Efficient anodic allylation and benzylation of carbons using allyl and benzyl trimethylsilanes.

An easy process for allylation and benzylation of different carbon materials, primarily of glassy carbon, in acetonitrile solutions containing tetraalkyammonium salts is described. The method relies on the capability of C(sp(2)) zones of glassy carbon (graphite and fullerene-like inclusions) to be anodically charged at potentials >1.5 V versus Ag/AgCl to form electrophilic centers reacting with substituted trimethylsilanes RSiMe3. Great propensity of the trimethylsilyl group (TMS(+)) to act as a cationic leaving group facilitates electrophilic reactions of the charged anodic surface with R-carrying silylated precursors, permitting efficient grafting of a large variety of R groups. The present preliminary work focuses only on the efficient grafting of benzyl and allyl moieties.

Novel method for grafting alkyl chains onto glassy carbon. Application to the easy immobilization of ferrocene used as redox probe.

Primary alkyl iodides (RI) have been found to react with a cathodically charged glassy carbon surface at potentials more negative than -1.7 V vs Ag/AgCl. In aprotic solvents, this reaction results in grafting of the alkyl chains onto carbon. It is proposed that the process corresponds to the cathodic charge of graphitized and fullerenized zones present in carbon followed by a displacement reaction (analogous to a nucleophilic attack) toward alkyl iodides. This new mode of grafting is applied to the immobilization of ferrocene used as an electrochemical probe. The present work points out the reaction of ω-iodoalkylferrocenes and quantifies the level of grafting of alkyl chains via this promising method for modification of carbon surfaces. Coverage levels were found to be high, reaching the apparent surface concentrations of 8 × 10(-9) mol cm(-2). These large values are explained on the basis of swelling of the interface provoked by progressive charging of the carbon surface via insertion of tetraalkylammonium cations concomitantly with the substitution process. Alkylferrocene layers deposited onto carbon were found to be chemically and electrochemically stable.

Electrochemical immobilization of a benzylic film through the reduction of benzyl halide derivatives: deposition onto highly ordered pyrolytic graphite.

The reactivity of electrogenerated benzyl radicals at carbon surfaces was examined through the cathodic reduction of the corresponding bromide derivatives. 4-Nitrobenzyl bromide and benzyl bromide were reduced in N,N-dimethylformamide (DMF) on highly ordered pyrolytic graphite (HOPG) surfaces. Electroproduced films were examined using electrochemistry, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Experiments show the formation of strongly adherent deposits and the occurrence of electrografting processes. They are based on radical generation and the reaction of the radical with the substrate. As expected, the thickness of the organic film increases with deposition time but the deposit displays a lower compactness than previously reported for the electroreduction of aryl diazonium salts. Interestingly for benzyl derivatives, the reduction potential required for the electrografting could be rendered much more positive by simply using an iodide-type supporting electrolyte.

Synthesis and immobilization of Ag(0) nanoparticles on diazonium modified electrodes: SECM and cyclic voltammetry studies of the modified interfaces.

A versatile method was used to prepare modified surfaces on which metallic silver nanoparticles are immobilized on an organic layer. The preparation method takes advantage, on one hand, of the activated reactivity of some alkyl halides with Ag-Pd alloys to produce metallic silver nanoparticles and, on the other hand, of the facile production of an anchoring polyphenyl acetate layer by the electrografting of substituted diazonium salts on carbon surfaces. Transport properties inside such modified layers were investigated by cyclic voltammetry, scanning electrochemical microscopy (SECM) in feedback mode, and conducting AFM imaging for characterizing the presence and nature of the conducting pathways. The modification of the blocking properties of the surface (or its conductivity) was found to vary to a large extent on the solvents used for surface examination (H(2)O, CH(2)Cl(2), and DMF).

PAS inclusions, immunoreactive tenascin and proliferative activity in low-grade chondrosarcomas.

To distinguish between chondrosarcoma (grade 1--borderline histology) and enchondroma, we examined six chondrosarcomas (grade 1--borderline histology) which looked like benign lesions. Their diagnosis, albeit based on clinical, radiologic and pathologic examinations, was not easily reached. Moreover, we examined six enchondromas and 11 chondrosarcomas, the diagnoses of which were straightforward. All cartilaginous tumors were studied, placing emphasis on PAS-positive intracytoplasmic globules. Anti-Ki67 proliferation-associated nuclear antigen antibody and tenascin antibody were applied. The following features were observed in low-grade chondrosarcomas: (1) masses of hyalin and/or myxoid cartilage invading spaces around the tumor, (2) host lamellar bone trabeculae surrounded by cartilage on all sides, (3) tumoral resorption of bone trabeculae. Intracytopasmic hyalin globules (ICG) were more frequently found in malignant than in benign neoplasm (p = 0.042). Moreover, tenascin matrix immunoreactivity was more likely to be observed in benign than in malignant neoplasm (p = 0.029). Ki67 immunoreactivity was more frequent in characterized than in low-grade chondrosarcomas or in enchondromas, where it was null (p = 0.0044).

[Recurring bone epithelioid hemangioma]. / Hémangiome épithélioïde osseux récidivant.

Bone vascular tumors are very rare. Epithelioid types are described according to their architecture, their degree of vascular differentiation, and their cytonuclear atypia. The include epithelioid hemangioma, epithelioid hemangioendothelioma, and angiosarcoma. We report a case of L4 corpus vertebral bone epithelioid hemangioma. The patient was a 25-year-old man with a tumor that recurred twice. The lesion was characterized by a vascular lumen lined by cells with regular nuclei and inflammatory infiltrates. Capillaries were lined by prominent epithelioid endothelial cells, associated with CD31+ and cytokeratin-.

Reactivity of platinum metal with organic radical anions from metal to negative oxidation states.

The reaction of platinum metal with an organic molecular radical anion leads to the formation of iono-metallic phases where Pt exists under negative oxidation states. This puzzling transformation of a "noncorrodible metal" was examined using localized electrochemical techniques in dimethylformamide containing different tetra-alkylammonium salts chosen as test systems. Our experiments demonstrate that the platinum metal is locally reduced as soon as the Pt faces relatively moderate reducing conditions, for example, when the Pt is used as a negative electrode or when the metal is in the presence of a reducing agent such as an organic radical anion. Scanning electrochemical microscopy (SECM) analysis, current-distance curves, and transient mode responses provide detailed descriptions of the reactivity of Pt to form negative oxidation states (the key step is the reaction of the metal with a molecular reducing agent), of the insulating nature of the "reduced" solid phases of the thermodynamics and kinetics conditions of the Pt conversion. The passage from the conductor to insulator states controlled the spatial development of the reaction that always remains in competition with the other "natural" roles of a metallic electrode. Formally, the phenomena can be treated by analogy with the C. Amatore's model previously developed for the mediated reduction of the poly(tetrafluoroethylene). Consequences of this general reactivity of Pt are discussed in view of a wide utilization of this metal in reductive conditions and the possible applications of such processes in the micropatterning of metallic surfaces.