PAM AMs dendrimers

Regen and Watanabe [158] fabricated multi-layers close to a thickness of 800 A by using fourth or sixth generation PAM AM dendrimers with 16 or 12 cycles, respectively. The construction techniques involved activation with K2PtCl4 on a silicon wafer containing amino groups on the surface, which was followed by deposition of the dendrimer layer. However, elimination of Pt2+ layer resulted in absence of layer growth, as examined by X-ray photoelectron spectroscopy. 

Dissolve the amine-containing PAM AM dendrimer in methanol or a buffered aqueous medium at a pH of 7-9 (e.g., 50mM sodium phosphate, pH 7.5) and at a concentration of at least lOmg/ml. Note that Singh (1998) used a concentration of llOmg/ml in methanol, but other dendrimer concentrations should work equally well. For nonaqueous reactions, the addition of a proton acceptor may aid in driving the reaction to maximal yields (i.e., triethylamine or dimethylaminopyridine). 

Most, but not all of the terminal units are near the outside of the dendrimer at any given time. The SAXS studies [17] of the segment density distribution have shown that there is an abrupt transition region at the outside of large PAM AM dendrimers. The combination of these two factors suggests that the terminal functionalities of dendrimers are accessible from the outside and available for chemical reactions such as attachment to surfaces, mounting of a catalyst, or for use as a crosslink junction. 

Goddard and Tomalia [1] investigated the encapsulation of 2,4-dich-lorophenoxyacetic acid and acetylsalicylic acid into methyl ester-terminated PAM AM dendrimers by measuring the 13C spin-lattice relaxation times (7 ) of the guest molecules. In the presence of dendrimer, the 7 values of these guest... 

Tomalia et al. reported that the surface amines of PAM AM dendrimer can successfully react with methyl esters of other PAMAM dendrimers to afford core-shell tecto-(dendrimer) molecules [65]. Furthermore, they also reported the synthesis of rod-shaped cylindrical dendronized polymers from poly(ethyleneimine) cores without any crosslinking, albeit with the use of excess reagents [58]. These reports lead us to propose a new approach toward hybridized dendrimers and polymers (path C, Figure 15.3). As shown in Scheme 12,... 

MALDl-TOF mass spectrometry (MS) has also been used to characterize PAM AM dendrimer composition with and without added Cu + [98]. linear-mode MALDI-TOF mass spectra of G2 and G3, and their complexes with Cu + ions, are shown in Fig. 9. 

The rate and mechanism of water exchange have been found to be similar for different generations (gen. 3, 4 and 5) of PAM AM dendrimers functionalized with the same Gd(III) D03A-monoamide chelate and for the monomer Gd(III) D03A-monoamide complex itself [43]. This study gave the first experimental evidence that the attachment of a Gd(III) chelate to a dendrimer did not significantly influence the water exchange kinetics. 

Several studies have shown that the amide bonds that comprise the PAM AM dendrimer backbone are relatively unstable and begin decomposing at temperatures as low as 75 °C [45,50,52,56-58]. The low onset temperature of dendrimer decomposition is not surprising given that PAMAM den-drimers can undergo retro-Michael addition reactions at temperatures above 100 °C [16]. Far more forcing conditions are required to fully activate the catalysts, which suggests that the dendrimer decomposes into various surface species that continue to poison the nanoparticle surfaces. 

Data for comparison to the model were obtained via the electrospray ionization mass spectrum of a Starburst PAM AM dendrimer (core = NH3) generation = 4 between m/z 600 and 1600. The ESI mass spectrum consisted predominantly of multiple charged ions at +7, +8, +9, +10, and +11 charge states. The deconvoluted mass spectrum between 9600 and 10747 daltons suggest the presence of at least 16 components in the sample. The last significant peak at 10632 daltons corresponds with the theoretical mass 10632.96, magic number which is within one mass unit for the ideal generation = 4 structure (see Fig. 33). 

As early as 1983, de Gennes and Hervet [85] proposed a simple equation derived from fundamental principles, to predict the Starburst limited or dense-packed generation mt for PAM AM dendrimers. Based on ideal dendrimer growth, with tertiary amine branch junctures connected by linear, flexible branch cell segments P, this equation relates m, to the branch cell segment length 1 or P ... 

EDA Core PAM AM Dendrimers in, http //www.dendri-tech.com/pamam.html (accessed April 2002). 

Eichman J D, Bielinska A U, Kukowska-Latallo J E, et al. (2000). The use of PAM AM dendrimers in the efficient transfer of genetic material into cells. Pharmaceutical Sci. Technol. Today. 3 232-245. 

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