Chemistry Reference
In-Depth Information
However, other Gd-MOF nanostructures have a potential for
T
-
1
T1-weighted MRI since higher
ratio close to 1 are
observed for aqueous suspensions of [Gd(1,4-bdc)(H
r
values and
r
/
r
1
2
1
] nanorods
(1,4-bdc for benzene-1,4-dicarboxylate) and for [Gd(1,2,4-btc)
(H
O)
2
2
O)
] nanoplates [129]. As revealed by the inverse size dependence
2
3
of
r
and
r
relaxivities obtained for [Gd(1,4-bdc)(H
O)
] nanorods,
1
2
2
2
3+
these high
r
values result mainly from the contribution of Gd
ions
1
at or near the surface of the MOFs since Gd
ions inside the material
may have a decreased water exchange because of hindered diffusion
of water molecules. The magnetic properties of MOFs can, therefore,
be controlled by the structure of the MOFs, which can behave as
3+
T
or
1
T
contrast agent for MRI. In addition to this attractive feature, MOFs
can be designed as a multifunctional platform combining FI and MRI
when their synthesis is performed from a mixture of gadolinium
salt and luminescent rare earth salt (Eu
2
3+
3+
, Tb
). Despite the great
3+
3+
potential of Gd-MOFs (eventually doped by Eu
or Tb
), their use
for
imaging could be impeded by their large size since in
most cases one of the dimensions of Gd-MOF structures is larger
than 100 nm.
The functionalization of Gd-MOFs constitutes another crucial
issue that should be addressed for
in vivo
application. The research
group of Lin succeeded in embedding Mn-MOF in a polysiloxane
shell to stabilize them and to facilitate their post-functionalization
with an organic fluorophore and a cell-targeting peptide [130]. The
functionalization of Gd-MOF nanoparticles ([Gd(1,4-bdc)(H
in vivo
O)
])
2
2
by well-defined polymers, including poly[
N-
(hydroxypropyl)
methacrylamide],
isopropylacrylamide), polystyrene,
poly(2-(dimethylamino)ethyl acrylate), poly(((poly)ethylene glycol)
methyl ether acrylate), and poly(acrylic acid), was performed
by reversible addition-fragmentation chain transfer (RAFT)
polymerization, which is one of the most versatile living radical
polymerization techniques. Besides the ability to obtain well-
defined polymers, RAFT polymerization provides polymer ended
by thiolate group after reduction of thiocarbonylthio group in basic
conditions. The thiolate groups favor the attachment to the Gd-MOF
nanoparticles through vacant orbitals on the Gd
poly(
N-
3+
ions at the surface
[132]. The RAFT polymer coated Gd-MOF nanoparticles behave as
positive contrast agents. Moreover, the encapsulation of Gd-MOF
nanoparticles in hydrophilic RAFT polymer shell (e.g., poly[
N-
(hydroxypropyl)methacrylamide]) induces an increase in the
r
and
1
