Chemistry Reference
In-Depth Information
types), with fullerenes (i.e., [S-1]:[H-5]
n
core-shell type), or with metal nano-clusters
(i.e., [H-1]
n
:[S-1] core-shell type) produced three unique core-shell nano-compound
category types designated in Figure 1.18. On the other hand, dendrimers have also been
used as templates toproduce precisely sized [H-3] type,metal oxide nanocrystalswhich
have exhibited interesting quantum size effects as described in the next section.
1.5.1 Dendrimer-Dendrimer; [S-1]:[S-1]
n
Core-Shell Type
Nano-Compounds
Saturated shell, nano-compounds (Figure 1.19) are prepared by a two-step approach
that involved: first, self-assembly of an excess of carboxylic acid terminated den-
drimers (i.e., shell reagent) around a limited amount of amine-terminated dendrimer
(i.e., core reagent) in the presence of LiCl. This was followed by covalent amide bond
formation between the core and dendrimer shell reagents using a carbodiimide
reagent [52-54]. The resulting nano-compounds (i.e., saturated core-shell tecto
(dendrimers), referred to as megamers), are prime examples of precise poly-
dendrimer cluster structures. These structures and their stoichiometries may be
mathematically predicted by the Mansfield-Tomalia-Rakesh equation (Figure 1.25)
[6,55] and have been unequivocally verified by experimental mass spectrometry, gel
electrophoresis, and atomic force field microscopy [6,52,53,56].
1.5.2 Dendrimer-Fullerene; [S-1]:[H-5]
n
Core-Shell Type
Nano-Compounds
Stoichiometric dendrimer core-fullerene shell nano-compounds were readily formed
by allowing a [core: 1,2-diaminoethane];
4); {dendri-poly(amidoamine)-
(NH
2
)
64
} (PAMAM) dendrimer to react with an excess of buckminsterfullerene
(C
60
) [7]. In the presence of an excess of (C
60
), only 30 (C
60
) moieties bonded to
the dendrimer surface to produce a well defined, stoichiometric [dendrimer core]:
[fullerene shell nano-compound] (i.e., [S-1]:[H-5]
n
core-shell type) as shown in
Figure 1.20. These structures were extensively characterized by MALDI-TOF, TGA,
(G
ΒΌ
FIGURE 1.19
The saturated-shell-architecture approach to megamer synthesis. All surface
dendrimers are carboxylic acid terminated [54].
