Aliphatic dendrimers

The techniques used for the characterization of the dendrimers Dl, D2, and D3 were H NMR, C NMR, and SEC. Self-diffusion studies were made by pulsed-field spin echo H NMR. The simplicity of the H NMR and C NMR spectra indicates high purity of Dl, D2, and D3. 

From H NMR self-diffusion measurements, the molecular diffusion coefficients could be calculated. Since the diffusion coefficients depend on the size and 

The self-diffusion coefficients were calculated, and the effective radii of the dendrimers were estimated from the diffusion coefficients by assuming a spherical geometiy for all dendrimers. The so-obtained radii were 7.8,10.3, and 12.6 A for the first, second, and third generation dendrimer, respectively. 

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In contrast to aliphatic dendrimers coated with cyano and benzyl ether moieties or amphiphilic groups reported by Freeh et et al. [ 14,53 - 56], our bifunctional dendrimers have the advantage that the distance of the two functionalities is predetermined. 

It is possible to take advantage of the differing characteristics of the periphery and the interior to promote chemical reactions. For example, a dendrimer having a non-polar aliphatic periphery with highly polar inner branches can be used to catalyse unimolecular elimination reactions in tertiary alkyl halides in a non-polar aliphatic solvent. This works because the alkyl halide has some polarity, so become relatively concentrated within the polar branches of the dendrimer. This polar medium favours the formation of polar transition states and intermediates, and allows some free alkene to be formed. This, being nonpolar, is expelled from the polar region, and moves out of the dendrimer and into the non-polar solvent. This is a highly efficient process, and the elimination reaction can be driven to completion with only 0.01 % by mass of a dendrimer in the reaction mixture in the presence of an auxiliary base such as potassium carbonate. 

The use of ordered supramolecular assemblies, such as micelles, monolayers, vesicles, inverted micelles, and lyotropic liquid crystalline systems, allows for the controlled nucleation of inorganic materials on molecular templates with well-defined structure and surface chemistry. Poly(propyleneimine) dendrimers modified with long aliphatic chains are a new class of amphiphiles which display a variety of aggregation states due to their conformational flexibility [38]. In the presence of octadecylamine, poly(propyleneimine) dendrimers modified with long alkyl chains self-assemble to form remarkably rigid and well-defined aggregates. When the aggregate dispersion was injected into a supersaturated... 

It has been demonstrated that dendrimers can be used also as fluorescent sensors for metal ions. Poly(propylene amine) dendrimers functionalized with dansyl units at the periphery like 34 can coordinate metal ions by the aliphatic amine units contained in the interior of the dendrimer [80]. The advantage of a dendrimer for this kind of application is related to the fact that a single analyte can interact with a great number of fluorescent units, which results in signal amplification. For example, when a Co ion enters dendrimer 34, the fluorescence of all the 32 dansyl units is quenched with a 32-fold increase in sensitivity with respect to a normal dansyl sensor. This concept is illustrated in Fig. 3. 

Keywords Dendrimers, linear aliphatic molecules, oligophenylenes, repetitive synthesis, supramolecular chemistry. 

Following the convergent procedure, dendrimers of type 58,59 and 60 have been prepared from the chiral core triol 54 and achiral Frechet-type [62] ben-zylic branch bromides. In the series of dendrimers with aromatic spacers (60) and without spacers (58), the optical activity [a]D decreased on going from the 1st (not shown in Fig. 21) to the 2nd generation, whereas with aliphatic spacers... 

In a separate study, we have reported the use of aliphatic ether dendrimers as a solubilizing platform for the preparation of soluble oligothiophenes with minimal main-chain substitution (Figure 7.16B) [67], Aliphatic ether dendritic blocks... 

Figure 13.5 PAMAM dendrimer G1(Cm) (with an aliphatic methylene chain as the central core) and the probe...

Preparation of Frechet-type Polyether Dendrons and Aliphatic Polyester Dendrimers by Convergent Growth An Experimental Primer... 

ALIPHATIC POLYESTER DENDRONS AND DENDRIMERS BASED ON 2,2-BIS-HYDROXYMETHYLPROPIONIC ACID... 

In contrast to dendrimers built up from aliphatic chains, polyphenylene dendrimers exist as shape persistent nanoparticles as we have demonstrated above. The preparation of functionalized dendrimers is the key step towards various applications. 

In contrast to dendrimers built up from aliphatic chains, polyphenylene dendrimer micelles possess shape and size persistent cavities due to their rigid scaffold which strongly depends on the type of dendrimer. In this case a selective incorporation of guest molecules, e.g., fluorescent dyes, should be possible, dependent on the size of the guest molecule and the cavity of the host. The non-covalent uptake of dyes with an appropriate size thus allows the investigation of their interactions within the dendritic micelle. In our case we made the second-generation polyphenylene dendrimer 48, which bears 16 carboxy-functions at the periphery, by starting from a tetrahedral core and an appropriately... 

For example, PPI dendrimers functionalized with azobenzene chromophores appended with aliphatic side chains assemble into large spherical vesicles in water below pH 8 (Fig. 11.14 Tsuda et al. 2000). 

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