Dendrimer using

The field of synthetic enzyme models encompasses attempts to prepare enzymelike functional macromolecules by chemical synthesis [30]. One particularly relevant approach to such enzyme mimics concerns dendrimers, which are treelike synthetic macromolecules with a globular shape similar to a folded protein, and useful in a range of applications including catalysis [31]. Peptide dendrimers, which, like proteins, are composed of amino acids, are particularly well suited as mimics for proteins and enzymes [32]. These dendrimers can be prepared using combinatorial chemistry methods on solid support [33], similar to those used in the context of catalyst and ligand discovery programs in chemistry [34]. Peptide dendrimers used multivalency effects at the dendrimer surface to trigger cooperativity between amino acids, as has been observed in various esterase enzyme models [35]. 

The first true dendrimers were the polyamidoamines (PAMAMs). They are also known as starburst dendrimers, and the term starburst is a trademark of the Dow Chemical Company, who have commercialized these materials for a range of applications. These dendrimers use ammonia as the core molecule, and this is reacted with methyl acrylate in the presence of methanol, after which ethylenediamine is added. This is shown in Scheme 9.2. 

Stang and coworkers also reported the synthesis of platinum-acetylide dendrimers using 1,3,5-triethynylbenzene as the bridging ligand [27]. Their strategy was very similar to the above, and they prepared dendrimers up to the second generation. 

SCHEME 60. Galactosylated PPI dendrimers used as inhibitors of cell infectivity by HIV-1.419... 

SCHEME 64. Convergent strategy for the construction of glucosylated dendrimers using TRIS as the branching component.229... 

N. Jayaraman and J. F. Stoddart, Synthesis of carbohydrate-containing dendrimers. 5. Preparation of dendrimers using unprotected carbohydrates, Tetrahedron Lett., 38 (1997) 6767-6770. 

Purify the derivatized dendrimer using gel filtration (size exclusion chromatography) on a desalting column or through use of ultrafiltration spin-tubes (for G-4 and above). For smaller dendrimers, the derivatives may be purified by repeated precipitation from a meth-anolic solution by addition of ethyl acetate, dioxane, or benzene. The SPDP-dendrimer may be dried by lyophilization (if in water or buffer) or by solvent evaporation in vacuo (if the precipitation method was used). 

Dissolve the purified SPDP-modified dendrimer of step 5 in 50 mM sodium phosphate, 0.15M NaCl, pH 7.5, or in DMSO at a concentration of at least lOmg/ml. Add a 10-20 X molar excess of an amine-reactive fluorescent molecule (i.e., NHS-rhodamine or a hydrophilic NHS-Cy5 derivative see section on fluorescent probes). React with mixing for 1 hour at room temperature. Purify the fluorescently labeled SPDP-modified dendrimer using gel filtration or ultrafiltration. Follow the method of either step 7 or 8 to conjugate the dendrimer to another protein or molecule. 

Purify the conjugate from unreacted protein or unreacted dendrimer using gel filtration chromatography with a matrix having an exclusion limit appropriate to accommodate the size of the molecules being separated (i.e., a HiPrep 16/60 column packed with Sephacryl S-200 HR, GE Healthcare). 

Add to the dendrimer solution a quantity of acetic anhydride that represents a molar ratio of anhydride-to-amines of 0.72 1.0 (680 pi of acetic anhydride was added for the G-5 dendrimer). Using a molar quantity of anhydride that is less than the amount of amines present on the dendrimer assures that only a portion of the amines will become blocked, so that further modification remains possible. 

Purify the biotin-dendrimer using size exclusion chromatography on a desalting matrix or by use of ultrafiltration (e.g., centrifugal concentrators). 

Purify the DTPA-dendrimer using dialysis, size exclusion chromatography, or spin-tube concentrators having a molecular weight cutoff of 5,000 Daltons. 

Crosslinking of amine- or hydroxy-terminated PAMAM dendrimers using cyclic anhydride - amine or cyclic anhydride - hydroxy addition reactions was employed for preparation of crosslinked thin films of very low permeability [73], Polyanhydrides, such as maleic anhydride-methyl vinyl ether copolymers, were used as crosslinking components. In the case of amine-terminated PAMAM, crosslinking and chemical stability were further increased by imidization of the maleamic acid groups retro-Michael eliminations were followed by Michael additions to further crosslink the film. 

In the first report, PAMAM dendrimers with primary amine surface groups were used [27]. It was found that complex formation is dependent both upon the size (generation) of the dendrimers used and the charge ratio between the (cationic and anionic species, i.e. ammonium groups on PAMAM to phosphate groups on DNA). Retardation of DNA migration was not observed with... 

For all three types of dendrimers described above, a flattened, disk-like conformation was observed for the higher generations. However, the molecular shape at the air-water interface is also intimately associated with the polarity, and hence the type of dendrimer used. In case of the polypropylene imine) and PAMAM dendrimers the hydrophilic cores interact with the sub-phase and hence these dendrimers assume an oblate shape for all generations. The poly(benzyl ether) dendrimers, on the other hand, are hydrophobic and want to minimize contact with the water surface. This property results in a conformational shape change from ellipsoidal, for the lower generations, to oblate for the higher generations [46]. 

Figure 16.7 TEM picture (uranyl acetate staining) of vesicles reported by Schenning etal. [44] (A) schematic representation of the bilayer, (B) palmitoyl-and (C) azobenzene-modified poly(propylene imine) dendrimers used in the construction of the aggregates...

Immune detection is a key utility of antibodies in biotechnology [3, 5]. Antiden-drimer sera efficiently detect dendrimers in multiple assay formats, including enzyme-linked immunosorbent assays (ELISA), and in Western and dot blots [3, 5], ELISA assays are commonly used to quantitate proteins, and a quantitative ELISA could be developed for dendrimers using our sera, though doing so would require development of dendrimer standards of known concentration that could be used for calibration. 

Figure 26.1 Synthetic scheme for polypropylene imine) dendrimers using 1,4-diaminobutane as core...

This dual linker approach allowed selective cleavage of the peptide from the dendrimer using 1% TFA/CH2CI2 without cleaving the dendrimer from the resin. Proceeding from the TentaGel resin the final product was obtained in 44% yield... 

Ma, Y. Kolomchin, S. V. Zimmerman, S. C. Supramolecular polymer chemistry Self-assembling dendrimers using the DDA AAD (GC-like) hydrogen bonding motif. J. Am. Chem. Soc. 2002,124, 13757-13769. 

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