Edmond Gravel

Catalytic oxidation of silanes by carbon nanotube-gold nanohybrids.

The selective oxidation of silanes has attracted wide interest as silanols are key synthons for the production of siliconcontaining materials and nucleophilic partners in organometallic cross-coupling reactions. Silanes are classically converted into silanols using strong oxidizing agents such as osmium tetroxide, permanganate, ozone, peracids, or peroxides. However, under these reaction conditions, significant amounts of siloxanes and toxic by-products are formed. To overcome these drawbacks, catalytic systems involving water and oxygen have been recently devised. They offer the advantage of cleanly producing silanols along with hydrogen gas as the only by-product. While initial catalytic silane oxidation studies relied on homogeneous transition metals, heterogeneous catalytic systems have emerged as very promising alternatives. 10] Indeed, the latter are more efficient (high conversion rate), recyclable, selective (little to no siloxane by-product formation), and usually operate under milder conditions. Amongst heterogeneous catalysts for silane oxidation, recent elegant examples include nanoporous gold by Asao, Yamamoto, and co-workers, and hydroxyapatite-supported silver or gold nanoparticles by Kaneda and co-workers. Herein we report an alternative strategy which has led to the discovery of the most efficient catalytic system to date for silane oxidation. Our approach involves layer-by-layer (LBL) assembly of gold nanoparticles on carbon nanotubes (CNTs). Nanotubes provide high specific surface area and excellent nanoparticle (NP) dispersion. In addition, nanotubes are electronically active and stabilization of transient higher oxidation states of gold are anticipated by collaborative interactions with the metal. To the best of our knowledge, this is the first report on silane oxidation by CNTsupported catalysts. The preparation of the CNT–gold nanohybrid (see the Supporting Information for details) started with aqueous selfassembly of amphiphilic nitrilotriacetic diyne lipids (DANTA) on multiwalled carbon nanotubes (Figure 1) to

Drug Delivery and Imaging with Polydiacetylene Micelles

This concept article summarizes our recent findings regarding photopolymerized micelles obtained from the self-assembly of diacetylene-containing amphiphiles. Their synthesis and characterization are presented as well as some biomedical applications, such as tumor imaging and drug delivery. Finally, ongoing studies and future challenges are briefly discussed.

Cooperative Dehydrogenation of N‐Heterocycles Using a Carbon Nanotube–Rhodium Nanohybrid

Rhodium nanoparticles were anchored on carbon nanotubes and the resulting nanohybrid was studied as co-catalyst, along with tert-butylcatechol, for the dehydrogenation of various N-heterocycles. The co-catalytic system operates in high yields, under the mildest conditions reported so far, and can be applied to a wide variety of secondary amine-containing scaffolds.

Tumor-targeted polydiacetylene micelles for in vivo imaging and drug delivery.

In vivo tumor targeting and drug delivery properties of small polymerized polydiacetylene (PDA) micelles (∼10 nm) is investigated in a murine MDA-MB-231 xenograft model of breast cancer. Three micelles with different surface coatings are synthesized and tested for their ability to passively target tumor through the enhanced permeability and retention effect. After injection (24 h), fluorescence diffuse optical tomographic imaging indicates a tumor uptake of nearly 3% of the injected dose for the micelles with a 2 kDa poly(ethylene glycol) (PEG)-coating (PDA-PEG2000). The uptake of PDA micelles in tumors is confirmed by co-localization with [(18) F]-fluorodeoxyglucose (FDG) positron emission tomography. Although FDG has a higher diffusion rate in tumors, 40 ± 19% of the retained micelles is co-registered with the tumor volume visualized by FDG. Finally, PDA-PEG2000 micelles are loaded with the hydrophobic anticancer drug paclitaxel and used in vivo to inhibit tumor growth. These findings demonstrate the potential of PDA-PEG2000 micelles for both in vivo tumor imaging and drug delivery applications.

