Cascaded clustering

Ar, Cs, Ga or other elements with energies between 0.5 and 10 keV), energy is deposited in the surface region of the sample by a collisional cascade. Some of the energy will return to the surface and stimulate the ejection of atoms, ions and multi-atomic clusters (figure Bl.25.8). In SIMS, secondary ions (positive or negative) are detected directly with a mass spectrometer. 

Precise placement of metal complexing sites within the infrastructure of a cascade molecule is of importance from a variety of perspectives. In the construction of the above noted Micellane family (cf. Sect. 3.1), we reported the construction of dendrimers with four alkyne moieties at sites equidistant from each other in the interior (17, Fig. 8) [60]. These were treated with decaborane (B10H14) to afford 1,2-dicarba-closo-dodecaboranes (o-carboranes) [71]. Rendering boron clusters soluble in water is of interest because of their use in cancer treatment by Boron Neutron Cancer Therapy. First and second generation water-soluble dendrimers containing four and twelve precisely located boron cluster sites, respectively, were synthesized (e.g., 18). These water soluble dendrimers and their precursors were characterized by 13C-, and nB-NMR spectroscopy (Fig. 8). 

Metal-sulfur clusters probably constitute the best known class of clusters due to their considerable importance and common occurrence in the biological world, where they fulfil the role of electron carriers (see Chapter 12). This function is related to their high capacity to undergo a cascade of reversible redox processes. As an illustrative and introductive example, Figure 1 shows the redox ability of [Fe4(/r3-S)40/-C5H5)4].la... 

Clusters may also behave as electron donors when formed in the presence of oxidizing reactants. For example, as far as < n, a cascade of electron transfers from M to S leading to corrosion of M is possible because ii°(M /M ) < ii°(S/S ), and it should be taken into account in the simulation. This corrosion process is generally negligible because... 

Rhodium carbonyl complexes catalyze the silane-initiated cascade cyclization of 1,6,11-triynes to form fused aromatic tricyclic compounds. For example, reaction of 83 [X = G(G02Et)2] with methyldiphenylsilane catalyzed by the tetrarhodium carbonyl cluster Rh4(GO)i2 in toluene at room temperature gave an 88 12 mixture of the silylated and unsilylated fused tricycles 84a and 84b [X = G(G02Et)2] in 85% combined yield (Equation (55)). The ratio of silylated to unsilylated tricyclic product formed in the reaction of 1,6,11-triynes was dependent on the nature of the substrate (Equation (55)). For example, Rh4(GO)i2-catalyzed reaction of diaminotriyne 83 (X = NBn) with methyldiphenylsilane gave unsilylated tricycle 84b (X = NBn) in 92% yield as the exclusive product (Equation (55)). 

SeeDs-2 library was generated from their in-house database called rCat of 1,622,763 unique chemical compounds assembled from 23 suppliers (25). The filtering cascade began with MW (same as SeeDs-1), then the functional groups and solubility filters which resulted in 43 unique compounds (no overlap with SeeDs-1). These were then clustered by 2D, 3-point pharma-cophoric features to provide 3 clusters, and the centroids of each cluster was submitted for chemist review. Of the 395 selected compounds that were ordered, 357 passed QC to become the SeeDs-2 fragment library. 

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