Nanoclusters, capped

Hydrogenation reactions have been most extensively studied for evaluating the catalytic activity of nanoclusters. Precious monometallic (Pd, Pt, Rh) nanoclusters capped by PVP or polyvinylalcohol have high catalytic activities for hydrogenation of olefins. We applied PVP-capped Pd/Pt and Au/Pd bimetallic nanoclusters prepared by the coreduction method to the selective hydrogenation of 1,3-cyclooctadiene to cyclooctene. In both cases the bimetallic nanoclusters with a Pd content of 80 % showed the highest activity. As shown in the previous section, such bimetallic nanoclusters were found to have Pt- or Au-core/Pd-shell structures and Pt- or Au-cores are completely covered with Pd monoatomic layers. This improvement in catalytic activity can be interpreted only by a ligand effect of the core elements. 

Lover T ef a/1997 Functionalization and capping of a CdS nanocluster a study of ligand exchange by electrospray mass spectrometry Chem. Mater. 9 1878... 

Hakkinen, H., Walter, M. and Gronbeck, H. (2006) Divide and Protect Capping Gold Nanoclusters with Molecular Gold-Thiolate Rings. The Journal of Physical Chemistry B, 110, 9927-9931. 

N. Toshima, Polymer-capped bimetallic nanoclusters as active and selective catalysts, in N. Ueyama, A. Harada (eds.) Macromolecular Nanostructured Materials, Kodansha/ Springer, Tokyo/Berlin, 2004, 182. 

Figure 20. I U) curves for Cg-Au (left) and Gal-Au (right) in H2O as a function of pH (adjusted with phosphate buffer). The numbers 1—4 in the Gal-Au data identify voltage plateaus. Cartoons of the experimental arrangements for measuring curves of individual nanoclusters in solution are shown at the top of each data column. The insulated STM tip, ligand-capped Au nanocluster and an octanethiol-coated planar Au substrate are shown. Length and shapes are not to scale. (Reprinted with permission from Ref. [35], 1998, American Chemical Society.)...

Similar to zero-dimensional metal nanoparticles, most of the work on one-dimensional metal nanostructures focuses almost exclusively on gold nanorods. The high interest in anisometric gold nanoclusters arises from their unique optical and electronic properties that can be easily tuned through small changes in size, structure (e.g., the position, width, and intensity of the absorption band due to the longitudinal surface plasmon resonance is strongly influenced by the shell as well as the aspect ratio of the nanorods), shape (e.g., needle, round capped cylinder, or dog bone), and the inter-particle distance [157]. 

Composite semiconductor nanoclusters can be classified into two categories, namely, capped- and coupled-type heterostructures. The capped nanoclusters essentially have a core-shell geometry while in a coupled system two semiconductor nanoclusters are in contact with each other. The principle of charge separation in capped and coupled semiconductor systems is illustrated in Fig. 12. 

Shanghavi, B. Kamat, P. V. Interparticle electron transfer in metal/semiconductor composites. Picosecond dynamics of CdS capped gold nanoclusters, J. Phys. Chem. B 1997, 101, 7675. 

Oxide layers were grown thermally on HF-cleaned Si (100) substrates at 500°C in air. Citrate-capped gold nanoclusters were prepared according to a well-established procedure and were directly deposited from their aqueous solutions onto the Si02/Si substrates.30,31... 

Many different applications for gold cysteine nanoclusters have been proposed. One application is the use of citrate capped nanoparticles as sensors for the detection of thiol containing stractures. This application rehes on the fact that thiols can easily displace oxygen coordinated moieties. Zhong et al. have studied this process between cysteine and homocysteine to develop an assay for the homocysteine biomarker, a correlate to cardiovascular disease. When citrate stabilized particles of 13 run were incubated with either thiolate structure, the solution color changed from a dark red to a deep blue. The displacement of citrate by these moieties resulted... 

Similar to Ag°, zero-valent platinum nanoclusters were synthesized with cysteine capping ligands under reducing conditions. The platinum clusters showed a larger size... 

Nasr C., Liu D., Hotchandani S. and Kamat P. V. (1996), Dye-capped semicondnctor nanoclusters. Excited state and photosensitization aspects of rhodamine 6G Pi-aggregates bound to SiOi and SnOi colloids , J. Phys. Chem. 100, 11054-11061. 

During the past decade, a new focus has developed. It was found that semiconductor particles can be made so small, typically into the nanometer size regime, that a quantum confinement effect occurs [6-15]. Particles of this size are often referred to as nanoclusters, nanoparticles, quantum dots, or Q-particles. The structures of these nanometer-sized semiconductor clusters are usually similar to those of the bulk crystals, yet their properties are remarkably different. With the proper surface-capping agents, clusters of varying sizes can be isolated as powders and redissolved into various organic solvents just like molecules. The availability of this new class of materials allows us to study the transition of a material from molecule to bulk solid, as well as its various properties and applications. 

Fig. 21. In vivo diagnostic application of hyaluronic acid immobilized gold nanoprobes. (A) The fluorescence quenching by nanoparticle surface-energy transfer between Hilyte-647 dye labelled oUgo-HA and gold nanocluster (left) is followed by fluorescence recovery after addition of reactive oxygen species/HAdase which release the dye labeled oUgo-HA fragments. (B) Tail vein injection of GNPs capped with HA conjugates labelled with Hilyte-647 in normal (up) and arthritis (bottom) mice. Adapted from Ref 103. (See Color Plate 43.)...

Polymer-capped Bimetallic Nanoclusters as Active and Selective Catalysts... 

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