methodology to synthesize exo‐glycals bearing both a sulfone and a phosphonate. This synthetic strategy provides a way to generate exo‐glycals displaying two electron‐withdrawing groups and was applied to eight different carbohydrates from the furanose and pyranose series. The Z/E configurations of these tetrasubstituted enol ethers could be ascertained using NMR spectroscopic techniques. Deprotection of an exo‐glycal followed by an UMP (uridine monophosphate) coupling generated two new UDP (uridine diphosphate)‐galactofuranose analogues. These two Z/E isomers were evaluated as inhibitors of UGM, GlfT1, and GlfT2, the three mycobacterial galactofuranose processing enzymes. Molecule 46‐(E) is the first characterized inhibitor of GlfT1 reported to date and was also found to efficiently inhibit UGM in a reversible manner. Interestingly, GlfT2 showed a better affinity for the (Z) isomer. The three enzymes studied in the present work are not only interesting because, mechanistically, they are still the topic of intense investigations, but also because they constitute very important targets for the development of novel antimycobacterial agents.     

Convenient grafting through approach for the preparation of stealth polymeric blood pool magnetic resonance imaging contrast agents

New hydrosoluble magnetic resonance imaging (MRI) macrocontrast agents are synthesized by reversible addition fragmentation chain transfer (RAFT) copolymerization of poly(ethylene oxide) methyl ether acrylate (PEOMA) with an acrylamide bearing a ligand for gadolinium, followed by the complexation of Gd³⁺. This convenient and simple grafting through approach leads to macrocontrast agents with a high relaxivity at high frequency that is imparted by the restricted tumbling of the Gd³⁺ complex caused by its attachment to the polymer backbone. Importantly a very low protein adsorption is also evidenced by the hemolytic CH50 test. It is the result of the poly(ethylene oxide) (PEO) brush that efficiently hides the gadolinium complex and renders it stealth to the proteins of the immune system. Improved contrast and long blood circulating properties are thus expected for these macrocontrast agents. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Dispersion of multiwalled carbon nanotubes in a rubber matrix using an internal mixer: Effects on rheological and electrical properties

The dispersion of multiwalled carbon nanotubes (CNTs) in an ethylene propylene rubber matrix was investigated using an internal mixer. Poly(ethylene‐co‐polyvinyl acetate) (EVA) statistic copolymer was used as a dispersing agent. The effects of the concentration of the dispersing agent and the matrix viscosity on the quality of the dispersion of 1 wt % of CNTs were studied by using microscopy and rheology in the melt state. It was demonstrated that the dispersion is governed principally by the viscosity of the matrix. As expected, better dispersion was observed when the matrix exhibited a lower viscosity. The influence of the filler content on the rheological and electrical properties is presented. A Cross model with a yield stress is proposed to describe the rheological behavior of these materials, which exhibit a viscoelastic solid behavior from 1 wt % CNT content. Electrical measurement data indicate that the electrical percolation threshold was 2.9 wt %. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1597–1604, 2011     

Structural and electronic properties of hexa-adamantyl-hexa-phenylbenzene molecules studied by low temperature scanning tunneling microscopy

The electronic and structural properties of large molecules composed of a central hexa-phenylbenzene core surrounded by six adamantyl groups (Ad₆HPB) adsorbed on Ag(111) have been investigated using low temperature scanning tunneling microscopy (STM), adsorption and image calculations. On large 2D domains, the molecular organization displays two lattices. In one of them, molecules are slightly nested as a result of their relative flexibility during packing. These compounds also exhibit contrast variations in terms of used bias voltage in the self-assembled domains as well as in single molecule observations. This is attributed to the peculiar electronic properties of Ad₆HPB and to the role of peripheral groups.