ABSTRACT

Figure 7.1 Anatomy of a dendrimer. Reprinted with permission from Ref. 69; Lee, C., et al. (2005) Nat. Biotechnol., 23, pp. 1517-1526. © 2005, Nature Publishing Group. See also Color Insert.

There are two approaches to synthesizing dendrimers, one being the divergent method, where one branching unit after another is successively attached to the core molecule [85, 115], and the other being the convergent method, where the synthesis starts from the end groups toward the inside and finally is treated with a core [46]. Dendrons consist of a subfamily of dendrimers, which contain nonbranched focal functionality and repeating units stretching out

from the core [69, 98, 100]. These molecules can be easily modified to have a larger size, a different protecting group, and a different terminal group. Numerous studies have been conducted for dendrimers, including varying properties such as solubility and reactivity [86], dendron monolayer films [118], and dendrimers in biomedical applications [77]. Surface immobilization of dendrimers is of particular interest, and the extensive study on coating a gold surface with dendrimers resulted in a more sensitive chemical sensor because of increased density of functional groups [118]. Nanoparticles were also modified with dendrimers for better dispersion stability, inhibition of nonspecific protein adsorption, and enhanced capture of target molecules [89]. Several reviews on dendrimers have been published, covering their synthesis and applications [5, 28, 34, 116]. Compared to the applications of dendrimers, the structural advantage of dendrons has led many scientists to utilize them in controlling the lateral spacing between functional groups on a surface. Examples of dendron-utilized surfaces include gold surfaces modified with first-and second-generation dendrons for enhanced alpha helix formation of the immobilized oligopeptides [119], organosiloxane thin films of SiCl3-terminated dendrons on mica by spin-coating [124], and allyl-terminated dendrons on hydrogenterminated silicon surfaces [125]. Figure 7.2 is a schematic illustration of both a dendrimermodified surface and a dendron-modified surface, clearly showing the different density of functional groups.