Dendrimers sizes

This increase was ascribed to diminished molecular flexibility on increasing dendrimer size. 

Larger dendrimers based on a Ru(bpy)2+ core and containing up to 54 peripheral methylester units (12) have recently been obtained [29a]. Both the metal-centered oxidation and ligand-centered reduction processes become less reversible on increasing dendrimer size [29b]. 

The SANS experiments [51] were performed with solutions of G8 PAMAM dendrimer in D20, methyl-d4, ethyl-d6, and n-butyl-d10 alcohol at a temperature of T = 20.0 °C. PAMAM dendrimers do not dissolve in acetone, but they readily dissolve in methyl alcohol/acetone mixtures over a wide range of composition. Solvents of different composition, were prepared and added to a weighed amount of dried G5 or G8 dendrimer. In a separate set of experiments, the NIST NG7 30 m instrument was used to measure the effects of charging on the dendrimer size. PAMAM G8 dendrimers in D20 were charged by addition of HC1 in the presence of various amounts of NaCl to the charged dendrimers to screen the electrostatic interactions. 

Figure 11.10 Schematic representations of the structural impact of charge repulsion on dendrimer size.

As expected, the distribution ratios KA are constant, even though the concentration of dendrimer changes. KA is also independent of the size of the filters. It is likely that the polymer is adsorbed on the organic filters. This hypothesis is confirmed by using different generation dendrimers and hence of compounds of different size. Distribution ratios were shown to be independent of the dendrimer size and also of the cation concentration (Table 4.35). 

In the case of ruthenium(II)-bis(terpyridine) dendrimers (Fig. 6.50) of stepwise increasing dendrimer size, an influence of dendrimer size on the reversibility of redox processes could be deduced from size-exclusion chromatography and from the electrochemical properties [95]. 

Starburst PAMAM dendrimers (Fig. 1), a specific class of commercially available dendrimers that have repeating amine/amide branching units, have drawn considerable interest in recent years due to their potential applications in medicine, nanotechnology, and catalysis [3-7]. These dendrimers are readily functionalized to terminate in diverse moieties such as primary amines, carboxylates, hydroxyls, or hydrophobic alkyl chains. Because dendrimer size and end groups can be varied, they are typically named by their generation (Gl, G2, etc.) and exterior functionality (- NH2, - OH). 

Fig. 1. (a) A chemical structure of a 2.5th generation carboxylic acid-terminated poly(amido amine) (PAMAM) dendrimer. (b) Transmission surface enhanced infrared absorption spectra (SEIRAS) of dendrimer adlayers prepared at 30 min adsorption from aqueous solutions (0.01 wt.%) of a dendrimer at different pHs. Numerical values are pHs of the solutions, (c) Adsorption-desorption profiles as a function of time at different pHs and adlayer thicknesses at adsorption and desorption equilibrium as a function of pH for aqueous solutions (0.1 wt.%) of the dendrimer. The symbols, j and J, in the top figure denote start of adsorption and desorption, respectively. In the bottom figure, filled circle and opened square denote adlayer thicknesses at adsorption and desorption equilibrium, respectively. The dark tie denotes the calculated dendrimer size width. A solid curve is drawn to be visual, (d) Schematic illustration of dendrimers adsorbed at different pHs. Reprinted with permission from Ref. [69], 2006, American Scientific Publishers. 

Dendrimer L2 was itself mesomorphic, showing a monotropic Colh phase, Cr (79.5 Colh) 98.5 I, [287] which upon complexation to CUCI2 became enan-tiotropic (Table 16). By UV/Vis spectrum, the complex was found to adopt a trigonal bipyramidal structure as [CuCl(Ll)]Cl. Thus, a dendritic effect could be observed in this series in that the stability of the mesophase increased considerably with the dendrimer size the complex [CuCl(Ll)]Cl cleared at 75 °C whereas the clearing point of the complex [CuCl(L2)]Cl was 140 °C. 

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