PAMAM dendrimer ester terminated

The preformed (BC) method is a one-step process used in this case to introduce high multiplicity of terminal hydroxy groups. The method involves direct coupling of branch cell reagents (i.e. tris(hydroxymethyl)aminomethane (Tris-)) by amidation of ester terminated PAMAM dendrimers. Advancement to the next generation of branch cells occurs in one step. 

DIVERGENT SYNTHESIS OF PAMAM DENDRIMERS VIA EXCESS REAGENT METHOD PREPARATION OF ESTER TERMINATED PAMAM STAR-BRANCHED PRECURSOR [NH2-(CH2)2 6-NH21 (G = -0.5) STAR-PAMAMICO E) [1]... 

PREPARATION OF ESTER TERMINATED PAMAM DENDRIMER INH2-(CH2)2 6-NH2l (G = 2.5) dendri -PAMAM(C02Me)32 [7]... 

Very little is known about these dendrimer properties, although it has been noted that ester-terminated PAMAM dendrimers form deep blue complexes with CuS04 solutions, and that NH2-terminated homologues produce deep purple solutions [2, 79]. The well-known coordination properties of the amide bond, which lead to the formation of metal-ion complexes [163], should make this a very rich area for further investigation. 

Fig. 13 Schematic of immobilization of amino-terminated PAMAM dendrimers to NHS reactive ester SAMs on gold via covalent bond formation reaction from solution provides homogeneously covered layers that can be labeled in order to determine the number of retained primary amino groups of the dendrimers. Micro and nanometer-scale patterning is possible via xCP and DPN...

In the same early publications [72-76], the reported observation that copper sulfate could be solubilized in organic solvents with ester terminated PAMAM dendrimers to produce deep blue transparent chloroform solutions, offered very early evidence for the unique enrto-receptor (i.e., unimolecular inverse micellar) properties of these macromolecules. These properties are discussed in the following section. 

This discovery has led to a vast array of small container-type molecules, which have been extensively reviewed [131]. Quite remarkably, this was approximately the same time that ester terminated PAMAM dendrimers were noted to dissolve and incarcerate copper salts to produce blue chloroform solutions due to their unimolecular, inverse micelle properties. This observation was publicly reported in 1984-1985 [72], during the same year that Smalley and Kroto et al. described the first synthesis of buckminsterfullerene [132]. Of course, it is well-known that bucky baUs will host a variety of metals. Thus, it is apparent that the emergence of container molecules" has followed the systematic enhancement of the organic host structure dimensions as illustrated in Figure 16. 

As early as 1989, Tomalia et al. [137] demonstrated with carbon-13, spin-lattice relaxation (Ti) techniques that small molecules such as acetylsalicyclic acid or 2,4-dichlorophenoxyacetic acid could be encapsulated within the interior of carboxymethyl ester terminated PAMAM dendrimers exhibiting guestihost stoichiometries of 4 1 by weight or 3 1 on a molar basis. These encapsulations appear to be driven by simple ion pairing of the acidic guest molecules with the tertiary amine sites located within the PAMAM dendrimer host. More recently, extensive work by Twyman et al. [138,139] and others [140] has shown that dendrimers may function as very versatile host molecules for drug delivery systems. Figure 18 illustrates the incorporation of benzoic acid within the interior of a hydroxyl terminated PAMAM dendrimer. 

The synthesis of radially layered poly(amidoamine-organosilicon) (PAMAMOS) copolymeric dendrimers starts from amine terminated PAMAM dendrimers, which, in turn, are obtained by a well-known excess-reagent divergent growth method that involves a reiterative sequence of (a) Michael addition reactions of methyl acrylate (MA) to primary amines, and (b) amidation of the resulting methyl ester intermediates with ethylenediamine (EDA), as shown in Reaction Scheme 1 (39-41). These PAMAM dendrimers are commercially obtained from Dendritech Inc., (Midland, MI) and they can be used for PAMAMOS preparation without any further purification. The synthesis then involves another Michael addition reaction, this time of a silylated acryl ester, such as (3-acryloxypropyl)dimethoxymethylsilane, as shown in Reaction Scheme 2 (4). 

To a vigorously stirred solution of 1,2-diaminoethane (107 g, 118 ml, 1.781 mol) in methanol (150 ml), at 0°C under nitrogen, was added a solution of (G = 1.5) dentin -PAMAM(C02Me)16 [5] (10 g, 0.004 mol) in methanol (30 ml). The addition was controlled such that the temperature did not rise above 40 °C. The mixture was stirred at room temperature for 96 h, after which time no ester groups were detectable by NMR spectroscopy. The methanol was removed by vacuum distillation at < 40°C, and the excess 1,2-diaminoethane was removed by azeotropic distillation using a mixture of toluene and methanol (9 1). The remaining toluene was removed by azeotropic distillation with methanol and finally the methanol removed under vacuum (10 1 mm Hg, 50°C, 48 h) to give the amine terminated G = 2.0 dendrimer as a pale yellow oil (10.9 g, 94%). 

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