Stabilizer dendrimers

Esumi K (2003) Dendrimers for Nanoparticle Synthesis and Dispersion Stabilization. 227 31-52 Famulok M, Jenne A (1999) Catalysis Based on Nucleid Acid Structures. 202 101-131 Fechter MH, see de Raadt A (2001) 215 327-345... 

Esumi K (2003) Dendrimers for Nanoparticle Synthesis and Dispersion Stabilization. 227 31-52... 

Figure 19 explains what in principle happens the cluster monolayer on the dendrimer film is mobilized by means of CH2CI2 vapour (a b). The phosphines are then removed by the SH functions (b->c). The bare AU55 nanoclusters move between the dendrimer molecules to form crystals (Auss) which finally appear on the surface (c d). The formation of crystalline superlattices of naked AU55 particles proves their stability which is founded in their perfect cuboctahedral shape. The (Auss) species is a novel modification of the element gold. 

Mesomorphic dendrimers containing electroactive units have potential for construction of dendrimer based molecular switches. Deschenaux et al. reported [154] the synthesis and liquid-crystalline properties of a novel dendrimer containing six mesomorphic ferrocene units. Apart from exhibiting a broad enantiotropic smectic A phase as determined by polarized optical microscopy, DSC, and XRD studies, thermogravimetry revealed the excellent thermal stability of the macromolecule. 

In our group, several dendrimers based on ( R)-3-hydroxybutanoic acid (HB) have been prepared [56-58]. The dendrimers were synthesized by the convergent strategy. Trimesic acid has been used as core unit and the benzyl esters of the dimer and the tetramer of HB as elongation units. In such a way dendrimers of 1st and 2nd generation (27-30) have been constructed (Fig. 13). Since poly(.R)-3-hydroxybutanoic acid (PHB) is known to be biodegradable [59, 60] the stability of the dendrimers 27-30 was tested in the presence of PHB-de-... 

Most of the supports so far studied are conventional in the field of catalysis. Some new kinds of support have emerged including mesostructured materials,193 dendrimers, organic-inorganic hybrids, and natural polymers such as polysaccharides or polyaminoacids. Nevertheless, at the moment, supported catalysts still suffer from relatively poor stability when compared to classical heterogeneous catalysts, and from limited activity when compared to homogeneous catalysts. The driving force for this research is thus to make up some of these deficits. 

Testing of G-l, G-2, and G-3 dendrimers in this application provided insight into the density of surface modification needed to passivate completely the particles and prevent aggregation. The G-l dendron was insufficient in this regard, but both the G-2 and G-3 dendron were big enough to create a surface barrier, which resulted in excellent colloidal stability of the particles in solution. 

Dendrimers are not only unreactive support molecules for homogeneous catalysts, as discussed in the previous paragraph, but they can also have an important influence on the performance of a catalyst. The dendrons of a dendrimer can form a microenvironment in which catalysis shows different results compared to classical homogeneous catalysis while peripheral functionalized dendrimers can enforce cooperative interactions between catalytic sites because of their relative proximity. These effects are called dendritic effects . Dendritic effects can alter the stability, activity and (enantio)selectivity of the catalyst. In this paragraph, different dendritic effects will be discussed. 

The use of dendrimers constitutes an attractive stabilization mode for the synthesis of metal nanoparticles for several reasons ... 

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