This article deals with some recent developments in metal and in semiconducting nanocluster science. Our studies on the properties, mainly of metal nanoclusters, with respect to future and also to current applications are reviewed, including a series of unpublished results. The general properties of metal clusters of one up to a few nanometers

The structure and bonding of a series of gold clusters and gold nanomaterials stabilized by ligands or confined within nanoporous alumina have been investigated using EXAFS, XANES, and WAXS. Two gold clusters stabilized by two different ligands, Au55(PPh3)12Cl6 and Au55(T8 -OSS−SH)12Cl6, were confirmed to be of face-centered cubic structure type with metal−metal distances of 2.785 and 2.794 Å, respectively, shorter than in bulk gold. Colloidal gold of 180 Å diameter stabilized by sulfonated phosphine ligands had structural and electronic properties very similar to those of bulk gold but smaller Debye−Waller factors. The cluster Au55(PPh3)12Cl6 adsorbed into nanoporous alumina membrane was found to retain its integrity inside the membrane but with slightly longer Au−Au bonds due to some aggregation. The same cluster thermally transformed into colloidal gold within the alumina membrane was found to be almost identical structurally and electronically to the bulk. Gold nanowires electrochemically grown within the nanoporous alumina were found to be composed on average of 120 Å diameter crystallites. These have the same structure as the bulk, but with smaller Debye−Waller factors, indicating either a better crystallinity or that the gold atoms are more tightly held than in the bulk. The difference of area method L3 − kL2 was used to quantify the d orbital occupancy. The two ligand-stabilized Au55 clusters both had a smaller value (2.7) than the bulk material (4.1). The nanomaterials inside the membrane also showed smaller L3 − kL2 values. The geometrical and electronic structures of these gold materials show a very clear pattern of buildup as the number of gold atoms increases from Au55 clusters through Au colloids and nanowires to the bulk metal.

To overcome the problem of in-stent restenosis, the concept of local delivery of antiproliferative or immunosuppressive drugs has been introduced into interventional cardiology. Local drug delivery can be achieved by drug-eluting stents coated with polymer surfaces used for controlled drug release. However, several polymer coatings have shown an induction of inflammatory response and increased neointima formation. In the present study, the effect of a new inorganic ceramic nanoporous aluminum oxide (Al(2)O(3)) coating on neointima proliferation and its suitability as a carrier for the immunosuppressive drug tacrolimus have been investigated. 316 L stainless steel coronary stents were coated with a 500 nm thin nanoporous aluminum oxide layer. This ceramic nanolayer was used as a carrier for tacrolimus. Bare stents (n = 6), ceramic coated stents (n = 6), and ceramic coated stents loaded with 60 (n = 7) and 120 mug (n = 6) tacrolimus were implanted in the common carotid artery of New Zealand rabbits. The ceramic coating caused no significant reduction of neointimal thickness after 28 days. Loading the ceramic stents with tacrolimus led to a significant reduction of neointima thickness by 52% for 60 mug (P = 0.047) and 56% for 120 mug (P = 0.036) as compared to the bare stents. The ceramic coating alone as well as in combination with tacrolimus led to a reduced infiltration of lymphocytes and macrophages in the intima in response to stent implantation. Ceramic coating of coronary stents with a nanoporous layer of aluminum oxide in combination with tacrolimus resulted in a significant reduction in neointima formation and inflammatory response. The synergistic effects of the ceramic coating and tacrolimus suggest that this new approach may have a high potential to translate into clinical benefit.

