Water-soluble dendrimers

Precise placement of metal complexing sites within the infrastructure of a cascade molecule is of importance from a variety of perspectives. In the construction of the above noted Micellane family (cf. Sect. 3.1), we reported the construction of dendrimers with four alkyne moieties at sites equidistant from each other in the interior (17, Fig. 8) [60]. These were treated with decaborane (B10H14) to afford 1,2-dicarba-closo-dodecaboranes (o-carboranes) [71]. Rendering boron clusters soluble in water is of interest because of their use in cancer treatment by Boron Neutron Cancer Therapy. First and second generation water-soluble dendrimers containing four and twelve precisely located boron cluster sites, respectively, were synthesized (e.g., 18). These water soluble dendrimers and their precursors were characterized by 13C-, and nB-NMR spectroscopy (Fig. 8). 

Zheng, J., and Dickson, R.M. (2002) Individual water-soluble dendrimer-encapsulated silver nanodot fluorescence./. Am. Chem. Soc. 124, 13982-13983. 

Electrophoresis is normally run in aqueous media, hence the analytes must be soluble in water. Presently only three types of water-soluble dendrimers have been successfully analyzed using gel electrophoresis techniques. The list includes Starburst PAMAM dendrimers [21], nucleic acid dendrimers [21] and poly(lysine) dendrimers [23, 24] (see Figures 10.2, 10.4 and 10.6). However, in each case appropriate water solubilizing terminal groups are required (i.e. -NH2, -OH or C02H groups) for suitable electrophoretic analysis. 

A water-soluble dendrimer zinc porphyrin 6a, having 32 carboxylate anion... 

Recently, several articles have been published dealing with water soluble dendrimers, due to their outstanding structure and properties which are similar to natural micellar systems, e. g., liposomes. Scheme 17 shows such an example of a dendritic micelle containing a hydrophobic inner core surrounded by a hydrophilic layer of carboxylate groups. The most important difference to natural micelles is that dendritic micelles are covalently bound structures and not dyn-... 

The structure and properties of water soluble dendrimers, such as 46, is, in itself, a very promising area of research due to their similarity with natural micellar systems. As can be seen from the two-dimensional representation of 46 the structure contains a hydrophobic inner core surrounded by a hydrophilic layer of carboxylate groups (Fig. 12). However these dendritic micelles differ from traditional micelles in that they are static, covalently bound structures instead of dynamic associations of individual molecules. A number of studies have exploited this unique feature of dendritic micelles in the design of novel recyclable solubilization and extraction systems that may find great application in the recovery of organic materials from aqueous solutions [84,86-88]. These studies have also shown that dendritic micelles can solubilize hydrophobic molecules in aqueous solution to the same, if not greater, extent than traditional SDS micelles. The advantages of these dendritic micelles are that they do not suffer from a critical micelle concentration and therefore display solvation ability at nanomolar... 

El Ghzaoui A, Gauffre F, Caminade A-M, Majoral J-P, Lannibois-Drean H. Self-assembly of water-soluble dendrimers into thermoreversible hydrogels and macroscopic hbers. Langmuir 2004 20 9348-9353. 

Some polyanionic dendrimers act as micellar molecules [58]. Newkome et al. first synthesised water-soluble dendrimers, whose hydrophobic molecular niches can accommodate guests. The periphery of such dendrimers was furnished with... 

Fig. 8.3 a) Transformation of a fifth-generation adamantyl-terminated POPAM dendrimer into water-soluble dendrimer by covering the adamantyl end groups with /fcyclo-dextrin (in excess) (schematic for the sake of simplicity neither all 64 adamantyl groups... 

Reactions 1-3 produce intermediates which can be hydrolyzed to give dendrimers with anionic surfaces. Intermediates derived from reaction 11 yield cationic surfaces after quaternization. Dendrimers possessing chiral surfaces were readily prepared from optically active epoxides, as in reaction 4. Hydrophobic surfaces result from reactions 4-10, 11, and 20-22. The resulting dendrimers are soluble in organic solvents, although their interiors might be quite hydrophilic. Conversely, water-soluble dendrimers are obtained from reactions 1-3 (after hydrolysis), 4 (R = H), 14, and 16-19. 

Twyman, L.J. Beezer, A.E. Esfand, R. Hardy, M.J. Mitchell, J.C. The synthesis of water soluble dendrimers, and their application as possible drug delivery systems. Tetrahedron Lett. 1999, 40, 1743-1746. 

Scheme 41 Water soluble dendrimers with TPA donors for singlet oxygen sensitization by Fr chet and Prasad [111]...

Synthesis of water-soluble dendrimers from hydrazine end groups... 

Water-soluble dendrimers offer the largest palette of properties and uses in biology. 

L. S. Kaanumalle, J. Nithyanandhan, M. Pattabiraman, N. Jayaraman, V. Ramamurthy, Water-soluble dendrimers as photochemical reaction media chemical behavior of singlet and triplet radical pairs inside dendritic reaction cavities, J. Am. Chem. Soc., 2004, 126, 8999-9006. 

WATER-SOLUBLE DENDRIMERS AS POTENTIAL DRUG CARRIERS... 

In a similar approach, water-soluble dendrimers were constructed by the reaction of PAMAM with varying amounts of Ph2P(CH20H)2Cl [131]. Additional sulfonate groups improved the water solubility further. 

These distinguishing features of dendritic macromolecules render these novel materials a reliable alternative to traditional polymers in a wide range of potential applications. The primary focus of this chapter is to cover the range of these potential uses of water-soluble dendrimers - it does not provide comprehensive coverage of these applications but has targeted a number of notable examples of the utilisation of water-soluble hyperbranched macromolecules. 

An important class of water-soluble dendrimers - the PAMAM dendrimers - have also been investigated as drug delivery systems. Twyman and co-workers have demonstrated that hydroxyl terminated water-soluble PAMAM dendrimer systems were capable of encapsulating small acidic hydrophobic molecules such as benzoic acid (Figure 8.3). The encapsulation capabilities of the PAMAM materials was first confined to benzoic acids and... 

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