Ester terminated dendrimer

Leon, J.W., Kawa, M., and Frechet, J.M.J. (1996) Isophthalate ester-terminated dendrimers versatile nanoscopic building blocks with readily modifiable surface functionalities. J. Am. Chem. Soc. 118, 8847-8859. 

Scheme 9.2. Representations of potential randomly constructed networks via the reaction of ester terminated dendrimer and amine terminated dendrimer.

The most facile entry into surface complexation involved hydrolysis of ester-terminated dendrimers (derived from Michael additions of surface NH2 groups to methyl acrylate) with stoichiometric amounts of alkali-metal hydroxides. In this manner, salts of Na+, K +, Cs+, or Rb+ were readily obtained (Scheme 31) as white hygroscopic powders. Dilute solutions of the sodium salts allowed direct observation of the individual dendrimer molecules by scanning transmission electron microscopy without the use of staining techniques [79-81]. Elemental analyses showed that essentially stoichiometric exchanges with divalent cations such as Ca2+ could be performed [164],... 

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... 

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]... 

Scheme 5.27. Tetrathiafulvalene terminated dendrimers have been prepared using ester connectivity.

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. 

The mixed anhydride method was successfully employed to effect immobihzation of an amino-terminated dendrimer to the surface. Treatment of the acid monolayer with the chloroformate ester gave rise to formation of a mixed anhydride on the monolayer terminus. Reaction of this surface with the dendrimer results in a multipodal attachment of the polymers to the surface357. 

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. 

Tomalia presented the synthesis of dendrimers as Starburst polymers, which consisted of poly(amide-amine)s as shown in Scheme 1 [2]. The core molecule in this case was ammonia, and the building block was methylacrylate. First, ammonia reacted with methylacrylate by a Michael-type addition. The obtained ester-terminated molecule was treated with a large excess amount of ethylene-diamine to form amino groups at the terminal positions (generation 0, GO). In this reaction, the methylester is the protected form of the amine, and the treatment with ethylenediamine (ester-amide transformation) corresponds to the deprotection of the ester function. Treatment of this amine-terminated molecule again with methylacrylate results in the formation of another terminal methyl-ester group. The molecule can be extended by repeating these operations. 

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