Room temperature Suzuki coupling of aryl iodides, bromides, and chlorides using a heterogeneous carbon nanotube-palladium nanohybrid catalyst

Palladium nanoparticles were immobilized on multi-walled carbon nanotubes by a layer-by-layer approach, resulting in a well-defined assembly. The nanohybrid was found effective in promoting Suzuki cross couplings of various halogenated aromatics, including chlorinated ones, with arylboronic acids under sustainable conditions. The heterogeneous catalyst could also easily be recovered from the reaction mixture and reused with no loss of activity over several cycles.

Direct Reductive Amination of Aldehydes Catalyzed by Carbon Nanotube/Gold Nanohybrids

Amines constitute a key scaffold of numerous biologically active compounds and are versatile intermediates in several organic transformations. However, in spite of their significance, there are only a limited number of methods for their synthesis, including the one-pot reductive amination of carbonyl compounds. In contrast to indirect methods, which involve the isolation of an unstable imine intermediate, direct reductive amination constitutes a more efficient and straightforward route. Classically, various boron and tin complexes have been used for this transformation, but they suffer from low selectivity (over-alkylation), require harsh conditions (acidic), and only afford the products in moderate yields, along with toxic by-products. More recently, the combination of noble metals (e.g. , Rh, Ir, and Ru) and H2 gas has been reported to efficiently promote direct reductive amination. 8] Other procedures involve hydride sources, such as isopropanol, Hanztsch esters, formates, and silanes. Indeed, silanes are mild hydride donors that are able to reduce imines in combination with Lewis or Brønsted acids, but they have not yet been shown to be effective in combination with gold nanoparticles. Although metallic gold has traditionally been regarded as a poor catalytic species, its activity is dramatically enhanced upon downsizing it to nanometer-sized particles (AuNPs). Nanoscale gold has found multiple applications in fine-chemical synthesis, including in selective hydrogenation, carbon carbon bond formation, and oxidation reactions. We have recently contributed to the field of reactions that are catalyzed by carbon nanotube (CNT)-supported nanogold by reporting efficient systems for the oxidations of silanes and alcohols. Compared to other supports, CNTs offer several advantages, including chemical, thermal, and mechanical stability, inertness (i.e. , little-to-no interactions with the catalyzed organic transformation), high surface area, and chemically tunable topography. Moreover, CNTs are electronically active and can contribute to the stabilization of transient higher oxidation states of the metal atoms. Herein, we report our investigations on the direct reductive amination of aldehydes catalyzed by our gold/carbon-nanotube nanohybrid (AuCNT, Figure 1).

Aerobic Oxidation of Phenols and Related Compounds using Carbon Nanotube–Gold Nanohybrid Catalysts

Gold nanoparticles supported on carbon nanotubes were investigated as catalysts in the aerobic oxidation of various substrates (phenols, hydroquinones, catechols, aminophenols, and thiols). The nanohybrid system compares favorably with other supported noble metal catalysts in terms of overall efficacy as it operates at room temperature, under air atmosphere (no external oxidant needed), and can readily be recycled.

Carbon Nanotube–Gold Nanohybrid Catalyzed N‐Formylation of Amines by using Aqueous Formaldehyde

The N‐formylation of a variety of primary and secondary amines by using aqueous formaldehyde at room temperature in open air affords the corresponding formamides in excellent yield under the catalytic influence of a gold–carbon nanotube nanohybrid. The reaction is also marked by excellent chemoselectivity, low catalyst loading, and recyclability of the catalyst.

Compact tridentate ligands for enhanced aqueous stability of quantum dots and in vivo imaging

We describe here a simple and versatile route for the preparation of a tridentate ligand that not only provides stable interactions with colloidal semiconductor nanocrystals (quantum dots, QDs) but also makes them water soluble. The designed ligand incorporates a biocompatible solubilizing polyethylene glycol (PEG) chain connected to a tridentate thiol motif with improved affinity towards the QDs surface. Stability experiments revealed better resistance to various drastic conditions compared to classical dihydrolipoic-based ligands. The enhanced stability of the assembly also enabled in vivo imaging experiments using near infrared-emitting QDs.

Advances in carbon nanotube-noble metal catalyzed organic transformations

Abstract This review article is dealing with heterogeneous catalysis applied to synthetic chemistry using various carbon nanotube-supported noble metals (e.g., ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold).