Electroactive gold nanoparticles protected by 4-ferrocene thiophenol monolayer

Numerous reports have focused on ferrocene-terminated electroactive self-assembled monolayers (SAMs) on a flat Au surface but only a few on ferrocene SAMs on Au colloid. In this paper, we employ 4-ferrocene thiophenol as a novel capping agent to produce electroactive gold nanoparticles in consideration of the peculiar pi-conjugated structure. Transmission electron microscopy shows the narrow-dispersed gold core with an average core diameter of ca. 2.5 nm. UV/vis spectra examine the pi-conjugated structure of 4-ferrocene thiophenol and surface plasmon absorbance of the indicated gold nanoparticles. X-ray photoelectron spectroscopy reveals electronic properties of the Au core and thiol ligands. Electrochemical measurement shows that the oxidation peak current is proportional to the scan rate, indicating the electrode process is controlled by adsorbed layer reaction. The formal potential of the Fc-MPCs is compared with that of free ferrocene in MeCN solution and the Fc-SAMs. The shifts are attributed to the phenyl moiety in the 4-ferrocene thiophenol and dielectric constant of the solvation environment.     

Controlled growth and catalytic activity of gold monolayer protected clusters in presence of borohydride salts

In the presence of large excesses of borohydride salts, gold monolayer protected-clusters can be grown to larger sizes simply by controlling the amount of reducing agent added to smaller clusters. In addition, gold monolayer clusters can be used as catalysts for reduction reactions by sodium borohydride; results suggest such catalysts have sterically constrained active sites.     

Electrochemical resolution of 15 oxidation states for monolayer protected gold nanoparticles

The first observation of 15 voltammetric quantized charging peaks for a solution of hexanethiol-capped gold nanoparticles (so-called monolayer protected clusters MPCs) at room temperature is reported where the variation in peak spacing with increasing charge stored in the metal core is discussed in terms of MPC capacitance.     

Synthesis and catalytic properties of soluble platinum nanoparticles protected by a thiol monolayer

Several new platinum monolayer protected clusters (MPCs) have been synthesized and characterized. Two methods of platinum reduction were used depending on the solubility of the thiol: sodium borohydride for the water-soluble thiols and lithium triethylborohydride for the organic soluble thiols. In general, reactant solutions containing a 1:1 thiol/Pt ratio yielded the best particles in a single-phase reaction. Higher thiol/Pt ratios produced lower yields of MPCs, while much lower ratios produced gray-black precipitates. The Pt MPCs were used as catalysts to hydrogenate allyl alcohol to propanol by reducing the carbon-carbon double bond. The Pt-mercaptoammonium MPCs were also used as catalysts in the hydrogenation of maleic acid to succinic acid. Differences in the catalytic hydrogenation rates among the various monolayer coatings for MPCs are attributed to the variations in ligand chain length, branching, charged functional groups, packing density, and core size.     

Double hydrophilic block copolymer monolayer protected hybrid gold nanoparticles and their shell cross-linking

This paper describes the syntheses of core/shell gold nanoparticles stabilized with a monolayer of double hydrophilic block copolymer and their stimuli responsiveness before and after shell cross-linking. The hybrid nanoparticles consist of gold core, cross-linkable poly(2-(dimethylamino)ethyl methacrylate) (PDMA) inner shell, and poly(ethylene oxide) (PEO) corona. First, diblock copolymer PEO-b-PDMA was prepared via the reversible addition-fragmentation chain transfer (RAFT) technique using a PEO-based macroRAFT agent. The dithioester end group of PEO-b-PDMA diblock copolymer was reduced to a thiol end group. The obtained PEO-b-PDMA-SH was then used to prepare diblock copolymer stabilized gold nanoparticles by the "grafting-to" approach. 1,2-Bis(2-iodoethoxy)ethane (BIEE) was utilized to selectively cross-link the PDMA residues in the inner shell. The stimuli responsiveness and colloidal stability of core/shell gold nanoparticles before and after shell cross-linking were characterized by laser light scattering (LLS), UV-vis transmittance, and transmission electron microscopy (TEM). At pH 9, the average hydrodynamic radius Rh of non-cross-linked hybrid gold nanoparticles starts to increase above 35 degrees C due to the lower critical solution temperature (LCST) phase behavior of the PDMA blocks in the inner shell. In contrast, Rh of the shell cross-linked gold nanoparticles were essentially independent of temperature. Core/shell gold nanoparticles before and after shell cross-linking exhibit reversible swelling on varying the solution pH. Compared to non-cross-linked core/shell gold nanoparticles, shell cross-linking of the hybrid gold nanoparticles leads to permanent core/shell nanostructures with much higher colloidal stability and physically isolates the gold core from the external environment.     