Abstract:The fabrication of a supported and insulated quantum wire would be of great interest, especially if electronic information could be accessed to determine charging and conductivity profiles. The feasibility of forming one-dimensional configurations of zz 15 nm gold colloids and 2.4 nm gold clusters via template methods of synthesis has now been demonstrated. The template host material consisted of porous alumina membranes formed by an electrochemical anodic process. The pores of the membrane, and hence the parallel pore channels, were packed in a hexagonal array. Alumina membranes are excellent template materials because of their high degree of order, thermal and chemical stability, and optical clarity. Pore diameter was controlled by regulation of the applied anodic potential (ca. 1.4 nm V -I ) . The pore channels were filled by one of three methods: vacuum induction (colloids only), electrophoresis (clusters only), or immersion (clusters, which were then converted into colloids by heating). Rudimentary wires consisting of colloids and clusters were successfully formed. In both cases, the diameter of the pore channel exceeded that Keywords clusters * colloids * goldnanostructures * quantum wires of the clusters or colloids. The wires thus formed conformed to the pore channel by forming helical secondary structures. It was not possible to form contiguous wires of clusters by immersion, or of colloids formed from clusters after heating. Composites (consisting of the gold-alumina system) were a bright scarlet color with an absorption maximum (A, , , , , ) at 519.5 nm. This is an unexpected result for spherical and small-diameter (10 nm) gold colloids, which normally absorb at i , , , 525-530 nm, a ruby-red color. Possible causes of this small but remarkable blue shift are discussed below. A new Au,, cluster ligand system consisting of a silsesquioxanederivatized thiol is also described.

Reaction of the thiol-terminated fourth-generation dendrimer 2-G4 (96 SH groups) with the gold cluster compound Au55(PPh3)12Cl6 in a 3:1 molar ratio in dichloromethane results in the formation of bare Au55 clusters. The cuboctahedrally shaped Au55 particles coalesce to well-formed microcrystals (Au55) infinity. The role of the dendrimer is not only to remove the phosphine and chlorine ligands but also to act as an ideal matrix for perfect crystal growth. Transmission electron microscopy (TEM), small- and wide-angle X-ray diffraction (SAXRD and WAXRD) measurements indicate a structure where rows of edge-linked Au55 building blocks form a distorted cubic lattice. The X-ray data fit best if a 5% reduction of the Au-Au bond length in the Au55 clusters is assumed, in agreement with previous extended X-ray absorption fine structure (EXAFS) measurements. Energy-dispersive X-ray spectroscopy (EDX) analyses and IR investigations show the absence of PPh3 and Cl in the microcrystals.

Nanopores in alumina membranes can serve as reaction vessels for the generation of nanosized gold particles. In addition, they enable a quasi one‐dimensional arrangement of nanoparticles, the optical properties of which can easily be investigated due to their transparency in the visible and near ultraviolet (UV) regions. Gold colloids inside the pores were produced either by thermal decomposition of [Au55(PPh3)12Cl6] clusters or by loading the pores with preformed colloids. The clusters as well as the colloids were transferred into the pores by simple immersion, and if necessary supported by applying a vacuum. The [Au55(PPh3)12Cl6] clusters were decomposed over the temperature range of 100 to 800 °C, using pores of different diameters. Transmission electron microscopy (TEM) was used to investigate the resulting nanoparticles. At decomposition temperatures up to ca. 500 °C, no specific influence of pore size or temperature was observed: 4–5 nm colloids were formed. However, temperatures > 500 °C resulted in colloids of up to 10–11 nm being formed. The optical properties of these and of preformed gold colloids in the membranes were studied. The extinction spectra of the colloidal assemblies generated from clusters exhibited two absorption peaks, caused by excitation of the plasmon resonance along the long and the short axes of the wire‐like arranged particles. The optical extinctions were measured with unpolarized and polarized light (0 and 90°). Depending on the angle of polarization, the polarized light caused either a blue‐ or a red‐shift in the absorption maximum. Theoretical calculations, using the so‐called generalized Mie theory and Maxwell Garnet theory, confirmed the experimentally observed behavior of these gold/alumina nanocomposites.

Micrometer sized crystals of close packed Au 55 (PPh 3 ) 12 Cl 6 clusters are formed from dichloromethane solution and are investigated by transmission electron microscopy and small angle X-ray diffraction.

As any surface induces some kind of tissue reaction promoting restenosis, an active stent coating with antiproliferative drugs has been proposed. However, while animal studies revealed convincing results, preliminary clinical studies not only showed active stent coating effective in preventing restenosis, but also demonstrated the potential risks of this new approach. Although this technique may harbor some specific risks, with the introduction of stent coating a new chapter of interventional cardiology has been flipped open.