Chemistry Reference
In-Depth Information
FIGURE 10.5
(a) The UV-vis spectral change upon the addition of SnCl
2
to
Ph-DPA G4
.
(b) Enlargements of the isosbestic points successively appeared with the displayed equimolar
amounts of SnCl
2
.
isosbestic points appeared in turn starting from each section at 0, 1, 3, and 7 equimolar
amount additions, and continued until the next section (finished at 15M amounts). In
addition, the number of equimolar amounts between each section (1, 2, 4, and 8)
completely agreed with the number of imines in each layer of the
Ph-DPA G4
. The
coordination profiles about each layer should be those shown in Figure 10.3.
A similar stepwise radial complexation was observed for the DPA derivatives
(Figure 10.4). When SnCl
2
was added to a solution of these dendrimers, four isosbestic
points were successively observed in the spectra. In
bearing two
dendrons (Figure 10.4), each shift occurred with the repeated additions of 2, 4, 8,
and 16 equimolar amounts of SnCl
2
[40,52]. On the other hand,
PPh-DPA G4
bearing
three dendrons (Figure 10.4) showed distinct shifts with the repeated additions of 3, 6,
12, and 24 equimolar amounts [74], while
TPA-DPAG4
Por-DPA G4
[53,54],
TPM-DPA
G4
[77] (Figure 10.4) bearing four dendrons showed the
distinct shifts with 4, 8, 16, and 32 equimolar added amounts. In each dendrimer, the
equimolar amounts of SnCl
2
added to the solution needed to shift the isosbestic point
also agreed with the number of imines in the first to fourth shells. These results support
the conclusion that the complexation in the DPA derivatives proceeds from the core-
side imines to the terminal ones, as shown in Scheme 10.2. The stepwise reaction is also
evidenced by several methods (transmission electron microscopy, electrochemical
measurement of coordinating iron complexes, and product analysis of metal assisting
reduction of imines) [52,54,56].
[75,76], and
Cyc-DPA G4
