Chemistry Reference
In-Depth Information
FIGURE 1.13
Options for modifying amine-terminated dendrimer-based nano scaffolding
by utilizing classical subnanoscale and nanoscale reagents.
even at low generations due to steric effects. These unique steric effects are referred to
as nanoscale sterically induced stoichiometries (N-SIS) [33].
The use of dendrimers as nanoscale scaffolding for MRI contrast agents was first
reported by Lauterbur, Wiener, Brechbiel, and Tomalia in 1994 [47] and generated
tremendous interest and activity which has been reviewed extensively else-
where [48,49]. It involved conjugating metal-specific (i.e., gadolinium) chelating
groups (i.e., DTPA or DOTA) to the terminal groups of Tomalia-type PAMAM
dendrimers to produce a continuum of very precisely sized nanoparticles with well-
defined nano dimensions (Figure 1.14). These surface saturated, dendrimer-metal
chelates werewell-characterized examples of: [dendrimer (core)-ligatedmetal (shell)
nano-compounds]. The stoichiometries of these nano-compounds were defined
accordingly as: [dendrimer]:[ligated metal]
Z
, where Z
¼
N
c
N
b
G
. These core:shell
nano-compounds manifested enhancements in relaxivity properties (i.e., R
1
)asa
function of the dendrimer generation level and the stoichiometry of dendrimer:metal.
Furthermore, the features of these soft particle-hard particle (i.e., [S-1]:[H-1] nano-
compounds) fit the proposed criteria for nano-compounds described else-
where [3,4,66]. These nano-compound possess a core derived from an [S-1] type
dendrimer nano-element and shells derived from well-defined nanoscale collections
of ligated metals (i.e., [H-1] type metal cluster nano-elements). Finally this series of
[core:shell nano-compounds] fulfilled additional criteria that were predicted for these
entities [4] by exhibiting unique emerging nano-periodic property patterns [4] as
evidenced by their unprecedented high relaxivity values (i.e., R
1
) that increased as a
function of dendrimer generation level. Empirical formulae for members of this core:
shell nano-compound series may be written as follows: [G
¼
1-8]@[M]N
c
N
b
G
.