Hexanethiolate monolayer protected 38 gold atom cluster

The nucleation-growth-passivation Brust reaction has been modified so as to enrich the product in useful quantities of a 38-atom gold nanoparticle coated with a hexanethiolate monolayer. Two modifications are described, using -78 degrees C reduction temperature and a hyperexcess of thiol. Compositional evidence is presented that establishes the product as a Au38(C6)24 hexanethiolate monolayer protected cluster (MPC), based on transmission electron microscopy, laser ionization-desorption mass spectrometry, thermogravimetric analysis, and elemental analysis. Reverse phase HPLC confirms the relatively good monodispersity of the MPC products, but high-resolution double-column HPLC reveals that the MPCs are a mixture of closely related but chromatographically distinct products. Voltammetry, low energy spectrophotometry, and spectroelectrochemistry reveal, respectively, a 1.6 eV electrochemical energy gap between the first oxidation and the first reduction, an optical HOMO-LUMO energy absorbance edge at 1.3 eV, and a bleaching of optical absorbance near the 1.3 eV band edge that accompanies electrochemical oxidation of the nanoparticle.     

Reductive desorption of thiolate from monolayer protected gold clusters

The "electrochemical potential window" of monolayer-protected gold cluster (MPC) nanoelectrodes is probed where the electrified liquid-liquid interface is used as the detector. The first observation of the reductive desorption of thiolate at negative MPC core charge is reported.     

Self-assembly and selective exchange of oligoanions on the surface of monolayer protected Au nanoparticles in water

Self-assembled monolayers on Au nanoparticles terminating with TACN·Zn(II) head groups are attractive scaffolds for the formation of multivalent supramolecular structures at submicromolar concentrations in water.     

Facile synthesis and excellent catalytic activity of gold nanoparticles on graphene oxide

For the first time,Au nanoparticles on graphene oxide（GO-AuNPs） were successfully fabricated without applying any additional reductants,just by the redox reaction between AuCl₄^-1 and GO.Their structure was characterized by transmission electron microscopy and X-ray powder diffraction.The results show that flower-like AuNPs were successfully dispersed on GO surface.Importantly,they showed a high catalytic activity for the Suzuki-Miyaura coupling reaction in an aqueous medium.     

Vibrational circular dichroism of N-acetyl-l-cysteine protected gold nanoparticles

Vibrational circular dichroism is used to determine the conformation of a thiol adsorbed on gold nanoparticles.     

Multidentate thioether ligands coating gold nanoparticles

The design and synthesis of oligomeric ligands based on benzylic thioethers is presented together with their ability to enwrap and stabilize gold nanoparticles with diameters below 2 nm, which become--with increasing length of the oligomer--more monodisperse and stable.     

In situ observation of place exchange reactions of gold nanoparticles. Correlation of monolayer structure and stability

Place exchange reactions were studied using dye displacement: subtle changes in ligand structure greatly affected both the rate of displacement and the stability of the monolayer.     

