Surface Functionalization of Metals by Alkyl Chains through a Radical Crossover Reaction

D, Decorse P, Pinson J, Podvorica FI. Surface Modification of Lignite with Alkyl and Mixed Alkyl-Aryl Films Generated from an Aryl Diazonium Salt and Alkyl Halides: Experimental Results and Theoretical Analyses

In search of new possible uses of cheap lignite from the Kosova Bassin, the surface of lignite powders is modified with alkyl or mixed alkyl-aryl layers. Modification is performed in aqueous acid solution containing an aryl diazonium salt and an alkyl halide compound in millimolar concentration, in the presence of potassium iodide as a reducing agent at equimolar concentration. Attachment of alkyl films substituted with carboxylic groups and aryl films with nitro or bis-trifluoromethyl groups is characterized by IRATR and XPS spectroscopy. The formation of a stable interface during the grafting reactions of alkyl and aryl moieties with lignite surface has been confirmed by theoretical calculations. Aryl diazonium salts once chemically or spontaneously reduced are a source of aryl radicals, able to attach chemically to the material surface or to react with alkyl halides by abstracting the halogen atom. If the aryl diazonium salts are unable to graft to the coal surface due to steric hindrance, they can, nevertheless, abstract an iodine or bromine atom to generate alkyl radicals that react with the material surface.

Alkynyl ligands-induced growth of ultrathin nanowires arrays

Ligands are almost essential in the synthesis of nanostructures. In this work, we introduce the alkynyl ligands into the synthesis of ultrathin gold (Au) nanowires arrays. The strong binding affinity of the alkynyl ligands enables one-dimensional (1D) growth via the active surface growth mechanism. The scope of the ligand generality was systematically investigated, and the alkynyl ligand-induced nanowire growth processes were compared and contrasted with those involving thiolated ligands. While strong ligands are usually difficult to dissociate from the nanostructure surface and therefore problematic for post-synthetic processing, the alkynyl ligands are readily dissociable, making the alkynyl ligand-stabilized Au nanowires potentially more modifiable and applicable. As a demonstration, direct palladium (Pd) deposition on the Au nanowires was successfully carried out without any ligand exchange process.

Direct vs Indirect Grafting of Alkyl and Aryl Halides

The direct and indirect electrochemical grafting of alkyl and aryl halides (RX, ArX) on carbon, metal and polymer surfaces is examined. Their electrochemical reduction occurs at highly negative potential in organic solvents and very often produces carbanions because the reduction potentials of RX and ArX are more negative than those of their corresponding radicals. Therefore, direct electrografting of alkyl and aryl radicals generated from RX and ArX is not easy to perform. This obstacle is overcome using aryl radicals derived from the 2,6-dimethylbenzenediazonium salt (2,6-DMBD), which do not react on the electrode surface due to their steric hindrance but react in solution by abstracting an iodine or bromine atom from RX (X=I, Br) or ArI to give alkyl or aryl radicals. As a consequence, alkyl and aryl radicals are generated at very low driving force by diverting the reactivity of aryl radicals derived from an aryl diazonium salt; they attack the electrode surface and form strongly attached organic layers. This strategy applies to the chemical modification of polymers (polyethylene, polymethylmethacrylate) by alkyl halides under heating.

From Langmuir-Blodgett to Grafted Films

A locally organized monolayer film strongly attached to a gold surface is obtained by transfer of a Langmuir-Blodgett (LB) film of octadecylamine (ODA) or alcohol (ODOH) onto a Au surface and simultaneous oxidative electrografting of this film still in contact with the aqueous subphase. As opposed to LB films, these films resist ultrasonication; and unlike electrografted films, they are organized monolayers by construction. They are characterized by AFM (atomic force microscopy), water contact angle, ellipsometry, XPS (X-ray photoelectron spectroscopy), IRRAS (infrared reflection absorption spectroscopy), and GIXD (grazing incidence X-ray diffraction).

Alkyl-Modified Gold Surfaces: Characterization of the Au-C Bond

The surface of gold can be modified with alkyl groups through a radical crossover reaction involving alkyliodides or bromides in the presence of a sterically hindered diazonium salt. In this paper, we characterize the Au-C(alkyl) bond by surface-enhanced Raman spectroscopy (SERS); the corresponding peak appears at 387 cm^-1 close to the value obtained by theoretical modeling. The Au-C(alkyl) bond energy is also calculated, it reaches -36.9 kcal mol^-1 similar to that of an Au-S-alkyl bond but also of an Au-C(aryl) bond. In agreement with the similar energies of Au-C(alkyl) and Au-S-(alkyl), we demonstrate experimentally that these groups can be exchanged on the surface of gold.