Water-soluble gold nanoparticles protected by fluorinated amphiphilic thiolates

The preparation and the properties of gold nanoparticles (Au NPs) protected by perfluorinated amphiphiles are described. The thiols were devised to form a perfluorinated region close to the gold surface and to have a hydrophilic portion in contact with the bulk solvent to impart solubility in water. The monolayer protected clusters were prepared, in an homogeneous phase using sodium thiolates because of the low nucleophilicity of the alpha-perfluorinated thiols, and fully characterized with (1)H, (19)F NMR spectrometry, IR and UV-vis absorption spectroscopies, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). Au NPs with core diameters ranging from 1.6 to 2.9 nm, depending on the reaction conditions, were obtained. Water-soluble NPs (MPC-F8-PEGs) were obtained with the thiol HS-F8-PEG ending with a short poly(ethylene glycol) unit (PEG-OMe 550), whereas thiols with shorter PEG chains give rise to NPs insoluble in water. MPC-F8-PEGs undergo an exchange reaction with amphiphilic alkyl thiols. ESR investigations, using a hydrophobic radical probe, indicate that the MPC-F8-PEG monolayer shows a greater hydrophobicity compared to the analogous hydrogenated monolayer.     

Formation and catalytic activity of spherical composites with surfaces coated with gold nanoparticles

Micelle-supported gold composites with a polystyrene core and a poly(4-vinyl pyridine)/Au shell are synthesized using NaBH(4) to reduce a mixture of micelle and HAuCl(4) in acidic aqueous solution (pH approximately 2). The template micelle with a polystyrene core and a poly(4-vinyl pyridine) shell is formed by self-assembly of block copolymer polystyrene-block-poly(4-vinyl pyridine). The gold nanoparticles coated onto the surfaces of the composites possess an average diameter of about 15 nm. The composites are applied to catalyze the reduction of p-nitrophenol in the presence of NaBH(4), and the results indicate that the kinetic constant of the reaction increases when the composite concentration and the reaction temperature increase. In addition, research results also indicate that composites with high content of gold show higher catalytic activity and higher catalytic efficiency.     

Preparation temperature dependence of size and polydispersity of alkylthiol monolayer protected gold clusters

The influence of preparation temperature on the size and size distribution of dodecylthiol monolayer protected gold clusters was studied. The monolayer protected clusters (MPCs) were synthesized by two different variations of the Brust-Schiffrin procedure. In all of the experiments, the stoichiometry of the reactants dodecylthiol, HAuCl(4), and sodium borohydride was kept constant, while the temperature was varied in the range of -18 to +90 degrees C. Two series were performed in which an aqueous solution of NaBH(4) was either added over 30 s or all in one portion. The size and size distribution of the MPCs were determined by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). It has been demonstrated that in general the MPC size increases with elevated preparation temperatures.     

Regulation of alpha-chymotrypsin activity on the surface of substrate-functionalized gold nanoparticles

A gold nanoparticle functionalized with substrates for alpha-chymotrypsin was fabricated to afford an enzyme modulator that exhibited enzyme-specific activation coupled with general inhibition of other proteases.     

Identifying G-quadruplex-binding ligands using DNA-functionalized gold nanoparticles

The G-rich overhang of human telomere tends to form a G-quadruplex structure, and G-quadruplex formation can effectively inhibit telomerase activity in most cancer cells. Therefore, it is important to identify the formation and properties of the G-quadruplex, with the particular aim of selecting G-quadruplex-binding ligands that could potentially lead to the development of anticancer therapeutic agents. With this goal in mind, we report a fluorescence resonance energy transfer (FRET) assay system for the identification of G-quadruplex ligands using DNA-functionalized gold nanoparticles (DNA-GNPs) as the fluorescence quencher and a carboxyfluorescein (FAM)-tagged human telomeric sequence (F-GDNA) as the recognition probe. A thiolated complementary strand of human telomeric DNA (cDNA), which first adheres to the surface of the GNPs and then hybridizes with F-GDNA, results in the fluorescence quenching of F-GDNA by the GNPs. However, fluorescence is restored when single-stranded F-GDNA folds into a G-quadruplex structure upon the binding of quadruplex ligands, leading to the release of F-GDNA from the surface of the GNPs. Combined data from fluorescence measurements and CD spectroscopy indicated that ligands selected by this FRET method could induce GDNA to form a G-quadruplex. Therefore, this FRET G-quadruplex assay is a simple and effective approach to identify quadruplex-binding ligands, and, as such, it promises to provide a solid foundation for the development of novel anticancer therapeutic agents.